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Executive Summary

This report contains a review of scientific literature relevant to establishment of a vision standard for award of the Commercial Drivers= License (CDL), and includes a summary of previous assessments of research in the driving domain as well as parallel research in aviation and in military applications. Research results are included in cases where the findings support the measure of visual performance attributes that are relevant to driving tasks.

The authors report the following critical findings:

  • The present testing philosophy lacks the requisite criterion validity to serve as a fair and useful vision standard. The principal shortcoming appears to be an narrow emphasis on central visual acuity, to the virtual exclusion of other, probably more important, visual capacities.
  • An improved standard would be most likely to result from testing a broader sample of visual tasks. This report summarizes a number of visual testing areas that show promise.
  • Although the visual standard can be improved, it is unlikely that overall highway safety will be improved dramatically. CMV operators comprise only a small proportion of drivers, and are represented in an even smaller proportion of crashes, and not all crashes are caused by failures of visual performance.
  • Insufficient research results presently exist on which to base a new vision standard; further research must be conducted to prove innovative concepts. This report includes an examination of traffic scenarios that may be used to develop and evaluate a new standard.

The authors recommend the following steps toward development of a new vision standard:

  • Establish a list of visual performance parameters that appear from the information available to hold significant promise as the basis for a new standard, and adapt or design performance tests.
  • Evaluate the predictive (criterion) validity of the tests using a combination of simulation and closed-course methods.
  • Based on the simulation, establish a trial vision standard, and test that standard for a sufficient period to establish its validity.

 

Table of Contents

Executive summary 1

1. Introduction 4

1.1 Purpose 4
1.2 Scope 4
1.3 Assumptions 5
1.4 Organization 6

2. Background 7

2.1 The need for a vision standard 7
2.2 Desired features of a vision standard 7
2.2.1 Reliability 8
2.2.2 Validity 8
2.2.3 Diagnosticity 12
2.2.4 Resistance to fraud or gaming 13
2.2.5 Enforceability 13
2.3 The current vision standard 15

3. Testing visual performance 17

3.1 Introduction 17
3.2 Perception and Vision 17
3.2.1 General 17
3.2.2 Direct perception 18
3.2.3 Event perception 18
3.3 The visual system 19
3.3.1 Description 19
3.3.2 Focal and ambient vision 20
3.3.3 Relation to driving tasks 20
3.4 The present standard 21
3.4.1 Emphasis on static acuity 21
3.4.2 Emphasis on central (focal) vision 21
3.4.3 Ignores perception 21
3.4.4 Disease v. Performance 22
3.4.5 Problems with single criteria 22
3.5 Potential testing areas 23
3.5.1 Sources 23
3.5.2 Contrast sensitivity 24
3.5.3 Useful field of view 29
3.5.4 Dynamic acuity 33

3.5.5 Low-contrast acuity 35
3.5.6 Dark focus 37
3.5.7 Vection 40
3.5.8 Focal and ambient vision 41
3.5.9 Event perception 43

4. Standards and visual performance 46
4.1 General lessons from research 46
4.2 Driving tasks and visual functions 47
4.3 Visual functions 48
4.4 Visual functions and visual parameters 49
4.5 Implications for vision standards and testing 51
4.6 Possible strategies 52

5. Scenarios for developing a standard 53
5.1 Criteria for selecting scenarios 53
5.2 Visual performance and crash categories 58

6. Conclusions and recommendations 59

Sources consulted 61
. . . . . . . . . .

ANNEX A: Summary of sources

1. Introduction

This report describes the process and outcome of a review of literature supporting evaluation and possible improvement of the vision standard for award of the commercial driver=s licence (CDL). The effort included a survey of a wide range of pertinent research, including efforts in areas such as defense and aviation that are not usually included in reviews of driving performance. In addition to the review and appraisal of prior research, this document is designed to serve as the basis for further applied research leading to the establishment of an improved vision standard; as such, it includes discussions of methods and other topics not usually included in a literature review.

Earlier reviews of visual assessment for CDL vision standards (e.g., Decina, et al., 1991) and for other applications (NRC, 1985; Kennedy & Turnage, 1985) were consulted extensively. However, this study is not intended to be an update of earlier reviews; our purpose was not merely to provide a chronicle of past efforts, but to apply these research themes to an innovative approach for vision testing.

1.1 Purpose

This study had the following objectives:

  • Survey the body of knowledge addressing vision standards relevant to commercial motor vehicle (CMV) operation.
  • Assess the adequacy of the present vision standard, as well as the present philosophy of vision testing, in light of what is known of visual processes.
  • Identify CMV-related traffic scenarios that can be used in simulation and testing of possible improved vision tests.

Unlike previous reviews (e.g., Decina, et al., 1991), this study is concerned with the establishment of a phased program of vision standard development and evaluation. It will serve as a bridge to more specific methods and strategies for improving the present standard, and as such is heavily influenced by likely methodological requirements.

1.2 Scope

This study includes consideration of research done in areas other than traffic safety. The reason for this expansion of scope is that driver performance studies have not been conducted in areas that appear to be extremely promising for vision standard development, but have been investigated in other applications. These include aviation (which shares many common visual performance features with surface transportation) and military studies, which have long emphasized visual performance as opposed to the more restrictive areas of eye testing.

The objectives of the review also broadened the scope to include the derivation of scenarios and considerations for test methodology, as well as a more thorough comparative evaluation of possible visual performance measures than is usual for a literature review.

1.3 Assumptions

This study was guided by a series of assumptions that permitted an organized and focused approach to CDL vision testing.

  • We did not limit our investigation to the philosophical and technical constraints of current testing philosophy. Our recommendations do not represent "tinkering" with the present standard, but describe an innovative approach.
  • We organized this effort with the understanding that the ultimate result will be a fair and valid standard, not a dramatic reduction in crash rates. Crashes are caused by a variety of factors, of which visual performance is only one. Restating the vision standard for CMV drivers can be expected to have, at best, a modest influence on crash events in which (1) visual performance plays the predominant role, and (2) the driver whose vision affects the crash is, to begin with, one of a small minority of operators (drivers of CMVs). A fair and valid standard is probably a reasonable outcome of this program; significant improvement in observed highway safety is not.
  • In selecting our topics, we presumed that further research can be undertaken to develop promising strategies. This assumption is fundamental to the success of the vision standard program. Limiting our investigation to established driver vision standard practices would be fruitless, since those practices are presently too narrow in scope to allow valid selection.
  • Some elements of the present standard require further examination. The role of color vision in CDL vision standards, for example, has been essentially discarded (see Decina, et al., 1991) since it does not appear to have any validity as a screening device. We do not summarize the color vision literature here. Nor do we examine stereopsis, which we believe is less valid as a measure of ability to judge distances in a visual event than more dynamic sources of information (e.g., optical flow).

 

1.4 Organization

This report considers the following topics:

  • Background and requirements for a vision standard
  • The authors= framework for measuring visual performance
  • Strengths and weaknesses of the present standard
  • Potential new testing areas and strategies
  • A proposed framework for a vision standard based on visual performance
  • Scenarios for use in developing and evaluating a new standard

The organization and style of this document are quite different from common scientific literature reviews, since the target audience is not other researchers, but rather managers and decision-makers within the Department of Transportation. We have not included long technical discussions of visual perception and the anatomy and biophysics of the visual sense, which are covered elsewhere. Emphasis is on the implications of specific areas of visual performance, not on the basic research underlying the present scientific body of knowledge.

More extensive background material on specific research strategies and findings is found in several reviews, most notably Decina, et al., (1991 — the "Ketron Report"), the National Research Council review of visual assessment strategies (1985), and an unpublished report by Berbaum, Kennedy, and Williams (1985). These and other reference documents are available on request for further examination.

2. Background

The following sections summarize the historical and technical background for a Commercial Driver's License (CDL) Vision Standard. The sections discuss the need for a standard and the features desired for a CDL Vision Standard, with some discussion of the challenges of achieving those features, and describe the current standard.

2.1 The need for a vision standard

The relationship between vision and the ability to drive a vehicle safely is so apparent on a common sense level that there is wide agreement that applicants for a driver's license of any sort should have to demonstrate satisfactory vision. A vision test is currently part of the requirement for obtaining a driver's license in every state. (Decina, Breton, & Staplin, 1991)

There is wide agreement as well that the vision requirements for commercial drivers should be more stringent than those for automobile operators. Drivers of trucks and buses must control massive vehicles that are less maneuverable than smaller ones, with longer stopping distances, wider turning radii, and larger "blind spots." At the same time, when they are involved in collisions, these vehicles= greater mass causes more severe consequences in property damage and loss of life. Commercial drivers also spend more time on the road than most private vehicle operators, and their exposure to the risks of the road is thus greater. The first Federal vision standard for interstate commercial carrier drivers appeared in the early 1930's, and by 1939 requirements were specified for visual acuity, visual fields, and color vision. (Decina, et al., 1991) The current standard, 49 CFR 391.41 to 391.49, was written in 1985. The OMC is currently considering whether that standard needs to be extensively revised.

2.2 Desired features of a vision standard

A vision standard, like any standard that will be used to qualify or disqualify people for an important privilege, must meet several requirements if it is to be accepted. First, and most obviously, it must specify and test individual characteristics that are clearly related to the applicant's ability to drive a truck or bus safely. It must specify the requirements clearly and test them reliably, so that if an applicant is tested in one place by one test examiner today and in another place by another examiner tomorrow, he will obtain approximately the same score on both tests. The standard must have pass/fail criteria that allow the majority of potentially safe drivers to pass while excluding as many potentially unsafe drivers as possible. The tests that support the standard should be resistant to any kind of "gaming" or faking that applicants might attempt. They should be easy to administer and reasonably inexpensive. These and other features are discussed in detail below.

2.2.1 Reliability

Reliability is one of the most basic requirements for any usable test. When a test is reliable, it measures the same thing each time it is given. Reliability is the characteristic of a test that ensures that any given applicant will score about the same on the test at a given time, no matter where he takes the test, no matter what qualified examiner administers the test, no matter which of several test forms is used. If a test is not reliable, if the results are not to be trusted as stable indicators of an applicant's status, its use cannot be justified. One of the most attractive features of the Snellen test of visual acuity is its reliability. One Snellen chart will give results just about like another, as long as the test administrator follows the standard guidelines for giving the test (ensuring adequate illumination, standard distance from observer to chart, etc.). Use of standard test equipment to present a test further assures uniformity and improves reliability.

The issue of reliability becomes critical when new tests are considered. The content of the test must of course be shown to produce reliable results in a research setting, but that is not enough. Any test proposed should be standardized so well that it is easy for examiners to administer it correctly under everyday working conditions, with little judgment or discretion required. Interpretation of an applicant's performance on the test should be as objective and standardized as possible, with little room for extraneous factors to bias the outcome. Reliability is one feature that makes automated testing attractive. Automated testing enforces standardization. It minimizes differences between individual administrations of a test by reducing the examiner's involvement and ensuring that the test will be presented the same way every time it is given.

The concept of reliability depends upon the assumption that you are testing an entity that is stable within an individual over reasonable time spans. Reliability will be impossible to attain if the characteristic being measured is not in fact stable within each individual. For example, if you try to develop a reliable test of a performance ability that varies widely within an individual from time to time as a result of changes in emotional state or level of fatigue, you are likely to fail. Such a failure may in fact indicate either that the underlying entity being tested may not be appropriate to test, or that you have chosen an inappropriate method to use in testing it.

2.2.2 Validity

Validity is the most critical characteristic of any test or standard. Put most simply, a test is valid when it measures the right thing. There are at least three kinds of validity that must be considered in designing the CDL Vision Standard and its supporting test: face validity, construct validity, and criterion validity.

The first is face validity. Face validity is the common sense criterion for a test or standard. Does the test look to a reasonably informed person as if it would test the ability it claims to test? In the case of the CDL Vision Standard, does it appear that the ability tested would be related to driving safety? Face validity is especially important in any test that is going to be used by a regulatory body to qualify or disqualify people for a privilege they deem important. If a test or standard does not have face validity, the public and their representatives or advocates will be unlikely to accept it as a fair test or standard. For example, the public accepts the Snellen test for vision partly because of its face validity and familiarity. The person being tested is required to see increasingly fine detail, and is scored on his ability to do so. This appears to be a reasonable "vision test" to the average person. It makes sense to nearly anyone that if an observer cannot see the "big E" at the top of the chart he or she probably cannot see well enough to drive safely.

Face validity will be especially important for any proposed changes to the CDL Vision Standard. If the CDL Vision Standard is to be made more stringent or complex, (or even if there is a perception that this is so) the reasons for change must be understandable. The new standard and tests, especially if they are unfamiliar, must make sense to the people who will be affected and to the advocacy groups who represent them.

The second important type of validity is internal or construct validity. This is the ability of the test to measure what it purports to measure. The designers of any test must go though the following logical process:

  • First, they must decide that a particular characteristic or ability is worth testing. This decision may be based on evidence of many different kinds, including face validity. As an example, the OMC might desire a test of night vision capability.
  • Second, they must decide what observable behavior in a test situation would demonstrate that characteristic or ability. What observable, measurable performance in a testing situation could serve as an indicator of the ability to see well at night? Perhaps some test involving detection or identification of moving targets under low illumination would be selected. The selection should be made on the basis of the expertise of scientists and practitioners who are expert in the characteristic to be tested. For each of the abilities to be discussed in this paper, there is at least some literature on testing methods and their rationale.
  • Finally, they must design a way to capture and measure that behavior. (This can be a difficult matter for testing more abstract characteristics, like intelligence, whose very definition is uncertain.) For our example, the designers would have to select the stimuli to be presented, the conditions under which they are to be presented, the behavior to be recorded (percent correct detections or identifications or error rate under specified conditions, or luminance threshold for a criterion level of performance are all possibilities), the criteria to be used to judge performance, the equipment to be used, etc. Again, the scientific literature will serve as the basis for designing or selecting specific test methods.

 

For vision tests, construct validity should not be especially difficult on the conceptual level. Most visual abilities are already defined in terms of observable behaviors, so the tests have only to capture those behaviors and quantify them. For example, based on the weight of the literature, if we wish to measure dynamic acuity, we should ask the test subject to identify a moving target; if we wish to test contrast sensitivity, we should vary the contrast of a set of stimuli and ask the test subject to tell us when he can see a pattern. However, the technical challenges in implementing such tests and ensuring their soundness can be considerable, especially when we move from the research laboratory to widespread public testing.

The third type of validity that must be assured is predictive or criterion validity. This answers the question of whether the characteristic we are testing is actually related to the outcome we are trying to control. In the case of a CDL Vision Standard, criterion validity addresses the issue of whether we can find and test visual abilities that are good predictors of driving safety.

There are two major issues related to the criterion validity of new elements and new tests of visual abilities that the OMC might propose for the CDL Vision Standard. These can be summarized in the following two questions.

"Can you prove that these tests can help us to predict who will be safe truck and bus drivers?"

"How can you justify the pass/fail criteria you are setting for the tests?"

To answer the first question, the designers of the standard and tests will need to develop evidence that test scores are statistically related to driving safety in a way that allows some prediction of driving safety from the test scores. Obviously, this can be done only in part through laboratory or relational research before the tests are implemented on a broad scale. Large numbers of people and long periods of driving experience are usually required to verify relationships of this sort. One way to do this, often used in the military when new selection tests are being developed, is to start administering the tests to all CDL applicants, but not use the results to determine who will be licensed, for some period of time. (Ginsburg, 1981) If OMC then monitors the safety experience of the people who have been tested and licensed, it should be possible to collect enough data to clearly demonstrate the predictive relationship, without using the new tests to disqualify anyone before the relationship has been shown.

Demonstrating criterion validity can be a very difficult task. Decina, et al. (1991) have listed the following factors that have complicated the problem of demonstrating the predictive value of current vision tests for driving safety.

  • Vision is only one of many factors influencing driving performance.
  • Some vision tests may not really relate to visual requirements of driving.
  • Reliability of criteria used to measure driving performance may be low.
  • Research methods may have used unrepresentative samples of the driving population.
  • Individuals with visual difficulties often place self-imposed limits on their driving, thus reducing their exposure to the risk of an accident.

Some, but not all of these problems can be overcome in any new effort to validate vision standard elements and tests. Certainly the research methodology issues can be addressed.

The OMC, if it proposes to change the CDL Vision Standard, will need to show some convincing preliminary evidence that the new standard elements and tests are predictive of driving safety. This preliminary evidence can be used to justify the research needed to develop a body of conclusive evidence and justify changes to the standard.

To answer the second question above, about pass/fail criteria, two kinds of information are needed. First, the OMC needs to know how the abilities being tested are distributed in the population of people who might conceivably apply for the CDL, effectively the general adult population. One must know the shape, range, and other parameters of a test score distribution to decide whether the test is appropriate for use, as well as to set pass/fail cutoffs. (For example, if everyone performed about the same on a test, that is, if there is little variability among individuals on the test, it would be unlikely that their scores on that test would provide information useful in licensing.)

Second, the OMC needs the same information as for establishing criterion validity in the first place. They need to know how the test scores are related to performance on measures they have agreed are valid indicators of driving safety. Thus they might look at how the test scores relate to accident experience, traffic violation citations, safe miles driven, or other safety indicators. To show criterion validity, the OMC needs to show that the test scores and the safety indicator measures vary together, for example that the higher the vision test score, the lower the probability of being involved in an accident. To set pass/fail criteria the OMC will require detailed quantitative analysis of the relationship between the measures.

There are two important problems to be avoided in setting test score criteria. First the OMC needs to avoid failing people on the standard whose vision in fact would allow them to be safe drivers. Second, they need to avoid passing people on the standard whose vision would in fact cause them to be unsafe drivers. The OMC is never likely to have a test or group of tests that can predict safety outcomes so well that no one will be misclassified in this way. The more of the variation in the outcome (measures of safety) can be predicted by the test or group of tests, the fewer people will be misclassified. Ultimately the OMC must make a judgment and set pass/fail criteria, using the best possible estimate of the proportion of applicants who will be misclassified. This judgment will depend on values as well as data. If the OMC sets the criteria relatively low, they will be licensing some people who may not be safe while assuring that most of the safe drivers are licensed. If they set it high, they will refuse licenses to a larger number of safe drivers, but will assure that most of the unsafe ones will not be licensed. Many factors enter into such a judgment, including the values placed on the safety of highway users, the rights of individuals to pursue their vocations, and the role of regulation in our society. (See Figure 1-1.)

Figure 1-1

Figure 1-1: The problem of false positives and false negatives. This drawing shows the distribution of cases for a vision test applied to a number of drivers (ellipse). Adjusting the pass/fail criterion to the right ("raising the bar" for qualification) will eliminate drivers who are unsafe, but at the cost of rejecting drivers whose performance would have been satisfactory. Lowering the criterion to avoid unfairly penalizing applicants because of the test's imprecision would increase the number of unsafe drivers licensed. This problem is impossible to avoid.

2.2.3 Diagnosticity

Another desired feature of a vision standard and the associated tests is the ability to reveal visual performance deficits that are unknown to the applicants. Many of the visual deficits that may be related to safe driving are not obvious to the person affected, and may not have been diagnosed by a family doctor or by previous vision exams for other purposes. It would be helpful if the OMC could include in proposed new tests ones that would reveal such deficits, especially in cases where treatment or intervention may be able to ameliorate the deficit. There are tests now available that claim to reveal problems not found by older tests used to evaluate nominally the

same visual functions. One example is testing useful field of view (UFOV), rather than testing visual field by perimetry. Investigators in this area have found that perimetry often does not show loss of ability when UFOV testing reveals deficits that could be important to safe driving. (Ball, Beard, Roenker, Miller, Griggs, 1988) This particular test, if validated, could be especially valuable because it is claimed that useful field of view can be improved by training.

2.2.4 Resistance to fraud or gaming

Any standard or test that is to be used to qualify or disqualify people for an occupation must be resistant to any anticipated effort to falsify test results. In the case of vision testing, attempts to inflate scores are not likely to be a major problem. Most vision tests are difficult to fake, especially if automated testing is used to scramble the order of stimuli (to avoid memorization of responses) and to reduce the vulnerability of testing personnel to attempts to have them manipulate scores. However, falsification in the opposite direction (malingering) could be a problem. There may be cases where disqualification on a vision standard would make a driver eligible for disability payments or other compensation. Any new standard and tests should be at least as resistant to such falsification as the current tests are.

2.2.5 Enforceability

In order for a standard to be useful, it must be enforceable. This means that the OMC must be able to ensure that the standard is applied uniformly nationwide, and that it is seen as credible by the commercial driver community and their advocates. Several specific characteristics of a standard and associated tests can contribute to or detract from such enforceability.

Uniformity. The tests associated with the standard must be administered uniformly to all applicants. This requires that the tests include carefully prescribed administration guidelines that are reasonably easy for states to follow. One weakness of the current standard is the vagueness of some of the instructions for its application. (Decina, et al., 1991) As mentioned previously, uniformity is most easily achieved by automated testing, to the extent that it is appropriate. Associated with the question of uniformity is the issue of the qualifications of those who enforce the standard. An example is the question of whether the vision portion of the physical examination must be performed by an ophthalmologist or optometrist, or whether it can be performed by a general physician. What are the qualifications of those administering licensing exams, if visual performance tests are to be given by the licensing agencies? What training is required of administrators? Must they be certified to perform such testing? Any selection of tests to support the CDL standard must address these questions.

Cost. Another issue of enforceability is the cost of enforcement. OMC must consider what new equipment or materials will be required for vision testing. They must determine whether the states can be expected to bear the costs of enforcement, or whether Federal funds will be provided. The costs of training test administrators must be considered, as well as the cost to administer each test. If the costs are not perceived to be justified by the benefits to be gained by the new standard and tests, the program will not be credible or enforceable.

Practicality. Finally, there are the issues of practicality and ease of administering the standard. The time to administer tests should be as short as possible. Ideally, the test equipment should be affordable enough so that states can establish numerous test sites, convenient to the applicants. The training process and required skill levels for test administrators should not be excessive. Administrative work associated with enforcement of the standard should be minimized, and record-keeping procedures should be efficient and understandable.

2.3 The Current CDL standard

The portion of the current (1985) Federal regulations on physical qualifications and examinations for CMV drivers (49 CFR 391.41 to 391.49) dealing with vision begins as follows. (49 CFR 391.41(b)(3))

Physical qualifications for drivers: A person is physically qualified to drive a motor vehicle if that person . . . (10) Has distant visual acuity of at least 20/40 (Snellen) in each eye without corrective lenses or visual acuity separately corrected to 20/40 (Snellen) or better with corrective lenses, distant binocular acuity of at least 20/40 (Snellen) in both eyes with or without corrective lenses, field of vision of at least 70 in the horizontal meridian in each eye, and the ability to recognize the colors of traffic signals and devices showing standard red, green, and amber.

The section on the physical examination of the head and eyes specifies:

When other than the Snellen test is used, the results of such test must be expressed in values comparable to the standard Snellen test. If the applicant wears corrective lenses, these should be worn while applicant=s visual acuity is being tested. If appropriate, indicate on the Medical Examiner=s Certificate by checking the box "Qualified only when wearing corrective lenses." In recording distance vision use 20 feet as normal. Report all vision as a fraction with 20 as numerator and the smallest type read at 20 feet as denominator. Note ptosis, discharge, visual fields, ocular muscle imbalance, color blindness, corneal scar, exophthalmos, or strabismus, uncorrected by corrective lenses. Monocular drivers are not qualified to operate commercial motor vehicles under existing Federal Motor Carrier Safety Regulations. If the driver habitually wears contact lenses, or intends to do so while driving, there should be sufficient evidence to indicate that he has good tolerance is well adapted to their use. [sic] The use of contact lenses should be noted on the record.

The vision test may be conducted by an optometrist or ophthalmologist, but also may be conducted by any physician as part of the general physical exam. The physical examination form includes blanks for entering distance visual acuity for each eye, specifying with or without corrective lenses; evidence of disease or injury for each eye; color test; and horizontal field of vision for each eye. A physical examination is required every 24 months.

No instructions beyond those quoted above are given for performing the vision examination, and no guidelines are given for deciding whether the ophthalmic conditions and diseases listed, or others, are to be considered disqualifying. The visual field requirement of 70 in each eye is evidently an error, derived from an earlier version of the standard that required a binocular visual field of 140 . The horizontal fields of the left and right eyes are not simply additive, since there is considerable overlap between the fields of the two eyes. This error has survived two revisions of the standard, but the FHWA has taken the position that each eye should have a horizontal field of 140. (Decina, et al., 1991) The current color vision requirement is unclear, and no test is prescribed. Decina, et al., have concluded that "it is doubtful that the standard intended to exclude typical red-green color-defective drivers." (1991, p. 8)

There is little definitive evidence of the criterion validity of the current standard, but as noted above, such evidence is not easily obtained. As mentioned, the Snellen test has face validity, as does the color vision requirement (since all vehicle operators should be able to differentiate between colors on traffic signals). The standard imposes few requirements on the applicant or examiner, but at the same time it may provide little assurance that applicants are visually fit to be safe CMV drivers. The vague instructions for enforcement and administration of the standard and tests provide no mechanism for ensuring that applicants are subject to uniform testing and uniform criteria for licensing. This reduces the potential reliability and enforceability of the standard and tests as well as their validity. Section 3.4 provides a detailed discussion of the technical weaknesses of the current standard, considered in light of current knowledge of visual system function.

3. Testing visual performance

3.1 Introduction

This section describes the current philosophy of vision testing and examines a variety of promising alternative or supplemental techniques. This ground has been covered before (see in particular Decina, Breton, and Staplin, 1991; NRC, 1985; and Berbaum et al., 1985), but has often been limited by consideration of tasks that do not have ready application to CDL standards (reviews, for example, that place emphasis on flying skills) or has taken a conservative approach out of deference to immediate practicality. In this study we have attempted to focus on strategies that can reasonably be applied to driving tasks, while accepting a wider view of what have been considered proper topics for discussion.

3.2 Perception and vision

Our discussion of vision testing departs from previous reviews in two critical ways, and readers should understand the implications and reasons for what may appear to be a break with tradition. Our assumptions have caused us to assess both the priorities and the conceptual range of current vision testing philosophies. In some cases, this approach pushes our investigation somewhat farther than present testing procedures and apparatus, as well as understanding of population norms, can support with the information at hand. We decided, however, that we should investigate possible strategies that meet the criterion of being necessary for safe driving, rather than apply a conservative a priori criterion of immediate practicality. Since this study is designed to be a precursor to further research, we believe a more liberal standard is justified.

3.2.1 General

Traditional approaches to vision testing have been limited to sensory measures such as static acuity, perimetry, and color vision C and have not generally recognized the contribution of perceptual processes in vision. In effect, most present tests address the eye rather than the visual system, which includes a rich array of brain processes that interpret and make sense of the visual world. Yet the task of driving safely includes so many visual demands that exceed simple sensory transductionC the conversion of patterns of light shifting across the retina of the eye into a code of electrical potentials suitable for analysis by the nervous system C and resolution that most of the performance requirements associated with driving tasks escape any rigorous assessment.

3.2.2 Direct Perception

An argument can be made that higher mental functions (e.g., attention) are not strictly "visual," and involve mental activities not generally included in visual screening tests. The lines dividing sensation, perception, and cognition (higher mental activity) are by no means fixed. James J. Gibson (1979) argued that perception is a largely a direct process by which information that resides in the visual world (which we shall call the optic array) is extracted and used by the observer, rejecting in the process the more prevalent view that perception involves much mediation and inference by the observer. We have adopted the Gibsonian position to some extent in our investigation, since it sets a definition of perceptual processes that encompasses most of the visual skills required by a driver. The important implication of this decision is that we have gone somewhat beyond the capacities of the eye and attempted to organize an understanding of the visual processes.

This decision entails an important departure from strict vision testing, since our interpretation of the visual world is not mediated solely by the eye. In the case of driving tasks, the dynamics of such visual information as optic flow (the relative movements of objects in the optic array during locomotion, such as passing vehicles, systematic expansion in size as objects are approached, and changes in texture) are assisted by other senses, most importantly the kinesthetic (the sense of body movement). For this reason, we include a discussion of vection and its possible implications for development of vision standards and testing strategies.

3.2.3 Event Perception

In addition to adopting a direct-perception viewpoint, we have chosen to discuss the general topic of event perception. Event perception is the process by which we make sense of dynamic events in the world, applying (to use the driving task example) a direct understanding of physical movement (velocity, acceleration, vectors) and other invariant properties of real situations appearing in the optic array. A driver seeking to merge into a busy highway must, for example, not only see important information (vehicles approaching from various directions, relative velocities and accelerations, the configuration of the highway), but judge its possible outcomes as well. We know, for example, that observers tend to underestimate acceleration and overestimate deceleration; such misjudgments can contribute significantly to the probability of a crash, but are not presently the subject of any test procedure. Our discussions in Sections 3.3 and 3.5 are heavily weighted toward discussion of the perception of dynamic events.

3.3 The visual system

Since this review is directed at traffic safety professionals rather than at an audience of professional researchers, we must provide a description of what we mean by "perception" and how this ability is supported by the visual system.

3.3.1 Description

This is not a study of the properties of the eye; it is an examination of the visual system as a whole, which includes a great deal more than just the eyes. The discussion must be relatively concise, but we consider it necessary for the reader to understand why we feel obliged to give consideration to so wide a variety of perceptual functions, and this can only be done in the context of visual perception as part of a functioning system.

Eye and brain. Technically speaking, the eye is part of the brain. Its extraordinarily complex structures have the task of sensing and transmitting to higher brain functions information arising from changes in patterns of light incident on the eye. This is of particular importance to vision testing for such tasks as driving a large truck. The eye does not "see" light C it sees changes in light. What allows the observer to make sense of these constantly shifting patterns (actually, changes in electrochemical flux as the retina=s receptor cells are stimulated by light) are the patterns= invariant properties. Certain patterns and changes are consistent with certain classes of events, and these events allow a confusing dazzle of colors and intensities to be perceived as a systematic whole. It is generally a grave conceptual mistake to liken the eye to a camera that records a series of static pictures of the world. What is important are the lawful dynamics that underlie changes in pattern. If our testing strategy stops at the eye, and fails to consider the processes that allow us to use the information captured by the eye, we will never really approach the most important demands placed on the visual system.

Sources of information. The visual system interprets the world (optic array) by combining a number of qualities inherent in the changes in light. These qualities include size, contrast, color (brightness, hue, and saturation), shape (derived largely from phase information), and motion. But perception of the optic array includes nonvisual information as well: observers also use auditory, somatosensory (sense of touch, as when a driver senses pressure of hands on steering wheel) and kinesthetic (sense of body movement, as when the driver feels lateral forces in a sharp turn or the backward pressure of acceleration) information. These sources are subtly added to strictly visual input, and yield a very sophisticated perception of what is happening in the observer=s relevant world.

3.3.2 Focal and ambient vision

One extremely important point that sometimes limits vision testing is the existence of two visual systems. These are generally called the focal and ambient processes, and have been described in some detail by decades of research. (Held, 1968; Schneider, 1967; Trevarthen, 1968)

In essence, focal and ambient vision result from the evolution of older, simpler visual processes that follow a pathway from the eye to the midbrain (tectopulvinar) and newer structures that lead to higher cortical areas (geniculostriate). Ambient vision, as the name suggests, encompasses the entire visual field; it has low resolution, but is very sensitive to levels of luminance and low spatial frequencies, and to movement. The focal mode is most efficient in the center of vision, much less so in the periphery; it is sensitive to details of form (high spatial frequency), and color, and requires more luminance for efficient functioning than does the ambient system. In effect, the ambient system is configured to provide a reflexive response to things in the peripheral areas, determining "where" a possibly important event is occurring; as such, it is closely interactive with hearing, touch, and kinesthesis. This is what operates when a driver reacts to movement seen "out of the corner of the eye." The focal mode is tied to attention, and allows the observer to focus on the pattern and to use the focal mode to determine "what" (as opposed to "where") the pattern is.

The existence of two visual systems is of particular importance because most traditional "eye tests" are designed to measure efficiency of focal vision only. The Snellen letters, for example, measure only a driver=s ability to resolve and recognize small shapes (called "optotypes") in the center of vision. While this is a necessary measure of ability to drive safely, it provides no information about other relevant visual processes. We will discuss testing implications in Section 3.5.8.

Visual field testing, as presently practiced, is confined to the establishment of limits of peripheral vision, ignoring the individual=s ability to use the information within that field. In effect, this amounts to no useful test of ambient processes.

3.3.3 Relation to driving tasks

The importance of these factors to the development of a useful vision standard is in the understanding that an effective vision standard must provide an assessment of each aspect of visual performance that must be employed to drive safely. Present vision standards do not meet this requirement. While it is not likely that all desirable measures can be applied to the CDL standard in the short term, because of shortfalls in technology, technical understanding of the processes involved, and practicality, the research program proposed by the Office of Motor Carriers can provide a rare opportunity to evaluate what can presently and potentially be done to establish fair and valid criteria for licensing.

3.4 The present standard

The shortcomings of the present standard are well understood. It is difficult to make a strong case for criterion validity, since the measures adopted are not strongly correlated with accident rate. (See Decina, Breton, and Staplin [1991] for a review of the performance of recent standards.) In particular, however, the present battery of tests measures only a small sample of the visual skills required for safe driving.

3.4.1 Emphasis on static acuity

One obvious shortcoming inherent in standards based on static acuity and perimetry is that most of the visible precursors to an accident involve dynamic events. Static visual acuity will predict a driver=s ability to read a road sign at a certain distance; however, it will not help in recognizing even structural details of moving events, since static acuity is not significantly correlated with dynamic visual acuity (see Section 3.5.4). It also ignores the driver=s ability to assess the dynamics of a traffic situation and to predict the outcome and take appropriate action. In fairness to the present standard, this problem is due not to a failure of knowledge or of imagination, but to an absence of proven testing strategies. Nevertheless, any standard based purely on static performance will fall short of criterion validity.

3.4.2 Emphasis on central (focal) vision

In addition to ignoring dynamic visual performance, the present standard measures only fine acuity in the center of vision C that is, it performs a limited test of the focal vision mode. But focal and ambient vision interact to allow a driver to evaluate the optic array and make appropriate decisions. Crash-threatening events occur in the periphery as well as in the center of vision; in fact, since focal vision encompasses only a tiny fraction of the total field, the signals that are associated with what may develop into a crash are far more likely to be outside focal vision, and thus outside the area tested by conventional standards.

3.4.3 Ignores perception C in particular, perception of dynamic events

Further, the present standard is concerned only with sensory qualities of vision: fine acuity, perimetry, and, arguably, the ability to discriminate colors. Yet the most important contributors to driving safety are likely to be perceptual, involving more complex and sophisticated ways of extracting and interpreting information.

3.4.4 Disease v. performance

We also suspect that there may be difficulty in making clear (in particular, to CDL applicants) that standards of visual performance may not be associated with definitive diagnosis of a clinical condition. In fact, defining a standard in terms of a disorder rather than in terms of the actual impairment of performance may be misleading. The present standard acknowledges this caution by requiring the examiner to "note" evidence of a number of visual conditions; presumably, a skilled ophthalmologist will judge the severity and likely progress of such conditions, and use this information as needed to supplement visual performance tests. But the apparent intent of this part of the examination is to estimate the performance effects of an impairment of disorder, not merely to note that the condition is present. In addition, the presence of a disorder in one applicant may be of such severity as to call safe operation of a CMV into question, while in another applicant it might not. The important aspects of the standard should be defined functionally in terms of why a particular deficit is unsafe.

3.4.5 Problems with single criteria

Finally, we caution that the result of this program may not be a series of scoring criteria or cutoffs for each dimension tested. Few dimensions we can imagine could be applied, one at a time, in such a way and avoid excessive false negatives and false positives. A more universal and valid standard may require the application of a number of variables which, taken in aggregate, may yield a high enough predictive value to allow fair and effective selection.

3.5 Potential testing areas

Examination of the body of knowledge in vision testing suggests that the present tests should be supplemented or replaced by more valid approaches. Previous studies have suggested a number of such strategies, and we have considered those most likely to match the skills required for safe operation of a CMV. The options considered cover a number of skills. The criterion for consideration was likely applicability (in terms of face validity and suggestive research outcomes), not practicality or level of development. In each case, we describe the nature of the test, its likely relationship to driving performance, the results of available research, and the level of development of testing techniques and norms.

3.5.1 Sources

The assessment of current literature in vision testing relevant to driving performance summarized here is somewhat broader than other recent reviews, since it includes a wider survey of journal articles, technical reports, and other sources in areas outside the driving canon. Research in Defense Department and NASA collections and elsewhere that appears to have relevance to driving tasks has been included, as well as academic research in areas that have not been extensively investigated in the driving literature.

This review used three general studies extensively. The first is the examination of visual disorders and commercial drivers by Decina, Breton, and Staplin (1991), which is the most recent survey of literature in the CDL vision test area, and which included extensive comments on potential areas for investigation (in particular contrast sensitivity, low-contrast acuity, glare sensitivity, dynamic visual acuity, and useful field of view). The second is Emergent Techniques for Assessment of Visual Performance by the Committee on Vision, Commission on Behavioral and Social Sciences and Education of the National Research Council (1985), which focuses on newer and potentially powerful assessment tools (contrast sensitivity, dark-focus, dynamic visual acuity and dynamic depth tracking, and implications of focal and ambient vision.) The last is the Survey of Vision Tests with Special Relevance for Military Jobs, by Berbaum, Kennedy, Williams, and May (1985), which added discussions of dynamic contrast sensitivity and vection (visual kinesthesis), topics not examined in detail elsewhere in the driving literature.

3.5.2 Contrast sensitivity

Description. Contrast sensitivity is a measure of the degree to which the visual system can discriminate between adjacent areas of light and dark, and usually includes a dimension of size (spatial frequency) as well. Unlike measures of static focal acuity such as the Snellen test, measurement of contrast sensitivity does not yield a single figure describing performance. The reasons for this are not clear in much of the summary literature, and require a brief explanation.

Campbell and Robson (1968) demonstrated that the human visual system is discretely sensitive to information of different sizes from the optic array. A very simple way of understanding this is to imagine the visual system has three channels through which information in different sizes is processed: "leaf detectors," "tree detectors," and "forest detectors." These size categories are roughly small, medium, and large. However, size in the visual sense is most commonly expressed in spatial frequency (cycles per degree [c/d]). Angular size is preferred over the measurement of the actual size of elements in the optic array because the visual size (the image projected through the pupil and on the retina) will vary with the actual object size and the distance to the object C in this way, size and distance are compressed into one figure.

The three example channels correspond roughly to low, medium, and high spatial frequencies. Low spatial frequencies provide general position, medium spatial frequencies provide general shape, and high spatial frequencies provide edges and fine details. This process is similar to the mathematical operation called Fourier analysis, in which periodic functions are decomposed into their constituent frequency elements.

In fact, there are certainly far more than three such "channels" (see for example Ginsburg, 1981) in the visual system. The example at Figure 3-1 shows four levels of contrast for three spatial frequencies (the lowest contrast is zero, at which no variation is visible). The forms generally used to measure sensitivity to contrast are sinusoidal gratings, shown in the example.

This discussion is included to make the point C often neglected C that the purpose of the measure of contrast sensitivity is not to assess the observer=s ability to see gratings. The gratings are used for test purposes because it is possible to control both dimensions (contrast and spatial frequency) with precision, and because more common scenes require complex apparatus to produce.

The result of a test of contrast sensitivity is called a contrast sensitivity modulation transfer function (MTF), like the example at Figure 3-2. The test generally measures contrast sensitivity (the inverse of the threshold contrast at which an observer can just discriminate the grating) over a range of spatial frequencies; differential sensitivity across this range yields the MTF.

Figure 3-1

Figure 3-1: Contrast and spatial frequency. Contrast decreases to the right and spatial frequency increases down.

Figure 3-2

Figure 3-2: Contrast sensitivity MTF. The two curves shown here represent typical modulation transfer functions. Note that the two observers tested (or perhaps one amblyopic observer tested in each eye) are similar in their performance at high spatial frequencies, but differ more dramatically in the middle range.

This example shows possible MTF=s for two drivers measured, and underscores a unique property of contrast sensitivity as a measure. The MTFs shown are quite similar at the lowest and highest frequencies, but differ substantially in the middle range (4-6 c/d).

This is important because the common tests of fine static acuity like the Snellen yield the same general information about an individual=s vision as the very high frequency extreme of the MTF. In other words, Snellen and like measures sample only part of the visual system=s capacity; and observers will differ across that spectrum. Some may have similar sensitivity for middle ranges, but differ noticeably at the higher frequencies, or show similar high-frequency sensitivity but differences in other ranges of spatial frequency. The last is of critical importance, since the Snellen test would not discriminate between two such observers.

As dynamic visual acuity differs from static visual acuity, so contrast sensitivity has static and dynamic features. Many studies of contrast sensitivity used drifting gratings, though the apparatus most likely to be used in assessing driver contrast sensitivity are stationary.

It has long been known that "sustained" and "transient" visual mechanisms operate within the visual system (Tolhurst, 1973; Robson, 1966), and that the first is best configured to decipher stationary parts of the optic array, while the latter is best suited for interpreting moving patterns. Figure 3-3 shows differences in sustained and transient MTFs. These are also related to focal and ambient vision (see Section 3.5.8) The MTFs derived from moving and stationary gratings differ (Pantle & Sekuler, 1968). The practical implication is that driving in fog may be affected more by the transient mechanisms measured by dynamic contrast sensitivity. (Berbaum et al., 1985) However, we find no evidence that norms are available for dynamic contrast sensitivity comparable to those for static measure.

Figure 3.3

Figure 3-3: Contrast sensitivity MTFs for sustained and transient presentation. (Adapted from NRC, 1985)

Importance. Contrast sensitivity provides a more universal test of acuity than Snellen or similar methods, which are limited to spatial frequencies of the optotypes C Snellen letters corresponding to an acuity of 1.0 (20/20) on that scale have a height of about 5 minutes of arc.

In addition, some research has suggested that contrast sensitivity is more strongly predictive of visual detection tasks C including complex tasks analogous to some driving requirements C than is Snellen (Ginsburg et al., 1981, 1982; O=Neill et al., 1988). The visual tasks tested are analogous to driving tasks that require a driver to discriminate information in the optic array. Ginsburg and associates, for example, used air-to-ground detection distance for Air Force pilots, and found high correlations between detection range and peak sensitivity. (We also note results reported by Kruk and Regan [1983], which found grating contrast not predictive.) O=Neill and associates used detection time, probability of detection and false alarm, and number of fixations required to make a reliable detection of a combat vehicle at varying distances and background, and found correlations of 0.58 for probability of detection and -0.67 for mean detection time. Turnage and Kennedy (in press) show correlation between contrast sensitivity and some simulated flight tasks. Decina, Breton, and Staplin (1991) cite contrast sensitivity as a promising technology for improvement of CDL vision testing, but caution that more investigation is needed to prove the applicability and practicality.

McKnight, Shinar, and Hilburn (1991), in a study of visual performance in monocular and binocular heavy truck drivers, noted that monocular drivers were significantly deficient in contrast sensitivity, but not in static or dynamic visual acuity and a variety of other visual faculties. This result supports the position that static acuity is not in itself an adequate testing strategy.

It should be noted that central vision and peripheral vision have different qualities of contrast sensitivity; this will be discussed later under Section 3.5.8 (Focal and ambient vision).

Status of testing methods. For many years, contrast sensitivity was measured using computer-generated drifting gratings on special video displays, an expensive and cumbersome method. More recently, commercial screening tests have reduced the time and operator expertise necessary to administer the test. (Decina, et al., 1991) Large-scale population norms for contrast sensitivity are described by Ginsburg and associates, (1981, 1984).

Methods and apparatus exist for testing dynamic contrast sensitivity; however, these are much more complex, costly, and demanding of trained personnel than those for measuring static contrast sensitivity.

Summary. This approach to vision testing is regarded as promising by three major reviews (NRC, 1985; Decina, et al., 1991; Berbaum et al., 1985), is supported by a broad and varied base of experimental research, appears to offer promise of valid application, and appears to have reliable and practical test strategies. While contrast sensitivity is probably not cost-effective as a simple substitute for Snellen acuity, it appears to offer significantly more information about individual visual performance.

Dynamic contrast sensitivity is theoretically at least as important as the commonly measured static sensitivity, since it is associated with mechanisms to some extent distinct from the static and may be more useful to a driver in judging dynamic events. At present, using dynamic contrast sensitivity as a measure is complex and costly; more information is necessary before its potential can be properly assessed.

3.5.3 Useful field of view

Description. This testing strategy differs from traditional visual screening approaches in that it goes well beyond simple measurement of sensory response. Useful field of view (UFOV) combines sensory, perceptual, and attentional processes that address one of the fundamental survival mechanisms for complex organisms: the ability to attend to the surroundings, detect information and identify that which demands action. UFOV is a measure that examines the interaction of field of view and attention.

In concrete terms, UFOV is the area from which information that can be gathered without head or eye movement from the optic array C in terms of behavior, what can be extracted from a glance. This measure is distinct from the commonly accepted visual field. How far to the periphery an observer can see does not address the more important question of what use can be put to what is "seen." The UFOV is an area surrounding the center of vision within which useful information can be extracted. It is not synonymous with the fovea C it is somewhat larger in visual angle C and varies with the observer and the situation.

Figure 3-4 shows the relationship between the visual field and the UFOV. The diagram represents the limits of visual capture for a binocular observer with head and direction of gaze constant, with the UFOV centered on the fovea. Note that the UFOV varies in extent across observers and within observers depending on a variety of factors. Note also that simple perimetric measure of the field of view does not address that area within which detailed information can be extracted.

Figures 3-5 and 3-6 show how the UFOV affects a driver=s ability to judge visual information. The first figure shows a notional "small" UFOV superimposed on a visual scene. Each occurrence of the elliptical UFOV represents one fixation by the driver=s eyes on a part of the scene. (Note that the scene is static, while the actual optic array is always in dynamic motion, so these examples are somewhat simplistic.) Capturing the information in this series requires seven fixations. In Figure 3-6, a notional "large" UFOV captures the same information in four fixations, hence in less time and with more detail.

Research in this visual factor is not new. Renshaw (1945; cit. O=Neill, et al., 1988) described a "visual form field" as a "... solid angle within and beyond the region of the anatomical macula in which an observer is able to see shapes." Smith (1961; cit. O=Neill, et al., 1988) describes a "visual lobe" as an area surrounding the fovea within which targets can be detected with some predetermined level of accuracy C that is, a "working field of view." Engel (1976; cit. O=Neill, et al., 1988) measured the extent of the visual lobe using a tachistoscopic presentation method, while Widdell and Kastner (1981; cit. O=Neill, et al., 1988) used eye fixations. Bellamy and Courtney (1981) and O=Neill, Batten and Woontner (1988) used brief presentations of target letters at various distances and directions from a fixation point to measure individual differences in visual lobe size, setting the points at which observers could reliably identify 50 percent of target letters as the boundary.

 

Figure 3-4

Figure 3-4: Approximate visual field and useful field of view

 

Figure 3-5

Figure 3-5: "Small" UFOV

Figure 3-6

Figure 3-6: "Large" UFOV

 

While these studies do not address attentional factors, they give some idea of the strength of this approach in predicting the ability to capture information. Bellamy and Courtney (1981), for example, report a correlation of 0.92 between measured working field of view and success in multiple fault search tasks; O=Neill and associates (1988) found a correlation of 0.66 between visual lobe size and probability of detecting a partially concealed vehicle, and -0.69 for mean detection time for similar tasks.

When attentional factors are included, the strong relationship between UFOV and safe driving remains. Decina and associates (1991) cite an unpublished study (Ball et al., in preparation) that reports a correlation of 0.55 between UFOV and measures of driving safety, which is an extremely powerful finding, and of itself argues for further investigation. Ball and associates (1988) found that the size of the UFOV decreases with age, creating safety problems that are not detectable by standard acuity and perimetry tests.

However, UFOV is subject to a variety of modifying factors, the most important being motion dynamics, foveal load, and practice. Cohen (1987) found, for example, that the driver=s UFOV tends to shrink during acceleration and deceleration (but is not affected by velocity), probably due to perceptual narrowing due to an overload on central vision information processing capacity. Ball and associates (1988) and Ball and Rebok (1994) found evidence suggesting that the UFOV can be expanded through practice. Williams (1989) reports that as demands are placed on central (foveal) vision, the UFOV processes diminish.

Importance. Decina and associates (1991) point out compellingly that the ability to "capture and direct attention to highly salient visual events [is] . . . crucial for effective driving, especially for CMV drivers who require exaggerated lead times for hazard recognition." UFOV is conceptually the most promising of the emerging approaches, but it differs from traditional measures in a critical way: it requires the measure not only of visual factors, but of more complex and unstable behavioral ones as well. This calls for what amounts to an expansion of the basic assumptions of vision testing.

Status of testing methods. The intuitive importance of UFOV testing is clouded by the lack of simple and accepted testing methods combining visual and behavioral factors. The purely visual elements can be extracted without elaborate testing equipment. Including such factors as susceptibility to "tunnel vision" under stress is a much more complicated task, and one that requires further development. No extensive samples of performance presently exist from which to determine norms.

Summary. Useful field of view is an extremely promising approach complicated by undeveloped measurement techniques and lack of data from which to establish norms. In some respects, this is a test case for a shift from purely visual/sensory measurement of the traditional type to more encompassing perceptual/behavioral methods.

3.5.4 Dynamic acuity

Description. Dynamic visual acuity is the ability to discriminate moving forms. It is measured in much the same way as static acuity (using the same optotypes, such as Landolt Cs, and Snellen letters), but in a movement (see Figure 3-7). While this measure has been the subject of nearly 100 reports by many authors, its development as a measure of practical visual performance has not been particularly systematic. Ludvigh and Miller (1953; and Miller and Ludvigh, 1953, cit. Miller & Ludvigh, 1962) first described the essentials of the phenomenon; programmatic efforts are fairly recent.

Figure 3-7

Figure 3-7: Dynamic visual acuity, measured by moving Landolt C. Curves at right show relationships between angular velocity and the size of the gap in the C required to produce detection. (After Miller, 1958)

An important aspect of findings with respect to dynamic acuity is that it is not significantly correlated with static acuity. Observers with similar measured static acuity may differ sharply in dynamic acuity (Ludvigh & Miller, 1953, cit. Miller & Ludvigh, 1962), particularly in cases where the target is not properly tracked by eye movements (Morgan, Watt, & McKee, 1983), suggesting that part of the apparent difference between static and dynamic acuity may be due to differences in central and peripheral functions. (Ludvigh & Miller, 1958, cit. Miller & Ludvigh, 1962; Berbaum et al., 1985) In addition, dynamic acuity decreases with the velocity (Ludvigh & Miller, 1953, cit. Miller & Ludvigh, 1962) and exposure duration of the target (Miller, 1959, cit. NRC, 1985) and increases with target contrast (Mayyasi et al., 1971) and with target luminance. (Miller, 1956, 1958) Dynamic visual acuity has also been the subject of studies specific to driving populations and driving tasks. Retchin and associates (1988) found significant correlations between dynamic acuity and self-reported driving frequency among older drivers, though the report did not deal with driving history. Kline and associates (1992) report declining dynamic visual acuity in older drivers (along with other visual faculties related to driving). Burg and Coppin (1966) describe relationships between dynamic acuity and age, sex (male dynamic acuity is slightly better than that of females), and static acuity.

Henderson & Burg (1974) and Shinar (1978; Shinar & Eberhard, 1976), in reports documenting the development of the Mark II vision tester, report low correlations between visual measures including dynamic acuity and accident rates. Hills and Burg (1977) reported a consistent relationship between dynamic acuity and accident rate in the over 54 age group, and argued for "perceptual rather than sensory tests" of driver vision. Burg (1968) reported that dynamic visual acuity is "closely and consistently correlated with driving record." McKnight, Shinar, and Hilburn (1991), investigating monocular and binocular heavy truck drivers, found that monocular drivers, while deficient in contrast sensitivity and other aspects of visual performance, were not typically deficient in dynamic acuity.

Importance. The 1985 report of the National Research Council assessment of visual performance measurement techniques (NRC, 1985) concludes that dynamic acuity "has real potential for the assessment of vision." This conclusion is somewhat constrained by the relatively low correlations (Bailey & Sheedy, 1988), lack of accepted measurement techniques, and high within-subject variability.

Status of testing methods. Though a variety of methods have been tried, no standardized test of dynamic visual acuity now exists, nor are there extensive observations on which norms can be based.

Summary. Dynamic visual acuity appears to offer potential benefit as a measure for the CDL vision standard, but is not as developed as some other measures.

3.5.5 Low-contrast acuity

Description. Static acuity is generally measured at high contrast: black optotypes against a well-illuminated white background. As we note earlier, however, there is an interaction between the ability to resolve visual information and the amount of contrast that separates the target figure from its ground. Drivers do not always have high-contrast information, and tests that presume otherwise may miss critical elements of visual performance.

Low-contrast acuity is generally measured by presenting traditional optotypes (Snellen letters, Landolt Cs) with less contrast than normally provided (Figure 3-8). This can, in fact, be accomplished by reducing field luminance. For these reasons, low-contrast acuity can potentially be tested using only minor modification of existing equipment.

Figure 3-8

Figure 3-8: Testing low-contrast acuity

 

Scientific literature describing low-contrast and low-luminance acuity goes back several decades. In general, findings show that acuity increases as background luminance increases for dark targets on light backgrounds (Baker, 1949; Craik, 1939). This effect holds true for dynamic acuity as well. (Mayyasi et al., 1971)

Low-contrast acuity is similar in some respects to contrast sensitivity. The difference lies in the ability to control critical aspects of the optic array. Simple use of low-contrast optotypes like Snellen letters may reproduce the contrast characteristic, but confuses dimensions such as spatial frequency and phase that are easily specified when gratings are used. A letter optotype, for example, will include many components of spatial frequency and phase, while the grating holds these aspects constant.

Unfortunately, research relating low-contrast acuity to driving tasks is too sparse to provide a clear sense of its applicability (Schieber, 1980), especially as a substitute for contrast sensitivity. For this reason, it is unclear whether the simplicity of application enjoyed by low-contrast acuity makes it a viable substitute for contrast sensitivity.

Importance. Many driving tasks are conducted under conditions of low luminance and low contrast (night, fog, etc.), and visual testing that presumes otherwise may fall short of specifying performance (see, for example, Burg, 1971).

Status of testing methods. While testing of low-contrast acuity is conceptually simple, no accepted tests currently exist, nor are norms available. The research reported on this dimension, however, suggests that tests can be developed with little difficulty.

Summary. The ability to discriminate shapes under low visibility conditions has intuitive appeal as a testing strategy. Testing complexity appears to be relatively low.

3.5.6 Dark focus

Description. Observers inspect objects in their visual field by accommodation, the process by which the image is focused on the retina. The focusing is accomplished by adjustment of the focal length of the eye=s lens, which responds to level of tension in a ring of tiny muscles that are attached to the lens circumference. Inability to focus (on far objects [myopia] or on near objects [hyperopia]) may require correction.

A special case of accommodation error can arise when the visual field is degraded C as, for example, at night or in a fog. In the absence of the usually rich array of surfaces on which to focus, the eye tends to slip into a relaxed state of "dark focus" or "tonic accommodation" or "empty field accommodation." In such a situation, the focal distance varies widely across observers, but appears to be at approximately 1.5 diopters (about 67 cm), or somewhat myopic (nearsighted) in the average observer. (Figure 3-9) (Leibowitz & Owens, 1978) As visibility worsens, the eye tends to shift progressively to the dark-focus. In the case of a very weak stimulus (for example, the shape of a vehicle at twilight in a dense fog), the eyes= accommodation may simply remain at the dark focus, whatever the distance to the target. (Johnson, 1976) Dark-focus is not significantly correlated with standard measures of refractive error. (Simonelli, 1983) There is a relationship between the spatial frequency spectrum of the object being viewed and observer empty field accommodation. (Charman & Tucker, 1977) Owens (1980) suggests that lower spatial frequencies initially attract the eye to focus, and higher frequencies maintain the focus.

This problem can be corrected to some extent with optical corrections (Owens & Leibowitz, 1976), but this approach is problematic because susceptibility to slipping into dark focus is dependent on environmental conditions. Leibowitz and Owens (1978) have reported myopia in drivers at night and under degraded conditions.

Figure 3-9

Figure 3-9: Dark focus

 

Poor visibility is not the only condition that leads to dark focus accommodation. If a textured surface such as a dirty windshield is placed between the observer and a distant object, there is a tendency to focus involuntarily on the screen, particularly if it is placed near the dark focus. (Owens, 1979) This problem, called Mandelbaum effect, could be particularly troublesome for truck drivers with a susceptibility to dark focus myopia and a dirty windshield in already degraded environmental conditions. (Figure 3-10)

Importance. Operators of CMVs are frequently required to drive in conditions of low visibility, and may thus have their ability to see critical information degraded. This is particularly disturbing when we consider the criticality of response time for large vehicles with long braking distance. If the driver=s eyes have relaxed to dark focus, visual recognition distance will be degraded. There is no evidence of extensive research in the driving application, but the effects of dark focus have been studied with respect to pilot performance (see NRC, 1985, for a review of this literature).

Figure 3-10

Figure 3-10: Mandelbaum Effect

Status of testing methods. Testing for dark focus is complex, time consuming, sensitive to testing conditions, and demanding of tester skills. Two methods are presently used: laser optometry and dark retinoscopy. These methods are significantly more demanding than present eye tests.

Research has demonstrated that there are wide individual differences in dark focus, and that these differences, as noted above, are not predictable on the basis of routine tests of clinical refraction. Liebowitz and Owens (1978) report a mean dark focus of 1.5 diopters; that is, the average eye tested tends to come to rest in conditions of reduced visibility focused at about 67 cm (standard deviation 0.77 diopters). However, most data appear to have been derived from college populations. Since operators of CMVs are typically older than college populations, these estimates should be used with caution and supplemented with measures based on more appropriate observers.

Summary. We believe that dark focus myopia may be a factor in truck-related crashes. There appears to be a wide variance in dark focus distance and susceptibility, which would support its inclusion as a testing strategy. Problems include testing complexity and an apparent lack of norms that can be applied to the commercial truck driver population.

3.5.7 Vection

Description. Vection, or visual kinesthesis, is a visually induced perception of self-motion. Gibson (1979) emphasizes its importance in the perception of the optic array. Vection appears to be the result of integration of the visual and kinesthetic (body motion) senses. Berbaum and associates (1985) provide a more detailed review.

Factors that may influence vection include fixation on a stationary object (as when a driver gazes at a distant sign), which decreases the perception of self-motion, and retinal area (sensation through only a small area decreases vection, as would occur if a driver is peering out through a small clear portion of a contaminated windshield). (Berbaum et al., 1985) Vection in most situations is perceived through such information as optical flow, the movement of areas of the optic array in a manner consistent with self-motion. (Gibson 1979)

Importance. Driving tasks are aided by vection C in particular steering, which depends heavily on optokinetic information. Much of the visual information contributing to perception of self-motion appears to come from the ambient processes (see Section 3.5.8), which are not presently evaluated. As noted elsewhere, we might speculate that relative lack of ability to process this information might cause guidance problems, particularly when the driver is attending to information in central vision. Note that the useful field of view (Section 3.5.3) tends to narrow when the information load being processed by central vision increases. If the processes that aid a driver in processing self-motion (and, for example, steering) are relatively weak, a safety problem may arise when central vision is directed elsewhere.

Status of testing methods. Vection can be tested neurologically, but neither population statistics nor practical testing methods are presently available. The concept makes intuitive sense, and there are limited experimental demonstrations that it is important to control tasks similar to driving a CMV (Leibowitz, Post, Brandt & Dichgans, 1980; Leibowitz & Post, 1982), but this area is not nearly as well developed as the others discussed in this review. However, we suspect that most of the visual input is mediated through ambient processes, and a testing strategy directed at ambient vision might provide a measure of vection as well.

Summary. Vection is likely to be a major factor in safe operation of CMVs, and a major contributor to the perception of traffic safety events (see below). Unfortunately, the present state of knowledge of the underlying processes and their practical implications complicates short-term contribution to the CDL vision standard.

3.5.8 Focal and ambient vision

Description. As noted in Section 3.3.2, human vision consists of inputs from two distinct, parallel, superimposed systems: the ambient and the focal. (Figure 3-11) We believe that a major problem in traditional vision standards is the lack of emphasis on the role played by ambient vision.

In describing the complementary roles of focal and ambient vision in driving-related tasks, we might consider the interaction of faculties necessary to keep a truck in its lane while searching for route information posted on highway signs. The steering task depends largely on optic flow and vection, which are in turn dependent on the ambient processes, which are integrated with the vestibular (balance and acceleration) and kinesthetic (body motion) modalities. Steering relies on ambient perception of self-motion, while the reading of signs and the detection of hazards relies on focal vision.

Ambient and focal vision are differentiated in the following ways (NRC, 1985, p. 26):

(1) The focal mode is almost exclusively visual, while the ambient mode acts in concert with the vestibular, somatosensory, and auditory sense to subserve spatial orientation, posture, and gaze stability.

(2) Object recognition by focal mode can operate over the full range of spatial frequencies. The ambient mode is adequately activated by low spatial frequencies typically stimulating large areas of the visual field.

(3) Adequate luminance and lack of refractive error are critical for some aspects of focal vision (visual acuity, for example) but play a much less important role in ambient vision. The low spatial frequencies subserving ambient vision are less sensitive to the degradation of retinal image quality by refractive error or by reduction of illumination.

(4) Focal vision is less efficient in the peripheral visual field. Although ambient functions are less efficient if restricted to a small area of the periphery compared with central vision, unlike focal vision, ambient functions improve when larger areas of the visual field are stimulated.

(5) Focal vision typically involves attention, while ambient visual functions are more reflexive in nature. Reading while walking illustrates the fact that although attention is dominated by the focal-mediated reading task, spatial orientation is adequately maintained by the ambient mode with little or no conscious effort.

Importance. This resource concludes that "because focal and ambient vision are critical in human performance, it is important that visual tests be employed that are sensitive to both functions." We strongly concur. Two important driving tasks are informed by ambient vision: useful field of view and vection. Under stress C and particularly under foveal load C the useful field of view shrinks (Leibowitz et al., 1982), and the amount of focal processing is narrowed. In effect, the ambient system is not as severely affected, but the ability to extract detailed information is limited. In addition, focal vision is severely degraded at night, while ambient vision is not. Leibowitz and and associates (1980) point out that this problem may contribute to crashes by giving drivers the illusion of control confidence under conditions where focal vision may not be able to detect hazards early enough to permit timely response.

Figure 3-10

Figure 3-10: Ambient and focal vision

 

Status of testing methods. The methodological gap here is clearly in measure of ambient vision, since all commonly used tests for vision screening concentrate on the focal processes. Methods similar to those used for focal vision could be employed, but modifications will be necessary to fit the unique qualities of ambient vision (for example, the range of spatial frequencies most important to ambient vision). Norms and population variability are likewise unknown.

Summary. We believe this is a major deficiency in traditional practice, and should be remedied before adopting a new standard.

3.5.9 Event perception

Description. A general problem with a testing approach that addresses a variety of isolated contributing factors is the danger that the problem being addressed C in this case, operating a CMV safely C may be significantly greater than the sum of its parts. The elusive and heretofore largely untested skill is that of integrating the dynamics of a traffic situation and, from the parallel inputs, understanding what is happening and, just as important, what is going to happen. Much of this task falls in the category of event perception.

The concept of event perception is a natural outgrowth of Gibsonian theory of direct perception, and a very important element in our view of vision and traffic safety. We describe the driver=s world as a "totality of events and not of things." (Shaw, McIntyre & Mace, 1974) The trick to safe operation of a CMV C essentially, the trick to surviving in the world C is the understanding of the nature of the environment and what is going on in it over time. To perceive an event correctly, the observer must understand the structure and lawful constraints (invariants) of events, not simply a series of pictures.

Faced with a traffic situation, a driver will generally have all the inputs needed to deal with a possible crash by acquiring information from the optic array (with help from other sensory modalities). It is not enough to simply perceive motion; the driver must perceive what that motion means in a dynamic sense.

For example, Runeson (1975) reports that an observer=s ability to predict the time of a collision is most likely to be accurate when the target is moving at a constant velocity, or when the object displays a "natural" motion function (rapidly decreasing acceleration). The visual system appears to apply a natural motion function to dynamic events, quite independent of whether the observer has previous visual experience with the phenomenon. There is a tendency to misjudge the time of collision C the estimate is too soon when the target is decelerating, too late when it is accelerating. In addition, there is evidence (Schiff & Detwiler, 1979) that observers tend to underestimate time to collision when a target is approaching from straight ahead, particularly as time to collision increases and the velocity of the approaching object decreases.

Simply acquiring the basic constituents of an event is constrained by limitations of visual perception. Drivers scan the environment using discrete eye movements (saccades) punctuated by stationary pauses (fixations) during which information is extracted from the useful field of view. During a saccade, there is significant degradation of the information received (saccadic suppression), including target movement. (Mack, 1970) Hence, when a driver=s eyes are searching for visual information, there is the risk of losing vital awareness of event outcomes.

Saccadic search is a series of movements punctuated by intense information-gathering. Pursuit eye movements, by contrast, are relatively smooth. If the driver is tracking a particular target (for example, a vehicle approaching an intersection perpendicular to the driver=s path), visual localization seems to be somewhat impaired (Stoper, 1973), leading to the risk of misjudging target position. The problem of gaze eccentricity also influences the driver=s performance in localizing events. When the eyes are not pointed to the center (as when a driver is preparing to merge, and the head and eyes are turned C see Figure 3-12), there is the tendency to misperceive direction. (Ebenholtz, 1976; see also Shebilske, 1981, for a review of the problem) This and similar problems may affect a variety of driver functions (Figures 3-12 C 3-14).

Figure 3-12

Figure 3-12: Problems faced by a driver in assessing a dynamic event (1)

Figure 3-13

Figure 3-13: Problems faced by a driver in assessing a dynamic event (2)

 

Figure 3-14

Figure 3-14: Problems faced by a driver in assessing a dynamic event (3)

 

Importance. Event perception is clearly critical to safe operation of a motor vehicle of any kind. Its associated skills have escaped testing scrutiny in traditional vision standards for a variety of reasons, but at least in part because they are not primarily attributes of eye function; they necessarily employ a combination of visual, somatosensory, vestibular, kinesthetic, and auditory functions. But the ability to gauge the consequences of a dynamic event is central to avoiding crashes.

Status of testing methods. Research in these topics is still largely relegated to the laboratory. No specific, practical tests currently exist, and knowledge of population norms is not adequate to support a testing program. However, some simple tests may be applied: for example, a collision-estimation approach like that reported by Runeson (1975) would be simple to program on a desktop computer, and might be useful in making an initial determination of the degree to which performance on simple exercises of this sort can predict crash probability. Used in concert with structured simulation of traffic situations that require dynamic event perception, such an approach might yield valuable information. The test could be modified to include multiple targets across a wide field, estimates during eccentric gaze, and other conditions that stress the visual system=s ability to make sense of the mechanics of the visual world.

Summary. This set of skills may be the most important determiner of crashes caused by human visual failure, but is at present the most difficult to test.

4. Standards and visual performance

Moving from a series of candidate testing areas to an organized plan for establishing a vision standard requires a step back from individual visual functions and quirks, and the establishment of a conceptual framework. This framework is very different from the established way of viewing licensing standards and eye tests, and requires some preparatory discussion

4.1 General lessons from research

Our evaluation of the relevant literature suggests the following:

  • The current vision standard provides neither construct validity nor criterion validity. Its principal advantage is familiarity. There is no suggestion in the decades of research in traffic safety that tests of central fine static acuity or visual field are more than weakly correlated with safe driving in the normal population.
  • Further incremental modification of the present standard will not yield useful results. Most of the studies that demonstrate the lack of validity have been competently conceived and conducted. We conclude that the lack of predictive validity lies in the real-world relationship between visual performance and driving and not in the ways in which earlier studies were conducted.
  • The traditional focus on narrow tests of central acuity fails to address many of the most important aspects of visual performance in the driving environment. We have identified a number of areas of visual performance that offer promise. However, successful employment of tests toward a vision standard requires redefinition of the visual task in terms of a driver/vehicle/environmental system.

The most important conceptual change from the scientific point of view, however, is the need to step beyond traditional eye tests and consider performance in a more dynamic sense:

  • Drivers do not perceive objects; they perceive events. The centerpiece of current testing procedure is static acuity, expressed as the resolving power of the eye measured against very small targets (visual field has apparent face validity but little criterion validity, and color vision appears to be included because of a reluctance to drop it from the standard rather than for a compelling need). In effect, observers are rated on their ability to discriminate very small forms under very uniform and favorable testing conditions and limited to no more than one degree of retinal angle in the center of vision. The task of driving a commercial vehicle, on the other hand, requires the complex and demanding processing of dynamic events. As a result, the most important visual contributions to safe operation seem to be outside the range of established testing procedures.

4.2 Driving tasks and visual functions

Listing visual functions will shed little light on their usefulness; the important consideration is their relationship to driving tasks. Decina and associates (1991) approached this problem by an expert evaluation using a Delphi technique (an iterative approach developed by the Rand Corporation for systematically creating consensus in a group of participants with content expertise). In this case, participants were asked to evaluate a series of six driving tasks, and to estimate the relative importance of a group of visual functions to each. The results are shown in Table 4-1.

Table 4-1: Visual Functions Judged Most Important for Safely Performing
Seven Critical CMV Driving Tasks

Driving Task

Visual Function by Order of Importance

1

2

3

Maintaining safe speed for conditions

Visual fields

Motion perception

Contrast sensitivity

Maintaining safe following distance

Depth perception/stereopsis

Motion perception

Visual fields

Staying in lane/steering control

Visual fields

Static acuity

Contrast sensitivity

Merging/yielding in traffic conflict situations

Visual fields

Visual search/attention

Motion perception

Changing lanes and

passing

Visual fields

Depth perception/stereopsis

Motion perception

Complying with traffic control devices

Static acuity

Visual fields

Contrast sensitivity

Backing up/parking operations

Depth perception

Visual fields

Contrast sensitivity

From Decina et al., 1991, p. 27

We observe several problems in this finding. First, the participants seem to have been rather constrained in their choice of visual functions. We are uncertain whether this list was provided to the expert panel or developed by them or was the result of free response, but the first case appears likeliest. Availability of accepted testing methods was apparently not a criterion: such functions as static acuity, contrast sensitivity, and stereopsis have such tests; it is uncertain whether "motion perception" does. Visual fields are included, but we presume, given the language elsewhere in the report, that this refers to total field established by perimetry. As we have seen, this does not appear to be a useful predictor of accident rate; we suspect that the extent of the visual field is less important than how effectively ambient visual processes operate in an observer. (An exception to this would obviously be cases of significant field deficit, particularly on the horizontal meridian.)

Second, the visual functions range from very specifically to very poorly defined. Motion perception, for example, probably has valid application to driving tasks in some form, but there are many forms of motion perception. It is uncertain whether the panel considered this function in the very broadest sense or in some more constrained fashion. We agree that the ability to "perceive motion" is necessary to driving tasks, and presume that the panel defined it in the general sense (as opposed, for example, to "the threshold angular velocity at which motion is detected in the fovea").

Third, while the tasks provided the panel are probably representative of driving operations, they tend to overlap and, we believe, confuse the issue by confounding tasks and performance parameters. To clarify the connection between common driving tasks and visual measures, we analyzed the tasks provided the expert panel in the earlier report and extracted from them the visual functions that serve those tasks.

Finally, we expanded and reorganized the "visual functions" in the Delphi structure to represent the wider range of activities described in Section 3.

4.3 Visual functions

To perform the driving tasks proposed by the 1991 report, we propose the following functions that are principally mediated by vision:

  • Perceive the path of self-motion. This reflects aspects of the first five driving tasks listed by Decina, et al. (1991). The driver must perceive the velocity, acceleration, direction, and directional stability of his or her movement relative to the desired path of motion.
  • Detect important events. Beyond simply staying in the lane and other self-motion tasks, the driver must sense events that may influence the flow of driving decisions. Such events as traffic signals, variable message signs, and the peripheral movements of other vehicles must be identified efficiently.
  • Direct attention to important events while maintaining path. Having detected an important event, the driver must identify it and process its contribution to safe operation without sacrificing the routine monitoring of motion paths.
  • Extract information from important events. The driver must be able to examine and process the information in a specific locality (traffic sign, ramp angle, distance to another vehicle) quickly and efficiently.
  • Analyze and predict the outcomes of dynamic events. Beyond merely identifying events in the optic array, the driver must be able to analyze their dynamics and predict their outcomes, as well as shape the behaviors necessary to operate safely.
  • Operate in low-visibility environments. Finally, a driver must be able to perform all these visual functions in less than perfect conditions (at night, in fog or rain, despite glare).

We must stipulate two qualifications to this list. First, not all functions are purely visual. Self-motion includes input from other senses (particularly the kinesthetic). Attention may be directed to events by auditory warnings (e.g., ambulance sirens). The visual system is integrated extensively with other systems and, while we emphasize the contribution of the visual processes and tailor our testing strategies to those processes, we should not ignore a visual function simply because it does not deal exclusively with inputs to the eye.

Second, these functions are not independent. The ability to read a sign and stay in lane is partly a function of the ability to extract information from the sign efficiently; if a driver must study a sign carefully because his or her perception of the shapes is blurred, attention may be focused on the sign at the expense of the information necessary to drive on the proper path.

4.4 Visual functions and visual parameters

We now considered the relationships between the visual functions and the candidate potential testing areas (visual parameters) described in Section 3.5, identifying the matches between testing strategies and functions. In Table 4-2 we indicate the measurable attributes of vision that may allow us to assess a driver=s ability to perform the vital visual functions associated with safe operation.

We have arranged the visual parameters by their dependence on focal and ambient vision processes. Some draw heavily on one or the other; some apply to both. We chose to emphasize this aspect in part because the present standard addresses only focal vision. As noted earlier, we consider this lapse to be one of the two most serious deficiencies of traditional standards (the other being absence of consideration of dynamic event perception).

It is worth noting that static acuity, the principal measure of driving competence now tested, is essential to only two functions (extracting information from events and operating in low-visibility environments), and one of those is a subset of the other. This makes the absence of significant correlation between static acuity and safety less mysterious.

Table 4-2: Visual Functions and Performance Measures

 

 

 

Visual Function

Performance Measure

Largely focal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Largely
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ambient

UFOV

DF

SA

CS

DA

LCA

VEC

Perceive self-motion path.

"

!

Detect important events.

!

"

!

Direct attention to important events while maintaining path.

"

"

"

!

!

Extract information from important events.

!

!

!

!

"

Analyze/predict outcomes of dynamic events.

!

"

!

!

Operate in low-visibility environments.

!

!

!

!

!

!

!

 

! = primary; " = secondary UFOV= Useful Field of View; DF=dark focus; SA=static acuity; CS=contrast sensitivity; DA=dynamic acuity; LCA=low contrast acuity; VEC=vection.

The designation primary or secondary indicates our assessment of the dependence of each visual function on the processes underlying each visual measure. In some cases, these processes are central or primary to the visual function; in some cases they are supporting or secondary processes. For example, the path of motion is perceived predominantly through the combination of ambient vision and kinesthesis called vection. But the perception of ambient events is secondarily influenced by contrast sensitivity as well, though contrast sensitivity in the periphery is not presently measured in CDL vision testing. This is of interest, since contrast sensitivity performance is different for focal and ambient processes (Section 3.5.8). Note that these assessments are speculative and based on our reading of the literature; further testing may show other relationships.

The relative importance of each performance measure is not necessarily a function of the number of visual functions it serves. Static acuity, for example, occurs as a primary factor only in the extraction of information from events; however, that function is so essential that static acuity cannot be diminished in importance merely because it only appears once (in functions other than low-visibility conditions). Note also that the performance measures are not entirely independent. The

same information drawn from tests of static acuity can also be drawn from tests of high spatial frequency contrast sensitivity.

One point noted during the analysis was the difficulty in isolating driving scenarios that actually call for static, as opposed to dynamic, acuity. Most crashes will occur when the driver and vehicle are in motion (arguably all crashes in which visual miscalculation is the principal factor). Dynamic acuity is defined as dynamic when the retinal image is in motion; even a fixed highway sign is viewed dynamically if the observer is in motion. We do not propose, however, that static acuity as a measure is unrelated to driving tasks. Acuity performance may be static or dynamic based on the rate of movement of the image; distant images move across the visual field more slowly than nearby ones at any constant vehicle speed. Very distant targets may be regarded, practically speaking, as static because their observed rate of movement is so low that static processes dominate (that is, the observer is unlikely to make visual pursuit errors C see Section 3.5.4). Ability to read distant signs should be strongly related to static acuity. However, ability to assess forms and details close to the driver is much more likely to involve dynamic processes. This may be why dynamic acuity has generally shown higher correlations with accident rate than has static acuity (Section 3.5.4).

We have separated operation in low-visibility conditions for two reasons. The first is clear: by definition, visual performance is impaired in low-visibility conditions, and it is reasonable to propose that crashes in which vision plays a significant role are more likely to occur when vision is degraded.

The second reason is less obvious. In general, all visual performance measures should relate to operation in low-visibility conditions C but not necessarily in the same way. Focal vision, for example, is significantly impaired under low levels of illumination, while ambient functions are not. This creates a distinct problem in night driving, since such tasks as staying in lane are not nearly as impaired as ability to see, interpret, and act upon specific threats. A possible result is a tendency for operators to drive at night as fast as ambient processes allow, but too fast for focal processes to respond. We speculate that many night crashes caused by visual performance errors are caused by this mismatch. This is a powerful argument for considering both focal and ambient vision.

4.5 Implications in vision standards and testing

Our analysis suggests that traditional vision tests have not, in general, assessed areas of visual performance central to driving tasks. The philosophy of such standards, as noted earlier, has been based heavily on clinical conditions rather than on the underlying areas of performance (many of which may complicate safe driving tasks without association with a clinical impairment). Our interpretation of the present body of knowledge of visual performance suggests that a testing strategy emphasizing critical performance measures may offer significant advantages in determining fair and effective standards.

A disadvantage of this approach is the relative scarcity of standardized and widely accepted tests of the critical performance areas. In fact, only static acuity and contrast sensitivity have such tests associated with useful norms. Some abilities, such as capability to use vection in maintaining a motion path, have no tests at all in the accepted sense. Others C for example, dynamic acuity and low-contrast acuity C can probably be tested with little modification of existing equipment.

The problem is that the relative availability of testing strategies and the relative importance of the performance measures to safe operation of a commercial motor vehicle may not be a good match. Processes that are largely ambient are presently untested, yet their importance to safe driving appears to be significant. A major challenge in pursuing a more useful vision standard may well be weighing the costs and development times associated with innovative strategies against their possible value in the establishment of a valid vision standard.

4.6 Possible strategies

The objective of this study is to evaluate the conclusions and implications of existing literature; later phases of the program will deal with methods for developing and evaluating possible standards. However, we feel obliged to offer several comments.

  • We doubt that the critical vision performance areas for driving tasks can be tested without significant modification of and additions to existing equipment. This is an unavoidable consequence of any program designed to screen drivers for visual performance and to fairly exclude applicants based on substandard visual capacity. We feel that existing equipment and strategies simply do not address vital performance areas, and until that testing deficit is corrected, it is unlikely that the vision standard will be significantly improved.
  • We believe that effective testing of vision performance will require increased use of innovative, dynamic, strategies that integrate performance areas in a realistic way. Driving is a dynamic, not a static, function, and performance measures must reflect the interaction of various processes that enable drivers to operate safely. This need not involve exceptionally costly or sophisticated equipment; we suspect that many of the functions now ignored can be tested using devices no more complicated than a desktop computer, employing dynamic, interactive applications that resemble low-end task simulation more than they resemble traditional eye tests.
  • We emphasize again that there are limits to the ability of vision testing to predict crash rates. Not all crashes are caused by visual performance errors, and dramatic reductions in crash rates will not result from imposition of a new standard, no matter how effective. There are practical limits to any such strategy. A crash is often a complex event that results from an unlikely combination of conditions and events, and preventing a crash by indirectly affecting only one of those conditions will yield a very modest effect.

5. Scenarios for developing a standard

Evaluating the effectiveness of testing strategies for a vision standard will require rigorous testing, since any dramatic change from the present practice will depend upon demonstrable criterion validity. The tests and standards chosen must be clearly related to driving tasks, and their application must be based on realistic evaluation using appropriate methods. Given the range of visual performance measures proposed for consideration, we envision use of simulation and controlled closed-track testing. These methods must test driver performance in scenarios that challenge all the critical performance areas.

While the choice of specific scenarios will necessarily be made at a later point in program development, an overview of the probable form of these test conditions can be constructed from a tentative analysis of existing data. The situations listed in this section include thirty specific precrash configurations. While it is not practical to simulate nearly that many, we find that there are commonalities in the events, and in particular in the visual performance areas that may influence their outcomes.

5.1 Criteria for selecting scenarios

The configurations used in this analysis are drawn from those routinely used in the General Estimate System (GES) code book. They are abstracted from descriptions used in various standard police accident report forms, and provide what appears to be close to an exhaustive descriptive list. The GES configurations include many multiple vehicle crash events, indicated by 88 separate codes for the individual vehicles involved (GES includes all vehicles; we apply the classification scheme with the assumption that the vehicle in question is a CMV). In such cases, we include a configuration with the stipulation that the CMV involved is the vehicle with the path and position characteristics suggestive of possible visual error, and eliminate all other codes.

In selecting scenarios for possible inclusion in the CMV vision standard test program, we first eliminated those configurations in which visual performance was unlikely to play a role. These included:

  • Cases in which the vehicle is stationary or when the crash results from impact from behind by a second vehicle.
  • Cases in which the crash results principally from loss of control or traction. We do not eliminate situations in which the loss of control or traction is due to dramatic precrash maneuvers, since those may have resulted from a failure to detect visually an impending traffic situation.

Thirty conditions remain. However, these can be collapsed across categories with similar characteristics. For example, configurations in which a CMV swerves to avoid a parked vehicle, a fixed object, a pedestrian, or an animal are included here as separate codes, but in most respects constitute one class of event: the operator=s failure to detect a stationary object in time to decelerate and stop before probable impact, triggering a maneuver that results in a crash. In cases where the principal cause of the event is a failure of visual performance, the likely contributing performance measures would include useful field of view and dynamic acuity, with static acuity and contrast sensitivity as contributing factors.

The principal differences between conditions and classes of conditions are:

  • The relative velocity of crash elements. If the CMV strikes a fixed object, the vection path is quite simple, and the likely visual contributor is failure to detect the obstacle. If a CMV and other elements are in motion (as at an intersection or merge crash), the failure may be detection as well, but perhaps complicated by misperceiving the dynamics of the situation and failing to take proper action. In these situations, dynamic acuity and vection may play relatively greater roles.
  • Conditions of visibility. If visibility is constrained by environmental conditions, factors such as contrast sensitivity, low-contrast acuity, and dark focus may contribute more substantially than would be the case under clear and well-illuminated circumstances.
  • The position of critical information in the visual field. We are concerned with crashes that are preceded by visual information that indicates their probability, since visual performance would otherwise not contribute to a safe outcome. The location of that information in the visual field may be critical, in particular whether it is initially positioned for focal or ambient processing. An obstacle in the direct motion path of the CMV is likely to be detected by focal processes, while a vehicle approaching an intersection from the side is more likely to appear in the periphery of vision, where ambient processes obtain.

In forming a preliminary list of scenarios suitable for simulation, we used the GES configurations on the following pages. Each configuration includes a sketch of the precrash dynamics and a first estimate of the relative contributions of the visual performance measures. Since no data are available to inform these judgments of criticality, the basis of the analysis was the relative importance of the three factors listed above. We suspect that all visual performance measures are related to some extent with virtually all scenarios; however, in many cases the contribution of one or more is likely to be negligible. The filled circle notation indicates that a particular visual parameter is likely to be critical for the scenario indicated; the unfilled circle indicates that the visual parameter may support the driver=s actions, but less directly.

Precrash Dynamics

 

UFOV

DF

SA

CS

DA

LCA

VEC

!

"

!

!

"

!

"

"

!

"

!

!

"

!

!

"

!

!

"

"

!

"

!

!

"

!

!

"

!

!

"

!

"

"

!

!

!

!

!

"

!

!

!

!

!

"

!

!

!

!

!

"

!

visual performance measures

5.2 Visual performance and crash categories

Selection of scenarios for simulation and testing should be based on the complete coverage of visual performance parameters. Both static and dynamic conditions should be evaluated, as well as different environmental conditions (e.g., haze, darkness). The configurations shown above appear to cover all common precrash conditions; selections from this list, with attention to coverage of visual performance areas, should provide a valid test of visual performance in support of CDL award.

6. Conclusions and recommendations

Our examination of the literature suggests the following:

  • The present testing philosophy lacks the requisite criterion validity to serve as a fair and useful vision standard. The areas tested C static acuity, perimetry, and color vision C do not address the most important visual functions required for driving tasks. Static acuity tests the observer=s ability to discriminate a small, high-contrast shape in the center 1E of vision, a task with very limited application to the range of driving activities. Field of view, as presently measured, tells little about an observer=s ability to employ the visual information sampled from outside central vision, and is not significantly correlated with driving safety. Color vision is of such low criterion validity that no test is required.
  • An improved standard would be probably result from testing a broader sample of visual tasks. Visual performance areas that offer promise include contrast sensitivity, useful field of view, dynamic acuity, low-contrast acuity, dark focus, and vection, with particular emphasis on testing visual performance in both focal and ambient pathways.
  • Although the visual standard can be improved, it is unlikely that overall highway safety will be improved dramatically. It is unlikely that large numbers of potential CMV operators will fail any fair and valid standard, and only a fraction of crashes appear to be caused by visual failures.
  • Insufficient research results presently exist on which to base a new vision standard; further research must be conducted to prove innovative concepts. Many of the areas studied in this review have been the subject of applied research in aviation and other areas; while they show promise in driving applications, there is at present a scarcity of empirical results, accepted test procedures, and, in particular, of normative data.

We believe that research toward the establishment of a valid vision standard for CDL qualification should proceed in the following way:

  • Establish a list of visual performance parameters that appear from the information available to hold significant promise as the basis for a new standard. The measures discussed in this report should provide such a basis. The list should include a sample of critical visual tasks, using probable relationship to safe CMV operation, balanced against availability of practical testing strategies.
  • Evaluate the predictive (criterion) validity of the tests using a combination of simulation and closed-course methods. The combination of methods is necessary because of the integrated nature of visual, kinesthetic, and somatosensory inputs. Low-end simulation is the most practical strategy for evaluating purely visual performance, but such a strategy may be inadequate in itself because it relies on too constrained a test environment.
  • Based on the simulation, establish a trial vision standard, and test that standard for a sufficient period to establish its validity. The time required to confirm the validity of the improved standard will depend on a variety of factors, including the number of drivers used in the validation, the driving activities of the confirmatory sample, and the predictive power of the tests. While this may appear to be an extremely time-consuming process, it is the approach most likely to yield satisfactory results.

Sources Consulted

 

Authors= note: Additional references obtained after the initial submission of this document have been added to this list.

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Annex A. Annotated Bibliography

 

This annex includes entries for nearly all of the references consulted in the preparation of this report. It provides bibliographic information, keywords to allow selection of references related to specific concepts, and abstracts for all references included. In addition, notes have been added by the study team in some cases. The notes were developed for use by the study team in reviewing and evaluating the literature. They address major findings, methodology issues, relevance of particular studies to issues addressed in this research effort, and relationships among references. The only references for which no entries are provided here are a few entire books or long book chapters that were cited in the report, but were impractical to abstract.

In the great majority of cases, abstracts were provided by the authors of the references cited. Where no author=s abstract was available, we have noted the source of the abstract or summary provided here. Some are authors= introductions, conclusions, or summaries; others were written by the study team.

Authors= note: Additional references obtained after the initial submission of this report have been added to this bibliography.

Author: Andre, J. T.

Date: 1995.

Title: Visual functioning in challenging conditions: Measuring and predicting the effects of alcohol consumption, stimulus motion, luminance and glare on contrast sensitivity.

Pub: Dissertation abstract.

Keywords:

Contrast sensitivity

Driving

Impairment

Low contrast acuity

Luminance

Motion detection

Spatial frequency

Holding: Full text ( ) Abstract/Summary (X) Reference only ( ) Other ( )

Abstract:

In an effort to assess the capabilities and limitations of human spatial vision, the present study investigated the individual and combined effects of the visual stressors of low luminance, alcohol consumption, stimulus motion and glare on contrast sensitivity for sine-wave gratings of different spatial frequencies. A secondary purpose was to explore the relationships among indices of intoxication, dark focus of accommodation and contrast sensitivity performance. Twelve naive subjects participated in two experimental sessions: Placebo (subjects expected alcohol but received only a negligible amount) and Alcohol (subjects expected and received 95% grain alcohol; mean breath alcohol content [BAC] = 0.073%). Contrast sensitivity was determined for 1.5, 3 and 6 cycles per degree gratings that were either stationary or traveled through a circular path, requiring pursuit eye movements.

Luminance was manipulated using a neutral density filter and the glare source consisted of six halogen bulbs that surrounded the stimulus. It was hypothesized that contrast sensitivity would be lowest in the condition with the greatest number of stressors, but it was not known if the stressors' effects would be interactive. Lowering luminance decreased contrast sensitivity by .27 log unit; adding the glare source further reduced contrast sensitivity by .28 log unit. Alcohol consumption and stimulus motion decreased contrast sensitivity by .16 and .10 log unit, respectively. All variables had interactive effects and decrements increased as spatial frequency increased.

The combined stressors effect was to decrease contrast sensitivity by 0.79 log unit, corresponding to 6.2 times more contrast necessary to reach threshold. Thus, the reduction or elimination of these effects should be of high priority in situations where optimal contrast sensitivity performance is desired. No useful relationships (for the drinker) were found between objective and subjective indices of intoxication. Further, subjective indices were not correlated positively with the alcohol-related loss in contrast sensitivity, although BAC was (r+.71). Subjective indices should not be used to predict BAC or alcohol related loss in contrast sensitivity. Dark focus values were unrelated to visual performance.

Authors: Andre, J. T., Tyrrell, R. A., Leibowitz, H. W., Nicholson, M. E., & Wang, M.

Date: 1994.

Title: Measuring and predicting the effects of alcohol consumption on contrast sensitivity for stationary and moving gratings.

Pub: Perception & Psychophysics, 56 (3), 261-267.

Keywords:

Acuity

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Low contrast acuity

Motion detection

Spatial frequency

Static acuity

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Contrast sensitivity was measured for 12 healthy young males while sober, after ingestion of an alcohol placebo, and after ingestion of alcohol (95% grain alcohol; mean estimated blood alcohol level = .088%). Observations were made for both stationary gratings and gratings that traveled through a circular path and required pursuit eye movements. The significant alcohol-related reduction in contrast sensitivity was 2.6 times greater for moving (.29-log-unit reduction) than for stationary gratings (.11-log-unit reduction). The loss in contrast sensitivity for the moving gratings of high spatial frequency (12 cpd) was particularly severe (.37 log unit). Estimated blood alcohol level was correlated with the loss in contrast sensitivity for moving gratings (r=.61), but not with the loss for stationary gratings. Estimated blood alcohol level was strongly correlated with the difference between the loss in contrast sensitivity to moving and stationary gratings (r=.75). These results are consistent with reports that alcohol consumption degrades the ability to make pursuit eye movements. Subjects' perceived intoxication level was not a reliable predictor of any index of visual performance.

Authors: Andre, J. T., Tyrrell, R. A., Leibowitz, H. W., Nicholson, M. E., & Wang, M.

Date: 1994.

Title: Measuring and predicting the effects of alcohol consumption on contrast sensitivity for stationary and moving gratings.

Pub: Perception & Psychophysics, 56 (3), 261-267.

Keywords:

Acuity

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Low contrast acuity

Motion detection

Spatial frequency

Static acuity

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Contrast sensitivity was measured for 12 healthy young males while sober, after ingestion of an alcohol placebo, and after ingestion of alcohol (95% grain alcohol; mean estimated blood alcohol level = .088%). Observations were made for both stationary gratings and gratings that traveled through a circular path and required pursuit eye movements. The significant alcohol-related reduction in contrast sensitivity was 2.6 times greater for moving (.29-log-unit reduction) than for stationary gratings (.11-log-unit reduction). The loss in contrast sensitivity for the moving gratings of high spatial frequency (12 cpd) was particularly severe (.37 log unit). Estimated blood alcohol level was correlated with the loss in contrast sensitivity for moving gratings (r=.61), but not with the loss for stationary gratings. Estimated blood alcohol level was strongly correlated with the difference between the loss in contrast sensitivity to moving and stationary gratings (r=.75). These results are consistent with reports that alcohol consumption degrades the ability to make pursuit eye movements. Subjects' perceived intoxication level was not a reliable predictor of any index of visual performance.

Authors: Bailey, L., & Sheedy, J.

Date: 1988.

Title: Visual screening for driver licensure.

Pub: Transportation in an aging society(Transportation Research Board special report, 218 (2)), 294-378.

Keywords:

Acuity

Aging

Driving

Dynamic acuity

Glare

Night vision

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract/Notes:

No author=s abstract or summary given. Fairly extensive review of history and issues in vision screening for driver licensure. Addresses issues of testing and setting of standards, and policies for possible restriction of driving privileges, rather than only pass/fail testing. Suggests screening and standards for acuity (using current methods) and visual field (using white object on dark background), and research on dynamic acuity testing and glare susceptibility and night driving issues (including contrast sensitivity). States that "for these three aspects of vision [dynamic visual acuity, contrast sensitivity, glare sensitivity], there is presently insufficient information to justify any particular standard for license denial." (p.316)

Author: Baker, K.

Date: 1949.

Title: Some variables influencing vernier acuity.

Pub: Journal of the Optical Society of America, 39, 567-576.

Keywords:

Acuity

Color vision

Contrast sensitivity

Illumination

Low contrast acuity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Since there is little experimental evidence on the influence of various stimulus factors on vernier acuity, functions relating vernier acuity to illumination have been obtained for two different exposure times and at three regions of the visible spectrum. An apparatus providing the necessary stimulus controls has been described in detail and the procedure is fully explained.

Vernier acuity, as measured by the reciprocal of the standard deviation of "alignment" setting, varies with illumination for both indefinitely long and for short exposures. At low brightness vernier acuity is low, rises rapidly with increase in illumination, and finally levels off at a constant level at high brightnesses.

Vernier acuity functions for short exposures are displaced downward and along the illumination axis relative to the function for long exposures. Thus maximum vernier acuity is never so high for short exposures and the maximum is reached at higher illuminations than with long exposures.

The relationship between vernier acuity and illumination for both long and short exposures is fitted by Hecht and Mintz=s theoretical equation for visual acuity based on the brightness discrimination of the eye.

Variations in the functions with duration of exposure of the acuity object are interpreted in the light of the intensity-time relationship and the findings of Graham and Kemp on the effect of exposure time on brightness discrimination.

To investigate the influence of wave-length on vernier acuity, acuity vs. illumination functions have been found for red, yellow, blue, and white light. The experiments were carried out on two different apparatus.

The two sets of data obtained on the two apparatus show that all the functions are of the same shape, but that slightly different maximum acuities are reached with the different colored illuminations. Red gives the highest acuity, yellow next, white next, and blue least. When refractive correction is made to allow for sharp focusing in blue illumination, the highest acuities are found with this color.

It was concluded that wave-length of illumination is of some significance in vernier acuity, since higher acuities are found with nearly monochromatic light than with white. This improvement is perhaps caused by reduction of blurring of retinal images by restriction of the range of wave-lengths.

Notes:

Compare to Craik. Similar curves obtained, with asymptote above which increasing "illumination" did not increase acuity. Author states she cannot explain the order of acuities among colors tested in second experiment.

Authors: Ball, K. K., Beard, B. L., Roenker, D. L., Miller, R. L., & Griggs D. S.

Date: 1988.

Title: Age and visual search: expanding the useful field of view.

Pub: Journal of the Optical Society of America A, 5(12) 2210-2219.

Keywords:

Aging

Central vision

Driving

Foveal vision

Peripheral vision

Useful field of view

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The useful field of view is defined as the visual area in which information can be acquired within one eye fixation. We studied visual search within this context and found a reduction in the size of the field of as a function of age. This loss, however, was recovered partially with practice. Standard acuity and perimetric tests of visual field, although diagnostic of disease, underestimated the degree of difficulty experienced by visually healthy older adults in everyday activities requiring the use of peripheral vision. To aid in predicting such performance, a model incorporating the effects of distractors and secondary task demands was developed.

Notes:

Subjects responded to dual tasks, one central, one peripheral (10B to 30B from fixation). Most interesting finding was a practice effect, where performance improved on peripheral task after practice, and improvement persisted six months post-training. If confirmed and extended to performance on clearly driving-related tasks, this could have implications for testing and licensing.

Authors: Ball, K. & Owsley, C.

Date: 1991.

Title: Identifying correlates of accident involvement for the older driver.

Pub: Human Factors 33 (5), 583-595.

Keywords:

Aging

Driving

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Most older adults rely on the automobile to maintain their mobility and independence, in spite of the fact that age-related behavioral and biomedical changes may make driving more difficult. Indeed, accident and fatality rates begin to rise after age 55. One research goal, therefore, is to identify functional measures that differentiate older adults who drive safely from those who do not. This paper discusses conceptual and methodological issues involved in addressing this question, considers why earlier research has been largely unsuccessful, presents a working model for approaching the problem, and argues the need for large-sample, prospective research in this area.

Notes:

Authors built predictive model for accidents in older drivers based on regression analysis. Independent validation needed. Conclusions and ideas for further research are useful. Authors strongly support prospective studies.

Authors: Ball, K., & Rebok, G. W.

Date: 1994.

Title: Evaluating the driving ability of older adults.

Pub: Journal of Applied Gerontology, 13(1) 20-38.

Keywords:

Acuity

Aging

Central vision

Driving

Motion detection

Peripheral vision

Useful field of view

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

As a society, we have the responsibility of continuing to meet the transportation needs of a growing population of older adults. Simultaneously, we must recognize that driving is the preferred mode of travel among older citizens and that the ability to drive provides the mobility that many older adults rely on to maintain their independence. Although some older adults experience changes that make driving more difficult in later life, most older drivers retain their driving competence. With highly publicized accidents involving older drivers, however, the issue of age as a risk factor has received considerable publicity. Therefore, recent research has focused on isolating risk factors with this population. These studies have indicated that a measure of visual attention, the Useful Field of View, is particularly promising as a functional measure of driving risk. Furthermore, research has shown that the Useful Field of View can be expanded with training. These findings have important implications for developing interventions that might aid in maintaining the skills needed to drive safely into older age.

Notes:

Presents model proposing UFOV as predictor of accident risk for older drivers, based on retrospective study in which UFOV scores were able to predict history of accident involvement with some accuracy.

Author: Beilock, R.

Date: 1995.

Title: Schedule-induced hours-of-service and speed limit violations among tractor-trailer drivers.

Pub: Accident Analysis and Prevention, 27, (1), 33-42.

Keywords:

Driving

Fatigue

Safety

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Driver fatigue is well recognized as an important causational factor in accidents involving long-distance truck drivers. Drivers may drive while fatigued for a variety of reasons. Important among these is the assignment of difficult or un reasonable delivery schedules. Using self-reported data, the frequency of violation-inducing schedules is estimated during their ongoing movement for a sample of 498 long-distance drivers. Assuming average legal speed limits of 55 MPH, 26% of the drivers were found to have violation-inducing schedules. Solo drivers, drivers hauling refrigerated loads, regular route drivers, and those with longer current trip distances are the most likely to have such schedules. Also estimated were total weekly work hours. Assuming average attained traveling speeds of 50 MPH, the average driver drives 46 hours per week and works a total of 58 hours.

Author: Beilock, R.

Date: 1988.

Title: 1988 RCCC Motor Carrier Safety Survey.

Pub: Alexandria, VA: Regular Common Carrier Conference.

Keywords:

Driving

Holding: Full text ( ) Abstract/Summary (X)

Abstract:

Safety on the highways is always a leading concern of the trucking industry. This report provides analyses and detailed results of the third RCCC Motor Carrier Safety Survey. In September 1988, 878 interviews were conducted with over-the-road truck drivers from the U.S. and Canada. These were the principal issues addressed: perceived speed limits, truck cruising speeds and compliance behavior; extent of driver training; extent of and truck drivers' opinions regarding drug and alcohol usage and testing; driver financial well-being, job intentions and employment alternatives; effectiveness of roadside inspections; role of driver fatigue in safety; off-Interstate access for larger combination rigs; acceptance and usage of certain safety devices (seat belts, antilock brakes, monitoring devices) and extent of radar detector usage.

Drivers (pp. 3-5). Average age, 41; average years of driving experience, 15.7. Average grade in school completed, 12, 52% completed high school; 18% completed at least one year of college. Ten percent belong to unions. For-hire carriers employ 52%, 27% are owner-operating under trip or permanent leases.

Equipment (pp. 5-8). Of the tractors in the 1988 Survey 52% are conventional (44% in the 1987 Survey); model years for 1984, 1985, 1986, and 1987 have progressively higher percentages of conventional tractors compared to cab-over-engine tractors. Single dry vans and single refrigerated vans account for 49% and 28% of all trailers, respectively. Single trailers 48 feet in length account for 57%.

Speed (pp. 10-13). Driver opposition to the 55mph speed limit approaches universality. Safety improved due to the 65 mph speed limit according to 59% of the drivers: 10% hold the opposite view. Rightly or wrongly, the large majority of truckers see the move to higher speed limits as both appropriate and safe.

Driver Training (pp. 13-19). Thirty percent received formal training; the least experienced are most likely to have had formal truck driver training. Where did they get trained? Private driver training schools: 51%; trained by companies that employed them: 28%; military: 21%. Surprisingly, it appears that drivers with formal training are somewhat more likely to have had accidents; the presence of formal training is not, in itself, indicative of a safer driver. There is a need for establishing and maintaining high standards so that drivers are taught accident-reducing skills, rather than given a false sense of security by just having had formal training.

Drug and Alcohol Testing and usage (pp.19-26). Drivers were asked for the percentage of their fellow drivers who regularly drive under the influence of illegal drugs. The mean response was 29%. Marijuana, "speed" and cocaine/"crack" were the most common illegal drugs used in the opinion of the respondents. Forty-three percent of the drivers indicate they have been tested for alcohol, up from 33% in 1987. Fifty percent had undergone drug testing, up from 38% in 1987. Support for mandatory random drug and alcohol testing among drivers remains high in 1988 (68%), albeit lower than in 1987 (73%).

Roadside Inspections (pp. 26-32). Median number of inspections per year: 3; 87% of the respondents have had at least one yearly inspection. Median delay per inspection: 20 and 30 minutes. Most truckers have favorable impressions of roadside inspections. When asked to rate on a scale with 10 as best, the average response on fairness is 7.0 and the average 6.9 on ability to get bad rigs off the road.

Driver Fatigue in Accidents (pp. 32-38). The average respondent claims that he/she can drive 10.6 hours before requiring an extended rest; 30% indicate that they can drive longer than 16 hours. Drivers estimate, on average, that 36% of truck accidents are due to driver fatigue. What to do about the driver fatigue problem? One third of the drivers indicate the need for greater (explicit) controls on those dictating the schedules -- the dispatchers, shippers, and receivers. Increased enforcement was the second most mentioned solution (16%).

Driver Shortage (pp. 39-45). Will drivers still be driving in 5 years? Just under one third indicate that they will not, with drivers over 50 years old nearly twice as likely as younger drivers to express such feelings. Reasons for leaving by those under age 50: 41% mention stress- and anxiety-related factors -- such as danger and tight schedules -- and being away from families at length; 27% say poor incomes; 21% mention stress from government agencies. To what occupations will they go? 21% to trucking-related occupations, like mechanic or dispatcher; 24% into other manual work professions such as carpentry, construction, and operating other types of vehicles; 19% say they'll be self-employed or in farming.

Off-Interstate Access (pp. 47-48). Just over one fifth of the drivers report at some time having pulled "twins." Of these drivers, over the past year, 15% pulled "twins" on roadways where they were not legal. Over four times as many truckers have at some time pulled 48-foot trailers compared to truckers who have pulled "twins." Of those with 48-footer experience, almost one third resort to driving on nondesignated roads. Georgia is the state that's most problematic about access.

Safety and Monitoring Devices (pp. 49-51). Seat Belts: Two fifths almost never use their seat belts and two fifths almost always use theirs; 34% favor a mandatory seat belt law and 53% are opposed. Antilock Brakes: 77% believe they have had some experience driving rigs with antilock braking systems. Of all drivers, 47% feel that antilock systems are safer than conventional braking systems; 24% are unsure or feel the systems are comparable; and 29% believe that conventional brakes are safer. Two thirds would oppose a law mandating the use of antilock systems on new rigs. Radar detectors: 62% of the drivers interviewed use radar detectors themselves, and the average respondent feels that 84% of all truck drivers use them; 94% of the respondents oppose a nationwide ban on radar detectors. On-board monitors: 12% of the respondents indicate that the tractor they were driving had an on-board monitoring device. Do drivers think that the mandatory installation of speed-and-driving-time-monitoring devices would improve safety? While only 28 percent say "Yes," 54% of those with monitoring devices say "Yes." Unlike a ban on radar detectors, most drivers are not philosophically opposed to a law requiring monitoring devices.

Notes:

This is the last year that this survey was conducted.

Authors: Bellamy, L. J., & Courtney, A. J.

Date: 1981.

Title: Development of a search task for the measurement of peripheral visual acuity.

Pub: Ergonomics, 24 (7) 497-509

Keywords:

Acuity

Peripheral vision

Visual field

Holding: Full text ( ) Abstract/Summary (X)

Abstract:

Results from 3 experiments with 27 18-56 yr olds indicate a relationship between peripheral visual acuity and search performance. It is suggested that use of this relationship can be made in assessing the relative extent of an individual's peripheral visual field (visual lobe) for target detection when visually screening them for industrial inspection tasks. A card sorting task involving visual search was developed that was shown to be sensitive to S differences in search speed. Speed of search correlated significantly with visual lobe area, but Ss' foveal acuities were not significantly related to search time. Test-retest reliability for Forms A and B of the card sorting task over a 1-wk period was r = .81 ( p < .001).

Authors: Berbaum, K. S., Kennedy, R. S., Williams, M. C., & May, J. G.

Date: 1985.

Title: A Survey of Vision Tests with Special Relevance for Military Jobs (Final Report for Phase I and Technical Proposal for Phase II).

Pub: Army Medical Research & Development Center and Essex Orlando, Technical Report EOTR 85-4.

Keywords:

Acuity

Contrast sensitivity

Driving

Dynamic acuity

Low contrast acuity

Motion detection

Spatial frequency

Static acuity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract: Authors= Summary

Our dependence on seeing is a fact of everyday life; persons with superior visual function will typically perform better on visual tests. These relations, which clearly hold for the extremes of vision, are widely supported both anecdotally and in the literature, but the extent of relationship is not always well defined. The three military services have active research efforts to study whether visual test scores are related to operational performance. The number of visual tests available for study is very large, a need exists to summarize this information, and to synthesize the schematic literature and other findings for application to military jobs. As a first step in this endeavor we selected five visual functions that we believe are not only important for military performance but also, properly implemented, could be used to select or classify persons so that improved operational performance could be expected and better allocation made of the human resources. Initially we had considered reviewing only contrast sensitivity in Phase I, but decided that a better choice would be to delay that review until Phase II and to cover several areas in Phase I that are less well known and perhaps not as actively studied within Army laboratories but which, in our opinion, show good promise for being predictive of operational performance. Throughout our reviews we attended to the practical issues of testing large numbers of individuals reliably, accurately, and quickly, and included sections in our reviews describing the apparatus to be employed.

In Phase II we propose two different activities to be conducted in parallel: 1) to complete our taxonomy of visual processes and visual tests, and to produce a handbook which reviews all this material; and 2) to conduct formal analyses of the visual functions and processes which comprise disparate military jobs. The handbook would contain cross-referencing of all tests to the visual requirements of the various jobs. It is expected that the handbook will take two years to complete, and the final report will contain 25-40 in-depth reviews according to the number of visual processes surveyed. Each of these reviews would be the product of a nationally recognized authority, although all reviews will be carefully edited and rewritten by the Essex key personnel to assure consistency in content, style and format. A publisher has expressed strong interest in production and distribution of the work provided the materials can be "civilianized" to broaden the interest for commercial markets. Essex has agreed to underwrite the necessary costs of transliterating the Phase II final report into a handbook that civilian vision and eye care professional would find useful.

Notes:

Extensive inventory of vision tests, along with review of independent and dependent variables related to several visual functions.

Authors: Blakemore, C., & Campbell, F.W.

Date: 1969.

Title: On the existence of neurones in the human visual system selectively sensitive to the orientation and size of retinal images.

Pub: Journal of Physiology, 203, 237-260

Keywords:

Acuity

Contrast sensitivity

Low contrast acuity

Spatial frequency

Holding: Full text (X) Abstract/Summary ( )

Abstract: Authors' summary

1. It was found that an occipital evoked potential can be elicited in the human by moving a grating pattern without changing the mean light flux entering the eye. Prolonged viewing of a high contrast grating reduces the amplitude of the potential evoked by a low contrast grating.

2. This adaptation to a grating was studied psychophysically by determining the contrast threshold before and after adaptation. There is a temporary fivefold rise in contrast threshold after exposure to a high contrast grating of the same orientation and spatial frequency.

3. By determining the rise of threshold over a range of spatial frequency for a number of adapting frequencies it was found that the threshold elevation is limited to a spectrum of frequencies with a bandwidth of just over an octave at half amplitude, centered on the adapting frequency.

4. The amplitude of the effect and its bandwidth are very similar for adapting spatial frequencies between 3 c/deg. and 14 c/deg. At higher frequencies the bandwidth is slightly narrower. For lower adapting frequencies the peak of the effect stays at 3 c/deg.

5. These and other findings suggest that the human visual system may possess neurones selectively sensitive to spatial frequency and size. The orientational selectivity and the interocular transfer of the adaptation effect implicated the visual cortex as the site of these neurones.

6. This neural system may play an essential preliminary role in the recognition of complex images and generalization for magnification.

Authors: Bourdy, C., Cottin, F., & Monot A.

Date: 1991.

Title: Errors in distance appreciation and binocular night vision.

Pub: Ophthalmic and Physiological Optics, 11(4), 340-349

Keywords:

Binocular/Monocular

Distance judgment

Low contrast acuity

Night vision

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Studying binocular vergence in relation to luminance levels, we isolated two types of behaviour which may explain differences in distance appreciation:

1. Underestimation of distances in subjects with overconvergence in darkness.

2. Overestimation of distances in subjects with underconvergence in darkness.

Progression towards the limiting value of convergence varies from one individual to another for each mesopic and scotopic luminance level and for different experimental conditions: variable discrepancy between the observation distance and the tonic vergence distance, accommodative or fusional stimuli at varying degrees of eccentricity, mobile stimuli in the observer's peripheral field. The study of bipartition in depth of a given interval for different observation distances confirms the existence of two major categories of individuals. Over- or underestimation of the nearer subjective half correlates to the binocular dark convergence capacity of each individual. These findings may explain errors in distance appreciation for road users in night vision.

Notes:

Part of driving-related research program whose goals include determining "the spatial behavior of road users at night." Found considerable individual differences in convergence in darkness, associated with differences in depth and distance judgements. This work is related to the body of work on dark focus by Leibowitz and Owens.

Author: Brennan, D. H.

Date: 1985.

Title: Entry visual standards and ocular examination techniques for future fighter aircrew.

Pub: Agard Conference Proceedings No. 396, Medical Selection and Physiological Training of Future Fighter Aircrew, pg. 35-1 to 35-6

Keywords:

Acuity

Binocular/Monocular

Color vision

Contrast sensitivity

Glare

Spatial frequency

Standards

Visual field

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Summary: The visual tasks of future fighter aircrew are likely to increase both in magnitude and complexity. The increasing adoption of devices for visual enhancement and protection, even now, poses problems of integration with spectacles.

The visual standards required for initial selection for training as a pilot or navigator should, if numbers permit, be such that trained aircrew are unlikely to require a visual aid until presbyopia physiologically demands correction in the latter half of the fourth decade.

This paper will discuss the visual standards considered apposite for future fighter aircrew and the related ocular examination techniques both conventional and those designed to test such specialized ocular functions as stereopsis, glare resistance, dark adaptation, hue discrimination and modulation transfer function.

Notes:

This paper supports others suggesting broadening of areas of visual function to be tested.

Authors: Brouwer, W. H., Waterinck, W., Van Wolffelaar, P. C., & Rothengatter, T.

Date: 1991.

Title: Divided attention in experienced young and older drivers; lane tracking and visual analysis in a dynamic driving simulator.

Pub: Human Factors 33 (5), 573-582.

Keywords:

Aging

Attention

Driving

Holding: Full text (X) Abstract/Summary ( )

Abstract:

A simulated driving task that required the simultaneous execution of two continuous visual tasks was administered to 12 healthy young (mean age 26.1 years) and 12 healthy older (mean age 64.4 years) experienced and currently active drivers. The first task was a compensatory lane-tracking task involving a three-dimensional road display. The second task was a timed, self-paced visual analysis task, involving either a vocal or manual binary response to dot patterns projected within the road display. Using adaptive tasks, single-task difficulty was individually adjusted for each subject. To control for individual differences in attention allocation strategy, the dual task was performed according to three different sets of instructions based on the relative importance of each task. Compared with young adults, older adults showed a significantly decreased ability to divide attention. This effect was apparent in lane tracking and in the accuracy of visual analysis. The impairment of divided attention was less pronounced in the vocal condition than in the manual one. This suggests that difficulty in integrating responses may be an important determinant of poor dual-task performance in old age.

Notes:

Ongoing research program; generally consistent results across studies.

Author: Burg, A.

Date: 1968.

Title: Vision and driving: A summary of research findings.

Pub: Highway Research Record, Number 216, 1-12.

Keywords:

Acuity

Driving

Dynamic acuity

Low contrast acuity

Peripheral vision

Static acuity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

To provide driver licensing administrators with heretofore unavailable information on which to establish effective vision-screening procedures for driver license applicants, a number of visual performance, personal, and driving habit characteristics of some 17,500 volunteer California driver license applicants were compared with their 3-year driving records (accidents and convictions). The vision tests included those for dynamic visual acuity, static visual acuity, field of vision, lateral phoria, low-illumination vision, glare recovery, and sighting dominance. Of these, dynamic visual acuity was most closely and consistently correlated with driving record, followed by static acuity, field of vision, and glare recovery. All relationships were in the "expected" direction, i.e., poor vision was associated with poor record. As expected, among all variables studied, age, sex, and average annual mileage play the largest role in influencing driving record. Accident and conviction frequencies increase with increasing mileage, are lower for females than for males, and are highest for the young age groups. Accident and conviction rates per 100,000 vehicle-miles decrease slightly with increasing mileage, are approximately the same for both sexes, and are highest for young drivers having the lowest rates. The report gives recommendations for additional research and suggests practical applications of the present findings.

Notes:

Based on records of 14,215 drivers. This early work is cited often in other papers.

Authors: Burg, A., & Coppin, R. S.

Date: 1966.

Title: Visual acuity and driving record.

Pub: Highway Research Record, Number 122, 1-6.

Keywords:

Acuity

Driving

Dynamic acuity

Low contrast acuity

Static acuity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The Institute of Transportation and Traffic Engineering at UCLA has for a number of years been conducting research on human factors in transportation. Within this general area considerable activity has been directed toward studying the visual requirements of the driving task. The California Department of Motor Vehicles, because of its responsibility for selecting individuals who should be licensed to drive a motor vehicle, also has a strong interest in knowing the visual requirements of driving, so that a more valid and reliable vision-screening procedure might be used.

It is not surprising, then, to find the Institute and the Department cooperating in a joint research venture whose purpose is to determine whether relationships can be found between how well a person sees and how well he drives, as reflected in his driving record. The U.S. Public Health Service is supporting a three-year research program to study the relationship between vision test scores and driving record. A preliminary report (1) presents a detailed description of the study as well as of the background research leading to it. The purpose of the present paper is to outline the general nature of the research program and to present the results obtained thus far from preliminary data analyses.

Notes:

Report from same study as Burg, 1968. Preliminary results only given here, show some relationship of dynamic acuity to sex, age, static acuity. Correlation of dynamic to static acuity decreases as target speed increases. See Burg, 1968 and other papers for later reports of this work.

Authors: Campbell, F. W., & Maffei, L.

Date: 1980.

Title: The influence of spatial frequency and contrast on the perception of moving patterns.

Pub: Vision Research, 21, 713-721.

Keywords:

Contrast sensitivity

Dynamic acuity

Low contrast acuity

Motion detection

Peripheral vision

Spatial frequency

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The perception of the apparent frequency of rotation of gratings of various spatial-frequencies and contrast is investigated. Increasing the spatial-frequency from 1 to 4 c/deg increases the perceived frequency of rotation. For higher spatial-frequencies, up to the limit of visibility, the perceived frequency of rotation decreases in inverse proportion to the spatial-frequency. At low contrast, near threshold, gratings are perceived to rotate very slowly and can actually appear to be stationary, hence the term "stopped motion". Above a contrast level of 0.05 the effects of contrast saturate, so that the apparent frequency of rotation equals the true frequency of rotation. If a rotating grating viewed by central vision is compared with an identical grating falling on the periphery of the visual field the latter is seen to rotate very much more slowly and indeed may appear to be stationary. If a rotating pattern consisting of small, randomly sited spots is compared with a similar target of large spots, the former is seen to rotate more slowly; the same being true for targets with only one spot thereon, providing they differ in size. Qualitative observations using gratings moving linearly appear to be as above. High spatial-frequency and low contrast gratings appear to move slower. Likewise an oscilloscope spot oscillating back and forth at a constant velocity appears to have a lower velocity in the peripheral field.

Notes:

Demonstration study looking at relationships between spatial frequency and apparent velocity or frequency of rotation. Needs to be extended to other types of motion, other situations.

Authors: Campbell, G., & Robson, J.

Date: 1968.

Title: Application of Fourier analysis to the visibility of gratings.

Pub: Journal of Physiology, 197, 551-566.

Keywords:

Acuity

Contrast sensitivity

Fourier analysis

Spatial frequency

Holding: Full text (X) Abstract/Summary ( )

Abstract:

1. The contrast thresholds of a variety of grating patterns have been measured over a wide range of spatial frequencies.

2. Contrast thresholds for the detection of gratings whose luminance profiles are sine, square, rectangular or saw-tooth waves can be simply related using Fourier theory.

3. Over a wide range of spatial frequencies the contrast threshold of a grating is determined only by the amplitude of the fundamental Fourier component of its wave form.

4. Gratings of complex wave form cannot be distinguished from sinewave gratings until their contrast has been raised to a level at which the higher harmonic components reach their independent threshold.

5. These findings can be explained by the existence within the nervous system of linearly operating independent mechanisms selectively sensitive to limited ranges of spatial frequencies.

Authors: Calabrese, O. J., Zwick, H.

Date: 1988.

Title: Meridian variations in spectral dark adaptation.

Pub: Letterman Army Institute of Research, Division of Ocular Hazards, Institute Report 372.

Keywords:

Acuity

Color vision

Dark Adaptation

Foveal vision

Impairments

Peripheral vision

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Spectral dark adaptation as a function of retinal meridian and of eccentricity was investigated by testing the absolute threshold dark adaptation curves for eight human volunteers at two retinal meridians. The horizontal and vertical meridians separately and together at eccentricities of 2 degrees and 16 degrees from a fixation point were studied. A microprocessor-operated dark adaptometer was used, and analysis of variance was performed on the data. The study indicated that meridian differences in the dark-adapted retina exist and that the horizontal meridian is more sensitive than the vertical meridian when the retina is tested at 16 degrees with medium wavelength light. This may indicate meridian differences in photoreceptor distribution.

Authors: Cavallo, V. & Laurent, M.

Date: 1988.

Title: Visual information and skill level in time-to-collision estimation.

Pub: Perception, 17, 623-632.

Keywords:

Binocular/Monocular

Driving

Event perception

Time to collision

Velocity

Visual field

Holding: Full text ( x ) Abstract/Summary ( )

Abstract:

Previous studies on the visual origin of time to collision (TC) information have demonstrated that TC estimates can be based solely on the processing of target expansion rate (optic variable τ). But in the simulated situations used (film clips), there was little reliable information on speed (owing to reduced peripheral vision) and distance (owing to the absence of binocular distance cues) available. In order to determine whether these kinds of information are also taken into account, it is necessary to take an approach where the subject receives a more complete visual input. Thus an experiment conducted on a circuit under actual driving conditions is reported. Experienced drivers and beginners, who were passengers in a car, had to indicate the moment they expected a collision with a stationary obstacle to take place. Subjects were blindfolded after a viewing time of 3 s. The conditions for speed evaluation, (normal vs. restricted visual field) and distance evaluation (binocular vs. monocular vision) by subjects were varied. The approach speed (30 and 90 km h-1) and actual TC (3 and 6 s) were also varied. The results show that accuracy of TC estimation increased with (I) normal visual field, (ii) binocular vision, (iii) higher speeds, and (iv) driving experience. These findings have been interpreted as indicating that both speed and distance information are taken into account in TC estimation. They suggest furthermore that these two kinds of information may be used differently depending on the skill level of the subject. The results are discussed in terms of the complementarity of the various potentially usable visual means of obtaining TC information.

Notes:

All subjects under all conditions underestimated time to collision. Binocular vision improved accuracy of estimation only at lower speeds, (confounded here with distance to target) where estimation was worst. Speed effect not found under normal visual conditions.

Authors: Charman, W., & Tucker, J.

Date: 1977.

Title: Dependence of accommodation response on the spatial frequency spectrum of the observed object.

Pub: Vision Research, 17, 129-139.

Keywords:

Accommodation

Contrast sensitivity

Dark (empty field) focus

Spatial frequency

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Experiments are described in which the monocular, steady-state, accommodation response to sinusoidal grating targets was assessed as a function of the spatial frequency of the grating and its vergence at the eye, using a laser optometer. At all levels of stimulus, the response is found to be dependent upon the grating frequency. At very low spatial frequencies the response is often substantially in error and is closely related to the accommodation exercised by the observer when viewing an empty field. At higher frequencies the response becomes more accurate and its exact value is probably dependent upon the observing conditions and upon the ocular aberrations and other properties of the observer. Further experiments with Snellen targets suggest that the accommodation to a target with a complex spatial frequency spectrum cannot be predicted from a knowledge of that spectrum and of the observer=s response to its component frequencies, under the same viewing conditions. The significance of the findings to theories of accommodation is indicated.

Authors: Chernysheva, S. G., Rozenblyum, Y. Z., Yachmeneva, E. I., Eremin, V. M., Utkin, A. V., & Eliseeva, L. A.

Date: 1993.

Title: Vision and Driving.

Pub: Human Physiology, 19, (1), 80-84.

Keywords:

Acuity

Color vision

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Motion detection

Peripheral vision

Spatial frequency

Standards

Time to collision

Velocity

Vision testing

Visual field

Holding: Full text (English Translation) Abstract/Summary ( )

Abstract: Authors' conclusion:

Thus, the problem of vision and transport has not been sufficiently investigated. The methods of visual function examination used in clinics, are most often traditional and not suitable for the evaluation of a driver=s professional fitness; the criteria of driving fitness being ill-founded and contradictory. So elaboration of ergophthalmological methods of visual function examination and of criteria of professional fitness of transport operators is of vital importance.

Quote: Yu. Z Rozenblum proposes the following functions corresponding to a driver's tasks be examined: detection and recognition of objects moving in the visual field; tracking of a moving object; prediction of point of intersection of moving and motionless objects; resolution under conditions of poor visibility, low luminosity, and blinding light sources.

Notes:

Review and comment article, not experimental work. Most references are to Russian articles, but some to US and European, especially military work. Valuable chiefly to show that scientists outside US are concerned about driver testing and are concluding that it needs to be made more task-relevant.

Authors: Cohen, A. S.

Date: 1987.

Title: Nutzbarer Sehfeldumfang und seine Variation in Feldsituationen.

Pub: Zeitschrift fur Experimentelle und Angewandte Psychologie, 34 (1), 17-37.

Keywords:

Driving

Peripheral vision

Useful field of view

Velocity

Visual field

Holding: Full text (in German) Abstract/Summary ( )

Abstract: (English abstract from PsychInfo)

The useful field of vision of a driver and its variation was investigated using a specially equipped car on a highway at velocities ranging from 80 to 130 km/h. The 22 subjects were experienced policemen. Their task was to detect signals mounted on the windshield and to respond as quickly as possible. The retinal locus of each signal was determined post hoc, using a new method described in this paper. The criteria for data evaluation were the rate of detected signals and the corresponding reaction time. The results showed that the size of the useful field of vision was not influenced by the speed of traveling. This finding contradicts the postulated tunnel vision at increased speed. However, the size of the useful field of vision decreased when the driver deviated from the prescribed speed of traveling, driving either too fast or too slow. It is assumed that the resulting internal workload exhausted the drivers' capacity and consequently caused perceptual narrowing, which is a peripheral manifestation of central overload. The results are discussed in terms of capacity limits in relation to the drivers' task demands.

Author: Craik, K.

Date: 1939.

Title: The effect of adaptation on visual acuity.

Pub: British Journal of Psychology, 29, 252-266.

Keywords:

Acuity

Adaptation

Illumination

Low contrast acuity

Holding: Full text (X) Abstract/Summary ( )

Abstract: Author=s Introduction

It was found by Mellone and Rawdon-Smith (1935, unpublished), and in a more extended investigation by the present author (1938), that visual adaptation has a considerable effect upon intensity discrimination. The differential threshold was found to be lowest when tested at the same illumination to which the eye was adapted, and to be raised considerably where these >test= and >adapt= illuminations were widely different.

It seemed that a similar investigation of visual acuity might throw some light on the relation between this and intensity discrimination. A positive result was to be anticipated from the experiments of Lythgoe (1932) in which acuity was diminished by a surrounding field, except when that field had approximately 1/10th the brightness of the smaller field containing the test object; for spatial and temporal proximity of an adapting field appear in general to have very similar effects.

Notes:

Classical work, but test conditions and measurement units are not those commonly used today. Curves were obtained for acuity vs. illumination, given equal adapting and test illumination levels (negatively accelerating increase asymptoting at about 100 e.f.c), and for acuity vs. illumination, given varying adaptation conditions (inverted u-shape curves, with best acuity near adapting illumination except at very low adapting levels).

Unit of illumination, e.f.c., appears to be "equivalent foot candles" (p.256).

Authors: Decina, L. E., Breton, M. E., & Staplin, L.

Date: 1991.

Title: Visual disorders and commercial drivers (Report No.DTFH61-90-C-00093).

Pub: Washington, DC: U. S. Department of Transportation, Federal Highway Administration, Office of Motor Carriers.

Keywords:

Acuity

Aging

Amblyopia

Binocular/Monocular

Central vision

Color vision

Contrast sensitivity

Driving

Dynamic acuity

Glare sensitivity

Impairments

Low contrast acuity

Peripheral vision

Spatial frequency

Standards

Static acuity

Useful field of view

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The objectives of the project were to reassess the adequacy of the current Federal vision standards for CMV operators (49, CFR, 391.41(b) (10), 1985). The technical approach included doing a critical review of existing literature; providing a preliminary draft of recommendations; preparing a risk assessment of visual criterion levels proposed; conducting a workshop to review draft recommendations with expert industry and vision panelists and providing a summary of the project with final recommendation.

A review and critical evaluation of the most significant scientific research, which investigated the vision performance of passenger and commercial drivers, revealed no conclusive evidence to support definitive changes to the current standard. However, it was deemed important to include visual acuity and visual fields requirements for the standard. Based on the critical review of the literature, opinion surveys, and workshop results collected from panelists representing the vision industry field, the following recommendations were made: distant visual acuity of at least 20/40 in each eye without corrective lenses or visual acuity separately corrected 20/40 or better with corrective lenses, distant binocular acuity of at least 20/40 in both eyes with or without corrective lenses, field of vision of at least 120 degrees in each eye measured separately in the horizontal meridian, and the ability to respond safely and effectively to colors of traffic signals and devices showing standard red, green, and amber. No test for color vision is required. The instructions to perform and record the visual examination were extensively revised. Identification of the type of equipment, the stimuli needed to conduct the testing, and instructions on how to perform the tests were added. The full description of the definition and testing procedures of the standard is provided in the body of the report. In addition, revisions were made to the list of visual disorders and impairments to be noted on the exam form.

Notes:

This report is useful background, provides history, and sets a baseline for the current vision standard.

Authors: Dichgans, J., & Brandt, T.

Date: (1978).

Title: Visual-vestibular interaction: Effects on self-motion and postural control.

Pub: In Held, R., Leibowitz, H. W., & Teuber, H.- L. (Eds.), Handbook of Sensory Physiology, VIII. Heidelberg: Springer.

Keywords:

Event perception

Motion detection

Relative motion

Self-motion

Posture

Situational awareness

Vection

Velocity

Vestibular effects

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Authors= introduction: The sensation of self-motion is a common visual illusion which allows inferences concerning visual-vestibular interaction. It may be perceived while gazing at moving clouds, streaming water, or when a train moves on the adjacent track in a railway station. This compelling sensation of body movement can even affect postural balance. On first approaching the problem, a psychologic explanation could be suggested in the sense of Helmholtz=s (1896) Urteilstäuschung. One might assume that these illusions are inferences based upon the conscious or unconscious assumption of a stable environment, so that when the environment does in fact move, the observer infers that he himself is moving. This interpretation would be consistent with the individual=s past experience as the entire visual surround seldom moves uniformly under natural conditions unless the body moves relative to the earth.

However, as in the case of other illusions, physiologic explanations may be more rewarding than psychologic ones. As Purkinje suggested, visual illusions reveal the truth about the visual system (Gesichtstäuschungen sin Sinneswahrheiten). An analysis consistent with his view takes into account that in the visually induced perception of self-motion, the term illusion only applies to the case in which the surround moves exclusively, and recognizes that identical visual stimulation occurs during actual body motion in which instance the same physiologic mechanism may maintain the veridical perception of body motion at constant velocity. The assumption of such a mechanism of visual-vestibular interaction, common to both illusion and veridicality, may lead to a better understanding of sensory control of body movement and spatial orientation than the psychologic explanation.

Under natural conditions with the eyes open, active as well as passive body motion is adequately perceived, be it of constant or varying velocity (Fig. 1 B). While riding in a vehicle with the eyes closed, however, the deficiencies of the vestibular system become apparent. Vestibular information about motion then is evoked only through acceleration or deceleration and dies out as the cupulae within the semicircular canals, or the otoliths, progressively return to their resting position during constant velocity. Consequently, constant velocity in the dark cannot be discriminated from rest for any extended period of time. Due to this lack of sustained labyrinthine information about constant velocity, deceleration from constant velocity is misinterpreted as acceleration in the opposite direction (Fig. 1 A). These two observations support the assumption that visual inputs are directly integrated with vestibular afferents. If so, the visual responses overcome the vestibular organ=s deficiency for constant velocity discrimination. Such a concept might also entail inborn neuronal networks for visual-vestibular interaction rather than solely experience and learning. Thus, the aforementioned illusion (see also Fig. 1 C) may in fact indicate a functionally important mechanism of multisensory interaction.

This chapter follows this line of reasoning. First, psychophysic evidence is presented indicating that motion-vision plays a predominant role not only in the perception of self-motion but much more generally, in dynamic spatial orientation and postural control. It will become apparent from this that visual and vestibular information must converge on the same locus somewhere in the brain where they are integrated to provide the basis for a unitary model of dynamic and static orientation in space. Second, neurophysiologic experiments, most of which were designed to test this postulate, are discussed. The results demonstrate the existence of at least one site of interaction within the central nervous system which is common to all vertebrate species tested so far: the vestibular nuclei.

In order to discuss the psychophysical evidence, it is necessary to first describe the various sorts of subjective localization and motion perception with their related reference systems, as well as the terminology.

Notes:

Detailed examination of many aspects of visual-vestibular interactions, vection, related topics. Extensive literature review.

Authors: Ebenholtz, S.

Date: 1976.

Title: Additivity of after effects of maintained head and eye rotations: an alternative to recalibration.

Pub: Perception & Psychophysics, 19, 113-116.

Keywords:

Eye position

Head position

Positional aftereffects

Potentiation

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Seven groups of 10 subjects each were exposed to various combinations of left and right head and eye rotations for a period of 10 min. Both head and eye produced significant aftereffects of prior position as measured by pointing at a visible target with the unseen hand, but there was no significant interaction. Thus, aftereffects of sustained head and eye rotation were shown to be additive and to account fully for the results of Craske and Crawshaw (1975). Eye muscle potentiation rather than recalibration may be assumed to be the cause of the altered direction of gaze resulting from exposure to displacing prisms.

Notes:

Argues that muscular potentiation resulting from sustained eye or head rotation can account for observed aftereffects on visual localization. This is in opposition to theory of "recalibration" to account for same observed effects.

Authors: Ebenholtz, S. M., & Fisher, S. K.

Date: (1982).

Title: Distance adaptation depends upon plasticity in the oculomotor system.

Pub: Perception and Psychophysics, 31, 551-560.

Keywords:

Accommodation

Binocular/Monocular

Distance adaptation

Phoria

Vergence

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Maintaining binocular fixation on a target at 20 cm in the absence of secondary cues to distance produced changes in apparent distance and lateral phoria. Positive lenses of 0, .5, 2.0, 3.5, and 5.0 spherical diopters (SD) were used to manipulate the level of accommodative convergence in force during the period of maintained fixation. An inverse relationship was found between the stimulus to accommodation and the magnitude of the induced esophoria, the phoria being linearly related to an increase in apparent distance. The distance aftereffect obtained in the condition with the lowest net accommodative stimulus (i.e., 0 D) equaled that typically produced by based-out prism adaptation with full secondary cues to distance available. In a second experiment, subjects walked through a well-lit hallway while viewing through a pair of 5 base-out prisms. It was shown that increasing the stimulus to accommodation by adding negative lenses of 0, 1.5, 3.5, and 5.5 SD reduced the adaptive change in apparent distance, as well as the change in phoria produced by the conventional base-out prism adaptation paradigm. It was concluded that a change in the resting tonus of the disparity vergence system underlies such adaptation, rather than recalibration of the oculomotor cues to distance. Monocular exposure data indicated that a small change in the tonus control for the accommodative system may be present as well.

Authors: Epstein, W., & Cody, J .W.

Date: 1980.

Title: Perception of relative velocity: A revision of the hypothesis of relational determination.

Pub: Perception, 9, 46-60.

Keywords:

Dynamic acuity

Velocity

Holding: Full text (X ) Abstract/Summary ( )

Abstract:

The conventional formulation of the hypothesis of relational determination asserts that the perceived relative velocities of two or more objects depend upon their relative rates of displacement with respect to stationary referents in the visual field. Experiment 1 showed that this formulation is too restrictive by demonstrating the transposition-of-velocity effect under conditions in which two light spots moved in the absence of static visible contours and traversed unequal path lengths. Experiment 2 showed that angular velocity per unit of relative angular extent, and not relative linear or perceived extent, of the respective motion paths influences perceived relative velocity in nonarticulated space. The retinal dimensions of static visible frameworks were shown in experiment 3 to influence perceived relative velocity in a direction consistent with the conventional formulation of the relational-determination hypothesis, but the weight of the evidence suggested a reformulation along the following lines: the perceived relative velocities of two objects are significantly affected by the proportions of the retinal projections of the respective movement fields traversed by the two objects in the same unit of time, even when the motion fields consist only of the objects' motion paths.

Notes:

This article concentrates almost entirely on testing opposing theories of velocity perception.

Authors: Fejer, T. P. & Girgis, R.

Date: 1992.

Title: Night myopia: implications for the young driver.

Pub: Canadian Journal of Opthamology, 27, (4), 172-176.

Keywords:

Acuity

Aging

Amblyopia

Contrast sensitivity

Dark focus

Driving

Impairments

Low contrast acuity

Luminance

Myopia

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

A total of 380 randomly selected patients aged 16 to 80 years, who did not have eye disease underwent testing for night myopia between August and October 1989 with a laser speckle generator under both photopic and scotopic conditions. For the first 308 subjects, the speckles were continuously run, and for the next 72 subjects a timer was used to minimize the accommodative stimulus. An increase in myopia of 0.75 dioptres or more from the photopic to the scotopic state, equivalent to a visual acuity of 20/45 or less, was considered indicative of night myopia. Overall, 17% of the subjects were found to have night myopia. Of the 26 subjects aged 16 to 25 in the timer group, 38% had night myopia of 0.75 D or more, 23% had night myopia of 1.00 D or more, and 4% had night myopia of 2.50 D, which is equivalent to an acuity of 20/265. The results indicate that driving in the dark could create visual difficulties for certain younger patients that a night myopic correction would eliminate.

Author: Fox, M. D.

Date: 1988.

Title: Elderly drivers' perceptions of their driving abilities compared to their functional visual perception skills and their actual driving performance.

Pub: Physical and Occupational Therapy in Geriatrics, 7(1-2) 13-49.

Keywords:

Aging

Color vision

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Peripheral vision

Standards

Static acuity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The rationale of occupational therapy is to help individuals develop and function independently within their environment. The privilege of driving affords people one aspect of independence by serving as a link for the accomplishment of other daily living tasks. Although evidence suggests an age related decline in the skills needed for safe driving, especially after age 55, the clinical predictors of driving performance are relatively unknown. This study examined the elderly drivers' perceptions of their driving abilities, compared to their clinically tested functional skills in the area of visual perception, and their actual in-car driving performance. The specific skills assessed included peripheral visual field, depth perception, color sensitivity, static visual acuity, dynamic visual acuity, and figure-ground discrimination. The comparisons were examined by the chi-square and analysis of variance (ANOVA) statistical procedures to determine whether a significant difference existed among the variables. A population sample of 115 males, 65 years and older, were selected from an outpatient clinic at the Veteran's Administration Hospital in Richmond, Virginia.

Results indicated that clinically tested visual perception skills and actual in-car driving performance can be predictive based on left and right peripheral vision, and brown/green color sensitivity. This study also indicated that people generally tend to over-rate their driving abilities. It is believed that a larger sample and some testing instrument changes could yield more significant results. Limitations of this study and ideas for future research are provided.

Author: Gallwey, T.

Date: 1982.

Title: Selection tests for visual inspection on a multiple fault type task.

Pub: Ergonomics, 25 (11) 1077-1092.

Keywords:

Acuity

Peripheral vision

Useful field of view

Vision testing

Visual field

Holding: Full text ( ) Abstract/Summary (X)

Abstract:

Although individual differences between inspectors is the most significant factor in differences in inspection performance there are no suitable selection tests. The task was analyzed to indicate the required mental characteristics, and from this a battery of 10 selection tests was devised. These were used with a simulated task to include the search and decision components of inspection. Presentation was by sets of slides that contained 2, 4, or 6 fault types; slides were classified as fault free, acceptable fault, or reject. 48 college students and 18 industrial inspectors (mean age 34.8 yrs) participated. A multivariate analysis of covariance showed no difference between the student and industrial Ss. The best predictor was a simplified version of the task. Good predictive ability was obtained with the Group Embedded Figures Test; other good predictors were lobe size and mental imagery. If these tests were not used, good predictive ability was obtained with a subset of the WAIS, Eysenck Personality Inventory Extraversion scale, and the Gordon Test of Visual Imagery Control.

Author: Ginsburg, A. P.

Date: (1984).

Title: Visual form perception based on biological filtering.

Pub: In Spillmann, L., & Wooten, B. R., (Eds.), Sensory Experience, Adaptation, and Perception. Hillsdale, N.J.: Erlbaum. pp. 53-72.

Keywords:

Acuity

Contrast sensitivity

Form perception

Illusions

Spatial frequency

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

A filtering approach to understanding visual perception is shown to provide a framework for understanding certain aspects of how we see contrast, size, and form in simple gratings and letters as well as more complex visual illusions and portraits. Gestalt laws of closure, wholeness, proximity, and similarity are demonstrated using filtered images. Complex variations in the perceived magnitude of Müller-Lyer illusions are well predicted from computer data based on biological filtering. A physics of form perception is used to relate the detection and identification of Snellen type letters to individual contrast sensitivity functions. These results suggest that biologically based filtering and linear systems analysis, typified by Fourier techniques, can provide important tools with which to probe the foundations of our visual world.

Notes:

Basic statement of Ginsburg=s theories, applied to well-known visual perceptual phenomena.

Author: Ginsburg, A. P.

Date: 1981.

Title: Proposed new vision standards for the 1980's and beyond: Contrast sensitivity (AFAMRL-Transparency-80-121).

Pub: Wright-Patterson Air Force Base, Ohio: Air Force Aerospace Medical Research Laboratory, Aerospace Medical Division, Air Force System Command.

Keywords:

Acuity

Contrast sensitivity

Spatial frequency

Standards

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Present visual standards are generally based on the observer=s ability to see small high contrast black and white letters or symbols. Current research shows that such vision tests are not adequate to evaluate an individual=s target detection and recognition capability over ranges of target size and contrast used in real situations. New vision tests are being developed that use the observer=s report of the visibility of sine-wave gratings (that look like fuzzy bars) to assess visual capability with much more sensitivity than that of standard tests. The new tests, called contrast sensitivity, assess vision using the same method used to assess hearing. Just as hearing tests use sound intensity and temporal frequency to measure audiometric sensitivity, contrast sensitivity tests use contrast and spatial frequency to measure visual sensitivity. Because standard eye charts do not change contrast, they cannot measure vision sensitivity to any except the smallest size symbols. The relationship between contrast sensitivity and eye charts will be discussed using normal and abnormal vision. Although standard eye charts are useful to create an in-focus image in the back of the retina, contrast sensitivity techniques are needed to measure the next physiological state that determines the observer=s response to that image. Data are presented that reveal individual differences in contrast sensitivity among normal observers that have definite implications for visual performance in operational environments. Since these differences in visual sensitivity can relate to detection and recognition ranges, these data can then be transformed into time to perform certain tasks and lead naturally towards visual standards being based on task performance under operational conditions. It is suggested that contrast sensitivity data be obtained in parallel with conventional vision tests to begin creating visual standards that relate to observer capability over the full range of operational environments.

Notes:

This work serves as background to the pubs looking at ability of contrast sensitivity and other tests to predict task performance.

Authors: Ginsburg, A. P., Cannon, M. W., Jr., & Nelson, M.

Date: (1980)

Title: Suprathreshold processing of complex visual stimuli: Evidence for linearity in contrast perception.

Pub: Science, 208, 619-621.

Keywords:

Contrast sensitivity

Spatial frequency

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Magnitude estimation experiments show that perceived contrast for both sine and square waves is a linear function of stimulus contrast. The suprathreshold sine: square ratio required for equal perceived contrast derived from these data was verified by contrast matching experiments. These findings imply a high degree of linearity in suprathreshold visual processing of contrast.

Notes:

This work was designed to answer questions about contrast sensitivity functions above threshold range. Showed nearly constant sine/square ratio for equal judged contrast at above-threshold contrasts, for spatial frequencies above about 1 c/deg, above contrast value of 0.1.

Authors: Ginsburg, A. P., Evans, D. W., & Cannon, M. W. Jr.

Date: 1984.

Title: Large-Sample Norms for Contrast Sensitivity.

Pub: American journal of Optometry and Physiological Optics, 61, 80-84

Keywords:

Acuity

Contrast sensitivity

Standards

Static acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

A portable microprocessor-controlled instrument automatically measured the static and dynamic contrast sensitivity functions (CSF=s) of 265 observers for a normal population at the Dayton Air Fair and Air Force Museum. Repeat measures for six observers taken 6 months later show small, nonsystematic differences from original measurements. Median values of contrast sensitivity as well as regions encompassing 75 and 90% of our sample are shown.

Notes:

Provides a beginning for the collection of population norms. Note that refractive state of subjects was not equated; subjects used their normal corrections for all testing. Subjects were self-selected volunteers; authors excluded those with history or evidence of pathology.

Authors: Ginsburg, A. P., Evans, D. W., Sekuler, R. & Harp, A.

Date: 1982.

Title: Contrast sensitivity predicts pilots= performance in aircraft simulators.

Pub: American Journal of Optometry and Physiological Optics, 59, 105-109.

Keywords:

Acuity

Contrast sensitivity

Spatial frequency

Pilot performance

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Contrast sensitivity was found to be better than visual acuity for predicting a pilot=s ability to detect a small, semi-isolated, air-to-ground target. Eleven instructor pilots had their acuity measured by both conventional and contrast sensitivity methods. Scotopic contrast sensitivity showed the highest correlation with slant detection range (0.83). Conventionally determined visual acuity proved to be a poor predictor of a pilot=s ability to detect a small low contrast target.

Notes:

One more piece of evidence for predictive validity of contrast sensitivity, but does not directly address driving. This article concentrates on target detection, which may be more generalizable to driving tasks than bombing accuracy or aircraft landing proficiency.

Authors: Good, M. C., & Baxter, G. L.

Date: 1986.

Title: Evaluation of short-range roadway delineation.

Pub: Human Factors, 28 (6), 645-660

Keywords:

Acuity

Driving

Low contrast acuity

Peripheral vision

Useful field of view

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

A distinction is drawn between long- and short-range delineation, the latter being provided to aid the driver in tracking the roadway at night and under poor visibility conditions. A quasi-linear describing function approach is employed to represent the driver as a sensor and controller, and it is hypothesized that reductions in the quality of the driver=s visual field will be reflected by an increase in the level of the "remnant" (interpreted in part as visual observation noise).

Experiments were performed on a rural road, to which a variety of delineation treatments were applied, using a vehicle that permitted the identification of driver-vehicle describing functions as subjects negotiated the test course. The results are generally supportive of the experimental hypothesis, with the describing function parameters yielding evaluations of delineation treatments that are consistent with each other and with subjective ratings of task difficulty.

Authors: Gurgold, G..D., & Harden, D. H.

Date: 1978.

Title: Assessing the driving potential of the handicapped.

Pub: The American Journal of Occupational Therapy, 32, (1), 41-46.

Keywords:

Driving

Impairments

Vision Testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

With a knowledge of available driving aids, the physical requirements needed to drive, the cognitive and perceptual deficits and their relationship to driving, the therapist should be able to make an early assessment of a client's driving potential. Other factors such as sensation, visual acuity, peripheral vision, distance judgment, reaction time, and spasms should not be overlooked in the preliminary driving evaluation.

Through the development of the Servo-hand control, physical requirements needed for driving have been reached. C-5 quadriplegic persons and other severely disabled individuals who cannot apply adequate force to drive with conventional hand controls are thus enabled to drive.

Authors: Held, R.

Date: 1968.

Title: Dissociation of visual functions by deprivation and rearrangement.

Pub: Psychologische Forschung, 31, 338-348.

Keywords:

Ambient vs focal

Analysis of form

Localization

Orientation

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Deficiency in visually-guided behaviors is the dominant effect of rearing kittens from birth without patterned visual stimulation of the two eyes. Following such deprivation, form discrimination is found relatively intact when the effects of the deficient orienting behavior are eliminated from the testing procedure. Recent experimental analyses implicate visual feedback contingent upon movement in a normal environment as the condition responsible for the losses in visually guided behavior produced by deprivation of patterned stimulation. Using the techniques of these experiments, the two eyes may be dissociated with respect to their ability to control movement but not in their performance of shape discrimination. Related research on adaptation to optical rearrangement has shown a high degree of lability in visually-guided behavior but only limited modifiability in perception of shape. It is suggested that the modification of a shape that does occur results from altered localization of its parts in space. The measurable modification of shape is limited by the fixedness of the pattern analyzing system. Certain implications for the earliest development of shape discrimination are drawn.

Notes:

Defense of "two modes of processing" concept. Classic early work.

Authors: Henderson, R. L., & Burg, A.

Date: 1974.

Title: Vision and audition in driving.

Pub: Santa Monica, CA: System Development Corporation.

Keywords:

Acuity

Driving

Dynamic acuity

Foveal vision

Low contrast acuity

Motion detection

Peripheral vision

Static acuity

Useful field of view

Vision testing

Visual field

Holding: Full text ( ) Abstract/Summary ( x )

Abstract:

A systematic analysis was made of the visual and auditory requirements of automobile and motorcycle driving which resulted in the identification of visual performance parameters that appear important to driving but that are not currently considered in the visual screening of driver license applicants. These include such parameters as perception of motion, dynamic performance of the total visual system, visual performance under low levels of illumination or in the presence of glare, and useful peripheral vision. The analysis did not identify similar requirements of auditory performance.

A device was designed and constructed to test performance on the new visual functions as well as on selected conventional measures. Performance on these tests was measured on 669 licensed California drivers and compared with past accident record. The results show that poor performance on several of the new vision tests is associated with poor driving record. Further, it was shown that some vision test scores serve as better predictors of accident involvement than such measures as age, sex, annual mileage or other biographical variables generally considered to be the best available predictors.

It is concluded that if the results of the study are verified and cross-validated on a much larger sample of the driving population, a basis will exist for developing and implementing a standardized visual screening program for driver license applicants that could contribute to improving highway safety.

Notes:

Early study, background for later papers in this series.

Author: Hess, R.

Date: (1984).

Title: Uses and abuses of assessing contrast threshold functions for anomalous vision.

Pub: In Spillmann, L., & Wooten, B. R., (Ed.), Sensory Experience, Adaptation, and Perception. Hillsdale, NJ: Lawrence Erlbaum Associates. pp. 633-650.

Keywords:

Acuity

Amblyopia

Contrast sensitivity

Foveal vision

Impairments

Spatial frequency

Supra-threshold vision

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

The contrast sensitivity approach has enjoyed much success in its recent applications to anomalous vision. The uses, abuses, limitations and extensions of this approach are detailed using examples of amblyopias from acquired (organic) as well as developmental (functional) origin. This approach is seen to extend our assessment of visual function and to have greater sensitivity than acuity. We are, however, severely limited in what we can say of the perceptual consequences using this approach for two reasons. First, sensory thresholds are rather special points on our sensory scale and second, they monitor a rather peripheral aspect of visual function.

Notes:

Notes both usefulness of CSF testing for certain diagnostic purposes, and limitations of such testing for assessment of visual function. Examples of problems: Cites evidence of differences between threshold and supra-threshold measures. Some impaired subjects show elevated thresholds with near-normal supra-threshold function. Some subjects can detect gratings, but show anomalous vision at detected frequencies, based on report of what is seen and on studies of phase discrimination. Discusses implications for testing of useful vision.

Authors: Hills, B. L., & Burg, A.

Date: 1977.

Title: A reanalysis of California driver vision data: General findings (Transport and Road Research Laboratory Report 768).

Pub: Crowthorne, Berkshire, U. K.: Transport and Road Research Laboratory.

Keywords:

Acuity

Aging

Driving

Dynamic acuity

Vision testing

Visual field

Holding: Full text ( ) Abstract/Summary ( x )

Abstract:

Data on over 14,000 drivers from the 1967 California driver vision study have been reanalyzed with a view to establishing their implications for driver vision standards. For the main analysis the sample was divided into four age groupings: under 25, 25-39, 40-54, and over 54.

The most consistent result throughout the study has been the failure to find a direct relationship between poor visual performance and high accident rates for young and middle-aged drivers. For the over 54 age group, Dynamic and Static Visual Acuity showed the most consistent relationship with accident rates but for an individual driver their accident prediction value remained very low. A more detailed age analysis failed to define more precisely the age at which these relationships develop. No evidence was found to support the use of Total Visual Field as a driver screening test. The results for two tests of night vision were regarded as inconclusive for the Over 54 age group. For the same nominal standard of binocular static visual acuity, the Ortho-Rater screener was found to fail markedly fewer drivers than the Snellen wall chart. The implications of varying the cut-off scores for each test were investigated, and the suggestion made that perceptual rather than sensory tests with greater accident predictive power would be needed before acceptable alternative screening methods could be specified for driver licensing purposes.

Notes:

Authors argue for "perceptual rather than sensory tests" of vision for drivers.

Authors: Janke, M. K.

Date: 1990.

Title: Safety effects of relaxing California's clean-record requirement for driver license renewal by mail.

Pub: Accident Analysis and Prevention, 22 (4), 335-349.

Keywords:

Driving

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

A pilot program was established in California in 1982 authorizing mail renewal of driver licenses for persons under age 70 lacking clean (accident- and conviction-free) 4-year driving records, but showing clean 2-year records at selection. Such drivers constitute about 14% of California's renewal population, or about 500,000 renewees per year. Eligible drivers whose licenses expired in 1983 were subjects of the present study. Half of them were randomly assigned to a group whose members were sent offers of renewal by mail and the other half were sent standard renewal notices requiring appearance in a field office and successful completion of vision and traffic law tests. Traffic accidents and convictions following the mailout of these documents were tracked for both groups; results presented here cover a 4-year period subsequent to mailout. During this period (a normal license term in California), no significant overall difference was shown between the groups with respect to subsequent convictions or accidents. However, significant detrimental effects on accidents were noted for a subgroup of drivers who had experienced recent traffic violations or accidents which were not on their records at selection. Implications of these results are discussed.

Notes:

Provides evidence that waiving current vision test for one or two renewal cycles may not have much effect on accidents or convictions, although authors speculate that poorer accident performance in age group 30-50 may involve incipient vision problems not being detected. This study and others in this series had very large number of subjects (hundreds of thousands).

Author: Johnson, C.

Date: 1976.

Title: Effects of luminance and stimulus distance on accommodation and visual resolution.

Pub: Journal of the Optical Society of America, 66, 138-142.

Keywords:

Accommodation

Acuity

Dark focus

Spatial frequency

Static acuity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Measurements of accommodation and visual resolution were obtained at a number of luminance levels and stimulus distances. With reductions in luminance the eye approached a "fixed-focus" condition of accommodation for intermediate distances, resulting in successively larger errors in accommodation for both near and far stimuli. The visual resolution values were initially affected by both the luminance and distance of the stimulus. Subsequent measurements of resolution, following the correction of accommodative errors, were found to be independent of the stimulus distance. The findings are discussed with regard to the problems of "night myopia" and variations in visual resolution with stimulus distance.

Notes:

Consistent with other work from Leibowitz lab on dark focus, night myopia.

Authors: Josephson, J. E., Erickson, P., Arthur, B., Holden, B., Harris, M., Tomlinson, A., Caffrey, B. E., Finnemore, V., & Silbert, J.

Date: 1990.

Title: Monovision.

Pub: Journal of the American Optometric Association, 61, (11), 820-826.

Keywords:

Acuity

Aging

Binocular/Monocular

Contrast sensitivity

Driving

Impairments

Low contrast acuity

Peripheral vision

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Monovision has been a controversial contact lens correction modality for over 30 years. This paper addresses the major issues and concerns and considers them in the light of patient safety, visual efficiency and practitioner liability.

Authors= Conclusion:

Information currently available indicates that monovision is an effective and reasonable prescription for correcting presbyopia, especially in the early period. Properly selected patients can expect to obtain good vision for most viewing distance under most circumstances. Patient selection criteria must include a full profile of ocular function, personal needs and regular activities. Patients should be fully informed of all correction alternatives, any visual limitations and how to exercise appropriate precautions. An informed consent document should be presented and explained to the patient and then signed.

"Clinical tests of binocular function, important in all patients, are critical in the fitting of monovision lenses. With properly exercised professional judgment and appropriate clinical screening, the safety and visual efficiency of the monovision corrected patient can be assured."

Notes:

Looks at advantages of monovision but concentrates on discussing possible disadvantages, impairments that might be created or exacerbated by monovision corrections. Notes possibility of increased glare sensitivity, effects on night driving, impairment of low contrast sensitivity, some other effects that are possible but not well documented.

Authors: Kelly, D. H.

Date: (1979).

Title: Motion and vision. II. Stabilized spatio-temporal threshold surface.

Pub: Journal of the Optical Society of America, 69, 1340-1349.

Keywords:

Acuity

Contrast sensitivity

Dynamic acuity

Flicker

Motion

Spatial frequency

Stabilized images

Static acuity

Velocity

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

The stabilized contrast-sensitivity function measured at a constant retinal velocity is tuned to a particular spatial frequency, which is inversely related to the velocity chosen. The Fourier transforms of these constant-velocity passbands have the same form as retinal receptive fields of various sizes. At low velocities, in the range of the natural drift motions of the eye, the stabilized contrast-sensitivity function matches the normal, unstabilized result. At higher velocities (corresponding to motions of objects in the environment), this curve maintains the same shape but shifts toward lower spatial frequencies. The constant-velocity passband is displaced across the spatio-temporal frequency domain in a manner that is almost symmetric about the constant-velocity plane at v=2 deg/s. Interpolating these diagonal profiles by a suitable analytic expression, we construct the spatio-temporal threshold surface for stabilized vision, and display its properties in terms of the usual frequency parameters; e.g., at low spatial frequencies, the temporal response becomes nearly independent of spatial frequency, while at low temporal frequencies, the spatial response becomes independent of temporal frequency.

Notes:

Concludes "our results suggest that retinal image motion is the sine qua non of vision." Looks at contrast sensitivity in combination with image motion, generated and measured in various ways. May be relevant if a contrast sensitivity test is to be included in CDL vision standard.

Authors: Kennedy, R. S., Ritter, A. D., Berbaum, D. S., & Hettinger, L. J.,

Date: 1987.

Title: Visual temporal acuities: model and prospectus for empirical study (report for contract number N62269-86-D-0109/0020).

Pub: Warminster, PA: Naval Air Development Center.

Keywords:

Acuity

Driving

Dynamic acuity

Event perception

Motion detection

Situational awareness

Velocity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Temporal acuity refers to the ability to accurately and quickly perceive events as they occur serially over time. Generally, audition is considered to be the most temporally acute sensory modality, functioning primarily in the frequency domain; however, many military tasks place strong demands on visual temporal acuity. We argue that an insufficient understanding of temporal factors in vision may lead to inadequate design of military man-machine systems. For instance, the inability to rapidly "switch" attention from one visual display to another may be a major factor in the "human error" component. Military Standards currently contain specifications for visual display design which are relevant to static visual acuity, but contain no corresponding specifications which are relevant to temporal acuity.

The current paper proposes the predicate for a plan of study to be undertaken to identify the determiners, factors or sensory channels that underline visual temporal acuity. Specifically, a series of tests, based on prior empirical research on temporal factors in vision, have been implemented on a portable, lightweight computer. These tasks can be administered to individuals to determine: 1) the degree of their stability and reliability as psychometric indices of temporal acuity, 2) if stable and reliable, the number of temporal "factors" or channels, 3) their uniqueness relative to what is presently measurable and predictive of operational performance (i.e., intelligence and visual acuity), and 4) to determine the extent to which temporal acuity can be tested and modeled in a manner sufficiently parsimonious to permit implementation in Military Standard 1472c.

Notes:

Provides some rationale for using tests of "temporal" acuity, and for selection of particular tests. Tests are proposed for: critical flicker fusion, dynamic visual acuity, simultaneity, metacontrast, Neisser's visual search.

Author: Klein, R.

Date: 1991.

Title: Age-related eye disease, visual impairment, and driving in the elderly.

Pub: Human Factors 33 (5), pp. 521-525.

Keywords:

Acuity

Aging

Impairments

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

As people age, a number of visual functions such as acuity, visual field, and night vision deteriorate. This decline in vision is associated in part with an increase in vehicular accidents per mile driven by the elderly. Four age-related ocular conditions - cataract, macular degeneration, open-angle glaucoma, and diabetic retinopathy - are primarily responsible for the decline in visual acuity and visual field in the elderly. Few epidemiologic data are available about these diseases, and at present they cannot be prevented. There is need for more information about visual decline and how it affects driving performance and for development of pragmatic approaches for detecting and assessing the elderly driver with functional visual deficits.

Notes:

Review article: concentrates on four specific medical conditions. Issues addressed include vision testing, changes in signage and lighting design, possible driving restrictions. References to epidemiologic papers on eye disease.

Authors: Kline, D. W., Kline, T. J. B., Fozard, J. L., Kosnik, W., Schieber, F., & Sekuler, R.

Date: 1992.

Title: Vision, aging, and driving: The problems of older drivers.

Pub: Journal of Gerontology, 47(1) 27-34.

Keywords:

Acuity

Aging

Driving

Dynamic acuity

Event perception

Impairments

Low contrast acuity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Although there are well-recognized declines in visual functioning with age, their contribution to the problems of older persons on tasks in the natural environment, including driving, are largely unknown. Adults ranging in age from 22-92 years were surveyed in regard to their visual difficulties when driving and performing everyday tasks. The visual problems of drivers increased with age along five different visual dimensions: unexpected vehicles, vehicle speed, dim displays, windshield problems, and sign reading. Several of the age-related visual problems that were reported appear to be related to the types of automobile accidents more common among older drivers. The study also replicated the findings from an earlier investigation of non-driving tasks that showed visual declines with age on five dimensions: visual processing speed, light sensitivity, dynamic vision, near vision and visual search. These findings indicate promising areas of research regarding the effects of visual aging on tasks in the natural environment.

Notes:

Survey study, using self-report only; no direct testing of visual functions. Findings are generally similar to other studies of vision and aging, but should be evaluated in light of other studies showing that self-evaluation of visual function and driving skills may not be well correlated with objectively tested visual function and driving skills.

Author: Kline, T .J. B., Ghali, L. M. , Kline, D. W., & Brown, S.

Date: 1990.

Title: Visibility distance of highway signs among young, middle-aged, and older observers; Icons are better than text.

Pub: Human Factors 32 (5), 609-619.

Keywords:

Acuity

Aging

Driving

Abstract:

The visibility distances for young, middle-aged, and elderly observers of four different highway signs were compared under day and dusk lighting conditions. No age differences were observed. Icon signs, however, were visible at much greater distances than were text signs for all three age groups, a difference that was more pronounced under dusk conditions. There were no age differences in the comprehension of icon signs, but there was considerable variability from one icon sign to another in the degree to which they were comprehended. Acuity was found to be a better predictor of the visibility distance of text signs in both day and dusk conditions than it was of icon signs. To the degree that they are comprehended, icon signs appear to offer drivers of all ages almost twice as much time in which to respond to them.

Notes:

Mean age of "middle-age" group was high (53+). Comprehension of icons is problematic.

Authors: Kruk, R. & Regan, D.

Date: 1983.

Title: Visual test results compared with flying performance in telemetry-tracked aircraft.

Pub: Aviation, Space, and Environmental Medicine, 54, 906-911.

Keywords:

Acuity

Contrast sensitivity

Dynamic acuity

Event perception

Motion detection

Pilot Performance

Velocity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

We compared flying performance with the results of laboratory and airborne visual tests. Pilots flew high-performance, telemetry-tracked A4 and F-14 aircraft. In the low-level task, the index of performance was bombing accuracy; in air-to-air combat, performance was assessed by the number of missile hits scored per hit received (win/loss ratio). The chief laboratory tests comprised discrimination between two speeds of a radially-expanding flow pattern, and manual tracking of a visual target. Airborne tests comprised visual acquisition distance of an A4 aircraft, and visual sensitivity to a change in the course of an approaching A4 aircraft. We found that the flow pattern and movement-in-depth tracking test results correlated with bombing accuracy, confirming previously reported simulator findings. The results of airborne visual tests correlated with the win/loss ratio in combat, and tracking test results correlated with the number of missiles fired per combat engagement. Subsidiary test of motion, grating contrast, and visual acuity thresholds were carried out for comparability with other studies, but these measures did not predict flying performance.

Notes:

Same general comments as for Kruk, Regan, et al., 1981. This study found somewhat more compelling correlations between visual and flight performance measures. Note, contrast sensitivity was not predictive.

Authors: Kruk, R., Regan, D., Beverley, K. I., & Longridge, T.

Date: 1981.

Title: Correlations between visual test results and flying performance on the Advanced Simulator for Pilot Training (ASPT).

Pub: Aviation, Space, and Environmental Medicine, 52, 455-460.

Keywords:

Acuity

Contrast sensitivity

Dynamic acuity

Motion detection

Pilot performance

Spatial frequency

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Looking for visual differences in pilots to account for differences in flying performance, we tested five groups of subjects: Air Force primary student jet pilots, graduating (T38 aircraft) students, Air Force pilot instructors, and two control groups made up of experienced nonpilot aircrew and nonflying civilians. This interim report compares 13 different visual test results with low-visibility landing performance on the Air Force Human Resources Laboratory ASPT simulator. Performance was assessed by the number of crashes and by the distance of the aircraft from the runway threshold at the time of the first visual flight correction. Our main finding was that, for student pilots, landing performance correlated with tracking performance for a target that changed size (as if moving in depth) and also with tracking performance for a target that moved sideways. On the other hand, landing performance correlated comparatively weakly with psychophysical thresholds for motion and contrast. For student pilots, several of the visual tests gave results that correlated with flying grades in T37 and T38 jet aircraft. Tracking tests clearly distinguished between the nonflying group and all the flying groups. On the other hand, visual threshold tests did not distinguish between nonflying groups except for grating contrast, which distinguished between the nonflying group and the pilot instructors. The sideways motion tracking task was sensitive enough to distinguish between the various flying groups.

Notes:

Preliminary findings. Useful mostly as a suggestion of predictive validity for some kinds of vision testing, but flying differs from driving in important ways. This whole body of research is limited by using mostly pilots as subjects. These subjects have high acuity and low incidence of other visual deficits. Lack of between-subjects variability on vision measures restricts correlations between visual and other performance measures.

Authors: Leibowitz, H. & Owens, D. A.

Date: 1978.

Title: New evidence for the intermediate position of relaxed accommodation.

Pub: Documenta Ophthalmologica, 46 (1), 133-147.

Keywords:

Accommodation

Acuity

Dark focus

Driving

Low contrast acuity

Holding: Full text ( X) Abstract/Summary ( )

Abstract:

Experimental evidence is presented that the focus of the eye tends to return passively to an individually characteristic intermediate resting position or dark-focus whenever (1) the stimulus to accommodation is degraded or (2) when the quality of the image is independent of focus. Based on measurements of the dark-focus with a laser optometer, it is possible to predict the magnitude of night, empty field, and instrument myopia on an individual basis. The role of the intermediate dark-focus as a factor in accommodation also provides an explanation for the paradoxical variation of visual acuity with observation distance. Applications to night myopia and night driving are described, and implications for clinical practice are discussed.

Authors: Leibowitz, H. W. & Owens, D. A.

Date: 1975.

Title: Anomalous myopias and the intermediate dark focus of accommodation.

Pub: Science, 189, 646-648.

Keywords:

Acuity

Accommodation

Dark focus

Low contrast acuity

Static acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

The dark focus of accommodation for an individual observer correlates highly with the magnitude of night, empty field, and instrument myopia. These anomalous myopias are interpreted as resulting from the passive return of accommodation to an individually determined intermediate dark focus when the stimulus for accommodation is degraded or absent, or when the need for accommodation is eliminated.

Authors: Leibowitz, H. W., Owens, D. A., & Helmreich, R. L.

Date: 1995.

Title: Research needs in transportation: from highways to airways.

Pub: Emerging Needs and Opportunities for Human Factors Research, Part II, Chapter 9, Page 1. (In Press)

Keywords:

Acuity

Aging

Binocular/Monocular

Contrast sensitivity

Driving

Dynamic acuity

Event perception

Foveal vision

Impairments

Low contrast acuity

Motion detection

Peripheral vision

Situational awareness

Spatial frequency

Standards

Static acuity

Useful field of view

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

This chapter discusses needs for behavioral research in transportation focusing on two diverse areas that are representative of the broad scope of human factors. One area, vehicular traffic safety, draws on traditional concerns with the individual and the machine, while the second, aviation safety, centers on team performance and training in a high technology environment. With regard to aviation, the definition of relevant human factors research includes components of organizational, social and personality, educational, and cross-cultural psychology, as well as more traditional cognitive, experimental, and engineering concerns.

All forms of modern transportation--aviation, maritime, rail, space, and vehicular--involve the interaction of individuals or groups with technology in a regulated system. The successful application of human factors research must reflect an understanding of systems influences on behavior and on the acceptance of solutions. Despite its concentration on the automobile and one aspect of aviation, many of the research needs discussed apply equally to other forms of transportation, such as railroad and maritime operations.

Authors: Leibowitz, H., & Post, R.

Date: 1982.

Title: The two modes of processing concept and some implications.

Pub: In Beck, J. (Ed.), Organization and Representation in Perception. Hillsdale, NJ: Lawrence Erlbaum Associates. pp. 343-363.

Keywords:

Ambient vs. focal

Driving

Holding: Full text (X) Abstract/Summary ( )

Abstract: Author=s Introduction (truncated)

The first hundred years in the history of modern psychology have resulted in the development of a number of theories. In particular, the study of perception has been enriched by theoretical formulations, such as those of the Gestalt psychologists and of J. J. Gibson, which have played such an important role in the conference. More recently, we have been introduced to sophisticated information processing models and to the spatial frequency analysis of visual scenes.

There are many advantages to theoretical points of view. One advantage is to suggest new and different ways to look at phenomena. Even though the scope of a given theory may be limited, it suggests new "mental sets" and unique ways of approaching interesting observations.

The purpose of the present paper is to discuss a recent theoretical position that has stimulated novel analyses and interpretations of surprisingly diverse findings. The "two-visual systems" concept of concern here originated with Gerald Schneider=s dissertation at M.I.T. in the early 1960s in which he discovered that object recognition and spatial orientation can be selectively impaired in the hamster by lesions of the cortex or the superior colliculus. In 1967 Schneider, along with Richard Held, Colwyn Trevarthen, and David Ingle, presented a symposium at the Eastern Psychological Association meeting where they described experiments, including studies on humans, which they interpreted in terms of the two systems concept (Held, 1968; Ingle, 1967; Schneider, 1967; Trevarthen, 1968). For anyone interested in the history and early development of this problem, these works represent a prime literature source.

Although the concept of two systems is derived from selective ablation studies and much of the literature has a strong anatomical flavor, the present treatment deliberately de-emphasizes anatomy. This is of course not meant to minimize the ultimate importance of neurophysiology, however. Because the nervous system is much more complex in humans than in the hamster and our concern is primarily with perception and behavior in humans, it seems appropriate to follow Held=s suggestion and to speak of "two modes of processing spatially distributed information" (Held, 1970).

The two modes of processing concept can best be described in functional terms. It posits two independent and dissociable modes of processing: (1) a "focal" mode that is in general concerned with the question of "what" and subserves object recognition and identification; (2) an "ambient" mode concerned with the question of "where" which mediates spatial orientation, locomotion, and posture.

In the original formulation of the two systems or modes of processing, reference was made to two visual systems, but this must be modified. Although visual information is adequate for the focal mode, the ambient mode involves the coordination of motor activity with the visual, vestibular, auditory and somatosensory system, particularly, kinesthesis. In the discussion that follows, examples of the diverse basis of the ambient mode and the importance of interaction among its various components are described. . .

Notes:

Longer exposition of one portion of material in Leibowitz, Post, Brandt, & Dichgans, 1980.

Stress on interactions with modalities other than visual.

Authors: Leibowitz, H., Post, R., Brandt, T., and Dichgans, J.

Date: 1980.

Title: Implications in recent developments in dynamic spatial orientation and visual resolution for vehicle guidance.

Pub: In Wertheim, A., Wagenaar, W. A., and , H. (Eds.), Tutorials on Motion Perception. pp. 231-260. New York/London: Plenum Press.

Keywords:

Acuity

Aging

Contrast sensitivity

Dark focus

Driving

Dynamic acuity

Event perception

Low contrast acuity

Motion detection

Peripheral vision

Situational awareness

Spatial frequency

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract: (Authors= Introduction)

The objective of the present chapter is to examine a number of problems of vehicle guidance within the context of recent developments in psychophysics, neurophysiology, anatomy and neurology. The theme of this presentation is that these, like other applied problems, exist primarily when the underlying physiological mechanisms are not well understood. With an increased understanding of fundamentals we can not only better appreciate the nature of applied problems but can also frequently identify methods towards their solution. In turn, applied problems serve a valuable function by directing attention to gaps in our basic understanding which leads to suggestions for fruitful areas for research. At the same time as we learn more about fundamentals, new application possibilities manifest themselves.

The plan of the present chapter is to review selectively three areas in which recent research has increased our understanding of fundamental mechanisms. These are 1) the two modes of processing concept; 2) the multisensory nature of spatial orientation; and 3) the intermediate dark-focus of accommodation. Space does not permit an exhaustive treatment of these topics. Rather, the literature will be reviewed briefly in order to provide a basis for describing the relevance of these developments to specific problems in vehicle guidance and locomotion. By juxtaposing basic developments and potential applications their close relationships should be apparent, and the value of an approach which purposely de-emphasizes differences between "basic" and "applied" science will, it is hoped, be demonstrated.

Notes:

Much useful information, and the authors make explicit connections between visual functions and driving. Rationale given for testing various visual functions for driver licensure.

Author: Lempert, P.

Date: ??

Title: Standards for contrast acuity/sensitivity and glare testing.

Pub: [GET PUB FROM PSYCHLIT] pp. 113-119

Keywords:

Acuity

Central vision

Contrast sensitivity

Glare

Low contrast acuity

Spatial frequency

Standards

Static acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract: (Study Team Abstract)

Differences in display area, luminance, test object design, statistical validation procedures, and contrast often generate inconsistent and/or contradictory test results. Therefore, the author suggests that there is an immediate need for general agreement on the critical design criteria of these devices and on uniform test procedures. Lempert briefly discusses NAS/NRC standards for the assessment of visual acuity, which specify test parameters. He asserts that the background luminance must remain constant at all levels of contrast for contrast acuity/sensitivity testing. In normal eyes, at high luminance, the peak sensitivity is about 5 cycles per degree, and high-frequency cutoff occurs at approximately 60 cpd. Contrast is sometimes defined as the maximum deviation from the background luminance divided by the background luminance. While this definition is usually applied to eye charts, a difficulty with this format is that the mean luminance decreases with optotypes that occupy a large proportion of the total screen. Accordingly, Lempert presents a definition of contrast in which contrast is regarded as modulation, the ratio of the maximum change in luminance from its mean value.

Dynamic optotype presentations can help detect degradation or retinal summation mechanisms, which is useful in selection of candidates for complex visual tasks. Lempert asserts that modern standards must include criteria for dynamic testing. In addition, Lempert suggests that an inadequate number of targets, such as a letter chart using only three letters at each contrast or with only one optotype of each size and contrast, seriously undermines test validity. Finally, the author states that the recommendations of the Committee on Vision for the Assessment of Distance Visual Acuity and the Committee's observations on contrast testing should be the basis for new clinical contrast acuity/sensitivity systems.

Author: Lippmann, O.

Date: 1979.

Title: The effect of the Texas Medical Advisory Board for driver licensing on driving performance.

Pub: Proceedings of the 23rd Annual Conference, American Association for Automotive Medicine, in cooperation with the University of Louisville School of Medicine, pp. 203-210.

Keywords:

Aging

Driving

Impairments

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Traffic offenses related to chronic medical conditions and the effect of a Medical Advisory Board for Driver Licensing are discussed.

The accident and violation ratio of 19,110 Texas drivers with medical limitations was studied. Ratios before and after Board review were compared in each category of illness and in each age group and related to the state average.

The effect was good in all categories of illness with the exception of limitations related to psychiatric and addiction disorders. The accident ratio of all drivers with chronic medical conditions improved by 51%. Traffic violations improved by 21%.

Other variables in the determination of the effect of the Board were discussed.

A substantial improvement of the statewide traffic safety may be attributed to the effect of the Medical Advisory Board.

Notes:

Medical model; Board review most beneficial for drivers over 40 yrs old, extremely beneficial for drivers with vision problems.

Authors: Long, G. M., & Garvey, P. M.

Date: 1988.

Title: The effects of target wavelength on dynamic visual acuity under photopic and scotopic viewing

Pub: Human Factors, 30 (1), 3-13.

Keywords:

Acuity

Color vision

Dynamic acuity

Foveal vision

Low contrast acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The effects of target wavelength on the resolution of moving targets were investigated over a range of target velocities under both photopic and scotopic viewing conditions. The wavelength of the photopically matched targets had no effect on dynamic acuity under the bright background condition. However, with low background luminance the wavelength of the targets had pronounced effects, with blue targets producing far superior resolution and red targets, the poorest resolution. These results were maintained over both 250- and 400-ms target durations and regardless of whether initial target position was foveal or peripheral. The likely contribution of the rod system to dynamic visual acuity under some conditions is proposed, and possible implications for applied settings are discussed.

Authors: Long, G. M., & Riggs, C.

Date: 1991.

Title: Training effects on dynamic visual acuity with free-head viewing.

Pub: Perception, 20, 363-371.

Keywords:

Dynamic acuity

Static acuity

Holding: Full text ( x ) Abstract/Summary ( )

Abstract:

Training effects on dynamic visual acuity (DVA) were determined over a range of target durations and target velocities under the viewing conditions of free-head movement. Dynamic acuity levels were lower than static acuity levels, and training was found to be very effective in improving performance, particularly under the most difficult conditions in which performance was poorest. Improvement was also most evident among those observers who initially exhibited the poorest DVA scores. Preliminary comparisons between DVA scores of a non-select sample of college students and those of a small group of college athletes indicated that the athletes were not very different from the nonselect group and would also benefit from training on the task.

Notes:

Authors raise many interesting questions about training effects: relation to real-world visual tasks, duration of training effect, etc. These are relevant to CMV driver licensing issues.

Authors: Lovsund, P., Hedin, A., & Tornros, J.

Date: 1991.

Title: Effects on driving performance of visual field defects: A driving simulator study.

Pub: Accident Analysis and Prevention, 23 (4), 331-342.

Keywords:

Central vision

Driving

Foveal vision

Impairments

Peripheral vision

Useful field of view

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

To elucidate the possible traffic safety risks induced by visual field defects, a method was developed based on a driving simulator. The capacity to detect stimuli of different size appearing in 24 different positions of the screen in front of the driver was measured. Two groups of normal subjects and a number of subjects with different visual field defects were studied. In the groups of normals, the median reaction times were fairly homogeneous. There was a slight difference between central and peripheral stimuli, which was somewhat larger for the older subjects. Among the subjects with field defects, the individual variations were very dominant. Very few of these showed a capacity to compensate for their deficiency. In order to gain insight into possible compensatory mechanisms of these persons, eye movement recordings were made. The results indicate that the visual search pattern may be of importance in this respect. Some comparisons with respect to detection capacity were also made with one-eyed subjects and with optically generated field restrictions (spectacles and spectacle frames).

Notes:

Most interesting finding is inability of most subjects to compensate for visual field defects under these conditions. Use of test methods that come close to duplicating real world driving tasks may reveal functional capabilities differing from what would be assumed based on clinical tests (e.g., ability of some subjects to compensate for visual field defects).

Authors: Ludvigh, E., & Miller, J.

Date: 1958.

Title: Study of visual acuity during the ocular pursuit of moving test objects. I. Introduction.

Pub: Journal of the Optical Society of America, 48, 799-802.

Keywords:

Acuity

Dynamic acuity

Motion

Static acuity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Visual acuity may be measured during the voluntary ocular pursuit of moving test objects. This visual function has been referred to as dynamic visual acuity. The apparent movement of the test object is produced by rotating a mirror in the desired plane of pursuit by means of a wheel and disk type variable speed drive. The range of angular velocities utilized is 10/ to 170/sec at the nodal point of the tested eye. It is shown that visual acuity deteriorates markedly and significantly as the angular velocity of the test object is increased. It is shown further that the relationship between visual acuity and the angular velocity of the test object may be described satisfactorily by the semiempirical equation Y=a+bx3. It also is pointed out that individuals possessing similar static acuity may differ significantly in their dynamic acuity. The possible causes for the observed deterioration of acuity are discussed and it is concluded that imperfect pursuit movements of the eye result in a continued motion of the image on the retina. This motion results in reduced intensity contrast, which is a factor in producing loss in acuity.

Authors: Lundh, B. L., & Arlinger, S.

Date: (1984).

Title: Three dB-scales for the standardized visuogram.

Pub: Vision Research, 24, 889-890.

Keywords:

Acuity

Contrast sensitivity

Scaling

Spatial frequency

Standards

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract/Notes:

Letter to the editors, proposing standardization of contrast sensitivity testing on model of clinical audiological testing. Proposes three alternative dB scales for quantifying contrast sensitivity, and use of "visuogram" comparable to audiogram to represent results.

Author: Mack, A.

Date: 1970.

Title: An investigation of the relationship between eye and retinal image movement in the perception of movement.

Pub: Perception & Psychophysics, 8, 291-298.

Keywords:

Event perception

Motion detection

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The question investigated was whether or not eye movements accompanied by abnormal retinal image movements, movements that are either or both at a different rate or in a different direction than the eye movement, predictably lead to perceived movement. Os reported whether or not they saw a visual target move when the movement of the target was either dependent on and simultaneous with their eye movements or when the target movement was independent of their eye movements. In the main experiment, observations were made when the ratio between eye and target movement (em/tm) was 2/5, 1/5, 1/10, 1/20, and 0. All these ratios were tested when the direction of the target movement was in the same (H+), opposite (H-), and at right angles to (V+, V-) the movement of the eyes. Eye movements, target movements, and reports of target movement were recorded. Results indicate that a discrepancy between eye and target movement greater than 20% predictably leads to perceived target movement, whereas a discrepancy of 5% or less rarely leads to perceived movement. The results are interpreted as support for the operation of a compensatory mechanism during eye movement.

Notes:

Authors clearly see results as supporting compensatory theory; also state that they do not believe that all movement perception is suppressed during saccades.

Author: Malfetti, J. L, Editor.

Date: 1985.

Title: Needs and problems of older drivers: Survey results and recommendations

Pub: Proceedings of the Older Driver Colloquium. Washington, DC: AAA Foundation for Traffic Safety.

Keywords:

Acuity

Aging

Color vision

Driving

impairments

Low contrast acuity

Peripheral vision

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Several papers dealing with various aspects of older driver population. One paper on vision:

Allen, M. J., Vision of the older driver: Implications for vehicle and highway design and for driver testing.

Presents non-technical review of vision impairments common to the elderly, and presents recommendations for vehicle and highway design changes to accommodate older drivers.

Authors: Matin, E., Rubsamen, C., & Schreyer, P.

Date: 1985.

Title: Rapid psychophysical measurements of orientation discrimination for basic research and clinical testing.

Pub: Bulletin of the Psychonomic Society, 23 (6), 500-502.

Keywords:

Acuity

Contrast sensitivity

Spatial frequency

Static acuity

Vision testing

Holding: Full text (x ) Abstract/Summary ( )

Abstract:

The yes-no signal-detection task was coupled to an interactive "tracking" procedure to create a rapid method for measuring orientation discrimination in clinical and basic research settings. As is the case in related physiological work, only one stimulus is presented on each trial: No simultaneous or successive matching is involved. Results obtained with this method show that orientation sensitivity for sinusoidal gratings depends on orientation (the "oblique effect") but is independent of spatial frequency.

Notes:

One example of a candidate quick and relatively inexpensive testing paradigm, "PEST," which might be adaptable to use in vision screening or testing for CDL.

Authors: Mayyasi, A., Beals, R., Templeton, A., & Hale, P.

Date: 1971.

Title: The effects of ambient illumination and contrast on dynamic visual acuity.

Pub: American Journal of Optometry and Archives of the American Academy of Optometry, 48, 844-848.

Keywords:

Acuity

Dynamic acuity

Illumination

Low contrast acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Thirty male college students, with 20/20 vision or better, were tested under two levels of ambient illumination and two levels of contrast. Dynamic acuity data were then analyzed by a randomized complete block design (2x2x30) with repeated measures. The results indicate that an ambient illumination-contrast combination exists where DVA is optimum.

Notes:

Main effect of ambient illumination was highly significant, as was interaction of room by projector illumination. In high room illumination, higher contrast gave better performance. In low room illumination, it did not. Note that authors used contrast calculation equivalent to C=(max - min)/min; not (max - min)/(max + min). The variations of illumination and contrast do not seem to have been completely independent.

Author: McColgin, F. H.

Date: 1960.

Title: Movement thresholds in peripheral vision.

Pub: Journal of the Optical Society of America, 50 (8), 774-779.

Keywords:

Motion detection

Peripheral vision

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The absolute velocity thresholds of movement were determined at 48 positions in peripheral vision. An aircraft-type instrument, with a standard altimeter hand, was located at random positions on the concave, black surface of an 80-in. Fiberglas hemisphere. Four types of movement were investigated (clockwise and counter-clockwise rotation, vertical and horizontal motion) under conditions of constant photopic lighting. While the subject fixated on the center point of the hemisphere, the absolute velocity threshold of each type of movement was determined for each position using the method of limits. Ten airline pilots served as subjects. The absolute threshold isograms on perimetric charts for both rotary and linear motion are elliptical in shape, with the horizontal axis approximately twice as long as the vertical axis. There is no difference between a subject's ability to see clockwise or counter-clockwise rotation. An individual's ability to perceive vertical motion is slightly better than his ability to perceive horizontal motion in the area adjacent to the horizontal axis. Velocity and area swept by the instrument hand are significant factors in the perception of movement, but they are not similarly correlated for all types of movement.

Notes:

Confirms other findings that area of high sensitivity extends further in horizontal than vertical directions from fixation point (threshold isograms were roughly elliptical).

Authors: McKnight, A. J., Shinar, D., & Hilburn, B.

Date: 1991.

Title: The visual and driving performance of monocular and binocular heavy-duty truck drivers.

Pub: Accident Analysis and Prevention - An International Journal, 23 (4), 225-237.

Keywords:

Acuity

Binocular/Monocular

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Low contrast acuity

Peripheral vision

Static acuity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

This study compared the performance of 40 monocular and 40 binocular tractor-trailer drivers on measures of both visual and driving performance. On the visual measures, the mononuclear drivers were significantly deficient in contrast sensitivity, visual acuity under low illumination and glare, and binocular depth perception. They were not significantly deficient in static or dynamic visual acuity, visual field of individual eye, or glare recovery. Driving measures of visual search, lane keeping, clearance judgment, gap judgment, hazard detection, and information recognition showed no differences between monocular and binocular drivers. Monocular drives were poorer than binocular drivers only in sign reading distance in both daytime and nighttime driving. This decrement correlated significantly with the binocular depth perception measure. There were large individual differences within each group for most of the visual and driving performance measures. It was concluded that monocular drivers have some significant reductions in selected visual capabilities and in certain driving functions dependent on these abilities, compared with binocular drivers. However, monocular drivers are not significantly worse than binocular drivers in the safety of most day-to-day driving functions. Implications of these findings and the large individual differences within each group are discussed.

Author: Miller, J. M.

Date: 1956.

Title: The effect of altered illumination on visual acuity measured during ocular pursuit. (Project NM 001 110 501, Report No. 12)

Pub: Pensacola, FL: U.S. Naval School of Aviation Medicine, Naval Air Station

Keywords:

Acuity

Dynamic acuity

Illumination

Motion detection

Velocity

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

The present study was an attempt to determine the effect of changing the intensity of the target illumination on dynamic visual acuity. The range of target velocities tested was 200/sec to 1200/sec, while the range of target intensities was 0.04 to 125.0 footcandles.

Previous studies have demonstrated that the amount of improvement in visual acuity resulting from an increase in illumination above a level of 1.0 footcandle is negligible when the test object is stationary. Ludvigh has theorized that when the eye is attempting to pursue a moving target there is frequently a velocity mismatch between the eye and target. This mismatch results in a reduction of the retinal intensity contrast which reduces visual acuity. It would be predicted then, that visual acuity would be improved by raising the illumination to higher levels when the test object is moving. The present study indicated that this is indeed what happens in that if the level of illumination was raised as the angular velocity of the test object was increased, the visual acuity did not deteriorate as rapidly as would otherwise have been expected.

It was also found that the semi-empirical equation, y = a + bx3, which had been used previously to describe dynamic visual acuity at a single brightness level described satisfactorily the data obtained throughout the entire range of brightnesses examined.

Author: Miller, J.

Date: 1958.

Title: Study of visual acuity during the ocular pursuit of moving test objects. II. Effects of direction of movement, relative movement, and illumination.

Pub: Journal of the Optical Society of America, 48, 803-808.

Keywords:

Acuity

Dynamic acuity

Illumination

Motion

Static acuity

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

It was demonstrated that the manner in which visual acuity deteriorates as the angular velocity of the test object increases is similar regardless of whether the motion is produced by moving the target vertically, horizontally, or by rotating the observer in a horizontal plane. It was shown also that the semiempirical equation Y=a+bx3 describes satisfactorily these three types of movement. It was pointed out that individuals having a low acuity threshold in the vertical plane of movement will be likely also to have a low threshold in the horizontal plane. It was shown that although 5 to 10 footcandles may be sufficient illumination when the test object is stationary, visual acuity is substantially benefitted by increases up to 125 foot-candles when the observer is rotated. This corroborates earlier findings reported by Ludvigh.

Notes:

No test with active movement of the observer; only passive movement. It would be interesting to see these findings confirmed with active movement, since its total sensory input would be different.

Authors: Miller, J., & Ludvigh, E.

Date: 1962.

Title: The effect of relative motion on visual acuity.

Pub: Survey of Ophthalmology, 7, 83-116.

Keywords:

Acuity

Foveal vision

Motion detection

Relative motion

Holding: Full text (X) Abstract/Summary ( )

Abstract: Authors= Introduction

This article deals with the effect on foveal visual acuity of relative motion between the test object and the observer. Curiously enough, this subject appears to have been investigated first only in 1947. However, a special case of visual acuity when the object is moving, namely, the size threshold or minimum visible, the ability to perceive the mere presence of an object but not its details, was discussed as early as 1937.

The classical method of testing visual acuity with the observer and test object both stationary is, of course, almost ideal for the determination of refractive errors, but the eyes are seldom employed under those conditions. An exception is the remarkable task of reading, during which task most individuals exhibit fixation pauses interspersed with saccadic movements. On the other hand, the eyes are frequently employed while the individual is himself walking, riding on or in some vehicle or viewing a moving person or object.

The questions which arise concerning visual acuity when relative motion exists between the eye and the test object are numerous. A few of these questions are enumerated:

1. In what manner does visual acuity deteriorate as the relative angular velocity of the test object is increased? Is the deterioration gradual and steady, or are there one or more critical velocities at which visual acuity suddenly worsens?

2. Are there marked differences between individuals in the functional relationship between visual acuity and relative angular velocity?

3. What is the effect of brightness, contrast, blurredness and other variables on visual acuity when the object is moving?

4. What is the effect on the normal individual of different types of movement in a frontal plane, such as horizontal, vertical, oblique and circular movements, and how does this differ in individuals with various oculomotor defects?

5. How is the ability to discriminate detail in a moving object affected by age, fatigue, drugs and other factors?

6. Can this faculty be improved by training? Does it deteriorate with lack of use?

7. Are the results different if the observer, rather than the test object, is moved?

8. What are the basic causes for the loss of visual acuity with increasing relative angular velocity of the test object?

This article reviews and interprets the experimental results obtained in an effort to answer some of these questions.

Author: Miller, R. J.

Date: (1980).

Title: Ocular vergence-induced accommodation and its relation to dark-focus.

Pub: Perception and Psychophysics, 28, 125-132.

Keywords:

Accommodation

Binocular/Monocular

Dark focus

Phoria

Vergence

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract: Two experiments were conducted in an attempt to develop an open-loop technique for assessing the influence of ocular vergence on accommodation changes. Past research had shown that a small point of light (1.2 mm in diameter) induces relatively small changes in monocular accommodation at viewing distances greater than 50 cm. However, Experiment 1 (using seven male and six female undergraduates as subjects) demonstrated that, even with a smaller light spot (.29 mm), subjects could accommodate to the stimulus at distances closer than 50 cm. It was only with a very impoverished target (.08 mm diameter), as used in Experiment 2 (in which five male and five female undergraduates served as subjects), that it was possible to present a stimulus that could induce ocular vergence without being a direct stimulus in itself for accommodation. It was also shown that ocular vergence can drive accommodation and that ocular vergence can vary systematically under conditions in which illumination is greatly reduced. In addition, both experiments showed significant relationships among dark focus and both monocular and binocular accommodation.

Authors: Monaco, W. A., & Hamilton, P. V.

Date: 1985.

Title: Visual capabilities related to fighter aircrew performance in the F-14 and adversary aircraft.

Pub: Agard Conference Proceedings No. 396, Medical Selection and Physiological Training of Future Fighter Aircrew. Neuilly sur Seine, France: North Atlantic Treaty Organization, Advisory Group for Aerospace Research and Development. pp. 38-1 to 38-9.

Keywords:

Acuity

Central vision

Contrast sensitivity

Glare

Low contrast acuity

Motion detection

Standards

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract: Summary:

Standards for aviation personnel should be based on capacities for performing critical tasks. The purpose of this study was to determine whether scores on task-relevant visual tests could be used to predict air-to-air target detection performance of pilots involved in air combat maneuver (ACM) training.

NAMRL has developed a series of automated vision tests in a mobile field laboratory located at a Tactical Air Combat Training System (TACTS) range. A computerized telemetry network provides extensive real-time data on observer and target aircraft flight dynamics, and environmental parameters. A pilot=s performance on each ACM engagement was measured by the slant range at the instant he sighted a target aircraft. (Slant range is the distance separating observer and target aircraft, inclusive of altitude separation.)

Preliminary analyses show that about 30% of the variance in slant range is accounted for by flight dynamics, environmental parameters, and vision data.

Notes:

Tests used were:

Central spot detection

Central acuity, high contrast

Central acuity, low contrast

Central acuity, low contrast, with glare

Accommodative flexibility

Lateral movement detection

Authors: Morgan, M. J., Watt, R., & McKee, S.

Date: 1983.

Title: Exposure duration affects the sensitivity of vernier acuity to target motion.

Pub: Vision Research, 23, 541-546.

Keywords:

Acuity

Central vision

Dynamic acuity

Foveal vision

Static acuity

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Threshold vernier acuity was measured under different conditions of target movement and exposure duration. In the case of a simple two-line vernier target, image motion up to about 3 deg/sec had little effect upon threshold for a briefly exposed (150 msec) target which is relatively poor even for a stationary stimulus but produced a decrement in acuity for a continuously exposed stimulus. This finding was repeated in a second experiment which used a centroid cue to vernier offset, and which compared the effects of horizontal and vertical target orientation. It is suggested that image motion and reduced exposure duration restrict the proportion of the light spread function that can be usefully sampled by the neural networks responsible for hyperacuity.

Notes:

Looks at effects of exposure duration and of motion, and at their interactions. Also varied target eccentricity independently.

Authors: Morris, A., Hamilton, P. V., Morey, W. A., & Briggs, R. P.

Date: 1985.

Title: Vision test battery threshold and response time as predictors of air-to-air visual target acquisition in F-14 and adversary aircraft.

Pub: Agard Conference Proceedings No. 396, Medical Selection and Physiological Training of Future Fighter Aircrew. Neuilly sur Seine, France: North Atlantic Treaty Organization, Advisory Group for Aerospace Research and Development. pp. 39-1 to 39-8.

Keywords:

Acuity

Central vision

Low contrast acuity

Standards

Static acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Summary: The NAMRL Vision Test Battery provides assessment of various visual functions, including spot detection, acuity at high and low contrast, glare sensitivity, and accommodative flexibility. Within these tests are measures of threshold, threshold stressed response time (for near-threshold stimuli), and unconfounded response time (for supra-threshold stimuli).

The contribution of response time variables to predicting flight performance was evaluated for 73 fighter pilots. Vision test data were compared to performance in air combat maneuver training. The distance (slant range) between the observer and target aircraft at time of initial visual detection was used as the performance variable.

Availability of response time variables enhanced the ability to predict the air-to-air visual target detection performance of these pilots. Four vision variables accounted for about 32% of the variance in performance of those pilots who detected target aircraft at slant ranges greater than the group average. Prediction of performance is improved by incorporating other vision data and additional refinement of the performance measure.

Notes:

Related to Monaco & Hamilton paper; tests were from same automated test battery.

Tests used:

Spot detection, high contrast

Acuity, high contrast

Acuity, low contrast

Acuity, low contrast, with glare

Accommodative flexibility

Authors: Morrison, T. R.

Date: 1980.

Title: A review of dynamic visual acuity (NAMRL Monograph 28).

Pub: Pensacola, FL: Naval Aerospace Medical Research Laboratory.

Keywords:

Driving

Dynamic acuity

Event perception

Motion detection

Velocity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

In many everyday situations relative motion exists between human beings and the visual information which they must acquire and resolve in order to perform their tasks successfully. In particular, tasks such as flying aircraft, driving automobiles and other vehicles, and resolving moving information presented via visual displays impose a requirement on the human operator to process moving information. Since Dynamic Visual Acuity (DVA) is a critical visual skill involved in performing such visual tasks, the present review was undertaken in order to better understand this visual skill and to provide a basis for continuing research in this area.

Considerable research in the area of DVA has been undertaken since the review published in 1962 by Miller & Ludvigh, which included DVA research performed prior to 1960. The present review summarizes the DVA literature and findings included in the 1962 review, presents findings of DVA investigations reported between 1960 and 1978, and relates some of the latter findings to the former.

Notes:

Much recapping of Miller & Ludvigh (1962), but also reviews literature from there to 1978, by topic:

Organismic variables

Effect of contrast

Relationship of initial eye movement and saccades to DVA

Cause of deterioration with relative motion

Methodological considerations

Authors: Moskowitz, H., & Burns, M.

Date: 1990.

Title: Effects of alcohol on driving performance.

Pub: Alcohol Health and Research World, 14 (1), 12-14.

Keywords:

Central vision

Driving

Impairments

Peripheral vision

Situational awareness

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The behaviors involved in driving a motor vehicle are impaired by alcohol in varying degrees. However, investigators have not found an absolute threshold below which there is no impairment of any kind. Certain skills important for driving are impaired at 0.01 to 0.02 percent BAC or, in other words, at the lowest levels that can be measured reliably.

The area most critical to driving - that is, the brain's ability to observe, interpret, and process information from the eyes and other senses - is also impaired by alcohol. A driver cannot operate a vehicle safely if:

*information processing is slowed

*visual perception is degraded

*ability to allocate attention to multiple sources of information limited.

With these kinds of central deficits, sooner or later a driver will fail to see something that is in the path of the vehicle - a car, a pedestrian, a fixed object - and an accident occurs.

It is important to understand that crashes are not limited to drivers with high BACs. Rather, there is a significant risk that extends to low and moderate BACs. Drivers need to know that they are impaired and are at increased risk of crash when they have consumed even small amounts of alcohol. The safety-minded consumer will restrict alcohol use to times and places that do not include driving.

Notes:

Stresses the effects of low BAC on attentional indicators.

Authors: National Research Council, Working Group 39, Comittee on Vision.

Date: 1980.

Title: Recommended standard procedures for the clinical measurement and specification of visual acuity.

Pub: Advances in Ophthalmology, 41, 103-148.

Keywords:

Acuity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract: Summary:

The primary objective of this report is to formulate test conditions, procedures, and criteria which can serve the clinical need associated with routine ophthalmological and optometric measurement of visual acuity. The aim is to enable different examiners to obtain the same test results.

The major emphasis is on the standardization of so-called >distance= acuity for distances approximating optical infinity. Recommendations are also made for tests at a suggested near distance of 40 cm (16 inches). The proposed near tests include (a) measures of acuity with capital letters under conditions comparable to those used to measure distance acuity, and (b) tests of ability to read continuous text. These recommendations are summarized as follows.

Standards for Assessment of Distance Acuity

(1) Optotypes, to be acceptable, must be shown to be approximately equal in difficulty to the Landolt ring. The ten Sloan letters as a group are recommended as meeting this requirement.

(2) The size are to approximate equal steps of 0.1 on a logarithmic scale, i.e., every successively larger size is about 1.26 times the preceding one. The horizontal spacing between the letters on a given line is to be such that the separation between adjacent borders shall not be less than the overall size of the letter. The vertical separation between the borders of letters on successive lines shall not be less than the size of the larger letters and not greater than twice this lower limit. When all ten letters are shown on a single line they are to be separated into two groups of five for easier orientation. In the case of the larger letters, space limitations may require that there be two lines of five each.

(3) The letters are to be black on a white background with a contrast not less than 0.85. The luminance of the white background is to be 85+/- 5 cd/m2.

(4) Acuity is determined by the smallest size at which 7 of 10 (or 6 of 8) letters are correctly identified at a given distance.

(5) To anticipate the future change to the metric system, it is recommended that the testing distance be specified in meters from the spectacle plane. Each letter size on the chart should be marked to show the distance, again in meters, at which the critical detail subtends a visual angle of 1 min. It is suggested for consideration that the standard testing distance be changed from the generally used 20 ft to a distance of 4 m. The arguments supporting these recommendations are listed on pages 121-123. The Committee proposes to review this question again in 4 years, as discussed in the preface.

(6) It is suggested that these standards be incorporated into protocols for clinical trials. Furthermore, so that sequential measures are not affected by memory of optotypes, it is recommended that more than one chart or projected chart be available with different optotype orders.

Standards for Assessment of Near Acuity

(1) On the basis of the specifications defined for the distance visual acuity test, the same test characteristics can be applied with modest modifications to a near test for single capital letters. It is suggested for consideration that the test be conducted at 40 cm (this is consistent with a 4-meter test distance); successive lines should not be crowded too closely, and it is desirable that pupil size be recorded and that luminance be compatible with that used at distance.

(2) Many near tests require continuous sentences and paragraphs (or other suitable material). Certain principles for such tests are outlined on pages 127-131. In general, the size of the letters used in such tests may be specified in terms of the height of lower case letters such as o and e.

Authors: National Research Council, Working Group on Aging Workers and Visual Impairment, Committee on Vision.

Date: 1987.

Title: Work, Aging, and Vision: Report of a Conference.

Pub: Washington, DC: National Academy Press.

Keywords:

Acuity

Aging

Color vision

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Low contrast acuity

Standards

Useful field of view

Vision testing

Visual field

Holding: Full text (X ) Abstract/Summary ( )

Abstract: No abstract; an entire book.

Notes:

This is a report of a conference, but does not contain full text of individual presentations. Discusses issues of aging and vision at non-technical level, with emphasis on workplace.

Authors: National Research Council, Working Group for Emergent Techniques for Visual Assessment, Committee on Vision.

Date: 1985.

Title: Emergent Techniques for Assessment of Visual Performance.

Pub: Washington, DC: National Academy Press.

Keywords:

Acuity

Aging

Central vision

Color vision

Contrast sensitivity

Dynamic acuity

Low contrast acuity

Motion detection

Peripheral vision

Spatial frequency

Standards

Static acuity

Useful field of view

Velocity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Explores the evidence for utility of testing contrast sensitivity, dark-focus functions, and dynamic acuity, and recommends research on how tests of ambient vision might be developed and used.

Authors: Nelson, D. E., Sacks, J. J., & Chorba, T. L.

Date: 1992.

Title: Required vision testing for older drivers.

Pub: New England Journal of Medicine, 326 (26), 1784-1785.

Keywords:

Acuity

Aging

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract: None

Notes:

Letter to the editor advocating vision testing for license renewal for older drivers. Cites fatal-crash involvement rates for older drivers in states with vs. without required testing. (Used within-state ratio of crash rate for drivers aged 65+ to rate for drivers aged 45-64 to control for between-state overall rate differences). Rate ratio was lower for vision testing states. (Authors were at Centers for Disease control.)

Authors: O=Neill, T. R., Batten, D. C., and Woontner, S.

Date: 1988.

Title: What the gunner=s eye tells the gunner=s brain. III: Predicting target detection skill.

Pub: Technical Report 88-1, Human Sciences Laboratory, United States Military. Academy

Keywords:

Foveal vision

Useful field of view

Peripheral vision

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

This report summarizes a program conducted for the Department of the Army Manpower and Personnel Integration (MANPRINT) program and the Army Research Institute for the Behavioral and Social Sciences, with the objective of developing a low-cost test battery for screening soldiers for skill areas requiring high visual performance. The method included use of a variety of measures of visual performance (Snellen acuity, contrast sensitivity, visual detection lobe, and other parameters) and assessing soldier detection performance against a variety of target detection tasks.

The results indicated strong correlations between target detection and contrast sensitivity (6, 12, and 18 cycles/degree) and size of the visual detection lobe (useful field of view). Two analytical methods were used: multiple regression against target detection time, which yielded a multiple R of .901, and canonical correlation of all measures of visual performance against three detection tasks, yielding a canonical correlation of .897. Visual detection lobe diameter (useful field of view) had a simple correlation of 0.66 with probability of detection and 0.68 with detection time.

Notes:

This study used Army personnel who were trained observers, and whose visual performance attributes were rather narrowly distributed compared to the general population. This makes the results particularly striking, and provides support for the use of contrast sensitivity and UFOV in an improved CDL vision standard.

Author: Owens, D. A.

Date: 1991.

Title: Vision in twilight.

Pub: Paper presented at Symposium on Psychophysical Issues in Practice, VIIth Meeting of the International Society for Psychophysics, Duke University.

Keywords:

Acuity

Central vision

Contrast sensitivity

Driving

Foveal vision

Impairments

Low contrast acuity

Night vision

Peripheral vision

Situational awareness

Useful field of view

Visual field

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Vision in twilight has long been of interest for both practical and theoretical reasons, and research has profited from inquiries from both these perspectives. Problems of twilight myopia and nighttime traffic accidents are presented as examples of the challenges and potential benefits of coordinating basic and applied modes of inquiry.

Authors: Owens, D. A.

Date: 1980

Title: A comparison of accommodative responsiveness and contrast sensitivity for sinusoidal gratings

Pub: Vision Research, 20, 159-167.

Keywords:

Accommodation

Acuity

Contrast sensitivity

Spatial frequency

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The accuracy of steady-state accommodation for high contrast sinusoidal gratings was compared with the observers= contrast sensitivities for the same gratings. Stimuli ranging in spatial frequency from 0.5 to 19 c/deg were presented at optical distances ranging from 0 to 5 diopters, and accommodative responses were measured with a laser optometer. Contrast thresholds were obtained by the method of constant stimuli. The results showed that optimal performance for both accommodation and contrast sensitivity was obtained for spatial frequencies of 3-5 c/deg. while progressively diminished performance was obtained for higher and lower spatial frequencies. The accuracy of accommodation for sinusoidal gratings of intermediate spatial frequencies was equivalent to that for a square-wave grating of 4 c/deg. These findings imply that sharp edges are not necessary for accurate accommodative responses, and they suggest that mechanisms underlying foveal contrast resolution are also involved in the control of steady-state accommodation.

Notes:

Thorough exposition of dark-focus theory and night myopia.

Author: Owens, D.A.

Date: 1979.

Title: The Mandelbaum effect: Evidence for an accommodative bias toward intermediate viewing distances.

Pub: Journal of the Optical Society of America, 69 (5), 646-652.

Keywords:

Accommodation

Acuity

Dark Focus

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Previous research has shown that ocular accommodation tends to correspond to an intermediate distance, the dark focus, in the absence of effective stimulation. The present experiments measured accommodative responses in the presence of two adequate, monocular stimuli superimposed optically at different distances. In Experiment I, observers attempted to maintain a matrix of letters in clear focus, as a superimposed mesh screen was varied in distance. In Experiment II, observers were instructed to focus the "easier" of two similar grating patterns that were presented over a range of distances with a constant separation of two diopters. The results of both experiments showed an accommodative response bias toward target distances near the observers= dark focus of accommodation. The implications of these findings for the theoretical resting state of accommodation and for practical problems of visual performance are discussed.

Authors: Owens, D. A., Antonoff, R. J., & Francis, E. L.

Date: 1994.

Title: Biological motion and nighttime pedestrian conspicuity.

Pub: Human Factors, 36(4), 718-732.

Keywords:

Acuity

Driving

Dynamic acuity

Low contrast acuity

Motion detection

Night vision

Peripheral vision

Situational awareness

Useful field of view

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Two experiments were conducted in the laboratory to evaluate potential benefits of different retroreflective markings for nighttime pedestrian visibility. Video recordings of a jogger wearing four different markings were made from a vehicle in four different road environments. Subjects viewed composite tapes that included each of the 16 jogger marking/road environment combinations as well as travel with no targets. The task was to step on a pedal immediately upon seeing a jogger, which had no effect on the flow of the video playback. The time between depression of the pedal and the point of "impact" was the major dependent variable. Experiment 1 showed that performance was better for all retroreflective markings than for the dark control and that it was better with markings of the limbs than of the torso. Experiment 2, which included a secondary video tracking task, showed that performance was better for markings that incorporate biological motion than for a vest or arbitrarily positioned stripes on the limbs. Questionnaire data indicated that 85% of the subjects judged the biological motion markings to be "easiest to see." Also, subjects reported more conservative estimates of nighttime visibility and greater willingness to take personal precautions at night after participating in the experiment.

Authors: Owens, D. A., Francis, E. L. & Leibowitz, H. W.

Date: 1989.

Title: Visibility distance with headlights: a functional approach.

Pub: Society of Automotive Engineers, Technical Paper Series (890684)

Keywords:

Acuity

Contrast sensitivity

Driving

Event perception

Low contrast acuity

Night vision

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

This paper reports a novel approach to quantitative prediction of nighttime visibility with headlight illumination. Unlike previous efforts to model nighttime visibility, our goal is to provide an index of visibility that can be understood by non-specialists, as well as scientists and engineers, as a useful approximation of visibility distance for ordinary objects. Specification of the functional range of recognition vision is based on the concept of Civil Twilight. Early astronomers defined Civil Twilight as the time period following sunset or before sunrise when normal outdoor activities can be conducted without supplementary illumination. Psychophysical research later showed that visual functions such as acuity and contrast sensitivity deteriorate rapidly over this range of illumination, thus providing scientific validation of the astronomers' observations. In the present approach, the headlight beam is treated as a spatial analogue of changes in illumination during Civil Twilight. Thus, the practical limit of useful recognition vision is defined as the Twilight Distance, which is the point that headlight illumination is equal to the darker limit of Civil Twilight. Twilight Distance distributions for low and high beams of different headlight systems are presented, and implications for driver performance are discussed.

Authors: Owens, D., & Leibowitz, H.

Date: 1976.

Title: Night myopia: Cause and a possible basis for amelioration.

Pub: American Journal of Optometry, 53, 709-717.

Keywords:

Acuity

Dark focus

Driving

Low contrast acuity

Night vision

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The relationship between night myopia under simulated night driving conditions and the dark focus of accommodation was examined. Over a range of luminance and contrast conditions typical of the night driving situation, college-aged subjects accommodated to about one-half the difference between a distant simulated road sign and their individual dark focus. Subsequent laboratory and field experiments demonstrated that: (1) a negative correction equal to one-half the value of the dark focus significantly improved night visual performance as compared with their normal or full dark-focus correction, and (2) greater improvements in performance were obtained for subjects who exhibited a relatively near dark focus.

Authors: Owens, D. A. & Sivak, M.

Date: 1993.

Title: The role of reduced visibility in nighttime road fatalities. (UMTRI-93-33)

Pub: University of Michigan: Transportation Research Institute

Keywords:

Ambient vision

Driving

Low contrast acuity

Motion detection

Night vision

Situational awareness

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Two quasi-experiments investigated the contribution of reduced visibility to fatal accidents recorded by the U.S. Fatal Accident Reporting System from 1980 through 1990. Quasi-Experiment 1 evaluated 104,235 accidents that occurred during morning and evening time periods, called Twilight Zones, during which natural illumination varied systematically in conjunction with the annual solar cycle. Fatal accidents were found to be overrepresented during darker portions of the Twilight Zones. This finding was no related to time of day, day of week, or drivers' consumption of alcohol. The contribution or reduced visibility was also indicated by higher overrepresentation of fatal accidents in low illumination under adverse atmospheric conditions and with pedestrians and pedalcyclists as opposes to all other accidents. Reduced visibility was more important than drivers' drinking as a contributor to fatal pedestrian and pedalcycle accidents, while the reverse pattern was found for all other fatal traffic accidents.

Quasi-Experiment 2 assessed the role of seasonal variables other than natural illumination by comparing the monthly distributions of 337,726 accidents recorded during three time period: the Twilight Zones plus equal-duration control periods of Daylight and Darkness. The distribution of fatal non-pedestrian accidents exhibited no substantial variation across months in any of the test periods. The incidence of fatal pedestrian/pedalcycle accidents covaried with natural illumination during the Twilight Zones, while showing no variation during Daylight and Nighttime Control periods, confirming that visibility is a key factor in pedestrian and pedalcycle accidents.

The present findings provide new evidence for both (1) the importance of visibility as a major contributing factor in fatal pedestrian and pedalcycle accidents, and (2) the relative success of previous efforts to deal with the difficulties of nighttime driving in other classes of fatal accidents.

Authors: Owens, D. A. & Tyrrell, R. A.

Date: 1995.

Title: Age-related variations in nighttime vehicle guidance: an extension of the selective degradation hypothesis.

Pub: Paper presented at the 74th Annual Meeting of the Transportation Research Board.

Keywords:

Ambient vision

Acuity

Aging

Driving

Central vision

Foveal vision

Impairments

Motion detection

Night vision

Peripheral vision

Static acuity

Useful field of view

Visual field

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract: (Study Team Abstract)

This study explored the possibility that drivers' ability to steer a vehicle under challenging conditions may decline with advancing age. Older drivers are frequently reluctant or unwilling to drive at night, apparently because they lack confidence in their visual capabilities. Although prudent, their insecurity at night stands in contrast to the overconfidence exhibited by younger drivers.

One theory proposes that the unrealistic confidence of younger night drivers is related to selective degradation of vision in low light. Reduced luminance is not uniformly deleterious to all visual functions. Over the range of luminances encountered in night driving, recognition or focal visual functions, like acuity and contrast sensitivity, deteriorate rapidly with reduced luminance. In contrast, guidance or ambient visual functions, such as visually induced feelings of self-motion (vection), remain highly efficient until luminance falls to near the absolute scotopic threshold. Theoretically, the latter class of visual function, which service in very low luminance, are of primary importance for guidance of locomotion.

Although appealing conceptually, the selective degradation hypothesis has not been tested in the context of the driving task. As a preliminary step toward such investigations, we have conducted experiments using a simple night driving simulator. Performance was investigated under challenging visual conditions that were designed to degrade selectively either recognition or guidance vision. Based on the selective degradation hypothesis, it was predicted that steering performance would be relatively unaffected by reductions of luminance and image clarity (blur). Experiment I tested this hypothesis in a small sample of middle-aged subjects, while Experiment II extended the investigation by evaluating the effects of reduced luminance on steering performance of younger and elder subjects.

Experiment I showed that the visual guidance in the simulator task was disrupted by a restriction of peripheral vision, which had little or no effect on visual acuity. Conversely, myopic refractive errors severely degraded visual acuity, but had [no] effect on steering accuracy. Experiment II showed that the resistance of steering performance to degradation in low light declines with age, and examination of the combined data from both experiments suggests that the age-related losses of visual guidance at night may develop progressively over the adult life span. In sum, the research findings provide new support, as well as interesting limitations of the selective degradation hypothesis.

Authors: Owsley, C., Sekuler, R., & Siemsen, D.

Date: (1983).

Title: Contrast sensitivity throughout adulthood.

Pub: Vision Research, 23, 689-699.

Keywords:

Acuity

Aging

Contrast sensitivity

Spatial frequency

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract: Previous studies of spatial contrast sensitivity in adulthood have produced conflicting results. To clarify the situation, we measured contrast sensitivity function on a large sample of adults (n=91), ranging in age from 19 to 87. All observers were free from significant ocular pathology and were individually refracted for the test distance. Sensitivity for stationary gratings of low spatial frequency remained the same throughout adulthood. At higher spatial frequencies, sensitivity decreased with age beginning around 40 to 50 years. When a low spatial frequency grating was drifted, young adults= sensitivity improved by a factor of 4-5 over sensitivity to a static grating; this motion enhancement was markedly diminished in adults over 60 years, implying an impairment of temporal processing in the elderly. Reduced retinal illuminance characteristic of the aged eye could account for a large part of older adults deficit in spatial vision, but appeared to play little role in their deficit in temporal vision.

Authors: Pantle, A., & Sekuler R.

Date: 1968.

Title: Velocity-sensitive elements in human vision: Initial psychophysical evidence.

Pub: Vision Research, 8, 445-450.

Keywords:

Acuity

Motion detection

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Luminance thresholds for contours moving at 2/sec, 5/sec, or 9/sec of visual angle were measured after adaptation periods in which contours moving at each of several different angular velocities were viewed. The range of velocities of adapting motion was 2/sec to 45/sec. Thresholds for conditions when adapting and test motions were in the same direction were elevated relative to conditions when adapting and test motions were in opposite directions. Largest threshold elevations were obtained when adapting and test contour velocities were similar. The results indicate that the human visual system contains different velocity-sensitive mechanisms, each of which is most responsive to a specific range of contour velocities.

Notes:

Tested luminance threshold for detecting moving contours, not dynamic acuity or velocity estimation. Adapting motion was vertical (upward) in all conditions. Point of greatest threshold elevation tended to be in conditions where adapting velocity was slightly higher than test velocity.

Authors: Pascarella, E. A., MacCormack, J. N., & Dean, R. L.

Date: 1972.

Title: An analysis of the North Carolina driver medical evaluation program.

Pub: Proceedings of 16th Conference, American Association for Automotive Medicine. Morton Grove, IL: American Association for Automotive Medicine.

Keywords:

Driving

Vision testing

Holding: Full text ( ) Abstract/Summary (X)

Abstract:

A study of the North Carolina Driver Medical Evaluation Program was undertaken to assess the effects of the program upon objective measures of the driving task. The study group was formed of 4,117 subjects who were medically evaluated and submitted to a system of restraints imposed upon their operation of motor vehicles during the two-year period from September, 1968 through August 31, 1970. Accidents and selected violations compiled from the official driving record were collected over a year's time in both retrospective and prospective periods relative to the subject's induction into the evaluation process. Driving performance was examined for each class of restriction and from every stage of the medical evaluation process. Driving performance was examined for each class of restriction and from every stage of the medical evaluation process. Comparisons were made within the experimental groups and against a random sample from the general driving population.

The data suggest a consistent measure of improvement in driving performance for medically evaluated subjects.

A DRIVER'S COMPETENCE to safely operate a motor vehicle is determined through one of several systems currently in operation in official state agencies throughout the United States. The North Carolina system is usually applied in three consecutive stages:

(1) A written exam testing the applicant's knowledge of motor vehicle laws, regulations, motor vehicle operation and adjustment to various road situations.

(2) A visual exam for static acuity and color perception, usually incorporating recognition of road signs and other traffic regulation devices.

(3) A road test in the applicant's vehicle over a prescribed course subjectively graded from a check list by the license examiner.

Author: Poser, C. M.

Date: 1993.

Title: Automobile driving fitness and neurological impairment.

Pub: Journal of the Neuropsychiatry and Clinical Neurosciences, 5(3) 342-348.

Keywords:

Aging

Driving

Impairments

Standards

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract: none given

Notes:

This is a "Practice and Opinion" article advocating a functional approach, rather than one based on medical diagnosis, to determine whether drivers with neurological impairments should be allowed to drive. It also suggests that simulator testing is useful for patient testing. Quotes Drachman (1988), recommending that "limitations of driving privileges should be based on the demonstration of impaired driving competence rather than on a stigmatizing label."

Authors: Ranney, T. A., & Gawron, V. J.

Date: 1986.

Title: The effects of pavement edgelines on performance in a driving simulator under sober and alcohol-dosed conditions.

Pub: Human Factors, 28 (5), 511-525.

Keywords:

Driving

Impairments

Holding: Full text (X) Abstract/Summary ( )

Abstract:

To identify the impairment effects of alcohol on driving performance and to determine whether providing enhanced visual information concerning roadway alignment would improve the performance of subjects when sober and/or alcohol-dosed, simulations of continuous roadway treatments (i.e., standard and wide edgelines) were evaluated experimentally. Twelve subjects drove a simulator at three levels of blood alcohol concentration (BAC: 0.00%, 0.07%, 0.12%). The effects of alcohol included increases in the number of times the speed limit was exceeded, the number of obstacles that were struck, and the magnitude of tracking errors that were made in the approach and negotiation of curves. Edgeline presence was associated with faster curve entry speeds and reduced amount of road used in curve negotiation, both interpreted as positive effects. Additional benefits associated with wide edgelines were minimal.

Notes:

Results which authors interpret as positive could be seen as negative. Increased speed entering curves could be one aspect of proposed (see Leibowitz, et al) outcome in nighttime and low-visibility conditions, when ambient cues are not degraded, leading driver to drive too fast for degraded focal visual abilities.

Authors: Ranney, T. A. & Pulling, N. H.

Date: 1990.

Title: Performance differences on driving and laboratory tasks between drivers of different ages.

Pub: Paper presented at the 69th Annual Meeting of the Transportation Research Board.

Keywords:

Aging

Attention

Driving

Event perception

Impairments

Situational awareness

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

A battery of closed-course driving and laboratory tests were developed for evaluating the skills required in routine suburban driving. Twenty-three younger (aged 30-51) and twenty-one older (aged 74-83) adults participated. Driving tests included responding to traffic signals, selection of routes, avoidance of moving hazards, and judgment at narrow gaps. Lab tests included measures of perceptual style, selective attention, reaction time, visual acuity, perceptual speed and risk-taking propensity. Older drivers were generally slower and less consistent in their driving. No differences were found between the groups on measures of caution. In the lab, older drivers scored lower on tasks requiring rapid switching of attention. Differences on lab measures were larger, reflecting the greater difficulty of these tasks and thee greater precision available in the laboratory. The pattern of greater variability of performance for the older drivers underscores the importance of not judging driving ability on the basis of chronological age.

Authors: Ranney, T. A. & Pulling, N. H.

Date: 1989.

Title: Relation of individual differences in information-processing ability to driving performance.

Pub: Proceedings of the Human Factors Society 33rd Annual Meeting.

Keywords:

Aging

Attention

Driving

Event perception

Impairments

Situational awareness

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Fifty subjects, ranging in age from 30 to 83, participated in a closed-course driving test and in laboratory tests of information processing. Driving tests included responding to traffic signals, selection of routes, avoidance of moving hazards, and judgment at stationary gaps. Lab tests included measures of perceptual style, selective attention, reaction time, visual acuity, perceptual speed and risk-taking propensity. Analyses were conducted to determine how well lab measures predicted driving performance. Results revealed different patterns of correlations for different age groups. For younger drivers (30-41), lab measures generally showed no association with measures of driving performance. For older drivers (74-83), measures of information-processing were associated with overall rated driving performance, while measures of reaction time showed strong correlations with objective driving measures. The results suggested that different mechanisms are utilized by drivers of different ages, and that the slowing of reaction time associated with aging has effects on driving skills related to vehicle control.

Authors: Rawlings , S. C., & Shipley T.

Date: 1969.

Title: Stereoscopic acuity and horizontal angular distance from fixation.

Pub: Journal of the Optical Society of America, 59, (8), 991-993.

Keywords:

Acuity

Binocular/Monocular

Peripheral vision

Stereoscopic Acuity

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The threshold of stereopsis (mean deviation in sec of arc) of three observers was measured at 2 intervals from 8 right to 8 left in the horizontal meridian of the binocular field. A simple two-point target, along with a binocular fixation point, was presented by use of a mirror haploscope. Disparity was introduced by varying the separation of the two peripheral points in one eye. Judgments of the relative depth of the two binocular peripheral points were based on these disparity cues. The data show a decrease of stereoscopic acuity as a function of horizontal offset. There is a slight discontinuity in the curve, near 4 to 6, which may correspond to a rod-cone density change.

Authors: Regan, D. and Neima, D.

Date: 1983.

Title: Low-contrast letter charts as a test of visual function.

Pub: Ophthalmology, 90, 1192-1200.

Keywords:

Acuity

Contrast sensitivity

Impairments

Low contrast acuity

Spatial frequency

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Visual pathway disorders can cause visual loss that is not detected by the Snellen test: visual sensitivity to coarse detail may be depressed, even when visual sensitivity to fine detail is unaffected. Sinewave grating test targets can detect such hidden visual loss. However, electronic apparatus for generating sinewave gratings is expensive, while the inexpensive Arden plates provide no check on the patient=s accuracy. We have tested 10 patients and 10 control subjects with a set of five letter charts (including the standard Snellen chart). These letter charts were of different contrasts, namely 10%, 22%, 31%, 64% and 93%, but otherwise were substantially alike. Subjects were also tested with sinewave gratings. We found good agreement between sinewave grating and letter chart findings. In particular, the charts picked up visual loss that was not detected by the standard Snellen chart: they detected visual pathway dysfunction in all seven patients whose sinewave data were abnormal. Our findings suggest that even one low-contrast letter chart could provide a valuable supplement to the standard Snellen chart. Compared with other available devices, these charts have the advantages of cheapness, simplicity and of providing the ophthalmologist with an immediate check on patients= accuracy.

Notes:

Presents possible inexpensive testing method. Presented as a clinical diagnostic tool, rather than as a test of vision in normals. Would need to be tested and validated for usefulness in vision screening.

Authors: Retchin, S. M., Cox, J., Fox, M., & Irwin, L.

Date: 1988.

Title: Performance-based measurements among elderly drivers and non-drivers.

Pub: Journal of the American Geriatrics Society 36, 813-819.

Keywords:

Aging

Driving

Dynamic acuity

Impairments

Peripheral vision

Static acuity

Vision testing

Visual field

Holding: Full text ( x ) Abstract/Summary ( )

Abstract:

Although driving is an important ability for maintaining independence in the later years, clinical factors that determine status are unknown. Aged male veterans (mean age, 70 years) were recruited from an outpatient clinic (N = 143), including 77 frequent drivers, 41 infrequent drivers, and 25 who drive rarely or not at all. There were 116 (84%) who completed a comprehensive performance-based assessment. There were no significant differences between the three groups in age, formal cognitive testing, or prevalence of stroke history. However, there were significant differences in grip strength, reaction time, static visual acuity, dynamic visual acuity, and peripheral vision. Using stepwise ordinal logistic regression, dynamic visual acuity, nondominant handgrip strength, and total horizontal peripheral visual field were significantly associated with driving frequency (p<.05), and together explained approximately 45% of the variance. Subtle motor and visual deficits that can be detected in a performance-based assessment may play an important role in determining driving frequency in the elderly.

Notes:

Looked only at association of vision and other measures with self-reported driving frequency. Did not test driving performance directly, nor did they look at driving history, accident records (discussion addresses these issues). These results may be seen as suggestive of tests that might be investigated as predictors of driving performance.

Author: Robson, J.

Date: (1966).

Title: Spatial and temporal contrast sensitivity function of the visual system.

Pub: Journal of the Optical Society of America, 56, 1141-1142.

Keywords:

Acuity

Contrast sensitivity

Dynamic acuity

Motion detection

Static acuity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Letter to the editor; no summary or abstract. Presents functions for contrast sensitivity vs. spatial frequency and vs. temporal frequency.

Authors: Rogers, P. N., Ratz, M., & Janke, M. K.

Date: 1987.

Title: Accident and conviction rates of visually impaired heavy-vehicle operators. (Report No. CAL-DMV-RSS-87-111).

Pub: California Department of Motor Vehicles.

Keywords:

Accidents

Acuity

Binocular/Monocular

Driving

Impairments

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

This study compared two-year accident and conviction rates of visually impaired heavy-vehicle operators (with Class 1 or 2 licensure) to those of a sample of visually nonimpaired heavy-vehicle operators. Nonimpaired drivers met current federal acuity standards (corrected acuity of 20/40 or better in both eyes) while impaired drivers had substandard static acuity and were assessed within either moderately (corrected acuity between 20/40 and 20/200 in the worse eye, 20/40 or better in the other) or severely (corrected acuity worse than 20/200 Snellen in the worse eye) impaired subgroups. California and total mileage estimates for Class 1 and Class 2 drivers obtained in a mailed questionnaire did not differ significantly between impairment groups. However, other potential bias issues remained and are discussed. Visually impaired drivers had significantly more total accidents (37.15%) and convictions (48.38%) than did the nonimpaired drivers. The severely impaired drivers had directionally worse records than did the moderately impaired drivers on three of the four traffic safety measures. These findings lead to qualified support for the current federal standard, particularly regarding the severely impaired, with less support of its application regarding the moderately impaired heavy-vehicle operator.

Author: Rubin, G. S.

Date: 1988.

Title: Reliability and sensitivity of clinical contrast sensitivity tests.

Pub: Clinical Vision Science, 2(3), 169-177.

Keywords:

Acuity

Contrast sensitivity

Foveal vision

Impairments

Low contrast acuity

Spatial frequency

Vision testing

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Test-retest reliability was measured for three contrast sensitivity testing procedures: a CRT-based test using a forced-choice staircase procedure, the Vistech VCTS sinewave grating chart, and the Pelli-Robson letter chart. Sixty-six normal subjects and 64 patients, 16 to 83 years of age, took each test twice.

Test-retest reliability was assessed by computing the intraclass correlation coefficient for each test at each spatial frequency. This correlation coefficient ranges from 0 to 1, with a value of 1 indicating perfect test-retest agreement.

Test-retest reliability was generally lower with the Vistech grating chart than with the CRT-based test. The difference was especially marked at low spatial frequencies. The Pelli-Robson letter chart had very high test-retest reliabilities.

The Vistech chart was twice as likely as the CRT test to produce anomalous CSFs. Twenty-four observers - 15 normal, 9 patient - had a significant "notch" or low frequency specific loss on one Vistech test that did not appear on the other Vistech test. Twelve observers-5 normal, 7 patient-had anomalous CSFs with the CRT test. A single measure of visual acuity was as good a predictor of CRT contrast sensitivity at each spatial frequency as was Vistech contrast sensitivity.

Author: Runeson, S.

Date: 1975.

Title: Visual prediction of collision with natural and nonnatural motion functions.

Pub: Perception & Psychophysics, 18 (4), 261-266.

Keywords:

Dynamic acuity

Event perception

Motion detection

Time to collision

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

A movement with constant velocity looks fast in the beginning and later slows down, whereas a certain type of accelerated motion (natural motion) looks constant throughout. It was predicted that early occlusion of a constant motion would lead to overestimation of velocity whereas late occlusion would not. With natural motion, there would be no such difference. Constant and natural motions together with constant deceleration and constant acceleration motions were tested in a modified prediction-of-collision experiment. The results agree well with the predictions. It was concluded that the phenomena previously found are operative also in a more complex perceptual task where the observer's attention is not focused on velocity directly. The visual system seems to achieve perception of partly occluded motion by applying a natural motion function rather than constant velocity. Acquaintance with the phenomena does not seem to alter the way they are perceived.

Notes:

Laboratory study, with no immediate link to driving tasks, but findings may support Gibsonian model (efforts to induce "cognitive override" of perceptions were unsuccessful).

Author: Schieber, F.

Date: 1988.

Title: Vision assessment technology and screening older drivers: Past practices and emerging techniques.

Pub: Transportation in an aging society (Transportation Research Board special report 218 (2)) . Washington, DC: National Academy Press. pp. 325-378.

Keywords:

Acuity

Aging

Color vision

Contrast sensitivity

Driving

Dynamic acuity

Impairments

Low contrast acuity

Spatial frequency

Standards

Vision testing

Visual field

Holding: Full text ( ) Abstract/Summary ( )

Abstract: Author=s "summary of recommendations and future research requirements@

The objective of visual screening for older drivers should be optimization rather that prohibition or restriction. Special tests that are sensitive to the frequent ocular pathologies of old age are emerging. When detected, most of these age-related visual disorders can be corrected by prompt medical intervention. Hence, successful optimization screening of the elderly would not result in significant increases in the loss of driving privileges; instead, it would yield improved visual functioning with an accompanying increase in driving safety, mobility, and efficiency.

Studies should be conducted to quantify the effectiveness of contrast sensitivity techniques and low-contrast acuity testing for improving the mobility and productivity of the older driver population. Laboratory and clinical evidence clearly demonstrates that contrast sensitivity provides screening sensitivity for age-related visual pathologies that most often elude detection by traditional acuity measures. The modes of contrast sensitivity measurement that yield the most information on age-related ocular pathologies (e.g., cataract, glaucoma, and retinal disorders) are expensive to administer because of the apparatus and testing time required. In addition, standardized procedures for collecting and scoring CSF data remain to be developed. Recent findings have indicated that low-contrast acuity tests may yield a large subset of the information made available by CSF procedures. Unlike the contrast sensitivity techniques, low-contrast acuity tests are simple to administer and interpret. The costs and benefits of these two emerging techniques need to be carefully examined before either is implemented in a mass-screening application such as driver vision testing. The potential for employing a glare stressor for increasing the diagnostic selectivity of these methods needs to be explored. Both the contrast sensitivity paradigm and the low-contrast acuity technique hold promise for improving the level of visual functioning of older drivers.

Advanced technology should be applied to automate driver-screening tasks. The emergence of low-cost computers and high-resolution displays has made it possible to develop a general-purpose vision test station for mass screening applications. Such a system could be used to implement fully automated administration of existing vision and driving knowledge and information tests. Computerized, video-based vision testers possess the characteristics required to implement emerging visual assessment techniques, such as contrast sensitivity and low contrast acuity testing, and have the design flexibility to support anticipated future developments in vision testing, such as those incorporating motion and higher-order information-processing skills.

Mandatory periodic retesting of older drivers should be initiated by all driver-licensing agencies. All of the data collected to date clearly indicate that visual function is prone to dramatic changes during the latter part of the human life span. These data need to be carefully analyzed to show changes in the incidence rates of various visual disorders as a function of age. These quantitative data should then serve as the basis for scientifically determining the age at and frequency with which visual retesting is to be conducted. Such a process would ensure that subsequently determined retest selection criteria would be based on facts rather than arbitrary conventions. The development of advanced automated vision-testing systems would make it possible to administer an ambitious retesting program in a cost-effective manner.

The following three steps need to be taken:

C Establish a photopic acuity illumination standard that is free of potential age bias.

C Transfer automated full-field perimetry technology to one amenable to mass screening.

C Explore the costs and benefits of employing CBI for continuing driver education.

Future attempts to establish causal relationships between measures of visual function and driving performance should employ simulation studies rather than rely entirely on correlational designs.

The feasibility and desirability of cognitive competence screening of driver=s license and renewal applicants also need to be studied.

Authors: Schiff, W., Detwiler, M. L.

Date: 1979.

Title: Information used in judging impending collision.

Pub: Perception, 8, 647-658.

Keywords:

Event perception

Time to collision

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Many subhuman species and human infants, children, and adults can use two-dimensional information of relative rate of angular-size change to anticipate collisions between the self and approaching objects or surfaces. But extant studies have not determined what information is used when subjects view simulated approach events providing two-dimensional information and three-dimensional information (distance and distance change), as well as lower-order visual information contained in real approach events. Three experiments suggest that, given these several possibilities, adults' judgments of collision time are best predicted by two-dimensional spatiotemporal values which are invariant over object size, distance traversed, approach velocities, and several lower-order variables such as absolute angular size. However, collision time is substantially underestimated, with absolute amount of underestimation increasing as a function of actual time-to-collision. Large constant errors and loss of judgment linearity beyond about 10 s to contact time suggest that current models of human performance based on use of time-to-collision information require modified assumptions of operator efficiency.

Author: Schneider, G. E.

Date: 1967.

Title: Contrasting visuomotor functions of tectum and cortex in the golden hamster.

Pub: Psychologische Forschung, 31, 52-62.

Keywords:

Ambient vs focal

Cortical function

Localization

Tectum

Visual discrimination

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Visually-guided orientation (spatial localization) and visual discrimination were dissociated by means of brain lesions in the golden hamster. After ablation of visual cortex, hamsters failed to discriminate visual patterns, but showed nearly normal ability to localize an object in space by means of vision. Ablation of the superior colliculus produced opposite effects: these animals were completely unable to orient to the position of a visual stimulus, but nevertheless showed excellent pattern discrimination.

Notes:

Establishes neural basis for "two modes of processing" concept.

Authors: Scialfa, C. T., Kline, D. W., Lyman, B. J.

Date: 1987.

Title: Age differences in target identification as a function of retinal location and noise level: examination of the useful field of view.

Pub: Psychology and Aging, 2 (1), 14-19.

Keywords:

Aging

Central vision

Foveal vision

Impairments

Peripheral vision

Useful field of view

Visual field

Holding: Full text (x ) Abstract/Summary ( )

Abstract:

Foveal and peripheral target detection were compared in young adults (M age = 22 years) and older adults (M age = 66 years) who were optically corrected for the viewing distance. In a two-alternative, forced-choice task, target letters were presented at 0 to 10.5 from fixation. Targets were presented alone, flanked on each side by one noise element (i.e., non-target letter), or embedded in a horizontal row of 19 noise elements. An Age x Noise Level x Location interaction was obtained, wherein age differences were largest for peripheral targets presented in noise. Slope analyses of latency data showed that the performance of young adults in the high-noise condition was most similar to that of older adults in the low-noise condition. At the functional level, results indicated that aging is associated with a restricted useful field of view. In addition, the data suggest that age differences in search can be described by a model in which older adults take smaller perceptual samples from the visual scene and scan these samples more slowly than do the young adults.

Notes:

If this finding is supported when tested in more naturalistic, driving-related scenarios, it would be a significant issue for CDL. Might support additional or more frequent testing of older drivers. Mean age of "older adults" group was only 66, suggesting that effect can be seen in people young enough to still be employed. Consider this in combination with other literature suggesting that useful field can be expanded by training.

Authors: Sekuler, R., Tynan, P. D., & Kennedy, R. S.

Date: 1981.

Title: Sourcebook of temporal factors affecting information transfer from visual displays (Technical Report No. 540).

Pub: Alexandria, VA: U.S. Army Research Institute for the Behavioral and Social Sciences.

Keywords:

Dynamic acuity

Event perception

Motion detection

Peripheral vision

Situational awareness

Velocity

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

This report collects in one document the important research literature on temporal factors in vision. Over 350 scientific articles are cited herein and this represents approximately 10 percent of the data base which was consulted. The literature searched was comprised of the following: 1) Several thousand articles (under the general rubric temporal factors and information processing) from existing reprint files of the authors and others; 2) Ergonomics Abstracts, Psychological Bulletins, Psychological Reviews and Human Factors for the last 12 years; 3) a listing from two automated look-up systems (Psychological Abstracts 1967-present and National Technical Information System 1964-present). An integrative review of the literature is provided and three chapters are included which deal with application of these findings to display design. The subject matter is perception of temporal events--specifically motion perception (real and apparent) and flicker/flash sensitivity. A small chapter covers some temporally based phenomena which distort or degrade perception. Features of these phenomena may be observed in visual displays. Only studies which report findings which are robust enough to be expected to be important outside the laboratory are included. Where sufficient data were available, equations are provided to the engineer for the calculation of design criteria (e.g., peripheral motion threshold, contrast thresholds, contrast thresholds and age, etc.). Where gaps exist in our scientific knowledge, recommendations are provided for applied research. General guidelines are offered for incorporating design criteria into Military Standard 1472 for perceptions due to temporal events.

Notes:

Extensive review of literature, but is confined to areas relevant to display design.

Authors: Sekuler, R., Wilson, H. R., & Owsley, C.

Date: (1984).

Title: Structural modeling of spatial vision.

Pub: Vision Research, 24, 689-700.

Keywords:

Contrast sensitivity

Linear models

Spatial frequency

Spatial vision

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract: A linear structural model of mechanism underlying spatial vision was generated from the variance-covariance matrix of contrast sensitivity data. The data had been collected on a large group of observers ranging in age from 19 to 87 yr, using gratings of 0.5-16 c/deg spatial frequency. Structural models incorporating various numbers of spatial frequency-tuned mechanisms were compared, with a three-mechanism model giving the best account of the data. The same analysis was applied to contrast sensitivity data simulated from Wilson and Bergen=s (1979) model. When the stimulated data covered 0.5-16 c/deg, only three mechanisms were needed to give a satisfactory account of the data; when the simulated data covered 0.25-16 c/deg, four mechanisms were required. Peak sensitivities and bandwidths of the mechanisms extracted from the simulated data resembled those extracted from the real, population data. This reinforces the idea that at an early stage of human vision a small number of spatially-tuned mechanisms are operative. In addition, the outcome of analyses with both real and simulated data illustrates the potential value of linear structural models for vision research.

Authors: Shebilske, W.

Date: 1981.

Title: Visual direction illusions in everyday situations: Implications for sensorimotor theories.

Pub: In Fisher, D. F., Monty, R. A., & Senders, J. W. (Eds.), Eye Movements: Cognition and Visual Perception. Hillsdale, NJ: Lawrence Erlbaum Associates. pp. 95-110.

Keywords:

Eye position

Position/direction illusions

Holding: Full text ( X ) Abstract/Summary ( )

Abstract:

None given.

Notes:

Investigated effects of manipulation of head/eye position on subsequent visual location. Found aftereffects implying shift in apparent position of targets related to adapting head/eye positions. Discusses relevance of findings to discriminating between sensorimotor and ecological theories. Concludes that both theories are unable to explain all observed results. Uses concept of "recalibration." See argument against this in Ebenholtz, 1976.

Authors: Shinar, D.

Date: 1978.

Title: Driver vision and accident involvement: new findings with new vision test.

Pub: Proceedings of the American Association for Automotive Medicine, 22nd Conference and the International Association for Accident and Traffic Medicine VII Conference, Vol II. Morton Grove, IL: American Association for Automotive Medicine. pp. 81-91.

Keywords:

Acuity

Driving

Dynamic acuity

Glare

Low contrast acuity

Peripheral vision

Situational awareness

Static acuity

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

An evaluation of a fully automated battery of driving related vision tests was conducted on 890 licensed drivers ranging in age from 17 to 89. The tests measured static central visual acuity under conditions of optimal illumination, low levels of illumination, and glare; dynamic visual acuity, visual field, movement detection threshold in the central and peripheral fields, and visual search-and-scan ability. In a previous paper (1) the test-retest reliability of the vision tests was discussed. The present paper summarizes the main findings of this study with particular emphasis on the relationship between driver accident involvement and drivers performance on the vision tests. Regression analysis regressing performance on the vision test against accident involvement yielded multiple correlations ranging from .09 to .30 - depending on the particular driver age group and the accident condition (day vs. night). The results indicated that: 1. dynamic visual acuity and static acuity under low levels of illumination were the two tests that were most consistently related to accidents in general, as well as to driver-caused and vision-related accidents in particular. 2. poor static acuity under low levels of illumination was specifically associated with overinvolvement in night-time accidents. 3. the third most relevant vision test was sensitivity to central angular movement. 4. When broken down by age groups, it was found that no single vision test was significantly associated with accident involvement for all age groups but each one of the vision tests was significantly associated with accident involvement for one or more of the age groups. Further analyses indicated that additional changes in equipment and procedures are necessary before the battery can be used in the driver licensing environment.

Notes:

Part of a body of work by Shinar and associates to develop new vision tests for drivers. Relevant to issues of validity and practicality of new tests.

Authors: Shinar, D. and Eberhard, J. W.

Date: 1976.

Title: Driver visual requirements: Increasing safety through revised visual screening tests

Pub: Proceedings of the 20th conference of the American Association for Automotive Medicine. Morton Grove, IL: American Association for Automotive Medicine. 241-252.

Keywords:

Acuity

Central vision

Driving

Dynamic acuity

Foveal vision

Low contrast acuity

Motion detection

Peripheral vision

Useful field of view

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

In a previous paper, Shinar, Mayer and Treat [1975] evaluated the reliability and validity of a battery of 17 driving-related vision tests. The present paper reports progress made in the development of these tests towards the establishment of an integrated battery of license branch oriented driver vision screening tests. In an effort to expedite the testing procedure, the eleven most promising tests of the original 17 were incorporated in a fully automated battery. The tests yield measures of static central visual acuity under conditions of optimal illumination, low levels of illumination, and glare; dynamic visual acuity, visual field, movement thresholds in the central and peripheral fields, and visual search-and-scan ability. Evaluation of the new battery is proceeding in four directions: the reliability of the tests; their validity as predictors of accident involvement; the practicality of the device as a license branch test; and the development of diagnostic and remediation procedures for people who might fail the tests. The results reported below indicate that most of the tests are reliable, insofar as yielding similar results on the test and retest. This is especially true for subjects who perform well, and less so for subjects who perform poorly, i.e., those who would be candidates for failing the test. In its present form, the device is not sufficiently portable to be transferred from one branch to another as the need demands. It does, however, constitute a large improvement over the previous battery in terms of the test administration time (approximately 15 minutes), the fact that administration and scoring is totally automated, and the high degree of acceptance of this type of test for licensing procedures (over 90% of the subjects enjoyed taking the test and indicated approval of its inclusion in the license testing and procedures). Validation data is incomplete at this time since 72% of the drivers tested to date have not had a single accident in the last five years. A diagnostic procedure has been developed which includes a battery of standard clinical tests and a diagnostically-oriented driver vision test battery to be installed in a vision specialist's office. Future plans include a nationwide validation effort oriented towards the establishment of pass/fail criteria that would be consistent with a driver's likelihood of accident involvement.

Notes:

This is part of same body of work as Shinar, 1978, and involves development of the "Mark II Tester", an integrated driver vision testing device.

Authors: Shinar, D., & Schieber, F.

Date: 1991.

Title: Visual requirements for safety and mobility of older drivers.

Pub: Human Factors, 33 (5), 507-519.

Keywords:

Aging,

Vision testing

Abstract:

Efforts to assess visual deterioration with increasing age, coupled with new mechanisms proposed to limit the exposure of visually impaired drivers to driving risks, have emerged in response to the increase in older drivers. Visual functions discussed in this context include static acuity (photopic, mesopic, and in the presence of glare), dynamic visual acuity, visual field, contrast sensitivity, and motion perception. Exposure control mechanisms discussed include alternative periodic vision testing strategies, visual training, and environmental and vehicular modifications to accommodate the older driver. Finally, relevant research needs are addressed.

Notes:

Review article: much literature covered. Also discusses policy and legal issues, especially around vision testing. Points out need for good research to determine relationships between visual and performance measures related to driving.

Authors: Shinar, D., Zaidel, D. M., & Paarlberg, W. T.

Date: 1978.

Title: Driver performance and individual differences in attention and information processing Volume II: Field dependence and highway safety(DOT-HS-8-01819-78-FD).

Pub: Washington, DC: U.S. Department of Transportation.

Keywords:

Driving

Peripheral vision

Personality

Situational awareness

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( ) Reference only ( ) Other ( )

Abstract:

Volume II consists of a review of the research on the personality characteristic of field dependence as it relates to driver behavior and accident involvement.

The review is divided into two parts. The first part is concerned with the nature of field dependence as a theoretical concept, its relationship to other measures of individual differences, and its methods of measurement. The second part deals with the relationship between field dependence and highway safety in terms of driving behavior and accident involvement.

Notes:

Looks at research (up to 1978) suggesting that field-dependent drivers may have reduced peripheral vision capabilities, other driving related deficits vs. field-independent drivers.

Authors: Simonelli, N.

Date: 1983.

Title: The dark focus of the human eye and its relation to age and visual defect.

Pub: Human Factors, 25 (1), 85-92.

Keywords:

Acuity

Aging

Dark Focus

Night Myopia

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The effects of age and ametropia (nearsightedness or farsightedness) on the dark focus of visual accommodation have not been extensively investigated. Participant pools of students are generally screened and their vision "standardized" by testing them while they wear their corrective lenses. In this study, nearsighted and farsighted subjects were measured for their near points, far points, and dark focuses. It was found that the more nearsighted the eye the larger the dark focus shift. Age was also found to have a relationship to the dark focus. Older individuals tended to have a smaller dark focus shift, and the dark focus was found to recede with age at roughly the same rate as the far point.

Notes:

Looked at age, near point, far point, dark focus. Used concept of "relative dark focus," measuring difference between far point and dark focus as index of relative dark focus effects across subjects. This is useful in addressing the issues of whether some populations (e.g., older subjects, myopes) are more severely affected than others by dark focus shifts.

Authors: Stoper, A. E.

Date: 1973.

Title: Apparent motion of stimuli presented stroboscopically during pursuit movement of the eye.

Pub: Perception & Psychophysics, 13, 201-211.

Keywords:

Event perception

Motion detection

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

In normal illumination, retrograde motion of the background (the Filehne illusion) can be seen during ocular pursuit, in contrast to stability seen during a saccade. In the present experiment, two stimuli were presented sequentially: (I) at disparate physical locations such that the pursuit movement of the eye caused them to excite the same retinal location, (II) at the same physical location, with pursuit movement causing disparate retinal excitations, and (III) with stationary fixation but with disparate physical locations such that the retinal excitation was identical to that of Condition II. Optimal movement was never reported for Condition I but was reported with essentially equal frequency in Conditions II and III. These results indicate a failure of compensation for pursuit movement, as does the Filehne illusion. The nature of the pursuit extraretinal signal was discussed, and it was argued that a distinctly different extraretinal signal is necessary for perceived stability during the saccade.

Author: Tolhurst, D.

Date: 1973.

Title: Separate channels for the analysis of the shape and movement of a moving visual stimulus.

Pub: Journal of Physiology, 231, 385-402.

Keywords:

Contrast sensitivity

Dynamic acuity

Motion detection

Spatial frequency

Static acuity

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

1. The effects of temporal modulation on the properties of spatial frequency channels have been investigated using adaptation.

2. Adapting to drifting sinusoidal gratings caused threshold elevation that was both spatial frequency and direction specific. Little systematic difference was found between the band widths of the elevation curves for drifting and stationary gratings.

3. It was confirmed that adaptation fails to reveal channels at low spatial frequencies when stationary gratings are used. However, channels were revealed at frequencies at least as low as 0 66 c/deg when the test gratings were made to move. These channels are adapted only a little by stationary gratings, confirming their dependence on movement.

4. The existence of movement-sensitive channels at low spatial frequencies explains the well known observation that temporal modulation greatly increases the sensitivity of the visual system to low spatial frequencies.

5. Temporal modulation was effective at revealing these channels only when the flicker or movement of the test patterns was apparent to the observer; only at low spatial frequencies did patterns, modulated at low rates, actually appear to be temporarily modulated at threshold. At higher spatial frequencies, they were indistinguishable from stationary patterns until the contrast was some way above the detection threshold.

6. It is suggested, therefore, that the movement-sensitive channels are responsible for signaling the occurrence of movement; the channels at higher spatial frequencies give no information about temporal changes. These two systems of channels are compared to the Y- and X-cells respectively of the cat.

Author: Trevarthen, C.

Date: 1968.

Title: Two mechanisms of vision in primates.

Pub: Psychologische Forschung, 31, 299-337.

Keywords:

Ambient vs focal

Cortical function

Midbrain function

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Experiments with split-brain monkeys led me to consider that vision of space and vision of object identity may be subserved by anatomically distinct brain mechanisms. In this paper I examine the visual mechanisms of the brain to test the idea that vision involves two parallel processes; one ambient, determining space at large around the body, the other focal which examines detail in small areas of space. In vertebrates there is a projection from eye to midbrain of a detailed topography of body-centered behavioral space. This visual map is integrated with the bisymmetric motor system to obtain correspondence between visual loci and the goal for movements. The midbrain visual system governs basic vertebrate locomotion behavior.

The phylogenetically more recent forebrain visual system looks almost exclusively at central behavioral space, and cortical motor control is likewise concerned with the formulation of highly specific acts in the same central territory.

Anatomy and brain surgery reveal a midbrain visual mechanism in primate which plays a part in ambient space perception over the whole field. In contrast, focal vision served by the fovea and parafovea and by the cortical visual areas picks out areas in the ambient field for close attention. Conjugate eye movements are the most direct sign of this attention.

The interplay between the two channels of visual analysis is a feature of vision in all active animals; but the complexity of focal vision in primates is revealed in their visual system at all levels, and in the parts of the motor system which orient vision, or which govern acts directed to specific visual objects.

Authors: Turnage, J. J., & Kennedy, R. S.

Date: In press.

Title: A hierarchical view of human performance: the neglected contribution of visual factors to predicting performance.

Pub: Advances in Industrial Ergonomics & Safety.

Keywords:

Acuity

Contrast sensitivity

Dynamic acuity

Motion detection

Spatial frequency

Static acuity

Vision testing

Holding: Full text (x) Abstract/Summary ( )

Abstract:

The development of computer-based cognitive test batteries for the assessment of human performance in applied work settings stems from models of human information processing that describe critical stages of processing in the order: sensor - central processor - effector. This study showed that unique limitations on sensory systems can influence the quality and quantity of information that may be initially registered and therefore may potentially affect all the processes that follow. The importance of accounting for simpler sensory processes first and before more centrally dependent cognitive and information processing factors should not be overlooked when attempting to predict human performance in the workplace.

Notes:

Shows some correlation between scores on tests of visual spatial and temporal acuity and performance in simulated flight tasks. Longer paper in preparation (personal communication, 1995) has more detail on method.

Authors: Westheimer, G., & McKee, S. P.

Date: 1978.

Title: Stereoscopic acuity for moving retinal images.

Pub: Journal of the Optical Society of America, 68, (4), 450-455.

Keywords:

Acuity

Binocular/Monocular

Dynamic acuity

Stereoscopic Acuity

Velocity

Holding: Full text (X) Abstract/Summary ( )

Abstract:

Stereoscopic acuity in the human fovea remains unimpaired with retinal image motions of up to 2 deg/s. These findings apply to lateral motion of the test target alone, and to simultaneous lateral motion of both test and comparison targets. For good stereoscopic acuity, depth motion can be tolerated only so long as the configuration does not move outside the disparity zone for optimal stereoscopic acuity, within 2-3 arc min of either side of the fixation plane. The presence during a short exposure of some stimulus components lying outside this zone leads to an overall reduction of stereoscopic acuity, either by dilution through summation, or by active inhibition of the best achievable depth resolution.

Authors: Williams, L. J.

Date: 1989.

Title: Foveal load affects the functional field of view.

Pub: Human Performance, 2 (1), 1-28.

Keywords:

Central vision

Foveal vision

Peripheral vision

Static acuity

Useful field of view

Visual field

Holding: Full text (x ) Abstract/Summary ( )

Abstract:

The results of three tachistoscopic experiments are reported, which suggest that the functional or useful field of view is very sensitive to foveal demands (load). As the foveal primary task becomes more difficult, peripheral information extraction is perturbed, and it is perturbed increasingly as the retinal eccentricity of the peripheral information increases. This is the case even when compensatory adjustments are made for acuity loss. The results are discussed in terms of tunnel vision and general interference models.

Author: Wood, J. M., & Troutbeck, R.

Date: 1994.

Title: Effect of visual impairment on driving.

Pub: Human Factors 36 (3) 476-487.

Keywords:

Driving

Impairments

Monocular/binocular

Abstract:

The aim of the study was to determine the effect on driving of restricting vision. This was undertaken by comparing the driving performance of young, normal subjects under conditions of simulated visual impairment with a baseline condition. Visual impairment was simulated using goggles designed to replicate the effects of cataracts, binocular visual field restriction, and monocular vision. All subjects had visual acuity greater than 6/12 [metric] when wearing the goggles and thus satisfied the visual requirements for a driver's license [Australian]. Driving performance was assessed on a closed-road circuit for a series of driving tasks including peripheral awareness, maneuvering, reversing, reaction time, speed estimation, road position, and time to complete the course. Simulated cataract resulted in the greatest detriment to driving performance, followed by binocular visual field restriction. The monocular condition did not significantly affect driving performance for any of the driving tasks assessed.

Notes:

Fidelity and generalizability issues: used closed course, with no traffic; simulated impairments in healthy young drivers.

Authors Wood, J. M. and Troutbeck, R.

Date: 1992.

Title: Effect of restriction of the binocular visual field on driving performance.

Pub: Ophthalmic & Physiological Optics, 12, (3), 291-298.

Keywords:

Binocular/Monocular

Driving

Impairments

Peripheral vision

Vision testing

Visual field

Holding: Full text (X) Abstract/Summary ( )

Abstract:

The importance of the visual field on driving performance was investigated. This was undertaken by simulating binocular visual field defects for a group of young normal subjects and assessing the impact of these defects on performance on a driving course. Constriction of the binocular visual field to 40 or less, significantly increased time taken to complete the course, reduced the ability to detect and correctly identify road signs, avoid obstacles and to manoeuvre through limited space. Accuracy of road positioning and reversing were also impaired. Constriction of the binocular visual field did not significantly affect speed estimation, stopping distance, or the time taken for the reversing and manoeuvring tasks. The monocular condition did not significantly affect performance for any of the driving tasks assessed.

Notes:

Simulated field restrictions with pinhole goggles, but used actual driving on closed course to assess impairment of driving functions. Provides limited evidence for validity of some kind of visual field testing for driver licensing. Authors seem most impressed by how little the subjects' performance was impaired. Does not speak to how testing should be done, or to visual field losses less severe than those tested here. Monocular condition showed little effect on driving scores, but authors caution that subjects were young and otherwise had no impairments, and were tested in daylight conditions only.

Authors: Zaidel, W. M., Paarlberg, W. T., & Shinar, D.

Date: 1978.

Title: Driver performance and individual differences in attention and information processing Volume I: Driver inattention ( Report No. DOT-HS-8-01819-78-DAP).

Pub: Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration.

Keywords:

Driving

Attention

Inattention

Testing

Holding: Full text (Vol I) Abstract/Summary ( )

Abstract:

This is a final report of a study whose purpose was to provide an evaluative review of existing knowledge in the fields of traffic safety, driver behavior, and psychology with respect to driver inattention.

Volume I represents the main part of the review and includes the following sections: a discussion of basic concepts, theories, measurement techniques, and research paradigms in studies of attention and driver performance; a multi-dimensional definition of attentional performance in the context of driving behavior; an analysis of inattention-related traffic accidents; a survey of behavioral and physiological indicators of inattention; a survey of individual differences in attentional performance; a detailed delineation of unresolved research issues; and recommendations for future research aimed at developing driver-oriented inattention countermeasures.

Authors: Zwick, H, Burri, B., & Beatrice, E.S.

Date: 1990.

Title: Vitamin A supplementation effects on photopic and scotopic visual function and measures of vitamin A status (Institute Report No. 448).

Pub: San Francisco: Letterman Army Institute of Research, Division of Ocular Hazards.

Keywords:

Color vision

Contrast Sensitivity

Dark Adaptation

Impairments

Vision testing

Holding: Full text (X) Abstract/Summary ( )

Abstract:

We investigated the effects of vitamin A supplementation in an individual with abnormally low vitamin A-containing transthyretin-bound retinol binding protein (RBP). Measures of spectral dark adaptation and spatial contrast sensitivity suggest a differential return of parafoveal and foveal receptor systems during supplementation. Parafoveal cone systems appear to return more rapidly than foveal cones and rods. Post-supplementation measurements of spectral dark adaptation demonstrated a crossing of spectral dark adaptation functions at 6.5 minutes, close to the appearance of the rod cone break attributed to achromatic measurements of dark adaptation. Contrast sensitivity for the finest spatial frequency showed a delay in its return to near normal levels relative to recovery of mid to low spatial frequencies. While measures of serum retinol, total RBP, and free RBP increased during supplementation, transthyretin-bound RBP failed to show any increase relative to its abnormally low presupplementation level. Bodily stores of vitamin A either require more time to return to normal levels than retinol delivered to the retina or this individual possessed a specific genetic deficiency in the bodily mechanism responsible for storing vitamin A.