The effect of variability of background elements on the conspicuity of objects.

The effect of complex backgrounds on target visibility was studied by asking observers to locate a disc target presented on a background of randomly arranged discs. A previous paper (Vision Res. 22, 1241-1252, 1982) explored the effect of increasing the density (numerosity) of the background elements when the elements were all the same size and luminance. In this investigation the size or the luminance of the background elements varied although mean size and mean luminance was held constant. Variability of the size of the background elements had a substantial effect on the size contrast necessary to detect the target. The data are well described by a contrast metric CT which assumes that observers detect the target by comparing it to a weighted average of the larger elements. The larger elements that determine the weighted average are those that all appear the same size because, at the eccentricity of target, the observers are unable to distinguish their differences in size. The threshold values of CT for detection of the target at a given level of probability were dependent on eccentricity but independent of the degree of variability of the background elements. The threshold contrast was also the same as the necessary for the more elementary task of discriminating size differences of two discs. In a second experiment it is shown that variability in the luminance of the background elements did not affect target visibility. This result is explained by reference to the data in our earlier paper from which it can be shown that the observers were unable to perceive the differences in luminance in their peripheral visual field so that, within limits, backgrounds that vary in luminance can be validly characterised by mean luminance.

The effect of the density of background elements on the conspicuity of objects.

Engel's concept of conspicuity is formalised to define a conspicuous object as one that will, for a given background, be seen with certainty within a short observation time regardless of the location of the object in relation to the line of sight. Thus for a defined level of probability of seeing and given observation time, the angle of eccentricity at which the defined level of probability of seeing occurs becomes the measure of the conspicuity of the target. Using this measure the conspicuity of disc targets has been determined when the targets are presented in complex backgrounds made up of random arrays of discs. A first experiment determined thresholds for discrimination of size differences and luminance differences for two discs since this was regarded as the elementary task in the detection of the target within a complex background made up of elements of the same shape. In the main experiment the task was the detection of a target disc located in a background consisting of randomly arranged discs. The target disc differed from the background discs in either size or luminance or both. The background array had three densities of background element. When the target discs differed in luminance from the background discs an increase in background density made the target disc less conspicuous but changing background density had no effect on the conspicuity of target discs that differed in size from the background discs. It was found that the task of detecting a luminance difference when there were only two discs (first experiment) was easier than detecting a target disc in the random arrays. However, the detection of a disc of different size in the random arrays appears to be no more difficult than the elementary task of comparing size differences between two discs. This suggests that the visual processes for detecting a target in a complex background by size difference are different from those for detecting the target by luminance difference.

Can clinical colour vision tests be used to predict the results of the Farnsworth lantern test?

Clinicians usually do not have access to a lantern test when making an occupational assessment of the ability of a person with defective colour vision to recognise signal light colours: they must rely on the results of ordinary clinical tests. While all colour vision defectives fail the Holmes Wright Type B lantern test and most fail the Holmes Wright Type A lantern, 35% of colour vision defectives pass the Farnsworth lantern. Can clinical tests predict who will pass and fail the Farnsworth lantern? We find that a pass (less than two or more diametrical crossings) at the Farnsworth Panel D 15 Dichotomous test has a sensitivity of 0.67 and specificity of 0.94 in predicting a pass or fail at the Farnsworth lantern test: a Nagel range of > 10 has a sensitivity of 0.87 and a specificity of 0.57. We conclude that neither the D 15 nor the Nagel Anomaloscope matching range are satisfactory predictors of performance on the Farnsworth Lantern.

Recognition of the aircraft navigation light color code.

Navigation lights are a set of color-coded signals intended to indicate the presence, orientation, and relative direction of aircraft at night, and thereby reduce the possibility of midair collisions. It is known that some people with defective color vision have difficulty with quite simple codes. Accordingly, the International Civil Aviation Organization (ICAO) has recommended -- and most countries apply -- that applicants for pilot's licences demonstrate the ability to recognise colored light signals. Pilots who fail to meet this requirement are restricted from flying at night. But is the navigation light signal system effective? This paper concludes that the navigation light system at night can serve as a crude screening method to categorize intruder aircraft into "potential threat" and "no threat" categories. An experiment is described which shows that observers with normal color vision can determine intruder aircraft orientation and relative direction from the navigation light code with a moderately high degree of reliability. The reliability of judgement is, however, decreased by the higher-intensity presence lights also displayed by aircraft.

Visual detection of commencement of aircraft takeoff runs.

Among other things, airport control towers should be sited so that controllers can readily detect whether an aircraft cleared for takeoff has commenced its takeoff run. The detection of movement is not well enough understood to enable confident prediction that a particular site for a tower will enable commencement of takeoff run to be easily observed. A field study was undertaken to establish detection times for commencement of takeoff run by groups of trained and trainee air traffic controllers and untrained observers. It was found that the mean response of observers occurs when the aircraft is displaced about 5' of arc, a value essentially independent of observer experience, observation distance, aircraft velocity, and the clarity with which the aircraft can be seen. Binoculars reduce the mean response time and response variability, although not as much as might be expected. Domains within which control towers can be located to enable detection of takeoff runs within 2 s and 4 s are defined.

A critique of the usefulness of inferential statistics in applied behavior analysis.

Researchers continue to recommend that applied behavior analysts use inferential statistics in making decisions about effects of independent variables on dependent variables. In many other approaches to behavioral science, inferential statistics are the primary means for deciding the importance of effects. Several possible uses of inferential statistics are considered. Rather than being an objective means for making decisions about effects, as is often claimed, inferential statistics are shown to be subjective. It is argued that the use of inferential statistics adds nothing to the complex and admittedly subjective nonstatistical methods that are often employed in applied behavior analysis. Attacks on inferential statistics that are being made, perhaps with increasing frequency, by those who are not behavior analysts, are discussed. These attackers are calling for banning the use of inferential statistics in research publications and commonly recommend that behavioral scientists should switch to using statistics aimed at interval estimation or the method of confidence intervals. Interval estimation is shown to be contrary to the fundamental assumption of behavior analysis that only individuals behave. It is recommended that authors who wish to publish the results of inferential statistics be asked to justify them as a means for helping us to identify any ways in which they may be useful.

Defective colour vision can impede information acquisition from redundantly colour-coded video displays.

Earlier findings showed that redundant colour coding decreased response times and reduced errors in carrying out various tasks that required information acquisition from the video display of an electronic flight instrument system. The results of this experiment showed that observers with defective colour vision have slower response times and higher error rates than normal observers for some of the tasks and that their performance is similar to that of colour-normal observers for a monochrome display. However, they were not disadvantaged when blue was used to colour code the target feature. Protanopes were shown to be especially disadvantaged in responding to a red 'fail' message.

Are colour vision standards justified for the transport industry?

Colour vision standards are imposed in the road, rail, maritime and aviation industries and are often subject to vigorous opposition by those excluded by the standard. With greater emphasis in recent years on equality of opportunity, it is important that standards of personal fitness, such as colour vision standards, be subject to critical scrutiny. Such appraisal should be able to demonstrate that the community benefit arising from the application of the standard is sufficient to justify the personal and other costs of retaining the standard. This paper reviews the evidence relating to colour vision standards in the transport industries and concludes that a strong case can be made for their retention in public transport.

What do color vision defectives say about everyday tasks?

A lengthy questionnaire was administered to 102 people with defective color vision and to an equal number of people with normal color vision. The questionnaire asked about the subjects' awareness of their defect and their knowledge of defective color vision as well as exploring the difficulties they experience with color at work and in pursuing leisure activities. The questionnaire was administered in the consulting room under conditions that might be expected to elicit frank replies. Nearly 90% of dichromats and up to two-thirds of anomalous trichomats reported difficulties with everyday tasks that involve color, nearly one-half of the dichromats and one in five anomalous trichromats reported difficulty with traffic lights, and similar proportions reported color difficulties in their present jobs. Substantial numbers reported that their color vision defect had affected their choice of career and many had been excluded from a chosen occupation. The screening of color vision in schools and provision of appropriate career counselling is urged.

A recommendation for illumination of the Farnsworth-Munsell 100-hue test.

The effect of illuminance on the performance of the Farnsworth-Munsell 100-hue (FM 100) test has previously been reported for young observers with normal color vision. However, information regarding these effects for older persons is lacking. This study reports the effect of illuminance level, over a wide range, on the FM100 performance of 10 elderly subjects with normal color vision compared to a control group of five young adult normal subjects. A recommendation is made for a standard level of illuminance for administration of the FM100-hue test.

Origins of colour vision standards within the transport industry.

Colour vision standards should reflect changes in our understanding of the nature of these defects as well as technological advances that place less importance upon the visual senses of the human operator. Therefore it is suggested that visual standards be subject to routine reviews in order to assess their suitability for modern work environments. This paper gives a chronological account of the introduction of colour vision standards by several national transport authorities and identifies historical reasons that led to their implementation. It is concluded that the same factors that gave rise to the adoption of early colour vision standards are still relevant for modern transport systems. However the recent deployment of automatic or semi-automatic control or navigational systems has substantially altered man's role from being the primary source of information input to one of a monitoring process. This has generated a good deal of debate and uncertainty regarding the level of responsibility that a human operator has for the control of modern transport vehicles. Nevertheless, it is argued that in the absence of complete automation some type of visual standard is needed whenever visual judgements must be made by human observers.

Action on worksite health and safety problems: a follow-up survey of workers participating in a hazardous waste worker training program.

In it's worker health and safety training program, the California-Arizona Consortium aims to promote worker action to improve health and safety conditions. To assess action on worker-identified health and safety problems, 278 trainees were interviewed 3-8 months after training. Associations with three outcomes were analyzed: (1) attempted action, (2) problem correction, and (3) trainee participation. Perceived management support was associated with all three outcomes, pointing to its key role in maximizing the impact of training. Odds of attempted action were 2-5 times greater with support than without. Trainees for whom English was not the primary language (mostly Spanish speakers) attempted action as often as English speakers. However, the odds of their correcting problems were half that of the English-speaking workers. It is suggested this was due to a perceived lack of control over organizational resources for change, not simply due to communication barriers.

The prevalence and symptoms of migraine in a consecutive series of patients attending an optometric practice.

The purpose of the investigation was to determine the prevalence of migraine in optometric practice and to document the variety of presentation. One thousand consecutively presenting patients of a suburban optometric practice were asked questions to establish whether they experience migraine or have experienced it in the past. Those with a history of migraine were asked further questions to establish the type of migraine and to document the variety of the symptoms they experienced. Eleven percent of male and 23% of female patients currently had migraine or had experienced it in the past. When corrected for the age distribution of the population of the state from which the sample was drawn, it is estimated that the general population prevalence of migraine is 9.5% for men and 19.7% for women. Half of the sample of migraineurs had not experienced a migraine within the last 12 months. A third had a known family history of migraine. Nearly half had not had a formal medical diagnosis of their migraine but only 7 had attended for optometric examination because of their migraine symptoms. Four of these patients had single migraine-like episodes and three had migraine equivalents (acephalic migraine, experiencing the visual aura without headache). Optometrists must be thoroughly familiar with migraine and its varied presentation because of its high prevalence, the explanatory value in offering a formal diagnosis of migraine, and the risk that headache or visual aura may be wrongly ascribed to migraine when there is some more sinister cause of the symptoms.

A survey and evaluation of lantern tests of color vision.

This paper reports a survey of the lantern tests that have been or are used to evaluate the color vision of people who wish to enter occupations that require the ability to recognize colored signal lights reliably. The origin of each lantern is traced and the principal features of each are described. The available data concerning failure rate of normals, the failure rate of people with defective color vision, and the extent to which scores on lantern tests correlate with field trials are summarized. Despite the fact that lantern tests have been used since the turn of the century and that some lanterns have been in use for more than 30 years and some for much longer periods, the available validation data are incomplete and sometimes conflicting. However, the data do indicate that some lanterns may fail a significant proportion of normals and that there is considerable variation between lanterns in the proportion of color vision defectives that will fail. It is noted that most lanterns will pass some protanomals despite their reduced sensitivity to red light and correspondingly short visual range for red signals. The view of Cameron is supported that a more rational approach would be to made a clinical diagnosis of the type of color vision defect, to reject protanopes, deuteranopes, and protanomals and to use a lantern test only to determine which deuteranomals should be accepted.

Who fails lantern tests?

A battery of clinical colour vision tests was given to a group of 100 observers with abnormal colour vision who were also tested on the Farnsworth lantern and the Holmes-Wright lanterns types A and B. It was found that clinical colour vision tests are imperfect predictors of lantern test performance. However, observers classified as having a 'severe' colour vision defect were found to fail the lantern tests but only one half to two-thirds of those who fail the lantern tests can be identified in this way. It is not possible to identify with certainty any of the people likely to pass the lantern tests: about one-third to two-thirds of observers classified as being mildly affected fail the lantern tests. The Farnsworth D-15 and City University tests were found to be the best predictors of lantern test performance but other tests such as the Nagel anomaloscope, the H-16, L'Anthony's desaturated test can also be used. The lack of a strong correlation between clinical tests and the recognition of the small coloured stimuli presented by the lantern tests suggests that clinical tests do not test the same aspect of colour vision that is important to the recognition of signal lights. For this reason lantern tests should be retained for occupational testing of colour vision.

Validation of the Holmes - Wright lanterns for testing colour vision.

The recently introduced Holmes - Wright Type A and Type B lanterns and the Farnsworth lantern were administered to 100 observers with normal colour vision and 100 observers with defective colour vision. With the fail criteria adopted, all normals passed the Holmes - Wright Type A lantern and with one exception all normals passed the Farnsworth lantern. However, 8% of normals failed the more difficult Holmes - Wright Type B lantern. It is noted that the normals who fail this lantern test appear to do so not because of poor colour discrimination but because the coloured stimuli presented by the lantern have a point brilliance close to the average chromatic threshold. About one-third of the colour vision defective group passed the Farnsworth lantern and between 14 and 17% passed the Holmes - Wright Type A lantern depending on the test procedure used. Only two mild deuteranomals in the sample of 100 colour abnormal observers succeeded in passing the Holmes - Wright Type B lantern. Dichromats and severe anomalous trichromats fail all three lanterns so that those who pass are all mild anomalous trichromats. A significant proportion of protanomals pass the Farnsworth lantern and some protanomals pass the Holmes - Wright Type A lantern despite their reduced sensitivity to red light and correspondingly reduced signal range for red signals.

Reliability and validity of simple photographic plate tests of contrast sensitivity.

Sets of edge and square wave grating photographic plates of varying contrasts were used to measure the mid to low spatial frequency range of the contrast sensitivity function (CSF) of 20 subjects with evident ocular disease and 20 age-matched normal subjects. Both plate tests were shown to have good test-retest reliability and to correlate well with electronic cathode ray tube (CRT) measures of CSF. The edge test, when administered in 2-dB steps of ascending contrast, has optimum sensitivity of 0.70 and specificity of 0.84 for detecting the patient with ocular disease with a fail criterion of less than 38 dB. A measure of edge contrast sensitivity was also shown to be a good predictor of the peak of the CSF, which is shown to be largely independent of the visual acuity of the subject. The 2 c/deg and 4 c/deg plates did not provide more information about the visual difficulties of subjects than the edge test. We advocate the use of an edge test as a simple clinical measure of low spatial frequency contrast sensitivity that provides information about visual dysfunction not provided by a measure of visual acuity.

Assessment of contrast sensitivity of patients with macular disease using reduced contrast near visual acuity charts.

A set of near Bailey-Lovie logMAR letter charts that varied in contrast from 0.40 dB (C = 0.95) to 58.0 dB (C = 0.001) were used to measure the middle and high spatial frequency range of the contrast sensitivity function (CSF) of 15 subjects with age-related maculopathy (ARM) and 15 age-matched normal subjects. The letter charts were shown to have good test-retest reliability. Compared with measures made using CRT generated square wave gratings of variable contrast and spatial frequency they were also shown to provide a valid measure of CSF in the mid to high spatial frequency range. The 20.0 dB letter chart alone was shown to be a good screening device for macular disease. The letter charts do not provide a measure of the peak of the CSF and a supplementary test of contrast sensitivity is needed to quantify contrast sensitivity at a low spatial frequency. Three measures are proposed as necessary to document foveal visual capability of patients with macular disease: distance logMAR visual acuity to measure high spatial frequency resolution, visual acuity with letter charts of 20 dB contrast to assess mid spatial frequency resolution; and contrast sensitivity for the detection of an edge to estimate contrast sensitivity for larger objects.

Effect of VDUs on the eyes: report of a 6-year epidemiological study.

One thousand, three hundred and sixteen office workers [692 visual display unit (VDU) users, 624 controls in the first year] were examined once each year over a 6-year period to establish whether or not VDU work was a factor in the occurrence of visual symptoms, ocular abnormalities, or ocular disease. Statistical analysis showed that although there were differences between VDU users and nonusers in the amount of myopia, the prevalence of some symptoms, and the prevalence of signs of fundal or vitreal disease, the differences were small and there were no clear trends or patterns to lend convincing support to the hypothesis that VDU work may be a risk factor. There were no significant differences in the prevalence and incidence of cataract.