Does Color Vision Needs to Test in Different Occupations?

Color blind tests are used for the various kinds of purpose. A number of these embody the speedy screening of noninheritable red-green defects in industry, transportation, and also the military. To test your vision you have to go through the color blind test. 

The classification of discrimination ability among the population of congenital red-green defects is employed for job assignment purposes. Another use for screening involves the popularity and diagnosing of congenital disorders for psychophysical or genetic study.

Within the the clinic, screening is used for the recognition and differentiation of congenital and bought disorders, for the classification of acquired disorders in patients with eye disease, and, in some cases, for the assessment of treatment or for trailing recovery from sickness or trauma.

Finally, in education and industry, screening for each visual modality defects and color aptitudes is employed for business steering in occupations or professions that need color judgments.

The 2 major issues long-faced by people who use color vision tests are

1. to understand the colour vision necessities of a given task and
2. to pick applicable color vision tests.

Abstract

Normal trichromatic colour vision is often required as a condition for employment in visually demanding occupations. If this requirement could be enforced using current, colour assessment tests, a significant percentage of subjects with anomalous, congenital trichromacy who can perform the suprathreshold, colour-related tasks encountered in many occupations with the same accuracy as normal trichromats would fail.

These applicants would therefore be discriminated against unfairly. One solution to this problem is to produce minimum, justifiable CV requirements that are specific to each occupation. This has been done successfully for commercial aviation (i.e. the flight crew) and for Transport for London train drivers.

An alternative approach is to make use of new findings and the statistical outcomes of past practices to produce graded, justifiable CV categories that can be enforced. To achieve this aim, we analysed colour assessment outcomes and quantified severity of CV loss in 1363 subjects.

The severity of CV loss was measured in each subject and statistical, pass/fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols.

This evidence and new findings that relate severity of loss to the effective use of colour signals in a number of tasks provide the basis for a new colour grading system based on six categories.

A single colour assessment test is needed to establish the applicant's CV category which can range from ‘supernormal’, for the most stringent, colour-demanding tasks, to ‘severe colour deficiency’, when red/green CV is either absent or extremely weak.

Background

Colour is by no means easy to define, but it is undoubtedly a perceptual attribute that affects significantly everything we see. A good place to start from when we question what we ‘see’ is the information available in the image formed on the retina by the optics of the eye.

The ability to see spatially structured objects, to resolve edges and contours and to see fine detail requires point by point processing of the amount of light present in the retinal image and this is achieved through the photopic luminance contrast channel (see below Fig) which captures and averages the light present over the middle- and long-wavelength regions of the visual spectrum.

This channel acts as a single detector of light and does not therefore contribute to colour vision (CV). A second, colour-insensitive channel with similar properties, but with much coarser spatial resolution operates best at lower light levels and is based on spatial summation of rod signals.

Variations in the spectral composition of light on the retina also carry useful information that is captured by the red/green (RG) and yellow/blue (YB) chromatic channels.

The way we perceive objects in human vision relies largely on the ‘luminance’ and ‘colour’ contrast signals objects generate in the eye with respect to its immediate surround. There are four principal ‘Vision Information Channels’ as shown in above Figure.

The contribution each of these channels makes to the perceptual representation of an object depends on a number of stimulus parameters such as the size of the object and its location in the visual field, the level of ambient illumination and the relative amounts of light reflected by the object in the short (S), middle (M) and long (L) wavelength regions of the visual spectrum.

Although these ‘channels’ are a gross simplification of the mechanisms involved in the extraction of information from the retinal image, this simple model helps to explain some of the difficulties involved in colour assessment when the signals generated in RG and YB chromatic mechanisms have to be assessed independently.

What may not be immediately obvious is that the majority of colours we perceive as red, green, yellow or white and many shades of blue generate both RG and YB chromatic contrast signals and that the perceptual experience of what we see relies on the relative strengths of these colour signals and the luminance contrast of the object with some contribution from rods at lower light levels.

It is therefore by no means easy to establish accurately how these signals interact and which channel contributes most to what we see in a given context.

Color Vision Requirements in Different Occupations

It is essential for the benefit of both employer and employee that the color vision requirements of a job be adequately described.

On the basis of these professional requirements and observer capabilities a decision can be made about whether an individuai's color vision is suitable for performing the particular duties encountered in daily work situations.

Such practical assessment of the relevant color qualifications helps to prevent the inappropriate allotment of manpower. A major difficulty in this regard is the lack of precise checklists of color vision requirements for different jobs; there are
no guidelines to help employers establish color requirements for a given job.

Broadly speaking, however, many occupations can be divided into three categories (e.g., Lakowski, 1968) depending on the quality of color vision required:

1. Those excluding major color defective observers;
2. Those requiring representative color vision;
3. Those requiring good color discrimination.

Occupations Excluding Major Color Vision Defects

There are many activities and occupations in which defective color vision is either undesirable or unacceptable. Generally observers with severe color defects should not be expected to work in any industrial situation in which a premium is placed on the recognition and/or classification of color surfaces, lights, or objects.

Abnormal color vision is therefore a serious handicap in all those areas of electronics and telecommunications that involve the identification, coding, and wiring of electrical equipment.

The exclusion of major color-defective observers is also essential in transportation industries (railway, marine, or aviation) in which confusion of signal lights can endanger public safety.

On the other hand, not all professions that validly exclude major color defective observers require normal color vision. Individuals with mild impairments can perform many operations involving color discrimination without any
special risk to their own or to public safety.

Occupations Requiring Representative Color Vision

There are a vast number of occupations in which the mere exclusion of color-defective observers is an inappropriate policy for selecting personnel.

In industry, especially, it seems more important to discover whether a person is fit for a particular job than to classify him or her as either normal or color defective. 

What is required in most situations is to establish whether the employee has the necessary skill to deal with a particular color task or to satisfy some criteria acceptable to the employer.

In such areas as color research, commercial painting, color photography, chemistry, papermaking, paint mixing, the graphic arts, lithography, cartography, and textile dyeing, it is especially important that those who must make color matches have color vision that is representative of the majority of consumers.

It is well known that color-matching ability may vary considerably from one observer to another; those observers who fall at the extremes of the distribution of normals may be considered to have an atypical form of normal color vision.

Usually such deviations from the mean are not diagnosed by routine testing, yet they may constitute serious practical color vision problems by reducing the individual's effective job performance.

Occupations Requiring Good Color Discrimination

In many professions, individuals are chosen for their ability to make fine or difficult decisions in color discrimination. Here the exclusion of color-defective observers is not the prime consideration.

Rather, people are selectively chosen for their precision in matching sample colors to standards or in classifying colors that differ only very subtly.

In addition, in some occupations the recognition of color at twilight levels of illumination is required.

Only individuals with good color discrimination or specific aptitudes can perform these types of jobs with facility and accuracy.

Selecting Color Vision Tests

It is possible to design appropriate task-specific field tests in order to establish the color vision requirements of different jobs, but such a job-by-job analysis would be inefficient and expensive.

On the other hand, selecting an available clinical color vision test for a particular application is not simple. 

First, information concerning the merits of these tests relative to each other and to various job requirements has not been readily available. 

Second, clinical color vision tests are not designed for the scaling of performance or for multiple cutoff criteria; the scoring standard for most clinical tests is stated in terms of a single pass/fail score.

Third, the classification of color discrimination ability by clinical tests might not predict performance in a real-life situation (Kinney et al., 1979). Many experts feel that to generalize from a clinical test to a job requirement is inappropriate at best and meaningless at worst.

Fourth, the determinants of performance on each test are sufficiently complex, ranging from colorimetric design to motivational factors, that no test can be considered to provide a single metric of color vision.

In the absence of good population studies that relate job performance measures to test scores in batteries of color vision tests, these problems might be essentially insolvable.

However, an understanding of the existing color vision tests may help an employer who is familiar with the job requirements to decide whether to use a clinical test or to have field tests designed to his specifications.

This report surveys the existing clinical tests of color vision and gives some general indications as to their design and use.