Anomalous Trichromats Research Articles

Analysis of Rayleigh match data with psychometric functions.

Color matches have been used for a variety of purposes, yet the psychometric properties of color-matching data have not been thoroughly investigated. A method is given for generating psychometric functions for the two ends of the color-matching range by use of a perceptual dimension for stimulus magnitude based on ratios of cone quantal catches. The analysis was applied to Rayleigh match data gathered from 250 naïve observers with an automated protocol. Slopes of the psychometric functions were significantly shallower for anomalous trichromats than for normal trichromats, consistent with the assumption that stimulus magnitude is based on ratios of cone quantal catches. These results indicate that the tester's criterion for response consistency can strongly affect Rayleigh match widths. The analysis may also be useful for other perceptual tasks, such as contrast matching and spatial alignment.

A study of women heterozygous for colour deficiencies

We have examined the colour vision of 43 female subjects in the age range 30–59 yr of whom 31 were obligate carriers of various forms of colour deficiency and the rest were women who had no known colour-deficient relatives. In the case of all the carriers we established the phenotypes of their colour-deficient sons. As a group, carriers made significantly more errors on the Ishihara plates and showed enlarged matching ranges on the Nagel anomaloscope, but we could not replicate earlier reports of increased error scores on the Farnsworth-Munsell 100-Hue test or of systematic shifts in Rayleigh match mid-points. We did find that the colour matches of carriers of deuteranomaly were significantly displaced from those of normals in a ratio-matching task in which a mixture of 546 and 600 nm was matched with a mixture of 570 and 690 nm. Owing to X-chromosome inactivation, women who are heterozygous for anomalous trichromacy ought to have at least four types of cone in their retinae and we ask whether this affords them an extra dimension of colour vision, by analogy to New World monkeys where heterozygous females gain trichromacy in a basically dichromatic species. Many carriers of anomalous trichromacy exhibited no evidence for tetrachromacy, in that they accepted large-field Rayleigh matches following a rod bleach and they were unable to set unique matches in our ratio-matching task. However, eight carriers of anomalous trichromacy—and no other subject—refused large-field Rayleigh matches; and we found one carrier of deuteranomaly who was apparently able to make unique matches in the ratio-matching task.

Absorption spectra of the hybrid pigments responsible for anomalous color vision.

Unequal homologous recombination events between green and red cone pigment genes produce the red-green or green-red hybrid pigment genes found in many individuals with variant color vision. Photobleaching difference absorption spectroscopy of hybrid pigments produced in cultured cells shows that the spectral sensitivity of each hybrid pigment is intermediate between the parental green and red pigment sensitivities. Amino acids encoded by exons 2, 3, 4, and 5 produce spectral shifts at the wavelength of maximal absorbance of 0 to 4, 0 to 4, 3 to 4, and 15 to 21 nanometers, respectively, the exact value depending on the identities of amino acids elsewhere in the hybrid.

Full-spectrum cone sensitivity functions for X-chromosome-linked anomalous trichromats.

We derived the cone fundamentals for X-chromosome-linked anomalous trichromats for the wavelength range of 400-700 nm. Pigment templates were constructed from the cone fundamentals of normal trichromats after correction for ocular media absorption. The resultant retinal-level sensitivities had small irregularities in the short-wavelength region that were smoothed. The pigment templates, expressed as quantal sensitivities, were then shifted on a frequency abscissa to solve for the lambda max of the pigments of anomalous trichromats needed to predict average anomaloscope matching data. We found that the protanomalous M- and L'-cone pigments are separated by 10 nm and the deuteranomalous M'- and L-cone pigments are separated by 6 nm (rounded to the nearest nanometer), where M and L indicate middle- and long-wavelength sensitive, respectively. The triads of peak wavelengths for the corneal energy-based sensitivities were as follows: normal: 440, 543, and 566 nm; protanomalous: 440, 543, and 553 nm; and deuteranomalous: 440, 560, and 566 nm.

The C‐100:a new dichotomiser of colour vision defectives

This paper evaluates a new instrument (G100) which employs flicker photometry or silent substitution to determine the type of colour vision defect (protan or deutan). Specifically, this study addresses the unit’s capacity to: 1. detect colour vision defects; 2. differentiate protans from deutans; and 3. produce reliable measurements under different viewing conditions. We find that an average of five readings enables protans to be clearly separated from deutans in all cases (p < O.OOOl), but that the distinction between these groups and normals is less clear. Dichromats are not distinguished from anomalous trichromats, so the instrument cannot be used as an index of severity. The results are shown to be robust to most of the test conditions likely to be encountered during normal clinical use. A clinical protocol is suggested that utilises the ClOO for classification of colour defective observers. It is concluded that normal, and some anomalous, trichromat settings are performed using flicker photometry, whereas dichromatic observers appear to utilise silent substitution. Accepted for publication: 30 June 1992

The use of colour difference vectors in diagnosing congenital colour vision deficiencies with the Farnsworth—Munsell 100-hue test

Colour difference vector analysis provides useful and meaningful information in scoring the Farnsworth-Munsell (FM) 100-hue test. However, the FM 100-hue test is limited in its ability to diagnose type and severity of congenital colour vision defect. Type classification for all subjects is incorrect in 21% of cases, and for deuteranomals the misclassification rate is 38%. Visual inspection of the plots yields a similar misclassification rate and classification of plots with few errors (under 180) is generally less reliable. The FM 100-hue test has a limited ability to separate dichromats from anomalous trichromats. A test protocol based on joint D15 and FM 100-hue tests should pass 36% of anomalous trichromats and 26% of all colour defectives yet fail all dichromatic observers. We conclude that administering the FM 100-hue test is of less value than a combination of D15 panels (Standard D15 and L'Anthony's desaturated D15) in the clinical diagnosis of congenital colour defective observers. Our results for the FM 100-hue panel are similar to those reported previously by other investigators.

The use of colour difference vectors in diagnosing congenital colour vision deficiencies with the Farnsworth-Munsell 100-hue test

Colour difference vector analysis provides useful and meaningful information in scoring the Farnsworth-Munsell (FM) 100-hue test. However, the FM 100-hue test is limited in its ability to diagnose type and severity of congenital colour vision defect. Type classification for all subjects is incorrect in 21% of cases, and for deuteranomals the misclassification rate is 38%. Visual inspection of the plots yields a similar misclassification rate and classification of plots with few errors (under 180) is generally less reliable. The FM 100-hue test has a limited ability to separate dichromats from anomalous trichromats. A test protocol based on joint D15 and FM 100-hue tests should pass 36% of anomalous trichromats and 26% of all colour defectives yet fail all dichromatic observers. We conclude that administering the FM 100-hue test is of less value than a combination of D15 panels (Standard D15 and L’Anthony’s desaturated D15) in the clinical diagnosis of congenital colour defective observers. Our results for the FM 100-hue panel are similar to those reported previously by other investigators.

Use of the Farnsworth-Munsell 100-Hue test in the examination of congenital colour vision defects.

Results for the Farnsworth-Munsell 100-Hue test are reported for 238 male subjects with congenital colour vision defects (47 protanopes, 17 protanomalous trichromats, 57 deuteranopes and 117 deuteranomalous trichromats). The results are analysed in terms of the error score and the presence of an axis of confusion. A wide range of results is obtained in each diagnostic group and the error score cannot be used to distinguish between dichromats and anomalous trichromats. Approximately 50% of subjects with anomalous trichromatism obtain error scores less than 100 without an axis of confusion. These subjects could be mistakenly identified as having normal colour vision if pseudoisochromatic and colour matching tests are not employed. The prime use of the F-M 100 Hue test is in vocational guidance.

Molecular patterns of X chromosome-linked color vision genes among 134 men of European ancestry.

We used Southern blot hybridization to study X chromosome-linked color vision genes encoding the apoproteins of red and green visual pigments in 134 unselected Caucasian men. One hundred and thirteen individuals (84.3%) had a normal arrangement of their color vision pigment genes. All had one red pigment gene; the number of green pigment genes ranged from one to five with a mode of two. The frequency of molecular genotypes indicative of normal color vision (84.3%) was significantly lower than had been observed in previous studies of color vision phenotypes. Color vision defects can be due to deletions of red or green pigment genes or due to formation of hybrid genes comprising portions of both red and green pigment genes [Nathans, J., Piantanida, T.P., Eddy, R.L., Shows, T.B., Jr., & Hogness, D.S. (1986) Science 232, 203-210]. Characteristic anomalous patterns were seen in 15 (11.2%) individuals: 7 (5.2%) had patterns characteristic of deuteranomaly (mild defect in green color perception), 2 (1.5%) had patterns characteristic of deuteranopia (severe defect in green color perception), and 6 (4.5%) had protan patterns (the red perception defects protanomaly and protanopia cannot be differentiated by current molecular methods). Previously undescribed hybrid gene patterns consisting of both green and red pigment gene fragments in addition to normal red and green genes were observed in another 6 individuals (4.5%). Only 2 of these patterns were considered as deuteranomalous. Thus, DNA testing detected anomalous color vision pigment genes at a higher frequency than expected from phenotypic color vision tests. Some color vision gene arrays associated with hybrid genes are likely to mediate normal color vision.

Performance of the standard pseudoisochromatic plate test.

The Standard pseudoisochromatic Plate (SPP) test was administered to 346 normals, 55 anomalous trichromats, and 46 dichromats. Its ability to detect and classify congenital color defectives was assessed. The performance of each plate was assessed separately and compared with its colorimetric properties. The test as a whole achieves a high level of accuracy in separating normals from color vision defectives [Youden's Index (YI) = 92.4%] and a high reliability (71.3%) in classification of the congenital color vision defectives. The performance of individual plates in separating color normals and color vision defectives of individual plates varies (YI ranges from 69.8 to 86.1%). A set of three plates can be chosen, which achieves a performance similar to that of the whole test. The test is found to be a reliable clinical screening method for congenital red-green color vision defectives.

Validation of a solid-state anomaloscope used to assess red-green color vision defects

Solid-state anomaloscopes whose stimuli are derived from light-emitting diodes (LEDs) are simpler and less expensive than conventional anomaloscopes. We have assessed the test-retest reliability and the validity of one solid-state anomaloscope and have obtained normative data for it. Reliability and validity were assessed by classifying 36 color-defective observers into one of five categories defined by degree of defect. When all color defectives were considered, both the validity and reliability of the solid-state anomaloscope were found to be high. The primary stimuli of the solid-state anomaloscope are less well separated in chromaticity space than are those of conventional anomaloscopes, but there is no evidence that this results in the incorrect classification of anomalous trichromats as dichromats. The solid-state anomaloscope appears to be an acceptable alternative to standard anomaloscopes for both research and screening applications.

Color atlas theory

A domain of color science based on color atlases has to be sharply distinguished from conventional colorimetry. If essentially colorimetric results are desired, a color atlas is at a severe disadvantage. Even a technically flawless atlas will yield results that depend on ideosyncrasies of the observer (e.g., if the observer is an anomalous trichromat, this shows up in the results) even if the light source is within strict tolerances. If the source is not well specified, the results will degrade even further. However, the use of a color atlas also has some very important advantages. These are, apart from the obvious practical assets such as cost savings, speed, and intuitive trustworthiness, as follows: first, if a sample looks like a fiducial sample (or a small environment of fiducial samples) for several illuminants, then its bidirectional reflection function (BDRF) must be similar to that of the fiducial samples; and second, the equality of materials can be established by any observer (anomalous or not) if the illuminant is varied. Thus the use of an atlas leads to a physical classification (i.e., one based on the BDRF’s) rather than a merely colorimetric classification. In order to serve well, the atlas must be composed of physically well-specified fiducial samples, and different atlases may be needed for different tasks. In this paper the rational construction of such atlases to optimize various desirable properties is discussed.

Analysis of the Mark II edition of The City University Colour Vision Test.

The City University (TCU) test was administered to 50 dichromats and 56 anomalous trichromats. Certain poorly performing plates are identified from the accuracy of diagnosis compared with the Nagel anomaloscope and the number of dichromats passing the plates. Some plates are indicated as providing a more reliable diagnosis, particularly when used in combination. The performance of the plates is compared with their colorimetric properties. The desaturated plates, which were not part of the Mark I test, are shown not to provide the intended extent diagnosis.

The Boström-Kugelberg pseudo-isochromatic plates. How efficient is the third edition?

The third edition of the Boström-Kugelberg pseudo-isochromatic plates was printed to the best possible visual match with the second edition. Slight colour differences between the 2 editions initiated this study where 72 colour defectives and 57 normal trichromats were tested with the plates and classified with the aid of Nagel's anomaloscope. Of the defectives, the plate test disclosed all but two anomalous trichromats. One normal subject was falsely classified as defective. The plates had to be shown twice according to the instructions since otherwise 13 of the 53 normals were misclassified. Three plates were shown to have low sensitivity; one is best used as a demonstration plate, and the other two can be deleted without lost efficiency. Forty-eight of the colour defectives were also studied with Farnsworth's lantern. The correlation between the numbers of plate and signal errors was weak. All subjects who failed the lantern test made several plate errors, but 15 subjects who passed the lantern test, made two or more errors on the plate test. The outcome of the plate test does not give evidence of the subject's lantern test performance.

Surrogate color vision by luster discrimination.

A selective filter, such as the X-chrom lens, which is placed before one eye, serves to create a luminance difference between the two eyes. The amount of the luminance difference is dependent upon the wavelength distribution of the stimulus and could therefore serve as a clue to assist color discrimination. The ability to detect and discriminate levels of luster is investigated. One of three subjects shows a crude ability to discriminate levels of luster. The performance level is such that a filter may aid dichromacy but not anomalous trichromacy.

Visual thresholds in the deutan type of red-green deficient colour vision.

Defective temporal integration for a foveally fixated 100' of arc red (660 nm) Btest flash presented on a 30 cd/m2 yellow ( Schott , OG 530) background was measured in subjects with deuteranopia , as well as in subjects with anomalous trichromacy of the deutan type. The mean integration time was 77 +/- 17 ms in 12 normal subjects but only 35 +/- 6, 46 +/- 11 Band 41 +/- 15 ms in respectively 6 subjects with deuteranopia , 7 with extreme deuteranomaly Band 9 with deuteranomaly . An increase in the test duration from 10 to 200 ms increased the mean relative sensitivity by 0.85 +/- 13 log units in the normal subjects compared with 0.45 +/- 0.05, 0.57 +/- 12 and 0.56 +/- 19 in subjects with deuteranopia , extreme deuteranomaly and deuteranomaly .

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.

Definition, measurement, and use of the spectral coefficient of retroreflection

AbstractTwo organizations, the International Commission on Illumination (CIE) and the American Society for Testing and Materials (ASTM), have recently agreed on the definition of the coefficient of retroreflection. This coefficient is determined using CIE Standard Illuminant A and a receptor responsivity matching that of the CIE 1931 Standard Observer. Although this coefficient is practical for day‐to‐day measurements, a more general quantity is needed to study new materials, differing vehicle illumination, and the effects of human responses ranging from scotopic to photopic, as well as anomalous color vision. A CIE technical report, soon to be published, suggests that a new quantity, the spectral coefficient of retroreflection, be used to aid in studying these properties. The measurement of the spectral coefficient of retroreflection over the visible spectrum is performed by spectroradiometric techniques. This property of the retroreflector is independent of the spectral power distribution of the illuminant and the responsivity of the receptor. The retroreflector may now be studied mathematically, applying other illuminants and human visual responses. A useful byproduct of the determination of the spectral coefficient of the retroreflection is the ease with which the nighttime color can be determined. The article concludes with various examples.

Suggestions for the design of a modern anomaloscope

Three variants of a new anomaloscope principle are described. This principle is distinguished by the fact that for generation of the mixed color and the reference color three interference filters with narrow band widths are used instead of an expensive dispersion prism. In the first variant the brightness of the mixed color field and the reference field is determined by three detectors (silicon diodes) and kept constant taking the relative spectral response into consideration. The degree of anomalous color vision present is indicated digitally by a microprocessor whose interface also permits data processing equipment to be connected. The second variant uses only one detector which sequentially pulses the three light sources and distributes the results to different signal channels for further processing. In the third variant, measurement is performed in the same way as in the second variant but with only one light source. Fiber optic bundles illuminate of the mixed color and reference fields and also permit adaptation of the eye to neutral. In this case additional optical attenuators are required to keep the luminance of the fields constant. An advantage shared by all three variants is that they have virtually no moving parts, employing monochromatic filters and cemented prism blocks with high-quality electronics. This has made it possible to produce a compact, rugged and efficient new-generation anomaloscope, which renders the considerable calibration and maintenance work previously necessary superfluous.

Color sensation of normal and anomalous trichromats measured by magnitude estimation

Colors perceived by normal, protanomalous, and deuteranomalous trichromats were scaled by magnitude estimation. As a result, opponent-colors functions were obtained which show the hue sensations produced by spectral lights. For color-normal observers, the loci of maximal hue sensations were different in some aspects from those expected from current opponent-colors theories.