648 research outputs found
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Sex-related differences in chromatic sensitivity
Generally women are believed to be more discriminating than men in the use of colour names and this is often taken to imply superior colour vision. However, if both X-chromosome linked colour deficient males (~8%) and females (<1%) as well as heterozygote female carriers (~15%) are excluded from comparisons, then differences between men and women in red-green colour discrimination have been reported as not being significant (e.g., Pickford, 1944; Hood et al., 2006). We re-examined this question by assessing the performance of 150 males and 150 females on the Colour Assessment and Diagnosis (CAD) test (Rodriguez-Carmona, 2005). This is a sensitive test that yields small colour detection thresholds. The test employs direction-specific, moving, chromatic stimuli embedded in a background of random, dynamic, luminance contrast noise. A four-alternative, forced-choice procedure is employed to measure the subject’s thresholds for detection of colour signals in 16 directions in colour space, while ensuring that the subject cannot make use of any residual luminance contrast signals. In addition, we measured the Rayleigh anomaloscope matches in a subgroup of 111 males and 114 females. All the age-matched males (30.8 ± 9.7) and females (26.7 ± 8.8) had normal colour vision as diagnosed by a battery of conventional colour vision tests. Females with known colour deficient relatives were excluded from the study. Comparisons between the male and female groups revealed no significant differences in anomaloscope midpoints (p=0.709), but a significant difference in matching ranges (p=0.040); females on average tended to have a larger mean range (4.11) than males (3.75). Females also had significantly higher CAD thresholds than males along the red-green (p=0.0004), but not along the yellow-blue discrimination axis. The differences between males and females in red-green discrimination may be related to the heterozygosity in X-linked cone photopigment expression common among females
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Loss of color and flicker sensitivity in subjects at risk of developing diabetes
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Colour vision requirements in visually demanding occupations
Normal trichromatic colour vision (CV) 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
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Colour assessment outcomes – a new approach to grading the severity of color vision loss
INTRODUCTION: Recent studies have shown that a significant percentage of subjects with anomalous, congenital trichromacy can perform the suprathreshold, colour-related tasks encountered in many occupations with the same accuracy as normal trichromats. In the absence of detailed, occupation-specific studies, an alternative approach is to make use of new findings and the statistical outcomes of past practices that have been considered safe to produce graded, justifiable categories of colour vision that can be enforced.
METHODS: We analyzed traditional color assessment outcomes and measured severity of colour vision loss using the CAD test in 1363 subjects (336 normals, 705 deutan, 319 protan and 3 tritan). The severity of colour vision 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.
RESULTS: The correlation between the number of Ishihara (IH) test plates subjects fail and the severity of RG colour vision loss was very poor. The 38 plates IH test has high sensitivity when no errors are allowed (i.e., only 0.71% deutans and 0.63% protans pass). Protocols based on zero errors are uncommon since 18.15% of normal trichromats fail. The most common protocols employ either the 24 or the 14 plates editions with two or less errors. These protocols pass almost all normal trichromats, but the deutans and some protans that also pass (when two or less errors are allowed) can be severely deficient. This is simply because the most challenging plates have not been included in the 24 and 14 plates editions. As a result, normals no longer fail, but the deutans and protans that pass have more severe loss of colour vision since they fail less challenging plates. The severity of colour vision 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.
DISCUSSION: Historical 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 Colour Vision category which can range from ‘supernormal’ (CV0), for the most stringent, colour-demanding tasks, to ‘severe colour deficiency’, when red / green colour vision is either absent or extremely weak (CV5)
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Occupational colour vision needs with emphasis on aviation
The novel experiments and tests developed for this study yield new data that describe how combinations of luminance contrast and Red / Green (RG) and Yellow / Blue (YB) colour signals affect task completion times (TCT) and the overall accuracy the operator can achieve. With appropriate design and choice of colours, it is possible for deutan applicants with thresholds < 4 standard normal CAD units to perform as well as normal trichromats when suprathreshold colours with RG and YB components are employed in visual displays. As many as 22% of deuteranomalous subjects can be included in this category. In spite of their congenital colour deficiency, such applicants can operate safely in the Air Traffic Control (ATC) environment as well as in many other occupations that involve the use of large-field, visual displays
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Processing of color signals in female carriers of color vision deficiency
The aim of this study was to assess the chromatic sensitivity of carriers of color deficiency, specifically in relation to dependence on retinal illuminance, and to reference these findings to the corresponding red-green (RG) thresholds measured in normal trichromatic males. Thirty-six carriers of congenital RG color deficiency and 26 normal trichromatic males participated in the study. The retinal illuminance was estimated by measuring the pupil diameter and the optical density of the lens and the macular pigment. Each subject's color vision was examined using the Color Assessment and Diagnosis (CAD) test, the Ishihara and American Optical pseudoisochromatic plates, and the Nagel anomaloscope. Carriers of deuteranopia (D) and deuteranomaly (DA) had higher RG thresholds than male trichromats (p < 0.05). When referenced to male trichromats, carriers of protanomaly (PA) needed 28% less color signal strength; carriers of D required ∼60% higher thresholds at mesopic light levels. Variation in the L:M ratio and hence the absolute M-cone density may be the principal factor underlying the poorer chromatic sensitivity of D carriers in the low photopic range. The increased sensitivity of PA carriers at lower light levels is consistent with the pooling of signals from the hybrid M' and the M cones and the subsequent stronger inhibition of the rods. The findings suggest that signals from hybrid photopigments may pool preferentially with the spectrally closest "normal" pigments
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Assessing the Severity of Color Vision Loss with Implications for Aviation and other Occupational Environments
Introduction: The Ishihara Test (IT) is arguably the most sensitive and commonly used color vision test within aviation and other occupational environments, but when no errors are allowed; 20% of normal trichromats fail the test. The number of allowed errors varies in different occupations and sometimes within the same environment (such as aviation) in order to reflect the difficulties of the color-related tasks. The implicit assumption is that the plates can be ranked in order of difficulty. The principal aim of this study was to investigate whether appropriate "weights" can be attached to each IT plate to reflect the likelihood of producing a correct response. A second aim was to justify the use of color thresholds for quantifying the loss of red-green (RG) and yellow-blue (YB) chromatic sensitivity.
Methods: We investigated 742 subjects (236 normals, 340 deutans, and 166 protans) using the first 25 plates of the 38-plate IT and measured RG chromatic sensitivity using the Color Assessment and Diagnosis (CAD) test. The IT error scores provided platespecifi c "weights" which were used to calculate a Severity Index (SI) of color vision loss for each subject.
Results: Error scores, SI values, and CAD thresholds were measured and compared in each of the three subject groups.
Conclusions: Color thresholds can provide a good measure of the severity of both RG and YB color vision loss. Neither the number of IT plates failed nor the SI value computed in this way can be used to determine reliably the severity of color vision loss
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A study of unusual Rayleigh matches in deutan deficiency
Rayleigh match data were modeled with the aim of explaining the locations of match midpoints and matching ranges, both in normal trichromats and in subjects with congenital color deficiency. Model parameters included the wavelength of peak sensitivity of cone photopigments, the effective photopigment optical density, and the noise amplitude in the red-green color channel. In order to avoid the suprathreshold, perceptual effects of extreme L:M cone ratios on color vision, selective post-receptoral amplification of cone signals is needed. The associated noise is also amplified and this causes corresponding changes in red-green threshold sensitivity. We propose that the noise amplitude and hence the size of the matching range in normal trichromats relates to the known inter-subject variation in the relative numbers of L and M cones. If this hypothesis can be shown to account for the extremes of the red-green matching range measured in normal trichromats, it is of interest to establish the extent to which it also predicts the unexpected, small matching ranges that are observed in some subjects with red-green color deficiency. A subset of subjects with deutan deficiency that exhibited less common Nagel matches were selected for genetic analysis of their cone pigment genes in order to confirm the type of deficiency, and to predict the corresponding peak wavelength separation (δλmax) of their two, long-wavelength cone pigments. The Rayleigh match model predicted accurately the midpoint and the range for the spectral differences specified by the genes. The prediction also required plausible selection of effective optical density of the cone pigments and noise. The noise needed varied, but the estimates were confined to lie within the limits established from the matching ranges measured in normal trichromats. The model predicts correctly the small matching ranges measured in some deuteranomalous subjects, principally accounted for by a low estimate of noise level in the red-green channel. The model also predicts the “normal” matches made by some subjects that rely on two hybrid genes and therefore exhibit red-green thresholds outside the normal range, typical of mild deuteranomaly
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