A study of unusual Rayleigh matches in deutan deficiency

Abstract

This is the unspecified version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractRayleigh 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~dl max ! 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.

Assessing the Severity of Color Vision Loss with Implications for Aviation and Other Occupational Environments

“…Such inconsistent findings make it difficult to quantify the subject's severity of color vision loss (21). The midpoint and the size of the matching range in anomaloscope matches, for example, are often used to screen for levels of deficiency, even when these parameters do not correlate well with the subject's loss of chromatic sensitivity (4,23). Previous studies also failed to show significant correlation between the number of errors subjects make on IT plates and the parameters of Nagel anomaloscope matches for both color vision deficient (6) and also for normal trichromats (15).…”

Differences in Chromatic Sensitivity Estimated Using Static and Dynamic Colour Stimuli

“…* Statistical analysis showed significant differences in chromatic thresholds between both age groups in deutan and tritan colour directions with static stimuli, and in all studied colour directions with dynamic test stimuli. ( Barbur et al, 2008). Linear regression functions between chromatic thresholds measured with computerised stimuli and the anomaloscope matching range indicated that slope did not significantly differ from 0, thereby confirming lack of correlation between anomaloscope matching range and chromatic thresholds measured along protan and deitan confusion lines (Table 5).…”

In Defense of Incompatibility, Objectivism, and Veridicality About Color

“…People's ability to distinguish wavelengths does degrade to about 6 nm at the ends of the spectrum where violet and red are located (Wright & Pitt, 1934), but recall that an nm is only one billionth of a meter. Of course, people with color deficient vision vary more in color perception tasks than those with normal color vision (Barbur, 2008), but only a small minority of the population (about 4%) have color deficiencies. Thus, while matching tasks do suggest disagreement, the disagreement is not nearly as much as naming tasks suggest and certainly not sufficient to support P-Disagreement.…”