Effect of the decrease of the luminance noise range on color discrimination of dichromats and trichromats

Abstract

Purpose : Pseudoisochromatic stimulus is a widely used design to evaluate color vision. This stimulus is featured by the presence of spatial luminance noise to avoid any clues in the discrimination task between a target and background differing exclusively with chromaticity. The present study investigated the effect of changing the luminance noise range while maintaining a normal mean luminance and luminance level in normal trichromats and dichromat subjects.

Methods : Eighteen normal trichromats (10 males, 8 females) and six congenital dichromats (4 protans and 2 deutans, 5 males and 1 female) had their color vision evaluated using the Cambridge Color Test. The stimuli were composed by a mosaic of circles in a 5° circular patch. A subset of the circles differed from the remaining field with chromaticity forming the perception of a 4.4° Lancdolt-C with a 1° gap. We used six luminance levels in the luminance noise and four luminance noise ranges: (i) 6-20 cd/m²; (ii) 8-18 cd/m²; (iii) 10-16 cd/m²; (iv) 12-14 cd/m². A four-alternative, forced-choice method was applied and a staircase procedure was used to estimate color discrimination thresholds in 8 chromatic axes. An ellipse model was fitted to the 8 color discrimination thresholds and the area of the ellipse was utilized as an indicator of the performance on the psychophysical task. We analyzed the relative area of the ellipses in comparison to the largest ellipse found among the four stimulus conditions. A one-way ANOVA was applied to compare the results (significance level of 5%).

Results : We observed that linear function described the color discrimination ellipse area as a function of the luminance noise range. For normal trichromats and dichromats we found that the larger the luminance noise range, the larger the ellipse area (p < 0.05). The dichromats rate of ellipse area growth as a function of the luminance noise range was larger for dichromats than for trichromats (p < 0.05). For normal trichromats, the rate of ellipse area growth as a function of the luminance noise range was 0.017 ± 0.02, while for the dichromats it was 0.031 ± 0.03.

Conclusions : The changes in luminance noise range had larger influence on the color discrimination thresholds in dichromats than in normal trichromats.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.