| Twenty-four X-linked color deficient human male subjects were tested in a series of Rayleigh matching experiments. For the Rayleigh match, a red/green primary admixture is compared to a yellow standard. The purpose of the present study was to test the hypothesis that Rayleigh matches are determined by the separation between the absorption maxima of the X-chromosome linked pigments contained in the cones.;The hypothesis was addressed in three parts. In the first part, four procedures for measuring match ranges were compared. Two degree match ranges were measured using a quasi-staircase procedure, and 9 degree match ranges were measured using a quasi-staircase procedure, a constant stimuli procedure, a double staircase procedure, and a two-interval forced choice procedure. In addition, a same/different experiment was used to test definitively for dichromacy. The sequences of the subjects' X-linked opsin genes, which had been inferred using molecular genetic techniques, were used to determine the separation between the absorption maxima of the subjects' X-linked pigments. The results showed that match ranges measured using the 9 degree fields were smaller and more similar to each other than were the 2 degree match ranges. Unexpectedly, an exponential relationship was shown between the 9 degree match ranges and the separations between the X-linked pigment absorption maxima.;For the second part, a model of red/green chromatic discrimination was developed wherein the match range was determined from the separation between the cone absorption maxima. The spectral sensitivities of the cones were used to calculate sensitivities to the Rayleigh primaries, and in turn, were used to calculate predicted match ranges.;The third part of the study compared the predicted match ranges to those measured in the first part of the study. In general, the predicted and measured match ranges agreed well. Normal variation in the effective pigment optical density was shown to be a possible mechanism by which "obligatory dichromats" were able to make chromatic discriminations. The results thus forward our understanding of genotype/phenotype relationships in human color vision. |
