Abstract

Variations in color vision have long been understood as reflecting variations in the photopigment complement. Beyond those photopigment variations that account for the differences between the classical color vision phenotypes, there are several lines of evidence to suggest further variation in the spectral positioning of photopigments found in individuals of a particular color vision type. For example, there are reliable variations in the color matches made by normal humans that cannot be accounted for by individual differences in preretinal filtering or photopigment density. Additional evidence implying photopigment variation comes from microspectrophotometric measurements of human cones and psychophysical measurements of color matching and visual sensitivity in color defective subjects. What is still a matter of dispute is the magnitude of the variation and the manner in which the variation is distributed across individuals. Recent evidence from photopigment biochemistry, from a comparative survey of photopigments in various mammals, and from the study of color matching in normal human trichromats suggests that all mammalian photopigments occupy one of several discrete spectral positions, and that the λ_max values of successive positions are separated by ~6 nm; individual variation around these discrete steps is small or (perhaps) nonexistent.

© 1986 Optical Society of America