Trichromatic vision in the pigeon as illustrated by the special hue discrimination curve

The pigeon''s eye would appear to be only slightly less sensitive to differences in wave length than the eye of normal man, over regions in the spectrum from 700 to 460 m[mu]. The mechanism is apparently trichromatic. The evidence which supports the idea that there are separate "red," "green" and "blue" sensory processes, does not in any way support the notion that there is a separate "yellow" process. The "hue discrimination curve" is definitely of the same type as that of man, having regions of low threshold in the yellow and in the blue-green.