The spectral information processing of the primate visual system will be measured by two techniques: hue discrimination and increment-threshold spectral sensitivity on rhesus monkeys and normal and anomalous trichromatic human subjects. Different conditions of adaptation and of recovery from induced dichromacy have been selected to reveal: 1. The differences between red- and green-sensitive cone response functions, 2. The relationship between cone response and the mechanism of color discrimination, 3. The similarities and any differences between induced and congenital dichromacy (color blindness). A mathematical model of the underlying processes of hue discrimination, and indeed of color vision in general, will be sought from these studies.