Color Vision Mechanisms in the Monkey

The monkey, Macaca mulatta, was chosen as the experimental animal for the investigation of the physiological mechanisms of color vision for two reasons: there is excellent behavioral evidence that the rhesus monkey has color vision (this is not true for some of the animals which have been used in similar investigations); furthermore, its color vision system is undoubtedly very similar to, if not identical with, that of man. There is good evidence (Walls, 1942) that color vision systems have evolved several separate times, once in the insects, again in fish, reptiles, and birds, and still again within the primate order. If this is correct, it would be little more than a coincidence ff the way in which information about the wavelength of light is encoded in the visual system of monkey and man were the same as the manner in which it is accomplished in fish or birds. In any case, if one is interested in relating the ways in which various neural elements respond to different wavelengths of light under various conditions to the manner in which these lights are perceived, one cannot go wrong in studying an animal as similar as possible to