Psychophysical studies of monkey vision. II. Squirrel monkey wavelength and saturation discrimination.

Abstract Squirrel monkeys (Saimiri sciureus) were tested in four-choice discrimination experiments to determine their wavelength and saturation discrimination ability. Their wavelength discrimination curve had only a single minimum, in the region of 480 nm, and the discrimination performance was far poorer than that of macaque monkeys tested under identical conditions. The saturation discrimination tests indicated that the whole spectrum is more desaturated for squirrel monkeys than for macaques, and that the least saturated region is about 500 nm rather than 570 nm. There is, however, no neutral point. These results, plus their depressed photopic sensitivity to long wavelengths, support the classification of squirrel monkeys as severely protanomalous trichromats.