Visual capacities of the owl monkey ( Aotus trivirgatus)—I. Spectral sensitivity and color vision

Abstract

Several features of spectral sensitivity and color vision were investigated in the owl monkey ( Aotus trivirgatus) using forced-choice discrimination tasks. Measurements of spectral sensitivity indicate that the Aotus monkey: (1) shows a clear Purkinje shift; (2) has a dark-adapted spectral sensitivity function much like that of other mammals; (3) as measured in an increment-threshold task has a photopic spectral sensitivity function which is bimodal in form with peaks at about 460–480 and 520–540 nm. Experiments involving chromatic adaptation indicated that these monkeys have multiple spectral mechanisms operative at photopic light levels. Several color vision experiments, including discriminations of chromatic from equiluminant achromatic lights, as well as purity and wavelength discrimination, show that the Aotus monkey has trichromatic color vision. However, this color vision capacity is both weak and aberrant relative to normal primate trichromacy. It is concluded that the Aotus monkey can be formally classified as a protanomalous trichromat.