Visual sensitivity: significant within-species variations in a nonhuman primate.

Among squirrel monkeys (Saimiri sciureus) there are significant sex-related differences in visual sensitivity. As measured behaviorally in an increment-thershold task, a sample of males was found to be substantially less sensitive to long-wavelength (640-nanometer) light than a group of females tested in the same way, although the two groups showed no significant differences in sensitivity to a middle-wavelength (540-nanometer) light. The two group also differed on a test designed to measure the effects of chromatic adaptation.