The magnitude of simultaneous color contrast and simultaneous brightness contrast for chimpanzee and man.

Abstract

On an apparatus of special design 3 chimpanzees were trained to obtain food rewards by pushing against either one of two 3-inch square stimulus areas, each within a separate background. The backgrounds and stimulus areas could be varied independently in color, brightness, and saturation. After they had been given suitable preparatory training on discrimination of fine color differences, the chimpanzees were tested with identical gray stimuli on red and green (contrast producing) backgrounds. The choices of the animals clearly demonstrated the influence of simultaneous color contrast. The magnitude of this effect was measured by finding the quantity of added color required in the stimuli to neutralize the contrast. In a 2d expt., using brightness instead of color differences, simultaneous brightness contrast was studied in a similar manner. These contrast effects were found to be highly similar in magnitude for chimpanzees and human beings. These data lend support to the belief that simultaneous contrast is mediated at a relatively low level in the optic system.