Shifts in categorization and identifiability of visual stimuli by rhesus monkeys

Four monkeys, trained to match to sample, were asked to judge seven stimuli which differed in lightness, in terms of five response categories. The sample stimulus was presented on a black or white background, and all responses were made on a gray background. The mean judgment category for a stimulus was a function of the adaptation reflectance, and, in general, the ease of categorization depended upon the distance of the stimulus from the adaptation level.