Saito, A., Mikami, A. Kawamura, S., Ueno, Y., Hiramatsu, C., Widayati, K. A., Suryobroto, B., Teramoto, M., Mori, Y., Nagano, K., Fujita K., Kuroshima, H. and Hasegawa, T. (2005). Advantage of dichromats over trichromats in discrimination of color-camouflaged stimuli in non-human primates. American Journal of Primatology, 67 (4): 425 - 436.

We compared the performance of dichromats and trichromats in a discrimination task of color-camouflaged stimuli. We examined tri- and dichromatic individuals of a New World monkey, brown capuchin monkeys (Cebus apella), and an Old World monkey, long-tailed macaques (Macaca fascicularis). We also examined one protanomalous chimpanzee (Pan troglodytes). The subject's task was to discriminate a circular pattern from other patterns in which textural elements differed in orientation and in thickness from the background. After being trained in stimuli of a single color, the subjects were presented with color-camouflaged stimuli with a green/red mosaic overlaid onto the pattern. The dichromatic monkeys and the protanomalous chimpanzee selected the correct stimulus under camouflaged conditions significantly above chance levels, while the trichromats did not. These findings demonstrate that dichromatic non-human primates possess a superior visual ability to discriminate color-camouflaged stimuli, and that such an ability might confer selective advantages with respect to the detection of cryptic foods and/or predators.