The Composite Face Effect in Chimpanzees (Pan troglodytes) and Rhesus Monkeys (Macaca mulatta)

The accurate recognition of individuals is a cornerstone of social exchange in primates. Current approaches to the study of individual recognition, however, are focused on human performance and only occasionally reference comparative research for support. A number of studies have suggested that humans can easily recognize thousands of individual faces and that this perceptual expertise is supported by holistic processing, a phenomenon best demonstrated by the composite face effect (CFE). Recent advances have indicated that the CFE in humans is robust to changes in contrast polarity (positive or negative). Here we apply a two alternative forced choice match-to-sample paradigm across two species of nonhuman primate, chimpanzees (Pan troglodyte) and rhesus monkeys (Macaca mulatta). We find strong evidence that chimpanzees and rhesus monkeys experience interference from holistic processing in the positive contrast condition. While there is some indication that the chimpanzees experienced a CFE in the negative contrast condition, there was no evidence of a CFE in the corresponding rhesus monkey data. These results suggest that, while holistic processing is a general mechanism, rhesus monkeys are more sensitive to contrast-polarity than humans.