Individual Recognition in Chimpanzees and Rhesus Monkeys. Journal of Comparative Psychology .
Faces are one of the most important and salient classes of stimuli involved in social communication.
They provide a variety of information about individual characteristics such as an individual's identity, sex, age, and emotion. The ability to use the information present in faces and respond to it discriminatively has undoubtedly played an important role in the evolution of social animals, particularly social mammals that that form affiliative networks and cooperative relationships. In the first experiment, face matching , subjects were required to match identical portraits of unfamiliar conspecifics. In the second experiment, individual recognition , subjects were required to match two different photographs of the same individual. These stimuli were part of the Living Links Stimulus Set R .