What can we learn about human individual face recognition from experimental studies in monkeys?

Typical human adults recognize numerous individuals from their faces accurately, rapidly and automatically, reaching a level of expertise at individual face recognition that is important for the quality of their social interactions. A non-human species of primates, the rhesus monkey, has been used for decades as a model of human face processing, in particular for understanding the neural basis of individual face recognition. However, despite responding specifically to faces behaviourally and neurally, this species, as well as other Old World and New World monkeys, is remarkably poor at individuating faces of conspecifics. Following extensive conditioning, monkeys only achieve moderate performance at individual face matching tasks where image-based cues are available. Contrary to humans, monkeys do not show a systematic inversion effect in such tasks, or an advantage for matching face pictures of familiar versus unfamiliar individuals, indicating that they do not rely on qualitatively similar individual face recognition processes as humans. These observations concur with the characteristics of the rhesus monkey cortical face processing system, which lacks two critical aspects for human expertise at individual face recognition: a distinct ventral face-selective pathway and a right hemispheric specialization. While the rhesus monkey brain is undoubtedly an informative non-human model for studying the neural basis of social behaviour and visual cognition, it does not provide an adequate model of human individual face recognition. More generally, this review urges for caution when drawing direct inferences across species without sufficient homologies in behaviour and anatomico-functional landmarks.