Facial recognition

Facial recognition, or the ability to quickly attend to and recognize faces, is common in most primates. However, this ability is particularly important for humans and non-human primates within a highly social group. Facial recognition has been suggested to be required for development of theory of mind, and even for basic learning in human infants.

First-order configuration (general features in a face-like pattern): newborn humans, macaques, and gibbons show a strong preference for face-like patterns versus non-face-like patterns.

Species-specific face preferences: human infants show no preference for human versus monkey faces at six months of age, but by nine months there is a strong preference for human faces. It seems as though this preference is due to familiarity; if macaques are deprived of faces for six months, their preference is toward the faces of whichever species they had been shown more (humans of conspecifics).4 Chimpanzee infants show no preference for their mother’s face at one month (compared to unrelated chimps), but by two months they show a strong preference. Furthermore, chimpanzees exposed to more human faces than chimpanzee faces will show a stronger preference for, and better discrimination of human faces, whereas those that experienced equal numbers of humans and other chimpanzees had no species bias.

Holistic face processing: inversion studies have demonstrated that humans and chimpanzees seem to be more impaired at matching an inverted familiar face than by non-familiar faces or other objects. This effect is strongly debated in the literature on monkeys.

Identifying individual faces: Chimpanzees are quick to match individual images from conspecifics to a different image of the same individual, requiring only two presentations to perform significantly above chance. Rhesus macaques require an additional generalization phase and several more presentations to match images from the same conspecific. Altering the spacing between features (second-order configural cues) or rearranging facial features (first- and second-order configural cues) impairs face recognition for chimpanzees, but showing only inner facial features has no effect. All three of these alterations cause a deficit in face recognition for rhesus macaques. Humans at 10-years of age struggle with changes in the spacing of features as well.

Functional processing: Face recognition tasks activate the fusiform gyrus, orbitofrontal cortex and posterior superior temporal sulcus in both humans and chimpanzees. In macaques, the superior temporal sulcus and the inferior temporal convexity is activated, but there is no activity in a region analogous to the fusiform gyrus.