Categorical perception of faces by human and monkey observers

When perceiving a face, we can easily decide whether it belongs to a human or non-human primate. The categorical decision of whether a face belongs to your own or a related species is of great importance for social interaction and mating. Face stimuli of humans, monkeys, and monkey - human hybrids (morphs) were used to shed light on categorization of faces into different species by humans and non-human primate subjects. Behavioral studies in both species were conducted with the goal of delineating the category boundary across the human - monkey continuum. In monkeys single unit recordings of face responsive neurons in inferior temporal cortex are currently conducted, with the goal of delineating the category boundary based on the response of these neurons to face stimuli. Preliminary findings suggest that both humans and non-human primates tend to draw the species boundary away from the centre of the continuum and that the boundary is shifted towards the category to which the observer belongs. The findings suggest differential neural mechanisms for categorization of human and monkey faces