A behavioral face preference deficit in a monkey with an incomplete face patch system.

Primates are experts in face perception and naturally show a preference for faces under free-viewing conditions. The primate ventral stream is characterized by a network of face patches that selectively responds to faces, but it remains uncertain how important such parcellation is for face perception. Here we investigated free-viewing behavior in a female monkey who naturally lacks fMRI-defined posterior and middle lateral face patches. We presented a series of content-rich images of scenes that included faces or other objects to that monkey during a free-viewing task and tested a group of 10 control monkeys on the same task for comparison. We found that, compared to controls, the monkey with missing face patches showed a marked reduction of face viewing preference that was most pronounced for the first few fixations. In addition, her gaze fixation patterns were substantially distinct from those of controls, especially for pictures with a face. These data demonstrate an association between the clustering of neurons in face selective patches and a behavioral bias for faces in natural images.