Multiple perceptual strategies used by macaque monkeys for face recognition

Abstract Successful integration of individuals in macaque societies suggests that monkeys use fast and eYcient perceptual mechanisms to discriminate between conspeciWcs. Humans and great apes use primarily holistic and conWgural, but also feature-based, processing for face recognition. The relative contribution of these processes to face recognition in monkeys is not known. We measured face recognition in three monkeys performing a visual paired comparison task. Monkey and humans faces were (1) axially rotated, (2) inverted, (3) high-pass Wltered, and (4) low-pass Wltered to isolate diVerent face processing strategies. The amount of time spent looking at the eyes, mouth, and other facial features was compared across mon-key and human faces for each type of stimulus manipula-tion. For all monkeys, face recognition, expressed as novelty preference, was intact for monkey faces that were axially rotated or spatially Wltered and was supported in general by preferential looking at the eyes, but was impaired for inverted faces in two of the three monkeys. Axially rotated, upright human faces with a full range of spatial frequencies were also recognized, however, the dis-tribution of time spent exploring each facial feature was signiWcantly diVerent compared to monkey faces. No nov-elty preference, and hence no inferred recognition, was observed for inverted or low-pass Wltered human faces. High-pass Wltered human faces were recognized, however, the looking pattern on facial features deviated from the pat-tern observed for monkey faces. Taken together these results indicate large diVerences in recognition success and in perceptual strategies used by monkeys to recognize humans versus conspeciWcs. Monkeys use both second-order conWgural and feature-based processing to recognize the faces of conspeciWcs, but they use primarily feature-based strategies to recognize human faces