"The study not only reveals that capuchin monkeys are able to individually recognize familiar faces, but it also convincingly demonstrates they understand the two-dimensional representational nature of photographs," says lead researcher Jennifer Pokorny. "The fact these monkeys correctly determined which faces belonged to in-group versus out-group members, corresponding to their personal experiences, validates the conclusion that capuchin monkeys view images of faces as humans do -- as individuals they do or do not know.
For the study, the capuchins viewed photographs of four different faces. One of the four pictures was of a capuchin from their own group, which they needed to tell apart from three strangers. They also needed to do the reverse, differentiating one stranger from three familiar individuals.
“This required monkeys to look at similar-looking faces and use their personal knowledge of group mates to solve the task,” says Pokorny. "They readily performed the task and continued to do well when shown new pictures in color and in gray-scale, as well as when presented with individuals they had never before seen in pictures, though with whom they were personally familiar."
Researchers often use two-dimensional images in experiments, yet there is little conclusive evidence to suggest nonhuman primates, particularly monkeys, truly understand the image represents individuals or items in real life.
Pokorny trained under Emory primatologist Frans de Waal, who says the study is the first to show face recognition in monkeys is fundamentally similar to that in humans, indicating that face recognition is an evolutionarily ancient ability. De Waal is director of the Yerkes Living Links Center.