Performance on a Face Discrimination Task by Orangutans Reflects a Possible Interaction between Familiarity and Novelty

Faces provide humans with information on the age, sex, individual identity, and emotional state of others. Although comparatively less is known about nonhuman primates’ face processing abilities, several gregarious group living species are able to discriminate conspecific faces. Here, we tested a less gregarious species, orangutans, to determine if they exhibit similar skills. Using a matching-to-sample paradigm, orangutans matched two identical portraits of unfamiliar orangutans. Next, subjects matched two different photographs of the same individual across viewpoints. During testing, subjects successfully transferred to novel photographs of familiar, but not unfamiliar, individuals with their first exposure to these stimuli. However, performance was not maintained throughout continued exposure to these stimuli, suggesting a possible novelty effect. Interestingly, orangutans performed significantly above chance when individuating familiar males, but not females. Further examination is needed to understand social organization and other social factors which were important in the evolution of face-processing. INDEX WORDS: Individual recognition, Primates, Pongo spp PERFORMANCE ON A FACE DISCRIMINATION TASK BY ORANGUTANS REFLECTS A POSSIBLE INTERACTION BETWEEN FAMILIARITY AND NOVELTY