Squirrel monkeys' (Saimili sciureus) peculiar facial recognition in the discrimination between own and other species

Abstract

PURPOSE: Previous research shows that squirrel monkeys have two different strategies for facial recognition in the individual discrimination of their own species and those of other species: one strategy is similar to that of humans, while the other is specific to squirrel monkeys. But it is unclear whether the monkeys use the same strategies for the discrimination between faces of their own and other species. This is the question we explore in this research. METHOD: Subjects were two squirrel monkeys. The stimuli were faces of squirrel monkeys and humans, which were unfamiliar to the subjects. In the training phase, the subjects were trained to discriminate between squirrel monkey and human faces so as to achieve a performance of 80% correct. In the test phase, we introduced several types of probe stimuli. Presented were only some facial features of the training stimuli (e.g., configuration of eyes, outer facial boundary and so on), and the whole body of both species. RESULTS AND DISCUSSION: One monkey could discriminate between his own and other species. The configuration of eyes had a significant effect (binominal test [[lt]] .05) on the discriminating performance in choosing other species in distinction from his own species. Furthermore, the monkey could use outside features of monkey faces in choosing his own species. These results suggest that squirrel monkeys utilize the same cues for discrimination between species through facial recognition as well as for individual discrimination between their own species. These two alternative strategies of facial recognition may reflect the face information including both communality to comprehensive species and peculiarity to particular species.