Spider monkeys (Ateles geoffroyi) and capuchin monkeys (Cebus apella) follow gaze around barriers: evidence for perspective taking?

Gaze following is an adaptive skill that might have been selected in social species, such as many nonhuman primates, to obtain information about food location, predators, and social interactions. The authors investigated the ability of spider monkeys (Ateles geoffroyi) and capuchin monkeys (Cebus apella) to follow the gaze of a human around barriers and the presence of "looking back" behavior. In the 1st experiment, a human looked to a target location inside the testing room, whereas in the 2nd experiment, the human looked behind an opaque barrier placed outside the testing room. The authors compared the frequency of looking at the target location with the corresponding baseline looking frequencies. Both species (a) showed evidence of spontaneous gaze following in the 1st experiment and (b) engaged in gaze following behind the barrier in the 2nd experiment. In contrast, neither species performed "looking back" responses. The authors conclude that both monkey species showed some indication of perspective-taking abilities, although the absence of "looking back" behavior suggests a potential difference from the abilities shown by the great apes.