Rhesus monkeys fail to use gaze direction as an experimenter-given cue in an object-choice task

Experiments were run to assess whether adult female rhesus monkeys would spontaneously learn to choose the correct (i.e. baited) of two objects on the basis of explicit behavioural cues given by the experimenter. In the first part of the study the experimenter either stood up straight with his arms by his side and fixated centrally between the two objects while the subject responded, or he engaged in various combinations of looking and pointing at the correct object. None of the three subjects learned to use gaze alone as a discriminative cue, but two performed better with gestural cues. During subsequent sessions the experimenter's head and eyes were positioned much closer to the objects than in the first experiment, but this did not significantly improve performance. These results confirm and extend a 'negative' finding obtained with capuchin monkeys, namely that during object-choice tasks monkeys do not readily use visual co-orientation or engage in perspective-taking to enhance their success.