Do nonhuman primates ascribe goals to the choices of conspecifics?

Abstract

-Numerous studies have investigated the extent to which nonhuman primates understand the goals of a partner. One limitation common to many of these studies, however, has been that animals are often required to interpret actions of heterospecifics, typically human experimenters. In this study, we tested capuchin monkeys' understanding of goal-directed actions by examining whether they would choose similarly after watching a volitional versus forced choice by a conspecific. In the task, a model subject chose between two different objects in view of a focal subject, after which the focal was presented with the same choice. In the Free Choice condition, the two objects were at equal distance and within reach of the model, whereas in the Limited Choice condition, one object was placed out of the model's reach. In Study 1, using objects that differed in material, size, shape and color, monkeys showed little evidence of copying the partner in the Free Choice condition; however, they chose the different object more often in the Limited Choice relative to the Free Choice condition. To try to rule out that these results were due to a preference for some feature of the objects, in Study 2, the objects differed only in color and pattern. Although subjects did not copy the partner more in the Free Choice condition, some showed, as in Study 1, a preference for the different object in the Limited Choice condition. These results weakly support the hypothesis that monkeys perceive volitional actions in a social learning context, in that individuals adapted their behavior based on the partner's choice in the task. We discuss the implications of the 'failure' to select the same object as the conspecific in the task.