Recognition and categorization of biologically significant objects by rhesus monkeys (Macaca mulatta): the domain of food

To survive, organisms must be able to identify edible objects. However, we know relatively little about how humans and other species distinguish food items from non-food items. We tested the abilities of semi-free-ranging rhe sus monkeys (Macaca mulatta) to learn rapidly that a novel object was edibl e, and to generalize their learning to other objects, in a spontaneous choi ce task. Adult monkeys watched as a human experimenter first pretended to e at one of two novel objects and then placed replicas of the objects at wide ly separated locations. Monkeys selectively approached the object that the experimenter had previously eaten, exhibiting a rapidly induced preference for the apparently edible object. In further experiments in which the same objects were used as tools or were manipulated at the face but not eaten, w e fail to observe an approach bias, providing evidence that the monkeys' pa ttern of approach in the earlier experiments was specific to objects that w ere eaten. Subsequent experiments tested how monkeys generalized their pref erence for an edible object by first allowing them to watch a human experim enter eat one of two objects and then presenting them with new objects comp osed of the same substance but differing from the original, edible object i n shape or color. Monkeys ignored changes in the shape of the object and ge neralized from one edible object to another on the basis of color in conjun ction with other substance properties. Finally, we extended this work to in fant rhesus monkeys and found that, like adults, they too used color to gen eralize to novel food objects. In contrast to adults, however, infants exte nded this pattern of generalization to objects that were acted on in other ways. These results suggest that infant monkeys form broader object categor ies than adults, and that food categories become sharpened as a function of maturational or experiential factors. (C) 2001 Elsevier Science B.V. All r ights reserved.