CATEGORIZATION OF 3-DIMENSIONAL STIMULI BY HUMANS AND BABOONS - SEARCH FOR PROTOTYPE EFFECTS

A symbolic matching-to-sample procedure was adopted to investigate whe ther humans (n = 2) and baboons (n = 2) discriminate more accurately t he prototypes of polymorphous categories than less typical exemplars. Subjects were initially trained to discriminate between two categories of stimuli defined by the possession of any two out of three possible binary features. In transfer, prototypes, which contained all the thr ee feature values of their categories, and novel two-out-of-three feat ure exemplars were presented for discrimination. Humans solved the tas k in a propositional way, and showed no evidence for a better performa nce with the prototypes than with other exemplars. By contrast, monkey s classified the prototypes more accurately than the other exemplars. The analysis of training performance showed however, that their discri minations did not involve prototypical representations of the categori es, but rather depended upon feature-and exemplar-response association s. It is argued that monkeys' better performance with the prototypes r ested on peak shift and/or novelty effects. (C) 1997 Elsevier Science B.V.