Formation of categories based on functions in a chimpanzee (Pan troglodytes)

Abstract

Four experiments examined the ability of an adolescent female chimpanzee (Pan troglodytes) to form categories of objects based on their function (i.e., tool, container, and food). In preliminary training, the subject learned three kinds of complementary relationships among real objects. In Experiments 1, 2, and 3, a matching-to-sample task presented real objects as samples and pictures of the objects as comparisons. Experiment 1 tested whether she could match pictures of items related to the sample when there was no picture of the sample among the comparisons. The subject showed a notable tendency to choose pictures of items that were complementary to the sample in preliminary training, but she chose few pictures of items from the same functional category as the sample. In Experiment 2, there were four comparisons, none of which were pictures of the items that were complementary to the sample; only one comparison showed a picture of an item from the same functional category as the sample. The subject chose pictures of items from the same functional category as the sample at only chance level. In Experiment 3, the subject was trained to match a picture of an item from the same category as the sample but showed no improvement in her performance. In Experiment 4, the subject was trained to choose a lexigram (geometrical figure) corresponding to the functional categories. After the subject matched the lexigrams correctly on the basis of functions, she correctly matched some of the untrained items on the basis of their functions. These results suggest that responding to lexigrams rather than pictures may improve ability to form functional categories. © 1997 Japanese Psychological Association. Published by Blackwell Publishers Ltd.