Prototype Effects in Categorization by Pigeons

A frequent finding from studies of categorization with humans is that exemplars that can be said to represent the central tendency of a category are the easiest to classify correctly. Reed (1972) described one example of such a prototype effect; Reed showed students cartoon drawings of faces that belonged t o two categories. The faces for one category had, on average, smaller foreheads, more closely spaced eyes, and shorter noses than those i n the other category. Once the subjects were able to sort the faces correctly, test trials with novel patterns were given. The test patterns that were most accurately classified were those that corresponded to the averages of the faces belonging to the two categories, that is, the prototypes. In a rather different study, Posner and Keele (1968) generated four prototypical patterns from a number of dots. They then distorted these patterns to some extent by moving the dots, and the resultant figures were used for a categorization study. Once subjects were able to sort the distorted patterns into groups on the basis of their prototypes, they were required to sort a number of novel patterns, including the prototypes. The more similar a novel pattern was to a category prototype, the easier it was to classify. For the above-mentioned experiments, the prototypes were based on the mean values of the various dimensions from which the exemplars of the respective categories had been constructed. Prototype effects can also be observed when the test stimulus is based on a rather different measure of central tendency. Goldman and Homa (1977) conducted a study based on cartoon drawings of faces, in which the prototypical faces were composed of the features that most frequently appeared in the training faces. Such modal faces were classified more efficiently than any other faces, in