Developmental differences in the use of prototype and exemplar-specific information.

This study is an attempt to clarify the nature of developmental differences in the use of prototypical features or information about specific exemplars for object categorization and to identify stimulus factors that may modulate the use of these information sources. To this end, 6-year-olds, 11-year-olds, and adults were taught to sort visual patterns into one of two overlapping categories. Immediately or 24 h following category acquisition subjects were presented with a set of transfer stimuli consisting of both old and new patterns, including the theoretical prototype. Categorization responses to these test stimuli were examined against predictions derived from the prototype and nearest-old-exemplar accounts of categorization. A significant developmental change in the process of categorization was noted. For the youngest group, only the prototype model was found to fit the test data, whereas for the older groups both models independently explained significant amounts of variance in performance. This trend was not affected by the delay between training and testing, nor by a manipulation of intracategory variability. The emergence of the specific exemplar model as a viable explanation of ill-defined categorization thus appears to be related to the developmental level attained.