Feature-based versus exemplar-based strategies in preschoolers' category learning.

Five experiments examined whether preschool children learn categories by formulating a categorization rule based on attention to one or two features, or by memorizing the category assignment for whole exemplars. Using fictitious animals as stimuli, children were taught a two-category discrimination at the basic level and were tested for their category learning using a procedure that required them to categorize from memory, rather than perform perceptual matching. Transfer stimuli manipulated the retention of features encountered in the training instances, and children were instructed to classify only the items about whose category membership they were certain. By measuring the extent of generalization, in addition to categorization accuracy, it was possible to assess whether children were applying a feature-based rule in making their categorization decisions. The studies found little evidence that children were employing rules. Analyses of the individual response patterns identified few children who categorized by attending to a single attribute such as shape, or else who used a two-feature disjunctive rule. In addition, a recognition memory test given after category gaining produced strong evidence that children had encoded the training examples as wholes, rather than focusing on individual features. Despite clear evidence that children had encoded the training examples, however, examplar information was not used successfully in categorization when subjects were trained on only a single instance per category. The implication of these results for theories of early categorization are discussed.