THE ROLE OF EXEMPLAR DISTRIBUTION IN INFANTS DIFFERENTIATION OF CATEGORIES

Three experiments investigated how the frequency of exposure to partic ular exemplars influenced 10-month-old infants' differentiation of lan d and sea animals in an object-examining task. In Experiments 1 and 2, one category exemplar was presented more frequently than the others d uring familiarization (i.e., that exemplar was presented on 6 of 12 fa miliarization trials, and 3 other exemplars were each presented on 2 f amiliarization trials). For half of the infants, the frequent exemplar was similar to other category exemplars (e.g., a zebra if the familia rization category was land animals), and for half the frequent exempla r was not similar to many other category exemplars (e.g., a rabbit). I nfants who frequently experienced the similar exemplar formed an exclu sive category, and differentiated land and sea animals. Infants who fr equently experienced a dissimilar exemplar, in contrast, formed an inc lusive category, and failed to differentiate between land and sea anim als. In Experiment 3, infants received frequent experience with a set of similar or dissimilar exemplars, and the same pattern was observed. Thus, 10-month-old infants are sensitive to the distribution of the e xemplars to which they are exposed, and they form different category b oundaries depending on that distribution.