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WHAT OUR VARIOUS CATEGORIZATION TASKS REVEAL ABOUT INFANT REPRESENTATION

Laraine McDonough

Department of Cognitive Science University of California, San Diego, La Jolla, CA. 92093-05 15

The traditional view of categorization is that infants initially form basic-level categories that are then used to guide their generalizations and provide the foundation for learning language. According to this view, development is thought to proceed from perceptually based categories that later become imbued with concepts. For example, infants as young as 3-months of age have been shown to habituate to a series of perceptually similar exemplars, and then dishabituate when a new exemplar from a different basic-level category is presented. Older infants around 18 months of age readily learn basic-level nouns and tend to extend them to appropriate referents. Three-year-olds make conceptually based inductions when reasoning about novel property attributes that are taught on a single exemplar. Such inductions are more frequently made to exemplars within the same basic-level than the same superordinate-level category. Thus, the data on infants and young children show similar results: the boundaries between basic-level categories are first learned and are later used to guide the generalization of nouns and constrain inductive reasoning.

More recently, data showing a very different developmental pattern have been presented. Sequential touching tasks and object manipulation tasks (where habituation is not required of subjects) show that infants and young children do not differentiate many basic-level categories even though these categories perceptually differ. Results from these two tasks also show relatively good performance when superordinate- or domain-level categories (e.g., animals and vehicles) are tested. Evidence that infants have formed these much larger global categories even though the exemplars included within them are perceptually varied was surprising. Given that the use of perceptual cues would have provided very different results, the data were interpreted to reflect early conceptual development. That is, it was presumed that the concepts infants have about such categories allowed them to generalize across features and consider such features as similar even though results from habituation tasks have shown that these features are perceived to be different by much younger infants. Since generalization across features has important implications for how inductions are made, an induction task was designed that was suitable for testing young infants. Infants from 9- to 16months of age were tested. The results showed that the boundaries between basic-level categories are largely ignored by infants when domain-specific properties are tested. For example, on seeing an exemplar of a dog being given a drink from a cup, infants generalized the drinking action to various animals, even some who actually do not drink (i.e., fish). When nonspecific or “accidental” properties are tested (such as being dirty), a different pattern of generalization is found. For example, when a washing action was demonstrated, it was generalized across both the animal and vehicle domains. These results show that infants’ inductions of both domain- specific and non-specific properties are made according to the boundaries of their conceptual categories as well as the meaning of the properties tested. In contrast to predictions based on the traditional view of early category formation, such inductions were not constrained by perceptual similarity.

Nevertheless, there remain sets of data from different tasks that are difficult to reconcile. These differences will be discussed. It will be proposed that one way to bridge the gap between these results is to consider the cognitive demands required for successful performance on each task. How the findings from various tasks are interpreted depend on the assumptions made about category learning in naturalistic versus highly structured settings.