Young infants learn common categorical distinctions, such as animals versus vehicles. But can they, like adults, rapidly form new categories, such as black-and-white animals? To answer this question, 6-, 10-, and 13-month-old infants were familiarized with four land animals that were black and white in coloring (e.g., a zebra and a black-and-white tiger) and then were tested with novel animals and a truck. The infants responded to an exclusive category that apparently included only black-and-white animals, suggesting that they formed a new categorical representation during familiarization. A comparison group of infants familiarized with a set of land animals that were more variable in coloring (e.g., a pale yellow horse and a yellow-and-brown tiger) formed a very general categorical representation that included many different kinds of animals, regardless of coloring. Therefore, like adults, infants rapidly form new categorical representations in response to the context.
Recently, there has been increasing interest in the origins and early development of categorization. This interest stems from the recognition that infants need a means for organizing and making sense of the enormous number of objects they encounter and reflects an interest in whether category formation is based on similar processes throughout the lifespan (e.g., Oakes & Madole, 2000; Quinn & Eimas, 1997). Many studies have shown that infants can respond to adult-defined categories, such as animals versus vehicles (Mandler & McDonough, 1993), dogs versus cats (Quinn, Eimas, & Rosenkranz, 1993), and food versus furniture (Ross, 1980), demonstrating that we have sensitive experimental measures to tap those abilities. Although such results provide a critically important foundation for our understanding of the early development of categorization, they tell us little about the processes of categorization or the information infants use to form category representations.
Research with adults, in contrast, focuses on just these questions. In a typical categorization study, adults are presented with a set of stimuli (often, novel stimuli that conform to an unfamiliar categorical distinction) under different conditions, and the categorical relations formed in those conditions are observed. These studies have revealed that adults' categorization is highly context dependentfor example, adults judge different items as typical category members in different contexts (Roth & Shoben, 1983), they categorize objects more easily if the features of those objects are consistent with their background knowledge (Spalding & Murphy, 1996), and they perceive such properties as object color differently as a function of how items are categorized (Goldstone, 1995). Thus, the adult literature has focused on categorization as a flexible process responsive to the context.
In the present investigation, we asked whether infants can form novel categorical representations of realistic items that may be included in adult-defined categories (in this case, land animals1). Previous research investigating infants' attention to such categories (e.g., dogs or vehicles) cannot establish whether infants respond on the basis of categorical representations that they possessed before coming into the lab or on the basis of categorical representations that they formed on line. For example, infants familiarized with a set of cats may form a categorical representation of cat at that moment, or they may recall a previously formed categorical representation of cat. Therefore, even when infants' responding seems to reflect an underlying stable concept, they may actually have formed a novel categorical representation during the experimental session. Indeed, studies have revealed that infants' categorization of objects from familiar categories (such as dogs) depends on the particular familiarization stimuli and on how those stimuli are presented (French, Mermillow, Quinn, & Mareschal, 2001 ; Oakes, Coppage, & Dingel, 1997; Quinn et al. …