Discovering category boundaries: The role of comparison in infants' novel category learning.

A key question in categorization is how infants extract regularities from the exemplars they encounter. Detecting similarities and dissimilarities across items is vital in order to determine category-relevant features. Previous research found evidence that infants acquire a single category more easily with paired presentations in comparison with single presentations (Oakes & Ribar, 2005, Infancy, 7, 85; Oakes & Kovack-Lesh, 2007, Cogniție, Creier, Comportament / Cognition, Brain, Behavior, XI, 661). Here, we focus on infants' acquisition of a category contrast, that is, when they are exposed to two categories. In an eye-tracking study, we examined 10-month-old infants' ability to learn two novel visual categories when presented with one item at a time and with items in pairs. Infants were familiarized with pairs of items from the same category or with pairs of items from different categories (cross-category pairs). Using a linear model with a priori contrasts, we show that infants' learning is directly related to the opportunity for category comparison: There is no evidence of category learning in the single-item condition, improved performance when familiarized with same-category pairs, and finally robust category learning when familiarized with cross-category pairs. We conclude that comparison which involves items from different categories promotes category formation, by highlighting differences and promoting a discovery of category boundaries.