INTRODUCTION At some point during development, humans must come to recognize discriminably different objects with important common characteristics as members of the same category. When and how category representations become available have been enduring issues for several generations of investigators, and a traditional view had it that category representations were a late achievement, dependent on the emergence of language, logic, and instruction (e.g., Bruner, Olver, & Greenfield, 1966). However, in the last 20 years, the results of a number of studies are consistent with the conclusion that at least some of the abilities needed for category formation are functional in preverbal infants (Mandler, 2000; Mareschal & Quinn, 2001).