Rules and Similarity in the Development of Category Learning in Children and Infants

<p><strong>Abstract</strong></p> <p>Most theorists agree that adults can learn and use categories that are both rule- and similarity-based. There is less agreement about the mechanisms involved or on the distinction between rules and similarity. We begin by reviewing two recent theoretical positions, that of Pothos (2005) and of Ashby & colleagues (Ashby et al., 1998; Ashby and O’Brien, 2005). Identifying the notion of a rule to be the most problematic concept, we continue with a broader survey of rules in cognition.</p> <p>We propose that a developmental perspective could provide insight into these prob- lems. We review the existing literature from infancy and early childhood to show that previous studies have only tangentially investigated rules and similarity. We adapt and extend existing methods and present novel procedures and analyses that allow us to focus on a range of questions; When do rules emerge? What form do early rules take? Can statistical mechanisms give rise to rule-like performance? Is there a competition between rule and similarity processes?</p> <p>Four groups of experiments explore these questions. One set of experiments looks at 5-month-olds’ (and adults’) performance on several artificial grammar tasks devel- oped from Kirkham et al. (2002). We demonstrate that participants are sensitive to the complexity of certain sequence structures. Another pair of tasks investigate infants’ learning of abstract Same-Different relations. We find that 8-month-olds will learn the relation in both an habituation and an anticipation task, whereas 4-month-olds only succeed on the latter. A third group of tasks juxtapose unidi- mensional and family resemblance categorization using both rich and impoverished stimuli. We find that infants form flexible classifications. Finally, we present a set of computer games for young children that explore these questions in a more ecologically valid setting than traditional laboratory classification tasks.