RESEARCH REPORT Episodic and prototype models of category learning Richard J. Tunney • Gordon Fernie Received: 7 October 2010 / Accepted: 28 March 2011 / Published online: 10 April 2011 Ó Marta Olivetti Belardinelli and Springer-Verlag 2011 Abstract The question of what processes are involved in the acquisition and representation of categories remains unresolved despite several decades of research. Studies using the well-known prototype distortion task (Posner and Keele in J Exp Psychol 77:353–363, 1968) delineate three candidate models. According to exemplar-based models, we memorize each instance of a category and when asked to decide whether novel items are category members or not, the decision is explicitly based on a similarity com- parison with each stored instance. By contrast, prototype models assume that categorization is based on the simi- larity of the target item to an implicit abstraction of the central tendency or average of previously encountered instances. A third model suggests that the categorization of prototype distortions does not depend on pre-exposure to study exemplars at all and instead reflects properties of the stimuli that are easily learned during the test. The four experiments reported here found evidence that categori- zation in this task is predicated on the first and third of these models, namely transfer at test and the exemplar- based model. But we found no evidence for the second candidate model that assumed that categorization is based on implicit prototype abstraction. Keywords Categorization Á Implicit learning A fundamental aspect of human cognition is the ability to acquire knowledge of categories. Precisely how the mind represents categories has received a substantial amount of attention and recently theories of categorization have been informed by studies involving amnesic patients and brain- images. These, however, tend to contradict the evidence obtained using traditional psychological methods. The present research is concerned with two classes of theory of categorization, in particular: episodic models and prototype models. Both prototype and episodic models assume that categorization decisions are based on similarity. According to episodic models, we memorize each instance of a cate- gory (e.g., Hintzman 1986). When asked to decide whether novel items are category members or not, the decision is based on a comparison of the item with each stored exemplar. In effect, categorization is little more than a form of episodic memory. 1 By contrast, prototype models assume that categorization decisions are made by judging the similarity of the item to a prototype, rather by com- paring it to the study items stored in memory (Smith and Minda 2002). A prototype is usually defined as an abstraction of the central tendency or an average of pre- viously encountered exemplars. Because the exemplars themselves need not be stored in memory, some proponents of prototype models have claimed that prototype abstrac- tion is an implicit process or that it results in an implicit representation (e.g., Reber et al. 2003; Squire and Knowlton 1995). Prototype distortion tasks Prototype distortion tasks (Posner and Keele 1968) have been highly influential in developing our understanding of R. J. Tunney (&) Á G. Fernie University of Nottingham, Nottingham, UK e-mail: richard.tunney@nottingham.ac.uk 1 Strictly speaking exemplar models are a subordinate category of episodic models we refer to them synonymously because exemplar models require some form of episodic memory to store the instances, although this need not be veridical. 123 Cogn Process (2012) 13:41–54 DOI 10.1007/s10339-011-0403-2