The cognitive neuroscience of implicit category learning

Abstract

There is much recent interest in the question of whether people have available a single category learning system or a number of qualitatively different systems. Most proponents of multiple systems have hypothesized an explicit, rule-based system and some type of implicit system. Although there has been general agreement about the nature of the explicit system, there has been disagreement about the exact nature of the implicit system. This chapter explores the question of whether there is implicit category learning, and if there is, what form it might take. First, we examine what the word "implicit" means in the categorization literature. Next, we review some of the evidence that supports the notion that people have available one or more implicit categorization systems. Finally, we consider the nature of implicit categorization by focusing on three alternatives: an exemplar memory-based system, a procedural memory system, and an implicit system that uses the perceptual representation memory system.

The Roles of the Caudate Nucleus in Human Classification Learning

“…The sensitivity of areas of caudate that were important for classification (e.g., the body and tail of the caudate) to feedback is consistent with theories that the striatum may play a general role in reward-mediated learning (Ashby and Casale, 2003). Behavioral and neuropsychological studies show that categorization learning is dependent on the presence of feedback.…”

“…The involvement of the body and tail of the caudate in learning is consistent with a large body of research with monkeys (Brown et al, 1995;Levy et al, 1997;Teng et al, 2000;Fernandez-Ruiz et al, 2001). Performance on complex visual stimulus-outcome tasks is impaired in patients with compromised striatal functioning (Knowlton et al, 1996a,b;Filoteo et al, 2001 (1998) and Ashby and Casale (2003) that the "visual" corticostriatal loop underlies human classification learning via feedback. ROI analyses indicated that the putamen was significantly activated during classification learning, with a pattern of activity more similar to the pattern in the body and tail of the caudate than the head of the caudate.…”

“…The present study is intermediate in complexity, using eight different stimuli and two different categories. It should be noted that the stimuli were not related to other stimuli within the category, and thus participants were not able to abstract a rule, pattern, or prototype or make similarity-based judgments (Seger, 1994;Ashby and Casale, 2003).…”

“…Common features of task that involve the caudate include the presence of feedback and indication of decisions via distinct motor responses. Tasks with these characteristics are learned by a system that is behaviorally and neurally dissociable from two other human category learning systems (Ashby and Casale, 2003): categorizing on the basis of verbalizable rules, reliant on lateral frontal systems (Smith et al, 1998;Seger et al, 2000;Filoteo et al, 2005b), and learning single categories consisting of distortions of a prototypical stimulus, reliant on extrastriate visual areas (Reber et al, 1998a(Reber et al, ,b, 2003Aizenstein et al, 2000) A puzzling discrepancy is that the main area of activity reported in human functional imaging studies is typically in the head of the caudate (Table 1), whereas research in monkeys shows the body and tail of the caudate to be crucial (Brown et al, 1995;Teng et al, 2000;Fernandez-Ruiz et al, 2001). Although there is a large degree of divergence in projections from the cortex to the striatum (Mink, 1996;Wise et al, 1996), it is generally accepted that the head and tail of the caudate participate in functionally dissociable corticostriatal loops.…”

Procedural interference in perceptual classification: Implicit learning or cognitive complexity?

“…A important debate in the modern perceptual classification literature concerns the issue of whether or not multiple cognitive systems underlie the learning and representation of perceptual categories (Ashby & Casale, 2003;Knowlton & Squire, 1993;Nosofsky & Johansen, 2000;Palmeri & Flanery, 2002;Shanks & St. John, 1994;Smith, Patalano, & Jonides, 1998). Much of the evidence for distinct representational systems is based on the demonstration of a variety of experimental dissociations involving classification performance.…”