The Neuropsychology of Perceptual Category Learning

Abstract There is widespread agreement that multiple qualitatively different category learning systems mediate the learning of different category structures. Two systems that have received support are a frontal-based explicit system that uses logical reasoning, depends on working memory and executive attention, and is mediated primarily by the anterior cingulate, the prefrontal cortex and the associative striatum, including the head of the caudate. The second is a basal ganglia-mediated implicit system that uses procedural learning, requires a dopamine reward signal and is mediated primarily by the sensorimotor striatum (i.e., the tail of the caudate and putamen). This chapter reviews a large body of work conducted in our laboratory and others that examines the details of the two proposed systems using neurological patients as experimental participants. Collectively the studies suggest significant involvement of the striatum and less involvement of the medial temporal lobes in category learning. They also suggest that, in striatal-damaged patients, the need to ignore irrelevant information is predictive of a rule-based category learning deficit, whereas the complexity of the rule is predictive of an information-integration category learning deficit.