ELECTROPHYSIOLOGICAL EVIDENCE FOR THE TYPICALITY EFFECT OF HUMAN COGNITIVE CATEGORIZATION

Event-related brain potentials (ERPs) were recorded from 14 normal sub jects during a category verification task. Stimulus words were selecte d from 17 semantic categories (e.g. 'vegetables'). Half of the words w ere typical category members (e.g. 'carrot', 'spinach') and the other half were atypical (e.g. 'parsley', 'asparagus'). Subjects were requir ed to judge whether each stimulus belonged to a target category ('vege tables' or 'sports') or a non-target category. For the non-target cate gory, the typicality effect was neither found in ERPs nor in reaction times. For the target category, typical words were responded to more q uickly than were atypical words and the ERP amplitudes between a 300-4 50 ms period were more negative after the atypical words than after th e typical words (typicality effect). These results suggested that typi cal words of the target were more primed by a target category than wer e the atypical words of the target and thus that a concept is represen ted by a prototype, the central tendency of all members of the categor y. (C) 1998 Elsevier Science B.V.