N400 and category exemplar associative strength.

The main purpose of this study was to examine if the N400 amplitude can be considered an index of category exemplar strength of association in a semantic categorization task. Series of six words from a particular semantic category were used as context, and the strength of association between the seventh word and the category was manipulated. Moreover, subjects were asked to perform two different tasks: one consisting of reading the words for comprehension and the other of making a decision regarding the congruence of the ending word. Results showed that the N400 component was elicited by whichever word that was not the best exemplar for the category (atypical members and nonmember of the category). No interaction between type of ending word and type of task was found around 400 ms poststimuli although the P3b component was present for infrequent stimuli in the decision task. It is concluded that the N400 amplitude is sensitive to category membership although no specific attention to the semantic relationship between words was required.