Copyright © 1995 Society for Psychophysiological Research The N400 as a function of the level of processing

In a semantic priming paradigm, the effects of different levels of processing on the N400 were assessed by chang-ing the task demands. In the lexical decision task, subjects had to discriminate between words and nonwords, and in the physical task, subjects had to discriminate between uppercase and lowercase letters. The proportion of related versus unrelated word pairs differed between conditions. A lexicality test on reaction times demonstrated that the physical task was performed nonlexically. Moreover, a semantic priming reaction time effect was obtained only in the lexical decision task. The level of processing clearly affected the event-related potentials. An N400 priming effect was only observed in the lexical decision task. In contrast, in the physical task a P300 effect was observed for either related or unrelated targets, depending on their frequency of occurrence. Taken together, the results indicate that an N400 priming effect is only evoked when the task performance induces the semantic aspects of words to become part of an episodic trace of the stimulus event. Descriptors: Levels of processing, Semantic priming, N400, P300 In this study, we investigated the influence of task demands on the N400 semantic priming effect. In particular, we focused on the impact on the N400 of different levels of processing of lexica