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, P300In 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 lexical stimuli. In this report, we first discuss the relevant semantic prim ing effects and the mechanisms responsible for these priming effects then we introduce the levels of processing framework within which semantic priming effects were investigated.One of the most consistent findings in the psycholinguistic literature is that words are processed faster and more accurately when they are preceded by a semantically related or associated word than by an unrelated word (e.g., Meyer & Schvaneveldt, 1971; see Neely, 1991, for a review). More recently, it has been demonstrated that semantic priming effects can also be recorded with the use of the event-related brain potential (ERP) method. Hillyard (1980, 1984) identified an ERP component, the N400, a negative peak with a mean latency of 400 ms and a centroparietal distribution, that is larger in amplitude for words that are semantically incongruent with a preceding sen tence context. Subsequent research has shown that the N400 is tied more to semantic expectancy than to anomaly (e.g., Kutas, Lindamood, & Hillyard, 1984).
