The N400 as a function of the level of processing

TLDR

The study used a semantic priming paradigm with two tasks—lexical decision and physical uppercase/lowercase discrimination—to manipulate processing depth by varying the proportion of related versus unrelated word pairs. Results showed that an N400 priming effect emerged only in the lexical decision task, whereas the physical task produced a P300 effect, indicating that N400 is elicited only when semantic processing is integrated into the episodic trace of the stimulus.

Abstract

ABSTRACT In a semantic priming paradigm, the effects of different levels of processing on the N400 were assessed by changing 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.