N400 processes inhibit inappropriately activated representations: Adding a piece of evidence from a high-repetition design

The N400 event-related potential could index the activation/integration of representations corresponding to the stimulus or, on the contrary, the inhibition of representations that have been inappropriately activated. To test this alternative, series of 3 words were visually presented to subjects in a relatively rapid succession in order to prevent any disengagement of attention. In one block, participants had to judge whether the meaning of the 1st word was related to that of the 3rd. Representations activated by the 2nd word were thus inappropriate and had to be ignored. In another block, these representations were task appropriate as subjects were asked to decide whether the meaning of the 2nd word was related to that of the 3rd. The new technique of massive repetitions was used in order to obtain early peaking and short lasting N400 effects that would be easier to distinguish from effects on the contingent negative variations (CNVs) triggered by the expectancy of 3rd words. The ERPs elicited by 2nd words were more negative in the N400 time window when their meanings were task inappropriate than when these meanings had to be used. These differences were maximal at the latency of the peak of the N400 deflection rather than at the latency of the maximum of the late positive complex or at that of the CNV. They appeared to be greater at centro-parietal sites and slightly larger over the right than over the left hemiscalp. The results thus bring further support to the idea that N400 processes are of an inhibitory nature.