Reversing the N400: event-related potentials of a negative semantic priming effect.

We investigated electrophysiological correlates of the access to semantic representations. Participants had to make word/nonword decisions to target words. A first word (i.e. the prime) preceded the target. The prime was either semantically related or unrelated to the target. Using a special masking technique we were able to present the prime rather long (approximately 140 ms) while preventing participants from consciously processing the prime. In line with former studies, participants showed a reversed priming effect: they reacted faster to unrelated compared with related targets. Interestingly, the N400 mimicked the behavioral effect: we observed more negative-going waveforms to related relative to unrelated targets. The result indicates that the N400 can reflect temporarily reduced access to semantic representations.