N400-like Potentials and Reaction Times Index Semantic Relations between Highly Repeated Individual Words

摘要

The N400 ERP is an electrophysiological index of semanticnprocessing. Its amplitude varies with the semantic category ofnwords, their concreteness, or whether their meaning matchesnthat of a preceding context. The results of a number of studiesnsuggest that these effects could be markedly reduced or suppressednfor stimuli that are repeated. Nevertheless, we have recentlynshown that significant effects of semantic matching andncategory could be obtained on N400-like potentials elicited bynmassively repeated target words in a prime–target semantic categorizationntask. If such effects could be obtained when primesnalso are repeated, it would then be possible to study the semanticnassociations between individual words. The present study thusnaimed to test this hypothesis while (1) controlling for a potentialncontribution of physical matching to the processing of repeatedntargets and (2) testing if the N400-like effects obtained in thesenconditions are modulated by task instruction, as are classicnN400 effects. Two category words were used as primes and twonexemplars as targets. In one block of trials, subjects had to respondnaccording to the semantic relation between prime and targetn(semantic instruction) and, in another block, they had tonreport changes in letter case (physical instruction). Resultsnshowed that the amplitude of the N400-like ERP obtained wasnmodulated by semantic matching and category but not by letterncase. The effect of semantic matching was observed only in thensemantic instruction block. Interestingly, the effect of categorynwas not modulated by task instruction. An independent componentnanalysis showed that the component that made the greatestncontribution to the effect of semantic matching in the time windownof the N400-like potential had a scalp distribution similar tonthat reported for the N400 and was best fit as a bilateral generatornin the superior temporal gyrus. The use of repetition could thusnallow, at least in explicit semantic tasks, a drastic simplification ofnN400 protocols. Highly repeated individual words could be usednto study semantic relations between individual concepts. ■