Functional significance of the N400 potential

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This research focuses on one of the mechanisms that allow the understanding of the meaning of the occurrence of items, such as words, faces and objects, in their context. This mechanism is indexed by a negative electrical field that is recorded by placing electrodes on the head. This field is maximum 400 milliseconds after the onset of the stimulus and is thus called the N400. It is thought to reflect processes dealing with memory representations corresponding to the item. However, we performed a series of work suggesting that it could index processes dealing with memory representations corresponding to inappropriate stimuli, whether they correspond a) to the expectation for other items, b) to the no longer relevant context(s) in which the item was previously encuntered or c) to items that resemble the stimulus. We developed the hypothesis that the N400 could index the inhibition of all types of inaccurate representations. We tested this hypothesis and developed a new type of experiments to focus on the inhibition of the first type of representations: those that correspond to expectations that are disconfirmed by the stimulus. This new type of experiments includes the presentations of only a few items which are massively repeated. It could allow the study of the N400 processes corresponding to individual concepts. The present research project aims at further studying the functional significance of the N400 potential by using this new type of experiments and a) by manipulating separately the expectation and the item itself, to verify that the N400 elicited by the item depend on the 1st type of manipulation; b) by testing that the N400 elicited by the highly repeated items of these experiments are impervious to the frequency with which the item is used in the language and to the number of letters of the item. We also want to see whether N400 can be elicited by highly repeated stimuli other than words: that is, faces and object; c) by looking for behavioural correlates of the inhibition with highly repeated word; and d) by using ambiguous words without massive repetition to see whether the N400 indexes the inhibition of the meaning that is inappropriate to the context and the inhibition of the context in which the ambiguous word was first encountered in the experiment.