How accentuation influences semantic short-term memory representations during on-line speech processing: an event-related potential study.

In the present study, the ERP (event-related brain potentials) technique was used to investigate how accentuation influences the semantic short-term memory representations during on-line speech processing, and how this accentuation effect interacts with the distance of accentuation in the speech signal. Chinese spoken sentences were used as stimuli. The sentences included two critical words: Noun1 and Noun2, with the ERP time-locked to Noun2. During sentence comprehension, when the listener hears Noun2, he needs to retrieve Noun1 from the working memory and integrate it with Noun2. We manipulated the (de-)accentuation of Noun1 and the semantic relationship between Noun1 and Noun2 by changing Noun1 in the sentence context. Moreover, we manipulated the distance of accentuation (distance between Noun1 and Noun2) by changing the syntactic structure of the sentences. The results revealed a significant main effect of semantic relatedness, indicating that the low semantic relatedness condition elicited a larger N400 than the high semantic relatedness condition. Importantly, there was a significant two-way interaction between semantic relatedness and accentuation and a significant three-way interaction between semantic relatedness, accentuation, and distance. Further analysis demonstrated that, the semantic relatedness effect was modulated by accentuation in the long-distance sentences, but not in the short-distance sentences. That is, in the long-distance sentences, the semantic relatedness effect reached significance only when the to-be-integrated expression in the preceding sentence context was accented; however, in the short-distance sentences, the semantic relatedness effects reached significance regardless of the presence or absence of accentuation. The results indicated that, during on-line speech processing, accentuation can enhance the corresponding information's semantic short-term memory representation, and that the effect of accentuation on semantic short-term memory is somewhat flexible and shows up only when the words in the speech signal were far apart.