The cognitive and neural oscillatory mechanisms underlying the facilitating effect of rhythm regularity on speech comprehension

Abstract

Abstract Although a larger number of studies with Indo-European languages as materials have demonstrated the facilitating effect of rhythm regularity on speech comprehension, the internal mechanisms underlying this facilitating effect is still not completely clear. The present electroencephalograph study examined whether and how a rhythmical sentence context affects Mandarin Chinese speech comprehension, and the cognitive and neural oscillatory mechanisms underlying this rhythm regularity effect. Participants listened to Mandarin Chinese sentences that had a regular or irregular rhythm context and that contained critical nouns that were semantically congruent or incongruent given the preceding sentence contexts. The results revealed that, relative to congruent nouns, incongruent nouns elicited a larger N1 and a larger N400 when they were embedded in a regular-rhythm context, but elicited only a larger P600 when they were embedded in an irregular-rhythm context. This difference in the timing of neural responses to incongruent nouns suggests that a temporal rhythmical context speeds up speech comprehension. Moreover, as compared to the irregular-rhythm contexts, regular-rhythm contexts induced neural oscillatory power increases in the beta band immediately preceding the critical nouns and power increases in the alpha band immediately following these nouns. The beta-power enhancement effect induced by the preceding rhythmic context was negatively correlated with the N400/P600 enhancement effect evoked by the subsequent incongruent nouns. The above results suggest that the facilitating effect of rhythm regularity on speech comprehension relies at least in part on alpha-beta band neural oscillations, especially on beta activity; a temporal rhythmical context facilitates speech comprehension both by enhancing neural excitability associated with early acoustic-phonological processing and by reducing cognitive costs associated with later semantic resolution. The present results were also discussed with regard to the dynamic attending theory.