Hemispheric roles in the perception of speech prosody

Abstract

Speech prosody is processed in neither a single region nor a specific hemisphere, but engages multiple areas comprising a large-scale spatially distributed network in both hemispheres. It remains to be elucidated whether hemispheric lateralization is based on higher-level prosodic representations or lower-level encoding of acoustic cues, or both. A cross-language (Chinese; English) fMRI study was conducted to examine brain activity elicited by selective attention to Chinese intonation (I) and tone (T) presented in three-syllable (I3, T3) and one-syllable (I1, T1) utterance pairs in a speeded response, discrimination paradigm. The Chinese group exhibited greater activity than the English in a left inferior parietal region across tasks (I1, I3, T1, T3). Only the Chinese group exhibited a leftward asymmetry in inferior parietal and posterior superior temporal (I1, I3, T1, T3), anterior temporal (I1, I3, T1, T3), and frontopolar (I1, I3) regions. Both language groups shared a rightward asymmetry in the mid portions of the superior temporal sulcus and middle frontal gyrus irrespective of prosodic unit or temporal interval. Hemispheric laterality effects enable us to distinguish brain activity associated with higher-order prosodic representations in the Chinese group from that associated with lower-level acoustic/auditory processes that are shared among listeners regardless of language experience. Lateralization is influenced by language experience that shapes the internal prosodic representation of an external auditory signal. We propose that speech prosody perception is mediated primarily by the RH, but is left-lateralized to task-dependent regions when language processing is required beyond the auditory analysis of the complex sound.