Wellcome Centre for Integrative Neuroimaging, Department of Experimental Psychology, University of Oxford, Oxford, OX2 6GG, United Kingdom.
School of Psychology, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
J Neurosci. 2021 Feb 3;41(5):1059-1067. doi: 10.1523/JNEUROSCI.1977-20.2020. Epub 2020 Dec 9.
Speech processing relies on interactions between auditory and motor systems and is asymmetrically organized in the human brain. The left auditory system is specialized for processing of phonemes, whereas the right is specialized for processing of pitch changes in speech affecting prosody. In speakers of tonal languages, however, processing of pitch (i.e., tone) changes that alter word meaning is left-lateralized indicating that linguistic function and language experience shape speech processing asymmetries. Here, we investigated the asymmetry of motor contributions to auditory speech processing in male and female speakers of tonal and non-tonal languages. We temporarily disrupted the right or left speech motor cortex using transcranial magnetic stimulation (TMS) and measured the impact of these disruptions on auditory discrimination (mismatch negativity; MMN) responses to phoneme and tone changes in sequences of syllables using electroencephalography (EEG). We found that the effect of motor disruptions on processing of tone changes differed between language groups: disruption of the right speech motor cortex suppressed responses to tone changes in non-tonal language speakers, whereas disruption of the left speech motor cortex suppressed responses to tone changes in tonal language speakers. In non-tonal language speakers, the effects of disruption of left speech motor cortex on responses to tone changes were inconclusive. For phoneme changes, disruption of left but not right speech motor cortex suppressed responses in both language groups. We conclude that the contributions of the right and left speech motor cortex to auditory speech processing are determined by the functional roles of acoustic cues in the listener's native language. The principles underlying hemispheric asymmetries of auditory speech processing remain debated. The asymmetry of processing of speech sounds is affected by low-level acoustic cues, but also by their linguistic function. By combining transcranial magnetic stimulation (TMS) and electroencephalography (EEG), we investigated the asymmetry of motor contributions to auditory speech processing in tonal and non-tonal language speakers. We provide causal evidence that the functional role of the acoustic cues in the listener's native language affects the asymmetry of motor influences on auditory speech discrimination ability [indexed by mismatch negativity (MMN) responses]. Lateralized top-down motor influences can affect asymmetry of speech processing in the auditory system.
言语处理依赖于听觉和运动系统之间的相互作用，并且在人类大脑中呈不对称分布。左听觉系统专门用于处理音素，而右听觉系统专门用于处理影响韵律的言语中的音高变化。然而，在声调语言使用者中，处理改变词义的音高（即音高）变化是左偏的，这表明语言功能和语言经验塑造了言语处理的不对称性。在这里，我们研究了声调语言和非声调语言使用者的听觉言语处理中运动贡献的不对称性。我们使用经颅磁刺激（TMS）暂时干扰右或左言语运动皮层，并使用脑电图（EEG）测量这些干扰对音节序列中语音和音高变化的听觉辨别（失匹配负波；MMN）反应的影响。我们发现，运动干扰对音高变化处理的影响在语言群体之间存在差异：右言语运动皮层的干扰抑制了非声调语言使用者对音高变化的反应，而左言语运动皮层的干扰抑制了声调语言使用者对音高变化的反应。在非声调语言使用者中，左言语运动皮层干扰对音高变化反应的影响尚无定论。对于语音变化，左但不是右言语运动皮层的干扰抑制了两种语言群体对语音变化的反应。我们得出的结论是，右和左言语运动皮层对听觉言语处理的贡献取决于听众母语中声学线索的功能作用。听觉言语处理的半球不对称性的基本原则仍存在争议。言语声音处理的不对称性受低水平声学线索的影响，但也受其语言功能的影响。通过结合经颅磁刺激（TMS）和脑电图（EEG），我们研究了声调语言和非声调语言使用者听觉言语处理中运动贡献的不对称性。我们提供了因果证据，即听众母语中声学线索的功能作用影响了运动对听觉言语辨别能力的影响的不对称性（以失匹配负波（MMN）反应为指标）。从大脑发出的有偏向的运动影响可以影响听觉系统中言语处理的不对称性。
