CAS Key Laboratory of Brain Function and Disease, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China.
Neuroimage. 2013 Dec;83:637-45. doi: 10.1016/j.neuroimage.2013.02.080. Epub 2013 Jul 12.
For nontonal language speakers, speech processing is lateralized to the left hemisphere and musical processing is lateralized to the right hemisphere (i.e., function-dependent brain asymmetry). On the other hand, acoustic temporal processing is lateralized to the left hemisphere and spectral/pitch processing is lateralized to the right hemisphere (i.e., acoustic-dependent brain asymmetry). In this study, we examine whether the hemispheric lateralization of lexical pitch and acoustic pitch processing in tonal language speakers is consistent with the patterns of function- and acoustic-dependent brain asymmetry in nontonal language speakers. Pitch contrast in both speech stimuli (syllable /ji/ in Experiment 1) and nonspeech stimuli (harmonic tone in Experiment 1; pure tone in Experiment 2) was presented to native Cantonese speakers in passive oddball paradigms. We found that the mismatch negativity (MMN) elicited by lexical pitch contrast was lateralized to the left hemisphere, which is consistent with the pattern of function-dependent brain asymmetry (i.e., left hemisphere lateralization for speech processing) in nontonal language speakers. However, the MMN elicited by acoustic pitch contrast was also left hemisphere lateralized (harmonic tone in Experiment 1) or showed a tendency for left hemisphere lateralization (pure tone in Experiment 2), which is inconsistent with the pattern of acoustic-dependent brain asymmetry (i.e., right hemisphere lateralization for acoustic pitch processing) in nontonal language speakers. The consistent pattern of function-dependent brain asymmetry and the inconsistent pattern of acoustic-dependent brain asymmetry between tonal and nontonal language speakers can be explained by the hypothesis that the acoustic-dependent brain asymmetry is the consequence of a carryover effect from function-dependent brain asymmetry. Potential evolutionary implication of this hypothesis is discussed.
对于非声调语言使用者，言语处理偏向于左半球，音乐处理偏向于右半球（即功能依赖的大脑不对称）。另一方面，声学时间处理偏向于左半球，频谱/音高处理偏向于右半球（即声学依赖的大脑不对称）。在这项研究中，我们研究了声调语言使用者的词汇音高和声学音高处理的半球侧化是否与非声调语言使用者的功能和声学依赖的大脑不对称模式一致。在被动Oddball 范式中，向母语为广东话的人呈现了言语刺激（实验 1 中的音节/jɪ/）和非言语刺激（实验 1 中的谐波音；实验 2 中的纯音）中的音高对比。我们发现，词汇音高对比引起的失匹配负波（MMN）偏向于左半球，这与非声调语言使用者的功能依赖的大脑不对称模式（即言语处理的左半球侧化）一致。然而，由声学音高对比引起的 MMN 也偏向于左半球（实验 1 中的谐波音）或偏向于左半球（实验 2 中的纯音），这与非声调语言使用者的声学依赖的大脑不对称模式（即声学音高处理的右半球侧化）不一致。声调语言和非声调语言使用者之间功能依赖的大脑不对称模式一致和声学依赖的大脑不对称模式不一致，可以用这样的假设来解释，即声学依赖的大脑不对称是功能依赖的大脑不对称的延续效应的结果。讨论了这个假设的潜在进化意义。
