Department of Chinese and Bilingual Studies, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Special Administrative Region.
Donders Institute for Brain, Cognition and Behaviour, Centre for Cognitive Neuroimaging, Radboud University, Kapittelweg 29, Nijmegen, 6525 EN, the Netherlands.
Neuropsychologia. 2021 Jun 18;156:107839. doi: 10.1016/j.neuropsychologia.2021.107839. Epub 2021 Mar 30.
In tonal languages, speech variability arises in both lexical tone (i.e., suprasegmentally) and vowel quality (segmentally). Listeners can use surrounding speech context to overcome variability in both speech cues, a process known as extrinsic normalization. Although vowels are the main carriers of tones, it is still unknown whether the combined percept (lexical tone and vowel quality) is normalized integrally or in partly separate processes. Here we used electroencephalography (EEG) to investigate the time course of lexical tone normalization and vowel normalization to answer this question. Cantonese adults listened to synthesized three-syllable stimuli in which the identity of a target syllable - ambiguous between high vs. mid-tone (Tone condition) or between /o/ vs. /u/ (Vowel condition) - was dependent on either the tone range (Tone condition) or the formant range (Vowel condition) of the first two syllables. It was observed that the ambiguous tone was more often interpreted as a high-level tone when the context had a relatively low pitch than when it had a high pitch (Tone condition). Similarly, the ambiguous vowel was more often interpreted as /o/ when the context had a relatively low formant range than when it had a relatively high formant range (Vowel condition). These findings show the typical pattern of extrinsic tone and vowel normalization. Importantly, the EEG results of participants showing the contrastive normalization effect demonstrated that the effects of vowel normalization could already be observed within the N2 time window (190-350 ms), while the first reliable effect of lexical tone normalization on cortical processing was observable only from the P3 time window (220-500 ms) onwards. The ERP patterns demonstrate that the contrastive perceptual normalization of lexical tones and that of vowels occur at least in partially separate time windows. This suggests that the extrinsic normalization can operate at the level of phonemes and tonemes separately instead of operating on the whole syllable at once.
在声调语言中，语音变异性既存在于超音段（即韵律）层面的音高（即声调），也存在于音段（即音节）层面的元音质量。听者可以利用周围的语音语境来克服语音线索的变异性，这个过程被称为外在归一化。尽管元音是声调的主要载体，但仍不清楚整体感知（即声调与元音质量）是通过整体归一化还是部分独立的过程来实现的。在这里，我们使用脑电图（EEG）来研究声调归一化和元音归一化的时间进程，以回答这个问题。粤语成年人听三音节合成刺激，目标音节的身份在高低调（声调条件）或/o/与/u/（元音条件）之间是不确定的，取决于前两个音节的音高范围（声调条件）或共振峰范围（元音条件）。观察到，当语境的音高相对较低时，歧义声调更常被解释为高音调，而当语境的音高相对较高时则更常被解释为中音调（声调条件）。同样，当语境的共振峰范围相对较低时，歧义元音更常被解释为/o/，而当语境的共振峰范围相对较高时则更常被解释为/u/（元音条件）。这些发现显示了外在声调与元音归一化的典型模式。重要的是，表现出对比归一化效应的参与者的 EEG 结果表明，元音归一化的效应可以在 N2 时间窗口（190-350 毫秒）内观察到，而声调归一化对皮质处理的第一个可靠效应仅可以从 P3 时间窗口（220-500 毫秒）开始观察到。ERP 模式表明，声调与元音的对比感知归一化至少在部分独立的时间窗口内发生。这表明外在归一化可以分别作用于音位和音位变体，而不是一次作用于整个音节。
