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.

在音调语言中，语音可变性在词汇语调（即，超分段）和元音质量（即，分段）中都出现。听众可以使用周围的语音上下文来克服两个语音提示中的可变性，这一过程称为外在归一化。尽管元音是声调的主要载体，但仍不清楚组合的感知（词汇声调和元音质量）是整体还是部分归一化。在这里，我们使用脑电图（EEG）来研究词汇音调归一化和元音归一化的时间过程，以回答此问题。广东成年人听了合成的三音节刺激，其中目标音节的身份-高音与中音（音调条件）之间或/ o /与音调之间是模棱两可的。/ u /（音调条件）—取决于前两个音节的音调范围（音调条件）或共振峰范围（音调条件）。可以看出，与上下文的高音调（语调条件）相比，语境具有相对较低的音调时，歧义语调更常被解释为高层次的语调。类似地，歧义元音在上下文具有较低共振峰范围时比在共振峰具有较高共振峰范围时（Vowel条件）通常被解释为/ o /。这些发现表明了外在语调和元音正常化的典型模式。重要的是，参与者的脑电图结果显示了对比归一化效果，表明在N2时间窗口（190-350毫秒）内已经可以观察到元音归一化的效果，而词汇音调规范化对皮层处理的第一个可靠影响只有从P3时间窗口（220-500毫秒）开始才能观察到。ERP模式表明，词汇声调和元音的对比感知规范化至少在部分独立的时间窗口中发生。这表明，外在归一化可以在音素和音调的级别上单独运行，而不是一次在整个音节上运行。