The University of Hong Kong, Hong Kong, SAR.
PLoS One. 2013;8(1):e54396. doi: 10.1371/journal.pone.0054396. Epub 2013 Jan 16.
This study investigated a theoretically challenging dissociation between good production and poor perception of tones among neurologically unimpaired native speakers of Cantonese. The dissociation is referred to as the near-merger phenomenon in sociolinguistic studies of sound change. In a passive oddball paradigm, lexical and nonlexical syllables of the T1/T6 and T4/T6 contrasts were presented to elicit the mismatch negativity (MMN) and P3a from two groups of participants, those who could produce and distinguish all tones in the language (Control) and those who could produce all tones but specifically failed to distinguish between T4 and T6 in perception (Dissociation). The presence of MMN to T1/T6 and null response to T4/T6 of lexical syllables in the dissociation group confirmed the near-merger phenomenon. The observation that the control participants exhibited a statistically reliable MMN to lexical syllables of T1/T6, weaker responses to nonlexical syllables of T1/T6 and lexical syllables of T4/T6, and finally null response to nonlexical syllables of T4/T6, suggests the involvement of top-down processing in speech perception. Furthermore, the stronger P3a response of the control group, compared with the dissociation group in the same experimental conditions, may be taken to indicate higher cognitive capability in attention switching, auditory attention or memory in the control participants. This cognitive difference, together with our speculation that constant top-down predictions without complete bottom-up analysis of acoustic signals in speech recognition may reduce one's sensitivity to small acoustic contrasts, account for the occurrence of dissociation in some individuals but not others.
本研究调查了一种理论上具有挑战性的分离现象，即神经健全的粤语母语者在产生和感知声调方面的出色表现和较差表现之间的分离。这种分离在社会语言学研究声音变化时被称为“近乎合并现象”。在被动Oddball 范式中，呈现 T1/T6 和 T4/T6 对比的词汇和非词汇音节，以从两组参与者中引出不匹配负波（MMN）和 P3a，一组是能够产生和区分语言中所有声调的人（对照组），另一组是能够产生所有声调但在感知上无法区分 T4 和 T6 的人（分离组）。分离组对词汇音节的 T1/T6 存在 MMN，对 T4/T6 无反应，证实了近乎合并现象的存在。对照组对 T1/T6 词汇音节表现出统计上可靠的 MMN，对 T1/T6 非词汇音节和 T4/T6 词汇音节的反应较弱，最后对 T4/T6 非词汇音节无反应，这表明在言语感知中涉及到自上而下的处理。此外，与分离组相比，对照组在相同的实验条件下具有更强的 P3a 反应，这可能表明对照组在注意转换、听觉注意力或记忆方面具有更高的认知能力。这种认知差异，加上我们的推测，即言语识别中没有完全基于声学信号的自上而下预测，可能会降低个体对小的声学差异的敏感性，这可以解释为什么在某些个体中会出现分离现象，而在其他个体中则不会出现。
