Effects of acoustic variation on amusia (Shao et al., 2019)

<b>Purpose: </b>Congenital amusia is an inborn neurogenetic disorder of fine-grained pitch processing. This study attempted to pinpoint the impairment mechanism of speech processing in tonal language speakers with amusia. We designed a series of perception tasks aiming at selectively probing low-level pitch processing and relatively high-level phonological processing of lexical tones, with an aim to illuminate the deficiency mechanism underlying tone perception in amusia.<b>Method: </b>Sixteen Cantonese-speaking amusics and 16 matched controls were tested on the effects of acoustic (talker/syllable) variations on the identification and discrimination of Cantonese tones in two conditions. In the low-variation condition, tones were always associated with the same talker or syllable; in the high-variation condition, tones were associated with either different talkers (with the syllable controlled) or different syllables (with the talker controlled).<b>Results: </b>Largely similar results were obtained in talker and syllable variation conditions. Amusics exhibited overall poorer performance than controls in tone identification. Although amusics also demonstrated poorer performance in tone discrimination, the group difference was more obvious in low-variation conditions, where more acoustic constancy was provided. Besides, controls exhibited a greater increase in discrimination sensitivity from high- to low-variation conditions, implying a stronger benefit of acoustic constancy.<b>Conclusions: </b>The findings suggested that amusics’ lexical tone perception abilities, in terms of both low-level pitch processing and high-level phonological processing, as measured in low- and high-variation conditions, are impaired. Importantly, amusics were more impaired in taking advantage of low acoustic variation contexts and thus less efficiently sharpened their perception of tones when perceptual anchors in talker/syllable were provided, suggesting a possible “anchoring deficit” in congenital amusia.<br><b>Supplemental Material S1.</b> Percentage of correct and incorrect trials in each condition.<br><b>Supplemental Material S2.</b> Reaction time (RT) results separated by correct and incorrect trials. <br>Shao, J., Lau, R. Y. M., Tang, P. O. C., &amp; Zhang, C. (2019). The effects of acoustic variation on the perception of lexical tone in Cantonese-speaking congenital amusics. <i>Journal of Speech, Language, and Hearing Research.</i> Advance online publication. https://doi.org/10.1044/2018_JSLHR-H-17-0483

<b>研究目的：</b>先天性失歌症（congenital amusia）是一种与生俱来的神经遗传性精细音高加工障碍。本研究旨在明确声调语言使用者罹患失歌症时的言语加工受损机制。我们设计了一系列知觉任务，用以选择性探查词汇声调（lexical tones）的低阶音高加工与相对高阶的语音加工过程，以期阐明失歌症患者声调知觉受损的潜在机制。<b>研究方法：</b>本研究招募16名以粤语为母语的失歌症患者与16名匹配对照组被试，考察两种实验条件下，声学（发音人/音节）变化对粤语声调识别与辨别的影响。在低变化条件中，声调始终与同一发音人或同一音节绑定；在高变化条件中，声调分别与不同发音人（音节保持恒定）或不同音节（发音人保持恒定）绑定。<b>研究结果：</b>发音人变化与音节变化两种条件下所得结果大体相似。失歌症患者在声调识别任务中的整体表现显著劣于对照组。尽管失歌症患者在声调辨别任务中同样表现较差，但组间差异在声学恒定性更高的低变化条件中更为显著。此外，对照组从高变化条件转向低变化条件时，其辨别敏感度的提升幅度更大，提示声学恒定性带来的增益效应更强。<b>研究结论：</b>本研究结果表明，通过高低变化条件测得的失歌症患者的词汇声调知觉能力，涵盖低阶音高加工与高阶语音加工两个维度，均存在受损。尤为关键的是，失歌症患者在利用低声学变化情境方面表现更差，当获得发音人/音节作为知觉锚点时，其对声调的知觉精细化加工效率更低，提示先天性失歌症可能存在“锚定缺陷”。<br><b>补充材料S1。</b>各条件下正确与错误试次的占比。<br><b>补充材料S2。</b>按正确与错误试次划分的反应时（RT）结果。<br>邵佳, Lau R.Y.M., Tang P.O.C., 张弛. (2019). 声学变化对粤语母语先天性失歌症患者词汇声调知觉的影响. <i>《言语、语言与听力研究期刊》</i> 预印在线发表. https://doi.org/10.1044/2018_JSLHR-H-17-0483