Categorical perception under backward masking (Shao et al., 2022)

Purpose: Evidence increasingly indicates that people with developmental stuttering have auditory perception deficits. Our previous research has indicated similar but slower performance in categorical perception of the speech sounds under the quiet condition in children who stutter and adults who stutter (AWS) compared with their typically fluent counterparts. We hypothesized that the quiet condition may not be sufficiently sensitive to reveal subtle perceptual deficiencies in people who stutter. This study examined this hypothesis by testing the categorical perception of speech and nonspeech sounds under backward masking condition (i.e., a noise was presented immediately after the target stimuli). Method: Fifteen Cantonese-speaking AWS and 15 adults who do not stutter (AWNS) were tested on the categorical perception of four stimulus continua, namely, consonant varying in voice onset time (VOT), vowel, lexical tone, and nonspeech, under the backward masking condition using identification and discrimination tasks. Results: AWS demonstrated a broader boundary width than AWNS in the identification task. AWS also exhibited a worse performance than AWNS in the discrimination of between-category stimuli but a comparable performance in the discrimination of within-category stimuli, indicating reduced sensitivity to sounds that belonged to different phonemic categories among AWS. Moreover, AWS showed similar patterns of impaired categorical perception across the four stimulus types, although the boundary location on the VOT continuum occurred at an earlier point in AWS than in AWNS. Conclusions: The findings provide robust evidence that AWS exhibit impaired categorical perception of speech and nonspeech sounds under the backward masking condition. Temporal processing (i.e., VOT manipulation), frequency/spectral/formant processing (i.e., lexical tone or vowel manipulations), and nonlinguistic pitch processing were all found to be impaired in AWS. Altogether, the findings support the hypothesis that AWS might be less efficient in accessing the phonemic representations when exposed to a demanding listening condition. Supplemental Material S1. t test results comparing the performance of adults who stutter in the first half and second half of the discrimination experiments. Shao, J., Bakhtiar, M., & Zhang, C. (2022). Impaired categorical perception of speech sounds under the backward masking condition in adults who stutter. Journal of Speech, Language, and Hearing Research. Advance online publication. https://doi.org/10.1044/2022_JSLHR-21-00276研究目的：越来越多的证据表明，发育性口吃（developmental stuttering）患者存在听觉感知缺陷（auditory perception deficits）。本团队前期研究发现，与言语流畅对照组相比，口吃儿童与成人口吃者（Adults Who Stutter, AWS）在安静条件（quiet condition）下的言语声音范畴感知（categorical perception）表现相似，但反应时更慢。我们提出假设：安静条件可能不足以敏感地揭示口吃患者细微的感知缺陷。本研究通过在反向遮蔽条件（backward masking condition，即目标刺激后即刻呈现噪声）下测试言语与非言语（nonspeech）声音的范畴感知，对该假设进行了验证。 研究方法：本研究招募15名以粤语为母语的成人口吃者，以及15名言语流畅成人（Adults Who Do Not Stutter, AWNS），采用辨认与辨别任务，在反向遮蔽条件下对四类刺激连续体开展范畴感知测试，分别为：嗓音起始时间（Voice Onset Time, VOT）变化的辅音、元音、词汇声调，以及非言语声音刺激。 研究结果：在辨认任务中，成人口吃者的范畴边界宽度显著大于言语流畅成人。在跨类别刺激辨别任务中，成人口吃者的表现显著差于言语流畅成人；但在类别内刺激辨别任务中，两组表现无显著差异，表明成人口吃者对不同音位范畴（phonemic categories）声音的感知敏感性降低。此外，尽管成人口吃者在VOT连续体上的范畴边界位置早于言语流畅成人，但四类刺激类型下的范畴感知受损模式相似。 研究结论：本研究结果提供了可靠证据，表明成人口吃者在反向遮蔽条件下的言语与非言语声音范畴感知存在受损。研究发现，成人口吃者的时序加工（temporal processing，即VOT操纵）、频率/频谱/共振峰加工（frequency/spectral/formant processing，即词汇声调或元音操纵），以及非言语音高加工（pitch processing）均存在受损。综合来看，本研究结果支持以下假设：当处于高要求聆听条件时，成人口吃者获取音位表征（phonemic representations）的效率可能更低。 补充材料S1：对比成人口吃者在辨别实验前半段与后半段表现的t检验结果。 引用：邵杰、巴赫蒂亚尔·穆罕默德、张驰（2022）。成人口吃者在反向遮蔽条件下的言语声音范畴感知受损。《言语、语言与听力研究期刊》，预在线发表。https://doi.org/10.1044/2022_JSLHR-21-00276