Impaired processing speed in categorical perception: Speech perception of children who stutter

There have been controversial debates across multiple disciplines regarding the underlying mechanism of developmental stuttering. Stuttering is often related to issues in the speech production system; however, the presence and extent of a speech perception deficit is less clear. This study aimed to investigate the speech perception of children who stutter (CWS) using the categorical perception paradigm to examine their ability to categorize different acoustic variations of speech sounds into the same or different phonemic categories. In this study, 15 CWS and 16 children who do not stutter (CWNS) completed identification and discrimination tasks involving acoustic variations of Cantonese speech sounds in three stimulus contexts: consonants (voice onset times, VOTs), lexical tones, and vowels. The results showed similar categorical perception performance in boundary position and width in the identification task and similar d' scores in the discrimination task between the CWS and CWNS groups. However, the reaction times (RTs) were slower in the CWS group compared with the CWNS group in both tasks. Moreover, the CWS group had slower RTs in identifying stimuli located across categorical boundaries compared with stimuli located away from categorical boundaries. Overall, the data implied that the phoneme representation evaluated in speech perception might be intact in CWS as revealed by similar patterns in categorical perception as those in CWNS. However, the CWS group had slower processing speeds during categorical perception, which may indicate an insufficiency in accessing the phonemic representations in a timely manner, especially when the acoustic stimuli were ambiguous.

发育性口吃（developmental stuttering）的潜在作用机制在多学科领域中始终存在诸多争议性探讨。口吃通常与言语产生系统的功能异常相关，但言语感知缺陷是否存在及其严重程度尚不明朗。本研究采用范畴感知范式（categorical perception paradigm），探究发育性口吃儿童（children who stutter, CWS）的言语感知能力，旨在考察其将不同声学变异的语音归类为相同或不同音位范畴的能力。本研究共纳入15名CWS与16名非口吃儿童（children who do not stutter, CWNS），让其完成三项涉及粤语语音声学变异的辨识与辨别任务，任务涵盖三类刺激情境：辅音（嗓音起始时间，voice onset time, VOT）、词汇声调与元音。结果显示，口吃组与非口吃组在辨识任务中的范畴感知边界位置、边界宽度表现，以及辨别任务中的d'得分均无显著差异。不过，口吃组在两项任务中的反应时（reaction time, RTs）均慢于非口吃组。此外，口吃组在辨识处于范畴边界处的刺激时，其反应时相较于辨识范畴边界外的刺激更为缓慢。总体而言，本研究数据表明，发育性口吃儿童的言语感知所评估的音位表征可能完好无损，这一点从其与非口吃儿童相似的范畴感知模式中得以印证。但口吃组在范畴感知过程中的加工速度更慢，这或许提示其无法及时调取音位表征，尤其当声学刺激存在歧义时。