Author: Wong, Chun Ho
Title: Pitch variation in Cantonese-speaking children and adults with apraxia of speech
Advisors: Wong, Min Ney (CBS)
Degree: Ph.D.
Year: 2024
Subject: Apraxia -- Diagnosis
Cantonese dialects
Cantonese dialects -- Tone
Hong Kong Polytechnic University -- Dissertations
Department: Department of Chinese and Bilingual Studies
Pages: 383 pages : color illustrations
Language: English
Abstract: Apraxia of speech is a motor-based speech sound disorder. In adults, it is known as acquired apraxia of speech (AOS), while in children, it is referred to as childhood apraxia of speech (CAS). Both AOS and CAS are characterized by impaired prosody, including lexical stress errors, particularly in English speakers. However, Cantonese speakers with AOS or CAS may not exhibit lexical stress errors, but rather show lexical tone errors due to their degraded pitch-variation skills. Research on the Cantonese-speaking population has been limited but it has been suggested that Cantonese speakers with AOS or CAS may struggle with pitch performance.
This thesis aims to establish diagnostic criteria for Cantonese-speaking adults and children with apraxia of speech, and to investigate pitch performance in these individuals. Additionally, it examines the impact of linguistic variables such as syllable structure, lexical status, and syllable position on pitch-variation skills, using the Tone Sequencing Task (TST). This thesis consists of five studies that align with the research objectives.
In Chapter 2, a scoping review of the literature on standards for assessment and diagnosis of Chinese (Cantonese and Mandarin) speakers with AOS or CAS was conducted. It followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA – ScR) guidelines. Articles with a focus on AOS or CAS in Chinese speakers were systematically searched in seven English and six Chinese databases. Three reviewers performed independent screening, data extraction, and quality assessment after obtaining 100% agreement on the pre-screening exercise. A qualitative analysis was conducted to rate the quality of diagnoses, ranging from high (level I) to low (level III), with level IV assigned to studies for which the appropriate rating was unclear due to insufficient evidence. A total of twenty-eight AOS articles and five CAS articles were identified. Although a variety of assessment and diagnostic methods were identified, no study of Chinese speakers with AOS or CAS received a rating of Level I. This means that there is no reliable and valid diagnostic test or method for apraxia of speech in Chinese. The current highest standard for diagnosing AOS in Chinese speakers is expert perceptual judgment without clear criteria, while CAS diagnosis is made upon expert perceptual judgment with a set of pre-defined clinical features, supported by quantitative data.
In Chapter 3, a survey study was conducted to examine the clinical practice of AOS in Hong Kong Cantonese speakers. A Google Form online questionnaire was designed. It included 12 questions covering (1) demographic information, (2) experience working with speakers with AOS, (3) confidence in making AOS diagnoses in Cantonese speakers, (4) assessment tasks or methods used for assessing AOS in Cantonese speakers, (5) clinical features used for diagnostic purposes, and (6) assessment tasks used to determine the presence of clinical features for diagnostic purposes. Twenty-seven speech therapists (STs) completed the online questionnaire. The results related to clinical practice of AOS in Cantonese speakers showed that all respondents (100%) made AOS diagnoses based on observed clinical features, while none used only standardised tests or quantitative measures. Six clinical features were commonly used by most respondents: articulatory groping (100%), inconsistent articulatory errors (100%), length effects (85.2%), difficulty initiating speech (81.5%), automaticity effects (81.5%), and sound distortions (77.8%). More than half of the respondents collected connected speech samples (64%) and conducted diadochokinesis (64%) and repetition tasks (64%). In addition to observing clinical features, some STs used the Apraxia of Speech Rating Scale (ASRS) to assist in the diagnostic process.
In Chapter 4, another survey study was conducted to examine the clinical practice of CAS in Hong Kong Cantonese speakers via a Google Form online questionnaire, which consisted of a total of 48 questions regarding knowledge of and experience with CAS in Cantonese speakers, including assessment, diagnosis, and treatment. A total of 77 responses were received from Hong Kong STs. About half (53.2%) of the respondents had worked with children with CAS. No standardized assessment or objective/quantitative measures were used clinically. Instead, seven assessment tasks, including imitation of polysyllabic words and speech and language samples, were commonly used. Perceptual judgment of clinical features is still the most popular approach for diagnosis, with a variety of lists in use.
In Chapter 5, a direct investigation of pitch-variation skills and the effects of three linguistic variables, namely syllable structure, lexical status, and syllable position on pitch variation in Cantonese speakers with AOS post-stroke is reported. Six Cantonese adults with AOS post-stroke (AOS group), six adults without AOS post-stroke (nAOS group), and six healthy controls (HC group) performed the TST, which was adapted from oral diadochokinetic tasks, with three different tone-syllables. The AOS diagnosis in the participants was confirmed by two experienced STs using the Apraxia of Speech Rating Scale, which was the most valid and reliable method identified in the survey study (Chapter 3). Values of f0 across 10-time points were analysed using growth curve analysis, in addition to tone accuracy and acoustic repetition durations. The results showed that the AOS group produced significantly lower tone accuracy and different f0 changes on the three Cantonese tone-syllables compared with the control groups. The AOS group also showed significantly longer repetition durations than the HC group. The AOS group had more difficulty with the tone-syllables with CV structure, while a priming effect was observed on the T2 syllables with lexical meanings. Additionally, a unique lowering of f0 in the final syllables of trisyllabic items was observed only in the AOS group.
In Chapter 6, a direct investigation of pitch-variation skills and the effects of the three linguistic variables on pitch variation in Cantonese speakers with CAS was reported. Six Cantonese-speaking children with CAS, six children with speech and language disorders, 22 children with speech sound disorder only, and 63 children with typical speech-language development performed the TST. The CAS diagnosis in the participants was confirmed using the diagnostic criteria reported by Wong et al. (2021), which was identified as being the highest quality level in the scoping review (Chapter 2). Values of f0 across 10-time points were analysed using growth curve analysis. The results showed that children with CAS not only produced reduced tone contrast compared with three control groups, but they were also unable to produce items with differing linguistic characteristics as distinctly as the control groups.
Overall, this thesis represents the first comprehensive investigation of apraxia of speech in Cantonese-speaking individuals, expanding upon existing literature that primarily focuses on English and other stress-timed languages. Based on the results of the scoping review and the two survey studies, this thesis provides clinical guidelines for diagnosing AOS and CAS in Cantonese speakers.
Regarding pitch-variation skills, the studies reported in Chapters 5 and 6 showed that participants with apraxia of speech have degraded pitch-variation skills compared to the control groups. Syllable structure, lexical status, and syllable position affect pitch-variation skills in speakers with AOS or CAS in the sequencing context. Investigation of tone production skills is suggested as a possible method for differential diagnosis of AOS or CAS in Cantonese speakers. In addition, the TST used in these studies can be further developed as a clinical tool to assist in the diagnosis of AOS or CAS in Cantonese speakers.
Based on the findings of this thesis, future investigations are recommended, including further investigation of tone production skills in Cantonese and other tonal language speakers with AOS or CAS, pitch-variation skills in English or other stress-timed language speakers with AOS or CAS, cross-linguistic investigation, and investigation of AOS or CAS in bilingual or multilingual speakers.
By contributing knowledge on assessment and diagnostic standards, clinical practices, and pitch-variation skills specific to Cantonese speakers, the findings of this thesis have enriched the understanding of apraxia of speech.
Rights: All rights reserved
Access: open access

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