Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Doctor of Philosophy

Program

Health and Rehabilitation Sciences

Supervisor

Adams, Scott G.

Abstract

Asking a person to speak slowly is a common technique in speech therapy for people with Parkinson’s disease (PD). Slowed speaking rates are thought to bring about changes in speech production that make it easier for people with speech impairments associated with PD to be understood, but this is not always the case. Furthermore, research suggests that using faster speech does not necessarily lead to decreases in speech intelligibility for some people with PD. Most studies of rate modification in PD have only included one or two rate adjustments to investigate the relationship between speech rate, intelligibility, and acoustic aspects of speech production. The present study adds to this literature and expands it by eliciting a broader range of speech rates than has previously been studied in order to provide a comprehensive description of changes along such a continuum.

Two groups of people with PD and documented speech changes participated: 22 receiving standard pharmaceutical intervention, and 12 who additionally had undergone deep brain stimulation surgery (DBS), a common surgical treatment for PD. DBS is often associated with further speech impairment, but it is unknown to what extent these individuals may benefit from speech rate adjustments. Younger and older healthy control groups were also included. All participants were asked to modify their speech rate along a seven-step continuum from very slow to very fast while reading words, sentences, and responding to prompts. Naïve listeners later heard these speech samples and were asked to either transcribe or rate what they heard.

Results indicated different patterns of speech changes across groups, rates, and tasks. Sentence reading and conversational speech were rated as being more intelligible at slow rates, and less intelligible at fast rates. All modified rates were found to negatively impact speech sound identification during a novel carrier phrase task. Slower speech was overall associated with greater acoustic contrast and variability, lower intensity, and higher voice quality. Differences in acoustic speech adjustments across the groups and speech rates emerged, however, in particular for the DBS group. Findings pointed to a complex relationship between speech rate modifications, acoustic distinctiveness, and intelligibility.

Summary for Lay Audience

Parkinson’s disease (PD) is a neurodegenerative disorder that often is associated with changes to a person’s speech. This makes it difficult for some people with PD to be understood when using speech to communicate. Speech-language pathologists who treat people with PD will often work with them to try and slow down their rate of speech. Slow speech is a common form of intervention that has been shown to improve spoken communication in people with PD, making it easier for them to be understood. However, not all people with PD benefit from using slow speech. Furthermore, speaking more quickly is not necessarily associated with speech that is more difficult to understand. The goal of this thesis was to explore speech changes that occurred in people with and without PD across many different speech rates from very slow to very fast in order to better understand these patterns.

Two groups of people with PD participated: 22 receiving standard antiparkinsonian medication, and 12 who additionally had undergone deep brain stimulation surgery (DBS), a common surgical treatment for PD. DBS is often associated with greater and more variable speech impairment. Younger and older healthy control groups were also included. All participants completed various speech tasks (i.e., sentence reading, nonsense word reading, and conversation) at seven different rates from very slow to very fast. Naïve listeners later heard these speech samples and were asked to either transcribe or rate what they heard.

Results indicated different patterns of speech changes across groups, rates, and tasks. Sentence reading and conversational speech were rated as being more understandable at slow rates, and less understandable at fast rates. Nonsense words were more difficult to understand at both slower and faster rates of speech compared to normal rates. Slower speech overall was produced more quietly, with greater hoarseness, and with more speech sound contrast compared to fast speech, though these patterns differed across groups. The findings suggest complex relationships between speech rate, speech characteristics, and understandability across the groups.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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