Graduation Year

2013

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Communication Sciences and Disorders

Major Professor

Ruth Huntley Bahr

Keywords

dysarthria, intelligibility, motor programming, neuromotor disorders, rate control, speech rhythm

Abstract

Relative timing ratios are a useful measure for determining the temporal regularities of speech. The timing intervals that make up these ratios are thought to be important when creating the motor plan for an utterance (Weismer & Fennell, 1985). In fact, these ratios have been shown to be remarkably stable, even when speakers deliberately increase their rate (Tuller & Kelso, 1984; Weismer & Fennell, 1985). The constancy of these ratios also has been demonstrated in speakers with known speech timing disturbances, like the dysarthrias associated with Parkinson's and Huntington's disease (Goberman & McMillan; Ludlow, Connor, & Bassich, 1987; Weismer & Fennell, 1985), apraxia (Weismer & Fennell, 1985), and stuttering (Prosek, Montgomery, & Walden, 1988). However, a slowed rate of speech has been noted to induce variability in relative timing (Clark, 1995). The current investigation was designed to further investigate the impact of a slow rate on relative timing, as well as the impact of a different type of dysarthria on the production of these ratios.

Eleven participants with MS and ten healthy controls participated. After screening the participants with MS for cognitive abilities and degree of dysathria, they produced four sentences at three different rates of speech: conversational, fast, and slow. Age-matched controls only provided the rate-controlled sentences. Relative timing ratios were extracted and an analysis of variance was conducted for each sentence to note the effects of speech rate, ratio type, and speaker condition on relative timing.

The results revealed that relative timing was not constant in the slow rate for any of the participants. The noted variability in slow speech was attributed to vowel characteristics and sentence length. Finally, people with MS demonstrated larger relative timing ratios than their healthy peers when producing lengthier or motorically complex sentences.

Consistent with previous research (Clark, 1995), these results indicated that relative timing ratios were not constant when rate was slowed. Hence, use of a reduced rate may have triggered the critical change required to alter relative timing. This difference may also correspond to a topological shift in the cortical planning of the utterance. These findings provide support for the use of slowed speech in the treatment of dysarthria and other speech timing disorders. It may be that slowed speech allows the speaker to access a motor plan better suited to his impaired muscular system.

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