Coarticulation has been studied extensively in neurologically normal speakers and figures prominently in theories of normal speech production. In so far as coarticulation presumably would have a similar status in a speech production theory of dysarthria, and a basic understanding of coarticulation is essential for elaborating such a theory, research investigating coarticulation in dysarthria appears warranted. The idea that coarticulation influences perceptual impressions of precision further indicates that studies investigating coarticulatory patterns in dysarthria may suggest articulatory characteristics that could be targeted in therapy to improve precision. The current project aims to study anticipatory coarticulation for speakers with Amyotrophic Lateral Sclerosis (ALS), Parkinson disease (PD), and Multiple Sclerosis (MS), as inferred from the acoustic signal. Neurologically healthy speakers will be studied for comparison purposes. The Perceptual-Acoustic Theory (PAT), a theory of normal speech production theory, will be used as a starting point for studying anticipatory coarticulation in PD, ALS, and MS. Specific predictions that the PAT suggests concerning anticipatory coarticulation for neurologic speakers will be tested. One goal of the project is to characterize anticipatory coarticulation for the typical or habitual speech of individuals with ALS, MS, and PD. A second goal is to determine the effects of two treatment techniques - slowed articulatory rate and increased vocal intensity- on anticipatory coarticulation in ALS, MS, and PD. A third goal is to document the relationship between perceptual impressions of precision and coarticulation. Second formant (F2) frequency values, first moment coefficients, and consonant F2 measures will be used to infer coarticulation. Scaled estimates of precision also will be related to select acoustic measures of coarticulation.
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