Spectral characteristics of /s/ and /∫/: Rate effects in Parkinson’s disease

Abstract

Comtemporary speech production theory proposes that speakers adjust rate to enhance or maximize acoustic-perceptual distinctiveness for listeners. In fact, the suggestion that rate impacts acoustic-perceptual distinctiveness is one rationale for using rate manipulation as a therapy to improve speech intelligibility in dysarthria. The relationship between rate manipulation, acoustic measures of production, and perceptual impressions of speech in dysarthria is poorly understood, however. For example, some studies report rate-induced acoustic changes in speech that are systematically tied to perceptual impressions. Other studies report no effect of rate on speech production characteristics in dysarthria. Further study of the relationship between speech production measures and rate variation in dysarthria therefore appears warranted. The present study examined spectral characteristics of word-initial /s/ and /∫/ produced at a variety of rates by speakers with hypokinetic dysarthria associated with Parkinson’s disease. Healthy speakers were studied for comparison purposes. Fricatives were produced in the words shores, shies, size, and soys embedded in a carrier phrase. A graded rate task was used to elicit an extensive range of rates. Spectral moment coefficients were used to characterize fricatives; phrase duration was used to index rate. The relationship between rate variation and spectral moment coefficients was quantified via regression analysis.