Contribution of vowel distinctiveness to intelligibility and vowel identification accuracy of dysarthric speech.

Abstract

Distorted vowel production is a hallmark characteristic of dysarthric speech and often is characterized by spectral and temporal degradation, flattening of spectral change formants, and vowel space distortions that may differentially affect high versus low or front versus back contrasts. Because acoustic information critical to accurate speech perception is contained in vowels, it is important to ask how such degradations influence the resulting percept. To date, attempts to characterize this relationship have met with mixed results. In the present investigation, a variety vowel space metrics were derived from vowels produced by 48 speakers with dysarthria to assess their ability to predict perceptual outcome measures (e.g., intelligibility and vowel identification accuracy). Novel metrics capturing distinctiveness of spectral neighbors (i.e., dispersion of vowels) were included in this analysis, as recent evidence suggests that vowel distinctiveness, not vowel space area, better predicts vowel intelligibility [Neel, J. Speech Lang. Hear. Res. 51, 574–585 (2008)]. Results of several stepwise multiple regressions support these findings as measures of vowel dispersion both novel and established were included in models that significantly predicted both intelligibility and vowel accuracy. Results of the present analysis provide compelling support of inclusion of such dispersion metrics in the study of dysarthric vowel perception.