Vowel Contrast and Speech Intelligibility in Dysarthria

Background/Aims: This study examined the spectral characteristics of American English vowels in dysarthria associated with cerebral palsy (CP), and investigated the relationship between a speaker's overall speech intelligibility and vowel contrast. Methods: The data were collected from 12 American English native speakers (9 speakers with a diagnosis of CP and 3 controls). Primary measures were F-1 and F-2 frequencies of 3 corner vowels /i, a, u/and 3 noncorner vowels /I, epsilon, upsilon/. Six acoustic variables were derived from the formant measures, and were regressed against intelligibility: corner vowel space, noncorner vowel space, mean distance between vowels, F-1 and F-2 variability, and overlap degree among vowels. Results: First, the effect of vowel was significant for both F-1 and F-2 measures for all speakers, but post hoc analysis revealed a reduced distinction at lower intelligibility. Second, regression functions relating intelligibility and acoustic variables were significant for overlap degree among vowels, F-1 variability, corner vowel space and mean distance between vowels. Overlap degree among vowels accounted for the greatest amount of variance in intelligibility scores. Conclusion: A speaker's overall intelligibility in dysarthric speech is better represented by the overlap degree among vowels than by the vowel space. Copyright (C) 2010 S. Karger AG, Basel