The Impact of Clear Speech on the Perceptual and Acoustic Properties of Fricative-Vowel Sequences in Speakers With Dysarthria.

Purpose Studies have reported that clear speech has the potential to influence suprasegmental and segmental aspects of speech, in both healthy and dysarthric speakers. While the impact of clear speech has been studied on the articulation of individual segments, few studies have investigated its effects on coarticulation with multisegment sequences such as fricative-vowel. Objectives The goals of this study are to investigate, in healthy and dysarthric speech, the impact of clear speech on (a) the perception of anticipatory vowel coarticulation in fricatives and (b) the acoustic characteristics of this effect. Method Ten speakers with dysarthria secondary to idiopathic Parkinson's disease were recruited as well as 10 age- and sex-matched healthy speakers. A sentence reading task was performed in natural and clear speaking conditions. The sentences contained words with the initial fricatives /s/ and /ʃ/ preceded by /ə/ and followed by the vowels /i/, /y/, /u/, or /a/. For the perceptual measurements, five listeners were recruited and were asked to predict the upcoming word by listening only to the isolated fricative. Acoustic analyses consisted of spectral moment analysis (M1-M4) on averaged time series. Results Perceptual findings report that identification rates were improved with clear speech for the speakers with dysarthria, but only for the fricative-/i/ sequences. Error pattern analysis indicates that this improvement is associated with an increase in the roundness parameter (lip spreading) identification. Acoustic results are unclear for M1 and M3 but suggest that M2 and M4 differentiation between the rounded versus unrounded vowel contexts is increased with clear speech for the speakers with dysarthria. Discussion Taken together, these findings suggest that clear speech may improve lip coordination in dysarthric speakers with Parkinson's disease. However, the impact of clear speech on the acoustic measures of fricative spectral moments is somewhat limited. This suggests that these metrics, when taken individually, do not capture the entire complexity of fricative-vowel coarticulation.