Anticipatory coarticulation in multiple sclerosis and Parkinson's disease.

Research investigating coarticulatory patterns in dysarthria has the potential to provide insight regarding deficits in the organizational coherence of phonetic events that may underlie deviant perceptual characteristics. The current study investigated anticipatory coarticulation for 17 speakers with multiple sclerosis (MS), 12 speakers with Parkinson's disease (PD), and 29 healthy control speakers. V1-C-V2 sequences were used to investigate intersyllabic vowel to vowel effects (V2 to V1 effects), intersyllabic consonant to vowel effects (C to V1 effects), and intrasyllabic vowel to consonant effects (V2 to C effects). Second formant frequencies and first moment coefficients were used to infer coarticulation. In general, patterns of intersyllabic and intrasyllabic coarticulation were similar for speakers with MS, speakers with PD, and healthy control speakers. It therefore appears unlikely that coarticulatory patterns for speakers diagnosed with MS or PD strongly contribute to deviant perceptual characteristics, at least for the current group of speakers, most of whom were mildly to moderately impaired. Anticipatory vowel effects in /k/+vowel sequences, however, tended to be reduced for speakers with MS and speakers with PD when data for these 2 speaker groups were pooled and compared to control speakers. These results were not attributable to group differences in speech rate or articulatory scaling, defined as the extent of articulatory movements, and further suggest that coarticulatory deficits are not unique to particular neurological diagnoses or dysarthrias. Potential explanations for the /k/+vowel results include difficulties with anterior-posterior tongue positioning and the competing influences of minimizing articulatory effort and maintaining sufficient perceptual contrast. Despite this subtle difference in coarticulation between disordered speakers and healthy control speakers, the overall results suggest that anticipatory coarticulation for speakers with MS and speakers with PD is preserved.