Vowel Variability in Speakers with Parkinson's Disease

This study investigates the production of Brazilian Portuguese (BP) vowels by subjects with hypokinetic dysarthria. Twelve subjects participated in the study, including six who had hypokinetic dysarthria, and six without any neurological disorders or speech disturbance. The data consist of the first two formant frequency values for the samples of the seven vowels in BP. Analyses were performed on the following parameters: (a) F1 and F2 range; (b) variability and (c) vowel dispersion. The results showed that subjects with PD tended to have restrictions on the F1 and F2 axis, a finding which is in accordance with the literature. There was a marked difference in the patterns of variability for vowel production between the two groups, as demonstrated in the analysis of vowel ellipses, as well as in the dispersion index, which tended to be higher in the dysarthric group. It is possible infer that this increase in vocalic variability may play a greater role in the reduction of intelligibility than does a restriction of vowel articulatory space.