Vowel Articulation in Parkinson's Disease

Abstract

The aim of the study was to analyze vowel articulation in Parkinson's disease (PD) speakers suffering from mild hypokinetic dysarthria as compared with healthy controls in correlation to net speech rate (NSR) and intonation variability (F(0)SD). Furthermore, we intended to reveal possible correlations among vowel articulation, global motor performance, and stage of disease. We examined 68 PD patients (34 male) with mild dysarthria (1 point according to the "speech" item 18 of the Unified Parkinson's Disease Rating Scale/UPDRS-III) and 32 age-matched control persons (16 male) using a reading task with subsequent acoustical analysis. F1 and F2 frequency values of the vowels /a/, /i/, and /u/ were extracted from defined words within the text. Description of vowel articulation was based on measures of triangular vowel space area (tVSA) and Vowel Articulation Index (VAI). PD patients were scored according to UPDRS-III and Hoehn and Yahr stages. VAI values were significantly reduced in male and female PD patients as compared with the accordant control group, whereas tVSA was only reduced in the male PD speakers. NSR was negatively correlated to tVSA and VAI only in female PD speakers. No correlations were seen between vowel articulation and UPDRS-III and stage of disease. VAI seem to be superior to tVSA in the description of impaired vowel articulation in PD. Reduced VAI could be detected in male and female parkinsonian speakers suffering only from mild dysarthria with preserved speech intelligibility and therefore might be applicable to identify subclinical changes of vowel articulation. Moreover, some aspects of altered speech performance in PD seem to feature some gender-specific patterns, which justify further investigation.