The purpose of this study was to analyze vowel articulation across various speaking tasks in a group of 20 early Parkinson's disease (PD) individuals prior to pharmacotherapy. Vowels were extracted from sustained phonation, sentence repetition, reading passage, and monologue. Acoustic analysis was based upon measures of the first (F1) and second (F2) formant of the vowels /a/, /i/, and /u/, vowel space area (VSA), F2i/F2u and vowel articulation index (VAI). Parkinsonian speakers manifested abnormalities in vowel articulation across F2u, VSA, F2i/F2u, and VAI in all speaking tasks except sustained phonation, compared to 15 age-matched healthy control participants. Findings suggest that sustained phonation is an inappropriate task to investigate vowel articulation in early PD. In contrast, monologue was the most sensitive in differentiating between controls and PD patients, with classification accuracy up to 80%. Measurements of vowel articulation were able to capture even minor abnormalities in speech of PD patients with no perceptible dysarthria. In conclusion, impaired vowel articulation may be considered as a possible early marker of PD. A certain type of speaking task can exert significant influence on vowel articulation. Specifically, complex tasks such as monologue are more likely to elicit articulatory deficits in parkinsonian speech, compared to other speaking tasks.
This research was partly supported by the Czech Science Foundation (GACR 102/12/2230), Czech Ministry of Health (NT 12288-5/2011 and NT14181-3/2013), Czech Ministry of Education (MSM 0021620849), and Charles University in Prague (PRVOUK-P26/LF1/4).
I. INTRODUCTION II. METHODS A. Participants B. Recording C. Speech samples D. Acoustic analyses E. Measurement reliability F. Perceptual assessment of speech performance in PD G. Statistical analysis and classification H. Overall evaluation III. RESULTS A. Group differences (Objective 1) B. Differences across speaking tasks (Objective 2) C. Differences across formant-based measurements (Objective 3) D. Comparison between objective measures and perceptual evaluation (Objective 4) IV. DISCUSSION A. Imprecise vowel articulation as an early marker of PD B. Effect of speaking task C. Acoustic changes in vowel articulation due to PD D. Perceptual and acoustic findings in the speech of early-stage PD individuals E. Limitations of the present study V. CONCLUSION