Acoustic characteristics of vowel sounds in patients with Parkinson disease.

The purpose of this study was to define the acoustic voice and speech characteristics of patients with Parkinson disease (PD). Seven female patients with PD and seven female healthy controls participated in this study. Each subject was instructed to vocalize extended corner vowels (/a/, /e/, /i/, /u/) three times for at least 5 seconds at a comfortable voice loudness and tone. The voice was analyzed using the Praat program. As a result, female patients with PD showed a significant increase in jitter and noise-to-harmonics ratio (NHR). In addition, F1 and F2 among the PD patients demonstrated asymmetric centralization of unrounded vowels (/a/, /e/, /i/) in high/low/front/back positions of the tongue, consequently leading to a significant decrease in vowel space area, compared to healthy controls. This study showed the acoustic characteristics of vowel sounds not only by laryngeal variables such as abnormal jitter and NHR, but also by articulatory variables such as asymmetric centralization and reduced vowel space area in female patients with PD. Therefore, it is important to use these objective and sensitive variables to evaluate the status or severity of hypokinetic dysarthria in patients with PD.