Vowel Production Associated with Cantonese Speakers of Parkinson's Disease

Patients of Parkinson's disease (PD) often show symptoms of hypokinetic dysarthria and vowel distortion. However, the exact change in vowel production and its relationship with disease progression is still not clear. The present study examined the vowel characteristics associated with PD individuals of different severities.

The first two formants (F1 and F2) associated with the vowels (/i, u, a/) produced by 18 (11 mild and 7 moderate) PD patients and 30 healthy controls were obtained. Based on these, six derived formant metrics were calculated and used to depict distribution of vowels.

Significant differences were found in all derived formant metrics between healthy and PD speakers, and there was a trend that the differences increased with severity of PD. Speakers of mild PD also exhibited a significantly smaller F1RR and tVSA than healthy speakers, and a greater F1RR than speakers of moderate PD.

The present findings suggest a reduced working vowel space with an apparent vowel centralization in PD speakers when compared with healthy controls. This was accompanied by restricted jaw and tongue movements. Such findings confirmed the articulatory undershooting in PD speakers, possibly due to hypokinetic dysarthria and other PD symptoms such as muscle rigidity and bradykinesia. It is also suggested that tVSA and F1RR are sensitive formant metrics for subtle changes in vowel articulation in PD.