Acoustic properties of vowel production in Mandarin-speaking patients with post-stroke spastic dysarthria

This study investigated the acoustic features of vowel production in Mandarin-speaking patients with post-stroke spastic dysarthria. The subjects included 31 native Mandarin-speaking patients with post-stroke spastic dysarthria (age: 33–73 years old) and 40 normal adults in a similar age range (age: 22–68 years old). Each subject were recorded producing a list of 28 Mandarin monosyllables that composed of six monophthong vowels (i.e., /a, o, ɣ, i, u, y/) embedded in the /CV/ context. The patients’ speech samples were evaluated by two native Mandarin speakers. The evaluation scores were then used to classify each patient into one of the two categories: mild or moderate-to-severe severity. Midpoint F1 and F2 of each vowel token were extracted and normalized. Results showed no significant differences between the patients and normal speakers on vowel duration. However, the vowel categories in the patients were more scattered and greatly overlapped than in the normal speakers. The magnitude of the vowel dispersion and overlap increased as a function of the severity of the disorder. The deviations of the vowel acoustic features in the patients from the normal speakers may provide guidance for clinical rehabilitation to improve the speech intelligibility of this type of patients.