Acoustic Effects of Speaker Sex, Speech Sample, and Mandarin Tone on Vowel Production of Poststroke Spastic Dysarthria

Introduction: Vowel production in dysarthria tends to be centralized, which is affected by many factors. This study examined the acoustic effects of speaker sex, tones, and speech samples (including sustained vowels, syllables, and sentences) and their interactions on vowel production in Mandarin speakers with poststroke spastic dysarthria. Methods: Twenty-eight patients with poststroke spastic dysarthria (18 males, 10 females) and 21 healthy speakers (11 males, 10 females) with no significant difference in sex and age with dysarthria were recruited. They were asked to read sustained vowels /a, i, u/, 12 syllables, and 12 sentences containing three vowels in four tones (bā, bá, bǎ, bà, bī, bí, bǐ, bì, pū, pú, pǔ, pù). Multiple spectral and temporal acoustic metrics were analyzed. Results: Results showed that regardless of the speech samples or tones, vowel production was more centralized in dysarthria than healthy controls, manifested as the decrease in F1 range, F2 range, vowel space area (VSA), and vowel articulation index (VAI). A similar performance was observed for male speakers compared to females, and vowel duration in males was shorter than females. F1 range, F2 range, VSA, VAI, and vowel duration were significantly different across speech samples and tones, decreasing in the order of vowel-syllable-sentence and T3-T2-T1-T4, respectively. Interactions of group, speaker sex, speech sample, and tone were more sensitive in VAI and vowel duration. Conclusion: VAI and vowel duration were recommended as the prior metrics to the assessment of vowel production. Specific influencing factors (speaker sex, speech sample, and tone) of vowel production need to be considered by speech and language pathologists in the assessment and rehabilitation.