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

Abstract

This study investigated the acoustic features of vowel production in Mandarin-speaking patients with post-stroke dysarthria (PSD). The subjects included 31 native Mandarin-speaking patients with PSD (age: 25-83 years old) and 38 neurologically normal adults in a similar age range (age: 21-76 years old). Each subject was recorded producing a list of Mandarin monosyllables that included six monophthong vowels (i.e., /a, i, u, ɤ, y, o/) embedded in the /CV/ context. The patients' speech samples were evaluated by two native Mandarin speakers. The evaluation scores were then used to classify all patients into two levels of severity: mild or moderate-to-severe. Formants (F1 and F2) were extracted from each vowel token. Results showed that all vowel categories in the patients with PSD were produced with more variability than in the healthy speakers. Great overlaps between vowel categories and reduced vowel space were observed in the patients. The magnitude of the vowel dispersion and overlap between vowel categories increased as a function of the severity of the disorder. The deviations of the vowel acoustic features in the patients in comparison to the healthy speakers may provide guidance for clinical rehabilitation to improve the speech intelligibility of patients with PSD.

Figure 1

Group mean vowel durations produced by the HA, PSD-1, and PSD-2 groups for each of the six Mandarin vowels. The error bar represents 1 standard deviation (SD).

Figure 2

Scatter plots based on rescaled normalized midpoint F1 and F2 values of six Mandarin vowels. Data from the HA, PSD-1, and PSD-2 groups are shown on the left, middle, and right panels, respectively. Different colors and symbols represent different vowel categories. Each ellipse encompasses ~95% of data points for one vowel category.

Figure 3

Vowel ellipse areas for individual Mandarin vowel categories in the HA, PSD-1, and PSD-2 groups.

Figure 4

Mandarin vowel space of the HA (left), PSD-1 (middle), and PSD-2 (right) groups. Each data point represents the rescaled normalized F1 and F2 values of /a, i, u/. The triangle was formed based on the group mean data of the rescaled normalized F1 and F2 values of /a, i, u/.

Figure 5

Boxplots of vowel space areas of the HA, PSD-1, and PSD-2 groups. Each data point represents vowel space from one participant. Each box shows horizontal lines at the lower quartile, median, and upper quartile values. The whiskers show the range of the data and the data points out of the whiskers are outliers. Some jitters along the abscissa were applied to the data for better visual representation.

Figure 6

Boxplots showing the F1 deviation (top panel) and F2 deviation (bottom panel) of the HA, PSD-1, and PSD-2 groups. Each box shows horizontal lines at the lower quartile, median, and upper quartile values. The whiskers show the range of the data and the data points out of the whiskers are outliers.