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. 2017 Jan 1;60(1):38-50.
doi: 10.1044/2016_JSLHR-S-15-0291.

The Impact of Contrastive Stress on Vowel Acoustics and Intelligibility in Dysarthria

Kathryn P Connaghan  1 , Rupal Patel  1
Affiliations

The Impact of Contrastive Stress on Vowel Acoustics and Intelligibility in Dysarthria

Kathryn P Connaghan et al. J Speech Lang Hear Res. .

Abstract

Purpose: To compare vowel acoustics and intelligibility in words produced with and without contrastive stress by speakers with spastic (mixed-spastic) dysarthria secondary to cerebral palsy (DYSCP) and healthy controls (HCs).

Method: Fifteen participants (9 men, 6 women; age M = 42 years) with DYSCP and 15 HCs (9 men, 6 women; age M = 36 years) produced sentences containing target words with and without contrastive stress. Forty-five healthy listeners (age M = 25 years) completed a vowel identification task of DYSCP productions. Vowel acoustics were compared across stress conditions and groups using 1st (F1) and 2nd (F2) formant measures. Perceptual intelligibility was compared across stress conditions and dysarthria severity.

Results: F1 and F2 significantly increased in stressed words for both groups, although the degree of change differed. Mean Euclidian distance between vowels also increased with stress. The relative probability of vowels falling within the target F1 × F2 space was greater for HCs but did not differ with stress. Stress production resulted in greater listener vowel identification accuracy for speakers with mild dysarthria.

Conclusions: Contrastive stress affected vowel formants for both groups. Perceptual results suggest that some speakers with dysarthria may benefit from a contrastive stress strategy to improve vowel intelligibility.

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Figures

Figure 1.
Figure 1.
The first by second formant (F1 × F2) plots of /æ/ (grey diamond), /i/ (black triangle), and /ɪ/ (white square) productions in unstressed (left panels) and stressed (right panels) words produced by one participant with dysarthria (DYSCP; top panels) and the healthy control (HC) match (lower panels). The relative probability density function (PDF) is provided for each vowel. The solid lines reflect the Euclidian distance between vowel centroids.
Figure 2.
Figure 2.
Means (with standard deviation bars) of the first formant (F1; left) and second formant (F2; right) measures for speakers with mild (top panels), moderate (middle panel), and severe (bottom panel) dysarthria classifications, across vowels. The unstressed productions are in grey, and stressed productions are in black.
Figure 3.
Figure 3.
The rationalized arcsine unit (RAUs) scores reflecting accurate identification of target vowels (/æ/, /i/, /ɪ/) in unstressed (light grey) and stressed (black) words. Panels depict productions by speakers with mild (top), moderate (middle) and severe (bottom) dysarthria.
See this image and copyright information in PMC

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