Acoustic identification of sentence accent in speakers with dysarthria : cross-population validation and severity related patterns

Dysprosody is a hallmark of dysarthria, which can affect the intelligibility and naturalness of speech. This includes sentence accent, which helps to draw listeners’ attention to important information in the message. Although some studies have investigated this feature, we currently lack properly validated automated procedures that can distinguish between subtle performance differences observed across speakers with dysarthria. This study aims for cross-population validation of a set of acoustic features that have previously been shown to correlate with sentence accent. In addition, the impact of dysarthria severity levels on sentence accent production is investigated. Two groups of adults were analysed (Dutch and English speakers). Fifty-eight participants with dysarthria and 30 healthy control participants (HCP) produced sentences with varying accent positions. All speech samples were evaluated perceptually and analysed acoustically with an algorithm that extracts ten meaningful prosodic features and allows a classification between accented and unaccented syllables based on a linear combination of these parameters. The data were statistically analysed using discriminant analysis. Within the Dutch and English dysarthric population, the algorithm correctly identified 82.8 and 91.9% of the accented target syllables, respectively, indicating that the capacity to discriminate between accented and unaccented syllables in a sentence is consistent with perceptual impressions. Moreover, different strategies for accent production across dysarthria severity levels could be demonstrated, which is an important step toward a better understanding of the nature of the deficit and the automatic classification of dysarthria severity using prosodic features

Acoustic features to characterize sentence accent production in dysarthric speech

This study investigated acoustic features and prosodic strategies used by both healthy speakers and speakers with dysarthria, to produce a perceptually-detectable sentence accent. Accordingly, 80 adult speakers (50 with a speech impairment) were asked to produce 3 pairs of sentences with different accent positions. All speech samples were perceptually judged by three experts, and were acoustically analyzed. The fundamental frequency, intensity, and duration were not only analyzed within the syllable, but also in contrast with the previous syllable, and in contrast with the entire sentence. These features were used as input for a linear discriminant analysis. This newly-developed acoustic approach reveals that healthy speakers mainly rely on the following features to produce a perceptually-detectable accent: a change in frequency within the target syllable, with a simultaneous increase of intensity and contrast in the frequency between the target syllable and the previous syllable. Speakers with dysarthria mainly use the contrast in frequency and intensity between the target syllable and the previous syllable, rather than the contrasting with the rest of the sentence. They also use durational parameters as an element in prosodic accent production. Although both groups use some common features, they differ significantly (p < 0.01) in the way they realize accent production. The results of this study show that sentence accent production in dysarthric speech can be adequately described by a set of acoustic features. Until now, such description in the literature was primarily based on perceptual evaluations. The current approach may assist in objective assessments and more appropriate therapy methods