Temporal and Spectral Aspects of Coarticulation in Ataxic Dysarthria

An Acoustic Analysis

ingo.hertrich{at}uni-tuebingen.de

In order to analyze the impact of cerebellar disorders on temporal and spectral aspects of coarticulation, 9 individuals with cerebellar dysfunction and 9 controls were asked to produce test sentences comprising a target vowel (V=[A], [i], or [u]) within a schwa-t-V-t-schwa environment. The control speakers were investigated both at their habitual speech tempo and under a slow speaking condition. The squared distances between averaged FFT spectra served as a quantitative estimate of target-induced coarticulation, a method that can be applied to consonants as well as vowels, and which avoids the shortcomings of formant analysis. In order to test the significance of coarticulation effects at the level of individual speakers and to obtain F values as a further measure of the strength of coarticulation, multivariate tests of target effects were performed, with the first 6 principal components derived from the spectra of each speaker. First, inconsistent patterns of anticipatory vowel-to-vowel (VV) interactions emerged across individuals, and neither significant group differences nor any effects of speech rate could be detected. The underlying control mechanisms thus seem to be segment-linked subject-specific specifications of the pretarget vowel, uncompromised by cerebellar dysfunction. Second, all participants exhibited highly significant anticipatory [t^h]-to-vowel (CV) coarticulation. This effect was slightly smaller in the cerebellar group than in the control group, which can be at least partially explained by reduced spectral distances among the 3 target vowels. Speech rate did not influence the CV effects of the control group. As concerns temporal aspects of coarticulation, no significant group differences emerged in terms of length adjustments of the pretarget consonant to the intrinsic duration of the target vowel. Third, ataxic speakers showed a tendency toward enlarged perseverative vowel-to-[t^h] (VC) and VV effects if their slow speech rate was taken into account. Retentive coarticulation turned out to be similar in slow ataxic speakers and in fast-speaking controls. However, significant attenuation of these effects emerged in the latter group under the condition of decreased speech tempo. In summary, these results corroborate the suggestion of different mechanisms of gestural overlap in the temporal domain: Whereas perseverative coarticulation, presumably, reflects biomechanical or motor constraints, anticipation seems to represent higher level phonetic processing.

KEY WORDS: ataxic dysarthria, coarticulation, timing, speech rate, acoustic analysis

Submitted on April 8, 1998
Accepted on November 4, 1998

CiteULike    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				Y. Yunusova, G. Weismer, J. R. Westbury, and M. J. Lindstrom Articulatory Movements During Vowels in Speakers With Dysarthria and Healthy Controls J Speech Lang Hear Res, June 1, 2008; 51(3): 596 - 611. [Abstract] [Full Text] [PDF]

				K. Tjaden and J. Sussman Perception of Coarticulatory Information in Normal Speech and Dysarthria. J Speech Lang Hear Res, August 1, 2006; 49(4): 888 - 902. [Abstract] [Full Text] [PDF]

				H. Ackermann, K. Mathiak, and R. B. Ivry Temporal Organization of "Internal Speech" As a Basis for Cerebellar Modulation of Cognitive Functions Behav Cogn Neurosci Rev, March 1, 2004; 3(1): 14 - 22. [Abstract] [PDF]