Vowel Distortion in Traumatic Dysarthria: A Formant Study

Abstract

The frequencies of the first two formants of three German vowels in word context were determined by a formant tracking routine for 8 male subjects with closed head trauma. A centralized formant pattern was found to characterize vowel articulation in traumatic dysarthria. Different degrees of severity could be assessed and the process of recovery was described by the parameter ‘formant triangle area’. An interpretation in articulatory terms is given and the results are discussed in the light of articulatory models.

Vowel formant dispersion as a measure of articulation proficiency

“…8 Based on the VAI/ FCR metrics in Eqs. (1) and (2), studies have been able to show a significant reduction in VAI (or an increase in FCR) due to hypokinetic dysarthria. 8,9,14 The VAI/FCR metrics have therefore been argued to provide an enhanced sensitivity over the VSA metric in quantifying vowel articulation change in dysarthric patients.…”

“…The size of the shape enclosed by these corner vowels has been shown to correlate well with intelligibility of the speaker 1 and has predominantly been quantified by its area, the vowel space area (VSA). 2 VSA estimates, based on either three (VSA3) or four vowel-systems (VSA4), have formed the basis of many studies investigating the reduction of articulation in patient groups due to a specific condition, or the restoration of articulatory range as a result of treatment. [2][3][4][5][6][7][8][9][10] The results have, however, been variable in terms of articulatory change shown by the VSA metric, with reductions in VSA at times failing to reach significance in cases where a consistent trend of articulatory reduction is observed [11][12][13] (see Sapir et al 9 for a review).…”

“…2 VSA estimates, based on either three (VSA3) or four vowel-systems (VSA4), have formed the basis of many studies investigating the reduction of articulation in patient groups due to a specific condition, or the restoration of articulatory range as a result of treatment. [2][3][4][5][6][7][8][9][10] The results have, however, been variable in terms of articulatory change shown by the VSA metric, with reductions in VSA at times failing to reach significance in cases where a consistent trend of articulatory reduction is observed [11][12][13] (see Sapir et al 9 for a review). In an attempt to address the observed lack of power in the VSA measure, a reorganization of the formant frequency values has been proposed to form a quotient of formant frequency sums into a formant centralization ratio (FCR), so that "the formant frequencies in the numerator are likely to increase, and the formant frequencies in the denominator are likely to decrease with vowel centralization."…”

“…As a result, the distances of a specific set of vowel productions within a space enclosed by four corner vowels would likely differ substantially from distances computed for the same vowel productions, but positioned within a system enclosed by three corner vowels. In light of the varying number of corner vowels used in previous studies of speakers with reduced articulatory range, [2][3][4][5][6][7][8]10,14 this instability in the placement of the center point offers a significant reduction in reliability of the metric. This lack of reliability will affect the study of significant articulatory impairment, as well as severely reduce comparability across studies.…”

Correlation Between Vowel Centralisation and Incomplete Stop Articulation in Individuals with Traumatic Brain Injury

“…Several acoustic analyses of post-traumatic dysarthria have been reported (e.g. Ziegler and von Cramon 1983;Weismer et al 2001;Wang et al, 2005), but these acoustic methods are rarely used in the investigation of sound simplifications and reductions called "natural phonological processes".…”