Effect of Speaking Rate Manipulations on Acoustic and Perceptual Aspects of the Dysarthria in Amyotrophic Lateral Sclerosis

Abstract

The current study explored the acoustic and perceptual effects of speaking rate adjustments in persons with amyotrophic lateral sclerosis (ALS) and in neurologically normal individuals. Sentence utterances were obtained from the participants at two self-selected speaking rates: habitual and fast. Total utterance durations, segment durations, and vowel formant frequencies comprised the acoustic measures, whereas magnitude estimates of speech intelligibility and severity of speech involvement were the perceptual measures. Results showed that participants in both the neurologically normal and ALS groups were able to increase their speaking rate when asked to do so, but that the participants with ALS were significantly slower than the neurologically normal participants at both rates. Both groups of participants also showed compression of the acoustic vowel space with increased speaking rate, with the vowel spaces of participants with ALS generally being more compressed than the vowel spaces of neurologically normal participants, at either rate. Most importantly, the perceptual measures failed to show any effect of the speaking rate adjustment on scaled intelligibility or severity, for either group. These findings are discussed relative to the general issue of slow habitual speaking rates among many speakers with dysarthria, and possible explanations for the slowness. The lack of an effect of increased rate on the perception of the speech deficit among speakers with ALS argues against the idea that the habitually slow rates are a form of compensation to reduce the complexity of speech production.

Clear Speech Variants: An Acoustic Study in Parkinson's Disease

“…Measures of VSA were included as an index of vowel segmental integrity (Turner et al, 1995;Weismer, Laures, Jeng, Kent, & Kent, 2000). Previous research has suggested that changes in clear speech differentially affect tense and lax VSA (Chen, 1980;Lam et al, 2012;Picheny et al, 1985).…”

Vowel formant dispersion as a measure of articulation proficiency

“…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.…”

Vowel Contrast and Speech Intelligibility in Dysarthria

“…Previous studies have noted vowel centralization and reduced vowel space as the common characteristics of vowels in dysarthric speech [1][2][3][4][5][6][7][8][9] . However, the strength of the relationship between intelligibility and the vowel space area varied widely across studies, ranging from 0 to 71%.…”