Kent, Raymond D.

This study seeks to examine the effect of level of presentation on scaling of speech intelligibility of speakers with dysarthria. Previous data [Kim et al. (2007)] reported the somewhat surprising result that different presentation levels do not cause a significant change in speech intelligibility scores of speakers with dysarthria, but do for healthy speakers. The current study reports further data using the same speech stimuli, however, with a main focus on the across-conditions effect of presentation level, since the previous data were limited to within-conditions effects. Four conditions of level of presentation were generated by varying absolute level of presentation (high and low) and normalizing each utterance for peak vowel intensity (adjusted and nonadjusted). In this presentation, we will report how scaled speech intelligibility is affected by the level of presentation of speech samples produced by speakers with various types and severity of dysarthria and by healthy speakers. The results of this study will be helpful to understand the rationale of speech therapy for dysarthria, especially considering the frequent use of speech intelligibility and speech therapy techniques designed based on intensity variation of speech. [Work supported by NIH DC00319 and internal fund from Louisiana State University.]

Purpose This study’s main purpose was to (a) identify acoustic signatures of hypokinetic dysarthria (HKD) that are robust to phonetic variation in conversational speech and (b) determine specific characteristics of the variability associated with HKD. Method Twenty healthy control (HC) participants and 20 participants with HKD associated with idiopathic Parkinson’s disease (PD) repeated 3 isolated sentences (controlled phonetic content) and 2 min of conversational speech (phonetic content treated as a random variable). A MATLAB-based program automatically calculated measures of contrastivity: speech–pause ratio, intensity variation, median and maximum formant slope, formant range, change in the upper and lower spectral envelope, and range of the spectral envelope. t tests were used to identify which measures were sensitive to HKD and which measures differed by task. Discriminant analysis was used to identify the combination of measures that best predicted HKD, and this analysis was then used as a general measure of contrastivity (Contrastivity Index). Differential effects of HKD on maximum and typical contrastivity levels were tested with interaction of maximum, minimum, and median observations of individual speakers and with pairwise comparisons of skewness and kurtosis of the contrastivity index distributions. Results Group differences were detected with pairwise comparisons with t tests in 8 of the 9 measures. Percentage pause time and spectral range were identified as the most specific (95%) and accurate (95%) differentiators of HKD and HC conversational speech. Sentence repetition elicited significantly higher levels of contrastivity than conversational speech in both HC and HKD speakers. Maximum and minimum contrastivities were significantly lower in HKD speech, but there was no evidence that HKD affects maximum contrastivity levels more than median contrastivity levels. The HKD speakers' contrastivity distributions were significantly more skewed to lower levels of production. Conclusion HKD can be consistently distinguished from HC speech in both sentence repetition and conversational speech on the basis of intensity variation and spectral range. Although speakers with HKD were effectively able to produce higher contrastivity levels in sentence repetition tasks, they habitually performed closer to the lower end of their production ranges.

A considerable amount of effort has been made to seek the acoustic correlates of reduced speech intelligibility in dysarthria, although some acoustic variables are under debate: For example, articulation rate, F2 slope, and vowel space have been frequently discussed in previous studies as acoustic predictors of speech intelligibility of dysarthria [Kim (2007)]. One variable that is not well understood, with respect to its effect on speech intelligibility in dysarthria, is level of presentation. This includes level generated by a speaker as well as level of presentation after the speaker has recorded utterances. Clearly, variations in level of presentation of recorded utterances will have some effect when an intelligibility test requires some segmental analysis (as in a minimal pairs test), but the potential effect when speech intelligibility is scaled is not so clear. This is an important question because of the frequent use of scaled intelligibility in dysarthria research. In this presentation, we will report data on how scaled speech intelligibility is affected by level of presentation of speech samples produced by speakers with various types and severity of dysarthria. [Work supported by NIH DC00319.]

PurposeTo review the principles of neural plasticity and make recommendations for research on the neural bases for rehabilitation of neurogenic speech disorders.MethodA working group in speech motor control and disorders developed this report, which examines the potential relevance of basic research on the brain mechanisms involved in neural plasticity and discusses possible similarities and differences for application to speech motor control disorders. The possible involvement of neural plasticity in changes in speech production in normalcy, development, aging, and neurological diseases and disorders was considered. This report focuses on the appropriate use of functional and structural neuroimaging and the design of feasibility studies aimed at understanding how brain mechanisms are altered by environmental manipulations such as training and stimulation and how these changes might enhance the future development of rehabilitative methods for persons with speech motor control disorders.ConclusionsIncreased collaboration with neuroscientists working in clinical research centers addressing human communication disorders might foster research in this area. It is hoped that this article will encourage future research on speech motor control disorders to address the principles of neural plasticity and their application for rehabilitation.

Purpose Darley, Aronson, and Brown (1969a, 1969b) detailed methods and results of auditory-perceptual assessment for speakers with dysarthrias of varying etiology. They reported adequate listener reliability for use of the rating system as a tool for differential diagnosis, but several more recent studies have raised concerns about listener reliability using this approach. Method In the present study, the authors examined intrarater and interrater agreement for perceptual ratings of 47 speakers with various dysarthria types by 2 listener groups (inexperienced and experienced). The entire set of perceptual features proposed by Darley et al. was rated based on a 40-s conversational speech sample. Results No differences in levels of agreement were found between the listener groups. Agreement was within 1 scale value or better for 67% of the pairwise comparisons. Levels of agreement were lower when the average rating fell in the mid-range of the scale compared with samples that had an average rating near either of the scale endpoints; agreement was above chance level. No significant differences in agreement were found between the perceptual features. Discussion The levels of listener agreement that were found indicate that auditory-perceptual ratings show promise during clinical assessment for identifying salient features of dysarthria for speakers with various etiologies.