Educational Information Improves Listener Attitudes Toward People With Dysarthria Secondary to Parkinson's Disease.

PURPOSE: People with dysarthria have been rated as less confident and less likable and are often assumed by listeners to have reduced cognitive abilities relative to neurotypical speakers. This study explores whether educational information about dysarthria can shift these attitudes in a group of speakers with hypokinetic dysarthria secondary to Parkinson's disease. METHOD: One hundred seventeen listeners were recruited via Amazon Mechanical Turk to transcribe sentences and rate the confidence, intelligence, and likability of eight speakers with mild hypokinetic dysarthria. Listeners were assigned to one of four conditions. In one condition, listeners were provided with no educational information prior to exposure to speakers with dysarthria (n = 29). In another condition, listeners were given educational statements from the American Speech-Language-Hearing Association website (n = 29). In a third condition, listeners were given additional information stating that dysarthria does not indicate reduced intelligence or understanding (n = 30). Finally, in a fourth condition, listeners only heard samples from neurotypical, age-matched adults (n = 29). RESULTS: Results revealed statistically significant effects of educational statements on ratings of speakers' confidence, intelligence, and likability. However, educational statements did not affect listeners' transcription accuracy. CONCLUSIONS: This study presents preliminary evidence that educational material can positively influence listener impressions of speakers with hypokinetic dysarthria, especially when it is explicitly stated that the disorder does not affect intelligence or understanding. This initial examination provides preliminary support for educational awareness campaigns and self-disclosure of communicative difficulties in people with mild dysarthria.

Beyond Speech Intelligibility: Quantifying Behavioral and Perceived Listening Effort in Response to Dysarthric Speech.

PURPOSE: This study investigated whether listener processing of dysarthric speech requires the recruitment of more cognitive resources (i.e., higher levels of listening effort) than neurotypical speech. We also explored relationships between behavioral listening effort, perceived listening effort, and objective measures of word transcription accuracy. METHOD: A word recall paradigm was used to index behavioral listening effort. The primary task involved word transcription, whereas a memory task involved recalling words from previous sentences. Nineteen listeners completed the paradigm twice, once while transcribing dysarthric speech and once while transcribing neurotypical speech. Perceived listening effort was rated using a visual analog scale. RESULTS: Results revealed significant effects of dysarthria on the likelihood of correct word recall, indicating that the transcription of dysarthric speech required higher levels of behavioral listening effort relative to neurotypical speech. There was also a significant relationship between transcription accuracy and measures of behavioral listening effort, such that listeners who were more accurate in understanding dysarthric speech exhibited smaller changes in word recall when listening to dysarthria. The subjective measure of perceived listening effort did not have a statistically significant correlation with measures of behavioral listening effort or transcription accuracy. CONCLUSIONS: Results suggest that cognitive resources, particularly listeners' working memory capacity, are more taxed when deciphering dysarthric versus neurotypical speech. An increased demand on these resources may affect a listener's ability to remember aspects of their conversations with people with dysarthria, even when the speaker is fully intelligible.

Comparing Lexical Cues in Listener Processing of Dysarthria and Speech in Noise.

Purpose The frequency of a word and its number of phonologically similar neighbors can dramatically affect how likely it is to be accurately identified in adverse listening conditions. This study compares how these two cues affect listeners' processing of speech in noise and dysarthric speech. Method Seven speakers with moderate hypokinetic dysarthria and eight healthy control speakers were recorded producing the same set of phrases. Statements from control speakers were mixed with noise at a level selected to match the intelligibility range of the speakers with dysarthria. A binomial mixed-effects model quantified the effects of word frequency and phonological density on word identification. Results The model revealed significant effects of word frequency (b = 0.37, SE = 0.12, p = .002) and phonological neighborhood density (b = 0.40, SE = 0.12, p = .001). There was no effect of speaking condition (i.e., dysarthric speech vs. speech in noise). However, a significant interaction was observed between speaking condition and word frequency (b = 0.26, SE = 0.04, p < .001). Conclusions The model's interactions indicated that listeners were more strongly influenced by the effects of word frequency when decoding moderate hypokinetic dysarthria as compared to speech in noise. Differences in listener reliance on lexical cues may have important implications for the selection of communication-based treatment strategies for speakers with dysarthria.

The Effects of Word Frequency and Word Probability on Speech Rhythm in Dysarthria.

Purpose In healthy speakers, the more frequent and probable a word is in its context, the shorter the word tends to be. This study investigated whether these probabilistic effects were similarly sized for speakers with dysarthria of different severities. Method Fifty-six speakers of New Zealand English (42 speakers with dysarthria and 14 healthy speakers) were recorded reading the Grandfather Passage. Measurements of word duration, frequency, and transitional word probability were taken. Results As hypothesized, words with a higher frequency and probability tended to be shorter in duration. There was also a significant interaction between word frequency and speech severity. This indicated that the more severe the dysarthria, the smaller the effects of word frequency on speakers' word durations. Transitional word probability also interacted with speech severity, but did not account for significant unique variance in the full model. Conclusions These results suggest that, as the severity of dysarthria increases, the duration of words is less affected by probabilistic variables. These findings may be due to reductions in the control and execution of muscle movement exhibited by speakers with dysarthria.

Predicting Montreal Cognitive Assessment Scores From Measures of Speech and Language.

Purpose This study examined the relationship between measurements derived from spontaneous speech and participants' scores on the Montreal Cognitive Assessment. Method Participants (N = 521) aged between 64 and 97 years completed the cognitive assessment and were prompted to describe an early childhood memory. A range of acoustic and linguistic measures was extracted from the resulting speech sample. A least absolute shrinkage and selection operator approach was used to model the relationship between acoustic, lexical, and demographic information and participants' scores on the cognitive assessment. Results Using the covariance test statistic, four important variables were identified, which, together, explained 16.52% of the variance in participants' cognitive scores. Conclusions The degree to which cognition can be accurately predicted through spontaneously produced speech samples is limited. Statistically significant relationships were found between specific measurements of lexical variation, participants' speaking rate, and their scores on the Montreal Cognitive Assessment.

Examining Listener Reaction Time in the Perceptual Assessment of Dysarthria.

OBJECTIVE: In the perceptual assessment of dysarthria, various approaches are used to examine the accuracy of listeners' speech transcriptions and their subjective impressions of speech disorder. However, less attention has been given to the effort and cognitive resources required to process speech samples. This study explores the relationship between transcription accuracy, comprehensibility, subjective impressions of speech, and objective measures of reaction time (RT) to further examine the challenges involved in processing dysarthric speech. PATIENTS AND METHODS: Sixteen listeners completed 3 experimental listening tasks: a sentence transcription task, a rating scale task, and an RT task that required responses to veracity statements. In each task, the speech stimuli included speech from 8 individuals with dysarthria. RESULTS: Measurements from the 3 tasks were significantly related, with a correlation coefficient of -0.94 between average RT and transcription-based intelligibility scores and -0.89 between RT and listener ratings of dysarthria. Interrater reliability of RT measurements was relatively low when considering a single person's response to stimuli. However, reliability reached an acceptable level when a mean was taken from 8 listeners. CONCLUSIONS: RT tasks could be developed as a reliable adjunct in the assessment of listener effort and speech processing.

Effects of Vocabulary and Implicit Linguistic Knowledge on Speech Recognition in Adverse Listening Conditions.

Purpose This study aims to examine the combined influence of vocabulary knowledge and statistical properties of language on speech recognition in adverse listening conditions. Furthermore, it aims to determine whether any effects identified are more salient at particular levels of signal degradation. Method One hundred three young healthy listeners transcribed phrases presented at 4 different signal-to-noise ratios, which were coded for recognition accuracy. Participants also completed tests of hearing acuity, vocabulary knowledge, nonverbal intelligence, processing speed, and working memory. Results Vocabulary knowledge and working memory demonstrated independent effects on word recognition accuracy when controlling for hearing acuity, nonverbal intelligence, and processing speed. These effects were strongest at the same moderate level of signal degradation. Although listener variables were statistically significant, their effects were subtle in comparison to the influence of word frequency and phonological content. These language-based factors had large effects on word recognition at all signal-to-noise ratios. Discussion Language experience and working memory may have complementary effects on accurate word recognition. However, adequate glimpses of acoustic information appear necessary for speakers to leverage vocabulary knowledge when processing speech in adverse conditions.

Predicting Intelligibility Gains in Individuals With Dysarthria From Baseline Speech Features.

Purpose: Across the treatment literature, behavioral speech modifications have produced variable intelligibility changes in speakers with dysarthria. This study is the first of two articles exploring whether measurements of baseline speech features can predict speakers' responses to these modifications. Methods: Fifty speakers (7 older individuals and 43 speakers with dysarthria) read a standard passage in habitual, loud, and slow speaking modes. Eighteen listeners rated how easy the speech samples were to understand. Baseline acoustic measurements of articulation, prosody, and voice quality were collected with perceptual measures of severity. Results: Cues to speak louder and reduce rate did not confer intelligibility benefits to every speaker. The degree to which cues to speak louder improved intelligibility could be predicted by speakers' baseline articulation rates and overall dysarthria severity. Improvements in the slow condition could be predicted by speakers' baseline severity and temporal variability. Speakers with a breathier voice quality tended to perform better in the loud condition than in the slow condition. Conclusions: Assessments of baseline speech features can be used to predict appropriate treatment strategies for speakers with dysarthria. Further development of these assessments could provide the basis for more individualized treatment programs.

Predicting Intelligibility Gains in Dysarthria Through Automated Speech Feature Analysis.

Purpose: Behavioral speech modifications have variable effects on the intelligibility of speakers with dysarthria. In the companion article, a significant relationship was found between measures of speakers' baseline speech and their intelligibility gains following cues to speak louder and reduce rate (Fletcher, McAuliffe, Lansford, Sinex, & Liss, 2017). This study reexamines these features and assesses whether automated acoustic assessments can also be used to predict intelligibility gains. Method: Fifty speakers (7 older individuals and 43 with dysarthria) read a passage in habitual, loud, and slow speaking modes. Automated measurements of long-term average spectra, envelope modulation spectra, and Mel-frequency cepstral coefficients were extracted from short segments of participants' baseline speech. Intelligibility gains were statistically modeled, and the predictive power of the baseline speech measures was assessed using cross-validation. Results: Statistical models could predict the intelligibility gains of speakers they had not been trained on. The automated acoustic features were better able to predict speakers' improvement in the loud condition than the manual measures reported in the companion article. Conclusions: These acoustic analyses present a promising tool for rapidly assessing treatment options. Automated measures of baseline speech patterns may enable more selective inclusion criteria and stronger group outcomes within treatment studies.

Effect of Dysarthria Type, Speaking Condition, and Listener Age on Speech Intelligibility.

PURPOSE: The aim of this study was to examine the effect of loud and slow speech cues on younger and older listeners' comprehension of dysarthric speech, specifically, (a) whether one strategy, as opposed to the other, promoted greater intelligibility gains for different speaker groups; (b) whether older and younger listeners' understandings were differentially affected by these strategies; and (c) which acoustic changes best predicted intelligibility gain in individual speakers. METHOD: Twenty younger and 40 older listeners completed a perceptual task. Six individuals with dysarthria produced phrases across habitual, loud, and slow conditions. The primary dependent variable was proportion of words correct; follow-up acoustic analyses linked perceptual outcomes to changes in acoustic speech features. RESULTS: Regardless of dysarthria type, the loud condition produced significant intelligibility gains. Overall, older listeners' comprehension was reduced relative to younger listeners. Follow-up analysis revealed considerable interspeaker differences in intelligibility outcomes across conditions. Although the most successful speaking mode varied, intelligibility gains were strongly associated with the degree of change participants made to their vowel formants. CONCLUSIONS: Perceptual outcomes vary across speaking modes, even when speakers with dysarthria are grouped according to similar perceptual profiles. Further investigation of interspeaker differences is needed to inform individually tailored intervention approaches.

Assessing Vowel Centralization in Dysarthria: A Comparison of Methods.

Purpose: The strength of the relationship between vowel centralization measures and perceptual ratings of dysarthria severity has varied considerably across reports. This article evaluates methods of acoustic-perceptual analysis to determine whether procedural changes can strengthen the association between these measures. Method: Sixty-one speakers (17 healthy individuals and 44 speakers with dysarthria) read a standard passage. To obtain acoustic data, 2 points of formant extraction (midpoint and articulatory point) and 2 frequency measures (Hz and Bark) were trialed. Both vowel space area and an adapted formant centralization ratio were calculated using first and second formants of speakers' corner vowels. Twenty-eight listeners rated speech samples using different prompts: one with a focus on intelligibility, the other on speech precision. Results: Perceptually, listener ratings of speech precision provided the best index of acoustic change. Acoustically, the combined use of an articulatory-based formant extraction point, Bark frequency units, and the formant centralization ratio was most effective in explaining perceptual ratings. This combination of procedures resulted in an increase of 17% to 27% explained variance between measures. Conclusions: The procedures researchers use to assess articulatory impairment can significantly alter the strength of relationship between acoustic and perceptual measures. Procedures that maximize this relationship are recommended.

The relationship between speech segment duration and vowel centralization in a group of older speakers.

This study examined the relationship between average vowel duration and spectral vowel quality across a group of 149 New Zealand English speakers aged 65 to 90 yr. The primary intent was to determine whether participants who had a natural tendency to speak slowly would also produce more spectrally distinct vowel segments. As a secondary aim, this study investigated whether advancing age exhibited a measurable effect on vowel quality and vowel durations within the group. In examining vowel quality, both flexible and static formant extraction points were compared. Two formant measurements, from selected [ɐ:], [ i:], and [ o:] vowels, were extracted from a standard passage and used to calculate two measurements of vowel space area (VSA) for each speaker. Average vowel duration was calculated from segments across the passage. The study found a statistically significant relationship between speakers' average vowel durations and VSA measurements indicating that, on average, speakers with slower speech rates produced more acoustically distinct speech segments. As expected, increases in average vowel duration were found with advancing age. However, speakers' formant values remained unchanged. It is suggested that the use of a habitually slower speaking rate may assist speakers in maintaining acoustically distinct vowels.