Perceptual Learning of Dysarthria in Adolescence

PURPOSE

As evidenced by perceptual learning studies involving adult listeners and speakers with dysarthria, adaptation to dysarthric speech is driven by signal predictability (speaker property) and a flexible speech perception system (listener property). Here, we extend adaptation investigations to adolescent populations and examine whether adult and adolescent listeners can learn to better understand an adolescent speaker with dysarthria.

METHOD

Classified by developmental stage, adult (n = 42) and adolescent (n = 40) listeners completed a three-phase perceptual learning protocol (pretest, familiarization, and posttest). During pretest and posttest, all listeners transcribed speech produced by a 13-year-old adolescent with spastic dysarthria associated with cerebral palsy. During familiarization, half of the adult and adolescent listeners engaged in structured familiarization (audio and lexical feedback) with the speech of the adolescent speaker with dysarthria; and the other half, with the speech of a neurotypical adolescent speaker (control).

RESULTS

Intelligibility scores increased from pretest to posttest for all listeners. However, listeners who received dysarthria familiarization achieved greater intelligibility improvements than those who received control familiarization. Furthermore, there was a significant effect of developmental stage, where the adults achieved greater intelligibility improvements relative to the adolescents.

CONCLUSIONS

This study provides the first tranche of evidence that adolescent dysarthric speech is learnable-a finding that holds even for adolescent listeners whose speech perception systems are not yet fully developed. Given the formative role that social interactions play during adolescence, these findings of improved intelligibility afford important clinical implications.

Vowel Acoustics as Predictors of Speech Intelligibility in Dysarthria

PURPOSE

This study sought to determine if alternative vowel space area (VSA) measures (i.e., novel trajectory-based measures: vowel space hull area and vowel space density) predicted speech intelligibility to the same extent as two traditional vowel measures (i.e., token-based measures: VSA and corner dispersion) in speakers with dysarthria. Additionally, this study examined if the strength of the relationship between acoustic vowel measures and intelligibility differed based on how intelligibility was measured (i.e., orthographic transcriptions [OTs] and visual analog scale [VAS] ratings).

METHOD

The Grandfather Passage was read aloud by 40 speakers with dysarthria of varying etiologies, including Parkinson's disease (n = 10), amyotrophic lateral sclerosis (n = 10), Huntington's disease (n = 10), and cerebellar ataxia (n = 10). Token- and trajectory-based acoustic vowel measures were calculated from the passage. Naïve listeners (N = 140) were recruited via crowdsourcing to provide OTs and VAS intelligibility ratings. Hierarchical linear regression models were created to model OTs and VAS intelligibility ratings using the acoustic vowel measures as predictors.

RESULTS

Traditional VSA was the sole significant predictor of speech intelligibility for both the OTs (R 2 = .259) and VAS (R 2 = .236) models. In contrast, the trajectory-based measures were not significant predictors of intelligibility. Additionally, the OTs and VAS intelligibility ratings conveyed similar information.

CONCLUSIONS

The findings suggest that traditional token-based vowel measures better predict intelligibility than trajectory-based measures. Additionally, the findings suggest that VAS methods are comparable to OT methods for estimating speech intelligibility for research purposes.

Cognitive Predictors of Perception and Adaptation to Dysarthric Speech in Young Adult Listeners

PURPOSE

Although recruitment of cognitive-linguistic resources to support dysarthric speech perception and adaptation is presumed by theoretical accounts of effortful listening and supported by cross-disciplinary empirical findings, prospective relationships have received limited attention in the disordered speech literature. This study aimed to examine the predictive relationships between cognitive-linguistic parameters and intelligibility outcomes associated with familiarization with dysarthric speech in young adult listeners.

METHOD

A cohort of 156 listener participants between the ages of 18 and 50 years completed a three-phase perceptual training protocol (pretest, training, and posttest) with one of three speakers with dysarthria. Additionally, listeners completed the National Institutes of Health Toolbox Cognition Battery to obtain measures of the following cognitive-linguistic constructs: working memory, inhibitory control of attention, cognitive flexibility, processing speed, and vocabulary knowledge.

RESULTS

Elastic net regression models revealed that select cognitive-linguistic measures and their two-way interactions predicted both initial intelligibility and intelligibility improvement of dysarthric speech. While some consistency across models was shown, unique constellations of select cognitive factors and their interactions predicted initial intelligibility and intelligibility improvement of the three different speakers with dysarthria.

CONCLUSIONS

Current findings extend empirical support for theoretical models of speech perception in adverse listening conditions to dysarthric speech signals. Although predictive relationships were complex, vocabulary knowledge, working memory, and cognitive flexibility often emerged as important variables across the models.

The Reliability and Validity of Speech-Language Pathologists’ Estimations of Intelligibility in Dysarthria

This study examined the reliability and validity of speech-language pathologists’ (SLP) estimations of speech intelligibility in dysarthria, including a visual analog scale (VAS) method and a percent estimation method commonly used in clinical settings. Speech samples from 20 speakers with dysarthria of varying etiologies were used to collect orthographic transcriptions from naïve listeners n=70 and VAS ratings and percent estimations of intelligibility from SLPs n=21. Intra- and interrater reliability for the two SLP intelligibility measures were evaluated, and the relationship between these measures was assessed. Finally, linear regression was used to evaluate the relationship between the naïve listeners’ orthographic transcription scores and the two SLP intelligibility measures. The results indicated that the intrarater reliability for both SLP intelligibility measures was strong, and the interrater reliability between the SLP ratings was moderate to excellent. A moderate positive relationship between SLPs’ VAS ratings and percent estimations was also observed. Finally, both SLPs’ percent estimations and VAS ratings were predictive of naïve listeners’ orthographic transcription scores, with SLPs’ percent estimations being the strongest predictor. In conclusion, the average SLP percent estimations and VAS ratings are valid and reliable intelligibility measures. However, the validity and reliability of these measures vary between SLPs.

A Perceptual Learning Approach for Dysarthria Remediation: An Updated Review

Purpose Early studies of perceptual learning of dysarthric speech, those summarized in Borrie, McAuliffe, and Liss (2012), yielded preliminary evidence that listeners could learn to better understand the speech of a person with dysarthria, revealing a potentially promising avenue for future intelligibility interventions. Since then, a programmatic body of research grounded in models of perceptual processing has unfolded. The current review provides an updated account of the state of the evidence in this area and offers direction for moving this work toward clinical implementation. Method The studies that have investigated perceptual learning of dysarthric speech (N = 24) are summarized and synthesized first according to the proposed learning source and then by highlighting the parameters that appear to mediate learning, culminating with additional learning outcomes. Results The recent literature has established strong empirical evidence of intelligibility improvements following familiarization with dysarthric speech and a theoretical account of the mechanisms that facilitate improved processing of the neurologically degraded acoustic signal. Conclusions There are no existing intelligibility interventions for individuals with dysarthria who cannot behaviorally modify their speech. However, there is now robust support for the development of an approach that shifts the weight of behavioral change from speaker to listener, exploiting perceptual learning to ease the intelligibility burden of dysarthria. To move this work from bench to bedside, recommendations for translational studies that establish best practices and candidacy for listener-targeted dysarthria remediation, perceptual training, are provided.

A Clinical Advantage: Experience Informs Recognition and Adaptation to a Novel Talker With Dysarthria

Purpose Perceptual training paradigms, which leverage the mechanism of perceptual learning, show that naïve listeners, those with no prior experience with dysarthria, benefit from explicit familiarization with a talker with dysarthria. It is theorized that familiarization affords listeners an opportunity to acquire distributional knowledge of the degraded speech signal. Here, we extend investigations to clinically experienced listeners, speech-language pathologists (SLPs), and advance models of listener recognition and adaptation to dysarthric speech. Method Forty-seven SLPs completed a standard three-phase perceptual training protocol (pretest, familiarization, and posttest) with a novel talker with dysarthria. Intelligibility scores were compared with historical data from naïve listeners. Potential relationships between intelligibility scores and characteristics of clinical experience were examined. Results Intelligibility scores of SLPs improved by an average of 19% from pretest to posttest. This intelligibility improvement was lower than naïve listeners, although the difference was small. Moreover, clinical characteristics related to level of dysarthria experience (e.g., percent of caseload composed of dysarthria) predicted pretest/initial intelligibility. No predictive relationships between clinical characteristics and intelligibility improvement were revealed. Conclusions As a group, SLPs benefitted from perceptual training, suggesting that, despite prior experience, the opportunity to acquire knowledge of talker-specific cue distributions is crucial for optimal adaptation. However, SLPs with greater dysarthria experience were better at initially understanding the talker with dysarthria. This suggests that, through regular interaction with individuals with dysarthria, clinicians acquire knowledge of the cue distributions of dysarthric speech more generally and can generalize this group-specific knowledge to aid in understanding other talkers with dysarthria. Consistent with theoretical models of perceptual learning, both talker- and group-specific knowledge informed recognition and adaptation to dysarthric speech.

Generalized Learning of Dysarthric Speech Between Male and Female Talkers

Purpose Perceptual training is a listener-targeted means for improving intelligibility of dysarthric speech. Recent work has shown that training with one talker generalizes to a novel talker of the same sex and that the magnitude of benefit is maximized when the talkers are perceptually similar. The current study expands previous findings by investigating whether perceptual training effects generalize between talkers of different sex. Method Forty new listeners were recruited for this study and completed a pretest, familiarization, and posttest perceptual training paradigm. Historical data collected using the same three-phase protocol were included in the data analysis. All listeners were exposed to the same talker with dysarthria during the pretest and posttest phases. For the familiarization phase, listeners were exposed to one of four talkers with dysarthria, differing in sex and level of perceptual similarity to the test talker or a control talker. During the testing phases, listener transcribed phrases produced by the test talker with dysarthria. Listener transcriptions were then used to calculate a percent words correct intelligibility score. Results Multiple linear regression analysis revealed that intelligibility at posttest was not predicted by sex of the training talker. Consistent with earlier work, the magnitude of intelligibility gain was greater when the familiarization and test talkers were perceptually similar. Additional analyses revealed greater between-listeners variability in the dissimilar conditions as compared to the similar conditions. Conclusions Learning as a result of perceptual training with one talker with dysarthria generalized to another talker regardless of sex. In addition, listeners trained with perceptually similar talkers had greater and more consistent intelligibility improvement. Together, these results add to previous evidence demonstrating that learning generalizes to novel talkers with dysarthria and that perceptual training is suitable for many listeners.

When Additional Training Isn't Enough: Further Evidence That Unpredictable Speech Inhibits Adaptation

Purpose Robust improvements in intelligibility following familiarization, a listener-targeted perceptual training paradigm, have been revealed for talkers diagnosed with spastic, ataxic, and hypokinetic dysarthria but not for talkers with hyperkinetic dysarthria. While the theoretical explanation for the lack of intelligibility improvement following training with hyperkinetic talkers is that there is insufficient distributional regularity in the speech signals to support perceptual adaptation, it could simply be that the standard training protocol was inadequate to facilitate learning of the unpredictable talker. In a pair of experiments, we addressed this possible alternate explanation by modifying the levels of exposure and feedback provided by the perceptual training protocol to offer listeners a more robust training experience. Method In Experiment 1, we examined the exposure modifications, testing whether perceptual adaptation to an unpredictable talker with hyperkinetic dysarthria could be achieved with greater or more diverse exposure to dysarthric speech during the training phase. In Experiment 2, we examined feedback modifications, testing whether perceptual adaptation to the unpredictable talker could be achieved with the addition of internally generated somatosensory feedback, via vocal imitation, during the training phase. Results Neither task modification led to improved intelligibility of the unpredictable talker with hyperkinetic dysarthria. Furthermore, listeners who completed the vocal imitation task demonstrated significantly reduced intelligibility at posttest. Conclusion Together, the results from Experiments 1 and 2 replicate and extend findings from our previous work, suggesting perceptual adaptation is inhibited for talkers whose speech is largely characterized by unpredictable degradations. Collectively, these results underscore the importance of integrating signal predictability into theoretical models of perceptual learning.

Regularity Matters: Unpredictable Speech Degradation Inhibits Adaptation to Dysarthric Speech

Purpose Listener-targeted perceptual training paradigms, which leverage the mechanism of perceptual learning, show strong promise for improving intelligibility in dysarthria, offsetting the communicative burden from the speaker onto the listener. Theoretical models of perceptual learning underscore the importance of acoustic regularity (i.e., signal predictability) for listener adaptation to degraded speech. The purpose of the current investigation was to evaluate intelligibility outcomes following perceptual training with hyperkinetic dysarthria, a subtype characterized by reduced signal predictability. Method Forty listeners completed the standard 3-phase perceptual training protocol (pretest, training, and posttest) with 1 of 2 talkers with hyperkinetic dysarthria. Perceptual data were compared to a historical data set for 1 other talker with hyperkinetic dysarthria to examine the effect of perceptual training on intelligibility. Results When controlling for pretest intelligibility, regression results suggest listeners of the 2 novel talkers with hyperkinetic dysarthria performed comparably to the listeners of the original talker on the posttest following training. Furthermore, differences between pretest and posttest intelligibility failed to reach clinical significance for all 3 talkers and statistical significance for 2 of the 3. Conclusion The current findings are consistent with theoretical models of perceptual learning and suggest that listener adaptation to degraded speech may be negligible for talkers with dysarthria whose speech is marked by reduced signal predictability.

The Effects of Speech Compression Algorithms on the Intelligibility of Two Individuals With Dysarthric Speech

Purpose Telemedicine, used to offset disparities in access to speech-language therapy, relies on technology that utilizes compression algorithms to transmit signals efficiently. These algorithms have been thoroughly evaluated on healthy speech; however, the effects of compression algorithms on the intelligibility of disordered speech have not been adequately explored. Method This case study assessed acoustic and perceptual effects of resampling and speech compression (i.e., transcoding) on the speech of 2 individuals with dysarthria. Forced-choice vowel identification and transcription tasks were utilized, completed by 20 naive undergraduate listeners. Results Results showed relative improvements and decrements in intelligibility, on various measures, based on the speakers' acoustic profiles. The transcoding of the speech compression algorithm resulted in an enlarged vowel space area and associated improvements in vowel identification for 1 speaker and a smaller vowel space area and decreased vowel identification for the other speaker. Interestingly, there was an overall decrease in intelligibility in the transcription task in this condition for both speakers. Conclusions There is a complex interplay between dysarthria and compression algorithms that warrants further exploration. The findings suggest that it is critical to be mindful of apparent changes in intelligibility secondary to compression algorithms necessary for practicing telemedicine. Supplemental Material https://doi.org/10.23641/asha.7291940.

Understanding dysrhythmic speech: When rhythm does not matter and learning does not happen

A positive relationship between rhythm perception and improved understanding of a naturally dysrhythmic speech signal, ataxic dysarthria, has been previously reported [Borrie, Lansford, and Barrett. (2017). J. Speech Lang. Hear. Res. 60, 3110-3117]. The current follow-on investigation suggests that this relationship depends on the nature of the dysrhythmia. When the corrupted rhythm cues are relatively predictable, affording some learnable acoustic regularity, the relationship is replicated. However, this relationship is nonexistent, along with any intelligibility improvements, when the corrupted rhythm cues are unpredictable. Findings highlight a key role for rhythm perception and distributional regularities in adaptation to dysrhythmic speech.

Effects of Familiarization on Intelligibility of Dysarthric Speech in Older Adults With and Without Hearing Loss

PURPOSE

Familiarization tasks offer a promising platform for listener-targeted remediation of intelligibility disorders associated with dysarthria. To date, the body of work demonstrating improved understanding of dysarthric speech following a familiarization experience has been carried out on younger adults. The primary purpose of the present study was to examine the intelligibility effects of familiarization in older adults.

METHOD

Nineteen older adults, with and without hearing loss, completed a familiarization protocol consisting of three phases: pretest, familiarization, and posttest. The older adults' initial intelligibility and intelligibility improvement scores were compared with previously reported data collected from 50 younger adults (Borrie, Lansford, & Barrett, 2017a).

RESULTS

Relative to younger adults, initial intelligibility scores were significantly lower for older adults, although additional analysis revealed that the difference was limited to older adults with hearing loss. Key, however, is that irrespective of hearing status, the older and younger adults achieved comparable intelligibility improvement following familiarization (gain of roughly 20 percentage points).

CONCLUSION

This study extends previous findings of improved intelligibility of dysarthria following familiarization to a group of listeners who are critical to consider in listener-targeted remediation, namely, aging caregivers and/or spouses of individuals with dysarthria.

Receptive Vocabulary, Cognitive Flexibility, and Inhibitory Control Differentially Predict Older and Younger Adults' Success Perceiving Speech by Talkers With Dysarthria

PURPOSE

Previous research has demonstrated equivocal findings related to the effect of listener age on intelligibility ratings of dysarthric speech. The aim of the present study was to investigate the mechanisms that support younger and older adults' perception of speech by talkers with dysarthria.

METHOD

Younger and older adults identified words in phrases produced by talkers with dysarthria. Listeners also completed assessments on peripheral hearing, receptive vocabulary, and executive control functions.

RESULTS

Older and younger adults did not differ in their ability to perceive speech by talkers with dysarthria. Younger adults' success in identifying words produced by talkers with dysarthria was associated only with their hearing acuity. In contrast, older adults showed effects of working memory and cognitive flexibility and interactions between hearing acuity and receptive vocabulary and between hearing acuity and inhibitory control.

CONCLUSIONS

Although older and younger adults had equivalent performance identifying words produced by talkers with dysarthria, older adults appear to utilize more cognitive support to identify those words.

Generalized Adaptation to Dysarthric Speech

PURPOSE

Generalization of perceptual learning has received limited attention in listener adaptation studies with dysarthric speech. This study investigated whether adaptation to a talker with dysarthria could be predicted by the nature of the listener's prior familiarization experience, specifically similarity of perceptual features, and level of intelligibility.

METHOD

Following an intelligibility pretest involving a talker with ataxic dysarthria, 160 listeners were familiarized with 1 of 7 talkers with dysarthria-who differed from the test talker in terms of perceptual similarity (same, similar, dissimilar) and level of intelligibility (low, mid, high)-or a talker with no neurological impairment (control). Listeners then completed an intelligibility posttest on the test talker.

RESULTS

All listeners benefited from familiarization with a talker with dysarthria; however, adaptation to the test talker was superior when the familiarization talker had similar perceptual features and reduced when the familiarization talker had low intelligibility.

CONCLUSION

Evidence for both generalization and specificity of learning highlights the differential value of listeners' prior experiences for adaptation to, and improved understanding of, a talker with dysarthria. These findings broaden our theoretical knowledge of adaptation to degraded speech, as well as the clinical application of training paradigms that exploit perceptual processes for therapeutic gain.

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.

Cognitive factors as predictors of accented speech perception for younger and older adults

Though some studies suggest that older adults are not differentially impacted by foreign-accented speech relative to younger adults, other studies indicate that older adults are poorer at perceiving foreign-accented speech than younger adults. The present study sought, first, to clarify the extent to which older and younger adults differed in their perception of foreign-accented speech. The secondary aim was to elucidate the extent to which the cognitive mechanisms supporting accented speech perception differ for older and younger adults. The data indicated that older adults were poorer at perceiving accented speech than younger adults. Older adults' speech perception accuracy was associated with a significant main effect of working memory as well as significant interactions between hearing acuity and cognitive flexibility and between hearing acuity and inhibitory control. Younger adults' speech perception accuracy, in contrast, was associated with a significant interaction between hearing acuity and processing speed. It therefore appears that the differences in performance between younger and older adults observed here may be attributable to differences in the cognitive mechanisms that support accented speech perception.

Listeners' attitudes toward accented talkers uniquely predicts accented speech perception

Listeners' sensitivity to indexical information influences their ability to perceive and remember speech, but it is less clear if listeners' subjective ratings of talker characteristics also impact speech perception ability. The present experiment tested the increase in variance accounted for by listeners' ratings of foreign accented talkers' manner of speaking and of the talkers themselves beyond the variance already accounted for by listeners' age, executive function, and hearing thresholds. Adding listeners' ratings significantly improved model fit, indicating that listeners' subjective experience of talker impacts speech perception accuracy along with objective listener characteristics such as hearing thresholds or executive function.

Rhythm Perception and Its Role in Perception and Learning of Dysrhythmic Speech

PURPOSE

The perception of rhythm cues plays an important role in recognizing spoken language, especially in adverse listening conditions. Indeed, this has been shown to hold true even when the rhythm cues themselves are dysrhythmic. This study investigates whether expertise in rhythm perception provides a processing advantage for perception (initial intelligibility) and learning (intelligibility improvement) of naturally dysrhythmic speech, dysarthria.

METHOD

Fifty young adults with typical hearing participated in 3 key tests, including a rhythm perception test, a receptive vocabulary test, and a speech perception and learning test, with standard pretest, familiarization, and posttest phases. Initial intelligibility scores were calculated as the proportion of correct pretest words, while intelligibility improvement scores were calculated by subtracting this proportion from the proportion of correct posttest words.

RESULTS

Rhythm perception scores predicted intelligibility improvement scores but not initial intelligibility. On the other hand, receptive vocabulary scores predicted initial intelligibility scores but not intelligibility improvement.

CONCLUSIONS

Expertise in rhythm perception appears to provide an advantage for processing dysrhythmic speech, but a familiarization experience is required for the advantage to be realized. Findings are discussed in relation to the role of rhythm in speech processing and shed light on processing models that consider the consequence of rhythm abnormalities in dysarthria.

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.

Modeling listener perception of speaker similarity in dysarthria

The current investigation contributes to a perceptual similarity-based approach to dysarthria characterization by utilizing an innovative statistical approach, multinomial logistic regression with sparsity constraints, to identify acoustic features underlying each listener's impressions of speaker similarity. The data-driven approach also permitted an examination of the effect of clinical experience on listeners' impressions of similarity. Listeners, irrespective of level of clinical experience, were found to rely on similar acoustic features during the perceptual sorting task, known as free classification. Overall, the results support the continued advancement of a similarity-based approach to characterizing the communication disorders associated with dysarthria.

Use of Crowdsourcing to Assess the Ecological Validity of Perceptual-Training Paradigms in Dysarthria

PURPOSE

It has been documented in laboratory settings that familiarizing listeners with dysarthric speech improves intelligibility of that speech. If these findings can be replicated in real-world settings, the ability to improve communicative function by focusing on communication partners has major implications for extending clinical practice in dysarthria rehabilitation. An important step toward development of a listener-targeted treatment approach requires establishment of its ecological validity. To this end, the present study leveraged the mechanism of crowdsourcing to determine whether perceptual-training benefits achieved by listeners in the laboratory could be elicited in an at-home computer-based scenario.

METHOD

Perceptual-training data (i.e., intelligibility scores from a posttraining transcription task) were collected from listeners in 2 settings-the laboratory and the crowdsourcing website Amazon Mechanical Turk.

RESULTS

Consistent with previous findings, results revealed a main effect of training condition (training vs. control) on intelligibility scores. There was, however, no effect of training setting (Mechanical Turk vs. laboratory). Thus, the perceptual benefit achieved via Mechanical Turk was comparable to that achieved in the laboratory.

CONCLUSION

This study provides evidence regarding the ecological validity of perceptual-training paradigms designed to improve intelligibility of dysarthric speech, thereby supporting their continued advancement as a listener-targeted treatment option.

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.

Free-classification of perceptually similar speakers with dysarthria

PURPOSE

In this investigation, the construct of perceptual similarity was explored in the dysarthrias. Specifically, we employed an auditory free-classification task to determine whether listeners could cluster speakers by perceptual similarity, whether the clusters mapped to acoustic metrics, and whether the clusters were constrained by dysarthria subtype diagnosis.

METHOD

Twenty-three listeners blinded to speakers' medical and dysarthria subtype diagnoses participated. The task was to group together (drag and drop) the icons corresponding to 33 speakers with dysarthria on the basis of how similar they sounded. Cluster analysis and multidimensional scaling (MDS) modeled the perceptual dimensions underlying similarity. Acoustic metrics and perceptual judgments were used in correlation analyses to facilitate interpretation of the derived dimensions.

RESULTS

Six clusters of similar-sounding speakers and 3 perceptual dimensions underlying similarity were revealed. The clusters of similar-sounding speakers were not constrained by dysarthria subtype diagnosis. The 3 perceptual dimensions revealed by MDS were correlated with metrics for articulation rate, intelligibility, and vocal quality, respectively.

CONCLUSIONS

This study shows (a) feasibility of a free-classification approach for studying perceptual similarity in dysarthria, (b) correspondence between acoustic and perceptual metrics to clusters of similar-sounding speakers, and (c) similarity judgments transcended dysarthria subtype diagnosis.

Vowel acoustics in dysarthria: speech disorder diagnosis and classification

PURPOSE

The purpose of this study was to determine the extent to which vowel metrics are capable of distinguishing healthy from dysarthric speech and among different forms of dysarthria.

METHOD

A variety of vowel metrics were derived from spectral and temporal measurements of vowel tokens embedded in phrases produced by 45 speakers with dysarthria and 12 speakers with no history of neurological disease. Via means testing and discriminant function analysis (DFA), the acoustic metrics were used to (a) detect the presence of dysarthria and (b) classify the dysarthria subtype.

RESULTS

Significant differences between dysarthric and healthy control speakers were revealed for all vowel metrics. However, the results of the DFA demonstrated some metrics (particularly metrics that capture vowel distinctiveness) to be more sensitive and specific predictors of dysarthria. Only the vowel metrics that captured slope of the second formant (F2) demonstrated between-group differences across the dysarthrias. However, when subjected to DFA, these metrics proved unreliable classifiers of dysarthria subtype.

CONCLUSION

The results of these analyses suggest that some vowel metrics may be useful clinically for the detection of dysarthria but may not be reliable indicators of dysarthria subtype using the current dysarthria classification scheme.

Vowel acoustics in dysarthria: mapping to perception

PURPOSE

The aim of the present report was to explore whether vowel metrics, demonstrated to distinguish dysarthric and healthy speech in a companion article (Lansford & Liss, 2014), are able to predict human perceptual performance.

METHOD

Vowel metrics derived from vowels embedded in phrases produced by 45 speakers with dysarthria were compared with orthographic transcriptions of these phrases collected from 120 healthy listeners. First, correlation and stepwise multiple regressions were conducted to identify acoustic metrics that had predictive value for perceptual measures. Next, discriminant function analysis misclassifications were compared with listeners' misperceptions to examine more directly the perceptual consequences of degraded vowel acoustics.

RESULTS

Several moderate correlative relationships were found between acoustic metrics and perceptual measures, with predictive models accounting for 18%-75% of the variance in measures of intelligibility and vowel accuracy. Results of the second analysis showed that listeners better identified acoustically distinctive vowel tokens. In addition, the level of agreement between misclassified-to-misperceived vowel tokens supports some specificity of degraded acoustic profiles on the resulting percept.

CONCLUSION

Results provide evidence that degraded vowel acoustics have some effect on human perceptual performance, even in the presence of extravowel variables that naturally exert influence in phrase perception.

The Effects of Topic Knowledge on Intelligibility and Lexical Segmentation in Hypokinetic and Ataxic Dysarthria

Benefits to speech intelligibility can be achieved by enhancing a listener's ability to decipher it. However, much remains to be learned about the variables that influence the effectiveness of various listener-based manipulations. This study examined the benefit of providing listeners with the topic of some phases produced by speakers with either hypokinetic or ataxic dysarthria. Total and topic word accuracy, topic-related substitutions, and lexical boundary errors were calculated from the listener transcripts. Data were compared with those who underwent a familiarization process (reported by Liss, Spitzer, Caviness, & Adler, 2002) and with those inexperienced with disordered speech (reported by Liss Spitzer, Caviness, & Adler, 2000). Results revealed that listeners of ataxic speech provided with topic knowledge obtained higher intelligibility scores than naïve listeners. The magnitude of benefit was similar to the familiarization condition. However, topic word and word substitution analyses revealed different underlying perceptual mechanisms responsible for the observed benefit. No differences attributable to listening condition were discovered in lexical segmentation patterns. Overall, the results support the need for further study of listener-based manipulations to elucidate the mechanisms responsible for the observed perceptual benefits for each dysarthria type.

A cognitive-perceptual approach to conceptualizing speech intelligibility deficits and remediation practice in hypokinetic dysarthria

Hypokinetic dysarthria is a common manifestation of Parkinson's disease, which negatively influences quality of life. Behavioral techniques that aim to improve speech intelligibility constitute the bulk of intervention strategies for this population, as the dysarthria does not often respond vigorously to medical interventions. Although several case and group studies generally support the efficacy of behavioral treatment, much work remains to establish a rigorous evidence base. This absence of definitive research leaves both the speech-language pathologist and referring physician with the task of determining the feasibility and nature of therapy for intelligibility remediation in PD. The purpose of this paper is to introduce a novel framework for medical practitioners in which to conceptualize and justify potential targets for speech remediation. The most commonly targeted deficits (e.g., speaking rate and vocal loudness) can be supported by this approach, as well as underutilized and novel treatment targets that aim at the listener's perceptual skills.