Vocabulary influences older and younger listeners' processing of dysarthric speech

The Influence of Sensorineural Hearing Loss on the Relationship Between the Perception of Speech in Noise and Dysarthric Speech

PURPOSE

The ability to understand speech under adverse listening conditions is highly variable across listeners. Despite this, studies have found that listeners with normal hearing display consistency in their ability to perceive speech across different types of degraded speech, suggesting that, for at least these listeners, global skills may be involved in navigating the ambiguity in speech signals. However, there are substantial differences in the perceptual challenges faced by listeners with normal and impaired hearing. This study examines whether listeners with sensorineural hearing loss demonstrate the same type of consistency as normal-hearing listeners when processing neurotypical (i.e., control) speech that has been degraded by external noise and speech that is neurologically degraded such as dysarthria.

METHOD

Listeners with normal hearing (n = 31) and listeners with sensorineural hearing loss (n = 36) completed an intelligibility task with neurotypical speech in noise and with dysarthric speech in quiet.

RESULTS

Findings were consistent with previous work demonstrating a relationship between the ability to perceive neurotypical speech in noise and dysarthric speech for listeners with normal hearing, albeit at a higher intelligibility level than previously observed. This relationship was also observed for listeners with hearing loss, although listeners with more severe hearing losses performed better with dysarthric speech than with neurotypical speech in noise.

CONCLUSIONS

This study demonstrated a high level of consistency in intelligibility performance for listeners across two different types of degraded speech, even when those listeners were further challenged by the presence of sensorineural hearing loss. Clinical implications for both listeners with hearing loss and their communication partners with dysarthria are discussed.

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.

Performance on stochastic figure-ground perception varies with individual differences in speech-in-noise recognition and working memory capacity

Speech recognition in noisy environments can be challenging and requires listeners to accurately segregate a target speaker from irrelevant background noise. Stochastic figure-ground (SFG) tasks in which temporally coherent inharmonic pure-tones must be identified from a background have been used to probe the non-linguistic auditory stream segregation processes important for speech-in-noise processing. However, little is known about the relationship between performance on SFG tasks and speech-in-noise tasks nor the individual differences that may modulate such relationships. In this study, 37 younger normal-hearing adults performed an SFG task with target figure chords consisting of four, six, eight, or ten temporally coherent tones amongst a background of randomly varying tones. Stimuli were designed to be spectrally and temporally flat. An increased number of temporally coherent tones resulted in higher accuracy and faster reaction times (RTs). For ten target tones, faster RTs were associated with better scores on the Quick Speech-in-Noise task. Individual differences in working memory capacity and self-reported musicianship further modulated these relationships. Overall, results demonstrate that the SFG task could serve as an assessment of auditory stream segregation accuracy and RT that is sensitive to individual differences in cognitive and auditory abilities, even among younger normal-hearing adults.

Web-based assessment of communication-related parameters in dysarthria: development and implementation of the KommPaS web app

This article describes the design of KommPaS, a web-based tool for the clinical assessment of communication impairment in persons with dysarthria. KommPaS (the German acronym for Communication-related Parameters in Speech Disorders) allows clinicians to recruit laypersons via crowdsourcing for the evaluation of samples of dysarthric speech with regard to communication relevant parameters, that is, intelligibility, naturalness, perceived listener effort, and efficiency (intelligible speech units per unit time). Moreover, a communication total score describing the KommPaS profile elevation, i.e., the arithmetic mean of the normalized KommPaS scores, is provided. Based on considerations regarding the theoretical underpinnings and methodological constraints of a clinical tool for the assessment of these parameters, the article describes how each theoretically and methodologically motivated feature is translated into design principles and how these principles are implemented in a web application. The paper reports efficiency data and details the data privacy and data security provisions that are essential in such an approach.

Clinical measures of communication limitations in dysarthria assessed through crowdsourcing: specificity, sensitivity, and retest-reliability

Assessing the impact of dysarthria on a patient's ability to communicate should be an integral part of patient management. However, due to the high demands on reliable quantification of communication limitations, hardly any formal clinical tests with approved psychometric properties have been developed so far. This study investigates a web-based assessment of communication impairment in dysarthria, named KommPaS. The test comprises measures of intelligibility, naturalness, perceived listener effort and communication efficiency, as well as a total score that integrates these parameters. The approach is characterized by a quasi-random access to a large inventory of test materials and to a large group of naïve listeners, recruited via crowdsourcing. As part of a larger research program to establish the clinical applicability of this new approach, the present paper focuses on two psychometric issues, namely specificity and sensitivity (study 1) and retest-reliability (study 2). Study 1: KommPaS was administered to 54 healthy adults and 100 adult persons with dysarthria (PWD). Non-parametric criterion-based norms (specificity: 0.95) were used to derive a standard metric for each of the four component variables, and corresponding sensitivity values for the presence of dysarthria were identified. Overall classification accuracy of the total score was determined using a ROC analysis. The resulting cutscores showed a high accuracy in the separation of PWD from healthy speakers for the naturalness and the total score. Study 2: A sub-group of 20 PWD enrolled in study 1 were administered a second KommPaS examination. ICC analyses revealed good to excellent retest reliabilities for all parameters.

Impaired perceptual phonetic plasticity in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative condition primarily associated with its motor consequences. Although much of the focus within the speech domain has focused on PD's consequences for production, people with PD have been shown to differ in the perception of emotional prosody, loudness, and speech rate from age-matched controls. The current study targeted the effect of PD on perceptual phonetic plasticity, defined as the ability to learn and adjust to novel phonetic input, both in second language and native language contexts. People with PD were compared to age-matched controls (and, for three of the studies, a younger control population) in tasks of explicit non-native speech learning and adaptation to variation in native speech (compressed rate, accent, and the use of timing information within a sentence to parse ambiguities). The participants with PD showed significantly worse performance on the task of compressed rate and used the duration of an ambiguous fricative to segment speech to a lesser degree than age-matched controls, indicating impaired speech perceptual abilities. Exploratory comparisons also showed people with PD who were on medication performed significantly worse than their peers off medication on those two tasks and the task of explicit non-native learning.

Lexical Effects on the Perceived Clarity of Noise-Vocoded Speech in Younger and Older Listeners

When listening to degraded speech, such as speech delivered by a cochlear implant (CI), listeners make use of top-down linguistic knowledge to facilitate speech recognition. Lexical knowledge supports speech recognition and enhances the perceived clarity of speech. Yet, the extent to which lexical knowledge can be used to effectively compensate for degraded input may depend on the degree of degradation and the listener's age. The current study investigated lexical effects in the compensation for speech that was degraded via noise-vocoding in younger and older listeners. In an online experiment, younger and older normal-hearing (NH) listeners rated the clarity of noise-vocoded sentences on a scale from 1 ("very unclear") to 7 ("completely clear"). Lexical information was provided by matching text primes and the lexical content of the target utterance. Half of the sentences were preceded by a matching text prime, while half were preceded by a non-matching prime. Each sentence also consisted of three key words of high or low lexical frequency and neighborhood density. Sentences were processed to simulate CI hearing, using an eight-channel noise vocoder with varying filter slopes. Results showed that lexical information impacted the perceived clarity of noise-vocoded speech. Noise-vocoded speech was perceived as clearer when preceded by a matching prime, and when sentences included key words with high lexical frequency and low neighborhood density. However, the strength of the lexical effects depended on the level of degradation. Matching text primes had a greater impact for speech with poorer spectral resolution, but lexical content had a smaller impact for speech with poorer spectral resolution. Finally, lexical information appeared to benefit both younger and older listeners. Findings demonstrate that lexical knowledge can be employed by younger and older listeners in cognitive compensation during the processing of noise-vocoded speech. However, lexical content may not be as reliable when the signal is highly degraded. Clinical implications are that for adult CI users, lexical knowledge might be used to compensate for the degraded speech signal, regardless of age, but some CI users may be hindered by a relatively poor signal.

Effects of word familiarity and receptive vocabulary size on speech-in-noise recognition among young adults with normal hearing

Having a large receptive vocabulary benefits speech-in-noise recognition for young children, though this is not always the case for older children or adults. These observations could indicate that effects of receptive vocabulary size on speech-in-noise recognition differ depending on familiarity of the target words, with effects observed only for more recently acquired and less frequent words. Two experiments were conducted to evaluate effects of vocabulary size on open-set speech-in-noise recognition for adults with normal hearing. Targets were words acquired at 4, 9, 12 and 15 years of age, and they were presented at signal-to-noise ratios (SNRs) of -5 and -7 dB. Percent correct scores tended to fall with increasing age of acquisition (AoA), with the caveat that performance at -7 dB SNR was better for words acquired at 9 years of age than earlier- or later-acquired words. Similar results were obtained whether the AoA of the target words was blocked or mixed across trials. Differences in word duration appear to account for nonmonotonic effects of AoA. For all conditions, a positive correlation was observed between recognition and vocabulary size irrespective of target word AoA, indicating that effects of vocabulary size are not limited to recently acquired words. This dataset does not support differential assessment of AoA, lexical frequency, and other stimulus features known to affect lexical access.

From Speech Acoustics to Communicative Participation in Dysarthria: Toward a Causal Framework

PURPOSE

We proposed and tested a causal instantiation of the World Health Organization's International Classification of Functioning, Disability and Health (ICF) framework, linking acoustics, intelligibility, and communicative participation in the context of dysarthria.

METHOD

Speech samples and communicative participation scores were collected from individuals with dysarthria (n = 32). Speech was analyzed for two acoustic metrics (i.e., articulatory precision and speech rate), and an objective measure of intelligibility was generated from listener transcripts. Mediation analysis was used to evaluate pathways of effect between acoustics, intelligibility, and communicative participation.

RESULTS

We observed a strong relationship between articulatory precision and intelligibility and a moderate relationship between intelligibility and communicative participation. Collectively, data supported a significant relationship between articulatory precision and communicative participation, which was almost entirely mediated through intelligibility. These relationships were not significant when speech rate was specified as the acoustic variable of interest.

CONCLUSION

The statistical corroboration of our causal instantiation of the ICF framework with articulatory acoustics affords important support toward the development of a comprehensive causal framework to understand and, ultimately, address restricted communicative participation in dysarthria.

Individual Differences in Phonetic Plasticity Across Native and Nonnative Contexts

Purpose Individuals vary in their ability to learn the sound categories of nonnative languages (nonnative phonetic learning) and to adapt to systematic differences, such as accent or talker differences, in the sounds of their native language (native phonetic learning). Difficulties with both native and nonnative learning are well attested in people with speech and language disorders relative to healthy controls, but substantial variability in these skills is also present in the typical population. This study examines whether this individual variability can be organized around a common ability that we label "phonetic plasticity." Method A group of healthy young adult participants (N = 80), who attested they had no history of speech, language, neurological, or hearing deficits, completed two tasks of nonnative phonetic category learning, two tasks of learning to cope with variation in their native language, and seven tasks of other cognitive functions, distributed across two sessions. Performance on these 11 tasks was compared, and exploratory factor analysis was used to assess the extent to which performance on each task was related to the others. Results Performance on both tasks of native learning and an explicit task of nonnative learning patterned together, suggesting that native and nonnative phonetic learning tasks rely on a shared underlying capacity, which is termed "phonetic plasticity." Phonetic plasticity was also associated with vocabulary, comprehension of words in background noise, and, more weakly, working memory. Conclusions Nonnative sound learning and native language speech perception may rely on shared phonetic plasticity. The results suggest that good learners of native language phonetic variation are also good learners of nonnative phonetic contrasts. Supplemental Material https://doi.org/10.23641/asha.16606778.

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.

Exploring the Acoustic Perceptual Relationship of Speech in Parkinson's Disease

Purpose Auditory perceptual judgments are commonly used to diagnose dysarthria and assess treatment progress. The purpose of the study was to examine the acoustic underpinnings of perceptual speech abnormalities in individuals with Parkinson's disease (PD). Method Auditory perceptual judgments were obtained from sentences produced by 13 speakers with PD and five healthy older adults. Twenty young listeners rated overall ease of understanding, articulatory precision, voice quality, and prosodic adequacy on a visual analog scale. Acoustic measures associated with the speech subsystems of articulation, phonation, and prosody were obtained, including second formant transitions, articulation rate, cepstral and spectral measures of voice, and pitch variations. Regression analyses were performed to assess the relationships between perceptual judgments and acoustic variables. Results Perceptual impressions of Parkinsonian speech were related to combinations of several acoustic variables. Approximately 36%-49% of the variance in the perceptual ratings were explained by the acoustic measures indicating a modest acoustic perceptual relationship. Conclusions The relationships between perceptual ratings and acoustic signals in Parkinsonian speech are multifactorial and involve a variety of acoustic features simultaneously. The modest acoustic perceptual relationships, however, suggest that future work is needed to further examine the acoustic bases of perceptual judgments in dysarthria.

Listener characteristics differentially affect self-reported and physiological measures of effort associated with two challenging listening conditions

Listeners vary in their ability to understand speech in adverse conditions. Differences in both cognitive and linguistic capacities play a role, but increasing evidence suggests that such factors may contribute differentially depending on the listening challenge. Here, we used multilevel modeling to evaluate contributions of individual differences in age, hearing thresholds, vocabulary, selective attention, working memory capacity, personality traits, and noise sensitivity to variability in measures of comprehension and listening effort in two listening conditions. A total of 35 participants completed a battery of cognitive and linguistic tests as well as a spoken story comprehension task using (1) native-accented English speech masked by speech-shaped noise and (2) nonnative accented English speech without masking. Masker levels were adjusted individually to ensure each participant would show (close to) equivalent word recognition performance across the two conditions. Dependent measures included comprehension tests results, self-rated effort, and electrodermal, cardiovascular, and facial electromyographic measures associated with listening effort. Results showed varied patterns of responsivity across different dependent measures as well as across listening conditions. In particular, results suggested that working memory capacity may play a greater role in the comprehension of nonnative accented speech than noise-masked speech, while hearing acuity and personality may have a stronger influence on physiological responses affected by demands of understanding speech in noise. Furthermore, electrodermal measures may be more strongly affected by affective response to noise-related interference while cardiovascular responses may be more strongly affected by demands on working memory and lexical access.

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.

Predicting Intelligibility Deficits in Parkinson's Disease With Perceptual Speech Ratings

Purpose This study investigated whether perceptual ratings of speech parameters were predictive of transcription intelligibility in quiet and in noise for speakers with Parkinson's disease (PD). Method Ten speakers with PD and five healthy controls read 56 sentences. One group of 60 listeners orthographically transcribed the sentences in quiet, and another group of 60 listeners transcribed in noise. An additional 23 listeners judged a variety of speech parameters, including articulation, prosody, resonance, voice quality, and ease of understanding on a visual analog scale. Scores of the visual analog scale ratings were regressed against transcription intelligibility in quiet and in noise. Results Perceptual ratings of all the speech parameters were lower for speakers with PD. Global speech understanding, indexed by ease of understanding ratings, was associated with transcription intelligibility in quiet and in noise with a stronger effect in noise. Among the rated speech parameters, ease of understanding and voice quality ratings were significant predictors of speech intelligibility in noise. Conclusions Speech in individuals with PD was more difficult for listeners to understand and was characterized by deficits in articulation, prosody, resonance, and voice quality compared to normal speech produced by healthy older adults. Ease of understanding ratings, even when performed in quiet, predicted intelligibility in noise. Poor voice quality ratings in PD, a sign of phonatory deficit, had a negative impact on intelligibility in noise for speakers with PD.

Neural Mechanisms Underlying the Processing of Complex Sentences: An fMRI Study

Previous research has shown effects of syntactic complexity on sentence processing. In linguistics, syntactic complexity (caused by different word orders) is traditionally explained by distinct linguistic operations. This study investigates whether different complex word orders indeed result in distinct patterns of neural activity, as would be expected when distinct linguistic operations are applied. Twenty-two older adults performed an auditory sentence processing paradigm in German with and without increased cognitive load. The results show that without increased cognitive load, complex sentences show distinct activation patterns compared with less complex, canonical sentences: complex object-initial sentences show increased activity in the left inferior frontal and temporal regions, whereas complex adjunct-initial sentences show increased activity in occipital and right superior frontal regions. Increased cognitive load seems to affect the processing of different sentence structures differently, increasing neural activity for canonical sentences, but leaving complex sentences relatively unaffected. We discuss these results in the context of the idea that linguistic operations required for processing sentence structures with higher levels of complexity involve distinct brain operations.

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.

Autoscore: An open-source automated tool for scoring listener perception of speech

Speech perception studies typically rely on trained research assistants to score orthographic listener transcripts for words correctly identified. While the accuracy of the human scoring protocol has been validated with strong intra- and inter-rater reliability, the process of hand-scoring the transcripts is time-consuming and resource intensive. Here, an open-source computer-based tool for automated scoring of listener transcripts is built (Autoscore) and validated on three different human-scored data sets. Results show that not only is Autoscore highly accurate, achieving approximately 99% accuracy, but extremely efficient. Thus, Autoscore affords a practical research tool, with clinical application, for scoring listener intelligibility of speech.

The Impact of Lexical Characteristics and Noise on Intelligibility of Parkinsonian Speech

PURPOSE

This study investigated the impact of lexical characteristics on the intelligibility of speakers with Parkinson's disease (PD). Intelligibility was compared for listening in a quiet versus a noisy environment.

METHOD

A total of 192 young listeners participated in the study, with 96 listeners listening in quiet and 96 listening in noise in which the spoken sentences were mixed with 10-talker babble. The listeners transcribed spoken sentences with target words controlled for word frequency and neighborhood density. The sentences were produced by 12 speakers with PD and 12 healthy control (HC) speakers. Transcription accuracy was compared across lexical categories between PD and HC and between the two listening conditions.

RESULTS

Transcription accuracy was higher for high-frequency words than low-frequency words for both speaker groups in quiet and in noise. The neighborhood density effect was evident only in the noise condition with better intelligibility for words from sparse neighborhoods than from dense neighborhoods. Regardless of listening condition, the PD group was less intelligible with a significant decrease in intelligibility in noise relative to quiet.

CONCLUSIONS

The lexical properties of the words affected listeners' understanding of Parkinsonian speech. Frequent words in sparse neighborhood enhanced intelligibility, especially under adverse listening conditions. Babble noise had a detrimental impact on the intelligibility of Parkinsonian speech. The extent of the lexical effect on intelligibility increased in noise.

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.

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.

A relationship between processing speech in noise and dysarthric speech

There is substantial individual variability in understanding speech in adverse listening conditions. This study examined whether a relationship exists between processing speech in noise (environmental degradation) and dysarthric speech (source degradation), with regard to intelligibility performance and the use of metrical stress to segment the degraded speech signals. Ninety native speakers of American English transcribed speech in noise and dysarthric speech. For each type of listening adversity, transcriptions were analyzed for proportion of words correct and lexical segmentation errors indicative of stress cue utilization. Consistent with the hypotheses, intelligibility performance for speech in noise was correlated with intelligibility performance for dysarthric speech, suggesting similar cognitive-perceptual processing mechanisms may support both. The segmentation results also support this postulation. While stress-based segmentation was stronger for speech in noise relative to dysarthric speech, listeners utilized metrical stress to parse both types of listening adversity. In addition, reliance on stress cues for parsing speech in noise was correlated with reliance on stress cues for parsing dysarthric speech. Taken together, the findings demonstrate a preference to deploy the same cognitive-perceptual strategy in conditions where metrical stress offers a route to segmenting degraded speech.

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.

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.

The role of stress and word size in Spanish speech segmentation

In English, the predominance of stressed syllables as word onsets aids lexical segmentation in degraded listening conditions. Yet it is unlikely that these findings would readily transfer to languages with differing rhythmic structure. In the current study, the authors seek to examine whether listeners exploit both common word size (syllable number) and stress cues to aid lexical segmentation in Spanish. Forty-seven Spanish-speaking listeners transcribed two-word Spanish phrases in noise. As predicted by the statistical probabilities of Spanish, error analysis revealed that listeners preferred two- and three-syllable words with penultimate stress in their attempts to parse the degraded speech signal. These findings provide insight into the importance of stress in tandem with word size in the segmentation of Spanish words and suggest testable hypotheses for cross-linguistic studies that examine the effects of degraded acoustic cues on lexical segmentation.

Individual differences in the perception of regional, nonnative, and disordered speech varieties

Speech perception abilities vary substantially across listeners, particularly in adverse conditions including those stemming from environmental degradation (e.g., noise) or from talker-related challenges (e.g., nonnative or disordered speech). This study examined adult listeners' recognition of words in phrases produced by six talkers representing three speech varieties: a nonnative accent (Spanish-accented English), a regional dialect (Irish English), and a disordered variety (ataxic dysarthria). Semantically anomalous phrases from these talkers were presented in a transcription task and intelligibility scores, percent words correct, were compared across the three speech varieties. Three cognitive-linguistic areas-receptive vocabulary, cognitive flexibility, and inhibitory control of attention-were assessed as possible predictors of individual word recognition performance. Intelligibility scores for the Spanish accent were significantly correlated with scores for the Irish English and ataxic dysarthria. Scores for the Irish English and dysarthric speech, in contrast, were not correlated. Furthermore, receptive vocabulary was the only cognitive-linguistic assessment that significantly predicted intelligibility scores. These results suggest that, rather than a global skill of perceiving speech that deviates from native dialect norms, listeners may possess specific abilities to overcome particular types of acoustic-phonetic deviation. Furthermore, vocabulary size offers performance benefits for intelligibility of speech that deviates from one's typical dialect norms.

Age-Related Differences in Lexical Access Relate to Speech Recognition in Noise

Vocabulary size has been suggested as a useful measure of “verbal abilities” that correlates with speech recognition scores. Knowing more words is linked to better speech recognition. How vocabulary knowledge translates to general speech recognition mechanisms, how these mechanisms relate to offline speech recognition scores, and how they may be modulated by acoustical distortion or age, is less clear. Age-related differences in linguistic measures may predict age-related differences in speech recognition in noise performance. We hypothesized that speech recognition performance can be predicted by the efficiency of lexical access, which refers to the speed with which a given word can be searched and accessed relative to the size of the mental lexicon. We tested speech recognition in a clinical German sentence-in-noise test at two signal-to-noise ratios (SNRs), in 22 younger (18–35 years) and 22 older (60–78 years) listeners with normal hearing. We also assessed receptive vocabulary, lexical access time, verbal working memory, and hearing thresholds as measures of individual differences. Age group, SNR level, vocabulary size, and lexical access time were significant predictors of individual speech recognition scores, but working memory and hearing threshold were not. Interestingly, longer accessing times were correlated with better speech recognition scores. Hierarchical regression models for each subset of age group and SNR showed very similar patterns: the combination of vocabulary size and lexical access time contributed most to speech recognition performance; only for the younger group at the better SNR (yielding about 85% correct speech recognition) did vocabulary size alone predict performance. Our data suggest that successful speech recognition in noise is mainly modulated by the efficiency of lexical access. This suggests that older adults’ poorer performance in the speech recognition task may have arisen from reduced efficiency in lexical access; with an average vocabulary size similar to that of younger adults, they were still slower in lexical access.

Effects of listeners' working memory and noise on speech intelligibility in dysarthria

The purpose of this study was to investigate the effects of listeners' working memory (WM), types of noise and signal to noise ratios (SNRs) on speech intelligibility in dysarthria. Speech intelligibility was judged by using a word transcription task. A three-way mixed design (2 × 3 × 2) was used with the WM group (high/low group) as a between-subject factor and the types of noise (multi-talker babble/environmental noise) and SNRs (0, +10 and +20 dB) as within-subject factors. The dependent measure was the percentage of correctly transcribed words. The results revealed that the high WM group performed significantly better than the low WM group and listeners performed significantly better at higher levels of SNRs on the speech intelligibility test. The findings of this study suggested that listeners' cognitive abilities and SNRs should be considered as important factors when evaluating speech intelligibility in dysarthria.

Cognitive-perceptual examination of remediation approaches to hypokinetic dysarthria

PURPOSE

To determine how increased vocal loudness and reduced speech rate affect listeners' cognitive-perceptual processing of hypokinetic dysarthric speech associated with Parkinson's disease.

METHOD

Fifty-one healthy listener participants completed a speech perception experiment. Listeners repeated phrases produced by 5 individuals with dysarthria across habitual, loud, and slow speaking modes. Listeners were allocated to habitual ( n = 17), loud ( n = 17), or slow ( n = 17) experimental conditions. Transcripts derived from the phrase repetition task were coded for overall accuracy (i.e., intelligibility), and perceptual error analyses examined how these conditions affected listeners' phonemic mapping (i.e., syllable resemblance) and lexical segmentation (i.e., lexical boundary error analysis).

RESULTS

Both speech conditions provided obvious perceptual benefits to listeners. Overall, transcript accuracy was highest in the slow condition. In the loud condition, however, improvement was evidenced across the experiment. An error analysis suggested that listeners in the loud condition prioritized acoustic-phonetic cues in their attempts to resolve the degraded signal, whereas those in the slow condition appeared to preferentially weight lexical stress cues.

CONCLUSIONS

Increased loudness and reduced rate exhibited differential effects on listeners' perceptual processing of dysarthric speech. The current study highlights the insights that may be gained from a cognitive-perceptual approach.