Lansford, Kaitlin L.

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

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.

Speaker normalization, a process whereby the perceptual system of a listener recalibrates to accommodate individual speakers, is proposed to account for the ease with which we understand speech produced by multiple speakers with different sized and shaped vocal tracts. A variety of vowel-, formant-, and speaker-intrinsic or extrinsic transforms have been proposed to model speaker normalization of vowels produced by multiple speakers (e.g., Mel, Bark, and Lobanov methods). Suitability of such normalization procedures has been examined extensively in non-disordered speaker populations. Unknown at this point, however, is the appropriateness of normalization procedures for transforming spectrally distorted vowels produced by speakers with dysarthria. Thus, we examined the suitability of two transforms, Bark and Lobanov, for normalizing vowels produced by a heterogeneous cohort of 45 speakers with dysarthria. Non-normalized (Hertz) and Bark transformed vowel tokens were classified via discriminant function analysis (DFA) with 55% and 56% accuracy, respectively. Classification accuracy of vowel tokens normalized using Lobanov’s method was 65%. The results of the DFAs were compared to perceptual data, which revealed listeners identified vowel tokens with 71% accuracy. These results suggest vowel-extrinsic and formant- and speaker-intrinsic normalization methods (e.g., Lobanov) are better suited to model speaker normalization of dysarthric vowels.

Although intelligibility deficits are common across various forms of dysarthria, it was hypothesized that the causes of intelligibility reductions depend on the ways the degraded signal challenges listener cognitive-perceptual strategies. This hypothesis was confirmed by analyzing the lexical boundary errors (LBE) elicited by 44 speakers with one of four forms of dysarthria (ataxic, hypokinetic, hyperkinetic, mixed spastic-flaccid). Error patterns from 60 listener transcripts revealed reliance on metrical stress to segment the 80 six-syllable phrases. However, reductions and disturbances in the acoustic cues to syllabic stress associated with each form of dysarthria resulted in different LBE patterns. Explanations for these unique patterns are found, in part, in the metrical structures of the dysarthric speech. For example, the temporal relationships among stressed and unstressed syllables varied widely in hyperkinetic speech, which ostensibly prevented listeners from optimally exploiting metrical stress as a cue for segmentation. The equal-even temporal structure of the spastic-flaccid speech resulted in the highest proportion of boundary insertions. The presence of interword pauses facilitated the assignment of word onset to strong syllables. Results will be presented relative to models of lexical segmentation and clinical implications for targets of remediation in the dysarthrias. [Work supported from NIH-NIDCD 5R01 DC6859.]

The detrimental effect of speaker variability on word recognition has been reported using a wide variety of tasks and stimuli. In this study, the use of dysarthric speech alongside unimpaired speech allowed us to examine the effect of indexical variability from a new perspective. We compared voice-specificity effects in words produced by healthy speakers and the same words produced by dysarthric patients suffering from Huntington’s disease (HD). The speech of persons with HD is particularly suited to this issue because of its idiosyncratic and variable manifestation. Reaction time and accuracy results provided confirmatory evidence for Luce et al.’s (2003) time-course hypothesis: The slower responses occasioned by processing dysarthric stimuli were accompanied with greater reliance on surface details of the stimuli. Thus, specificity effects can be seen as resulting from a coping strategy called upon when the system is presented with an input that is highly dissimilar from canonical lexical representations. In addition, we found some evidence that the time-course hypothesis holds even when intelligibility is controlled. This finding confirms that time, rather than processing effort, is the cause of specificity effects, with activation confined to abstract representations in an early stage and spreading to episodic traces later on.

Disturbances in speech rhythm are common in dysarthria, and deficit patterns vary among dysarthria subtypes. Attempts to quantify differences in disordered rhythm patterns have met with limited success. Here, we attempt to differentiate various forms of dysarthria using metrics designed to quantify linguistic rhythm on a stress-timed versus syllable-timed continuum. Speakers with hypokinetic, ataxic, hyperkinetic, or mixed flaccid-spastic dysarthria read sentences. Rhythm metrics were calculated for these utterances based on vocalic and consonantal interval durations. Differences among groups were discovered for %V (percentage of utterance duration comprised of vocalic intervals), VarcoV (rate-normalized standard deviation of vocalic interval durations), and nPVI-V (normalized pairwise variability index for vocalic intervals). Differences were independent of variable speaking rates among groups. All dysarthric groups produced rhythm patterns less stress-timed than the control American English speakers, with lower VarcoV and nPVI-V and higher %V. Those with flaccid-spastic dysarthria secondary to amyotrophic lateral sclerosis exhibited a syllable-timed pattern more extreme than even control Spanish speakers, indicating minimal differentiation of stressed and unstressed syllables. These results show that the various types of rhythmic disturbance accompanying dysarthria can be effectively described and distinguished within a stress-/syllable-timed continuum and relative to healthy speech.

High-density electroencephalography (EEG) was used to evaluate cortical activity patterns during the auditory processing of speech presented at various levels of degradation in a sentence verification task. 25 healthy participants listened to true-false sentences produced with one of 3 channel levels (1, 6, 16), ranging from unintelligible, moderately intelligible, and highly intelligible. Behavioral data were collected via button press (reaction time and accuracy) for each sentence. The analysis of cortical activation patterns includes 1) the identification of independent components that account for variations of activity associated with degradation levels and 2) the examination of associated event-related potentials. Statistical analyses will be performed on individuals' cortical activity, in tandem with behavioral data. Preliminary results reveal differences in the timing and magnitude of frontal and temporal lobe activation that coincide with task difficulty. Results of the present investigation will inform hypotheses about regions of interest for further investigation and will bear on models of connected speech perception, including the neurobiological underpinnings of individual differences and manifestations in a listener's understanding of degraded speech.

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.

Purpose In this study, the authors examined whether rhythm metrics capable of distinguishing languages with high and low temporal stress contrast also can distinguish among control and dysarthric speakers of American English with perceptually distinct rhythm patterns. Methods Acoustic measures of vocalic and consonantal segment durations were obtained for speech samples from 55 speakers across 5 groups (hypokinetic, hyperkinetic, flaccid-spastic, ataxic dysarthrias, and controls). Segment durations were used to calculate standard and new rhythm metrics. Discriminant function analyses (DFAs) were used to determine which sets of predictor variables (rhythm metrics) best discriminated between groups (control vs. dysarthrias; and among the 4 dysarthrias). A cross-validation method was used to test the robustness of each original DFA. Results The majority of classification functions were more than 80% successful in classifying speakers into their appropriate group. New metrics that combined successive vocalic and consonantal segments emerged as important predictor variables. DFAs pitting each dysarthria group against the combined others resulted in unique constellations of predictor variables that yielded high levels of classification accuracy. Conclusions This study confirms the ability of rhythm metrics to distinguish control speech from dysarthrias and to discriminate dysarthria subtypes. Rhythm metrics show promise for use as a rational and objective clinical tool.