The Effect of Tongue-Jaw Coupling on Phonetic Distinctiveness of Vowels in Amyotrophic Lateral Sclerosis

A multimodal approach to automated hierarchical assessment of bulbar involvement in amyotrophic lateral sclerosis

Introduction

As a hallmark feature of amyotrophic lateral sclerosis (ALS), bulbar involvement leads to progressive declines of speech and swallowing functions, significantly impacting social, emotional, and physical health, and quality of life. Standard clinical tools for bulbar assessment focus primarily on clinical symptoms and functional outcomes. However, ALS is known to have a long, clinically silent prodromal stage characterized by complex subclinical changes at various levels of the bulbar motor system. These changes accumulate over time and eventually culminate in clinical symptoms and functional declines. Detection of these subclinical changes is critical, both for mechanistic understanding of bulbar neuromuscular pathology and for optimal clinical management of bulbar dysfunction in ALS. To this end, we developed a novel multimodal measurement tool based on two clinically readily available, noninvasive instruments-facial surface electromyography (sEMG) and acoustic techniques-to hierarchically assess seven constructs of bulbar/speech motor control at the neuromuscular and acoustic levels. These constructs, including prosody, pause, functional connectivity, amplitude, rhythm, complexity, and regularity, are both mechanically and clinically relevant to bulbar involvement.

Methods

Using a custom-developed, fully automated data analytic algorithm, a variety of features were extracted from the sEMG and acoustic recordings of a speech task performed by 13 individuals with ALS and 10 neurologically healthy controls. These features were then factorized into 10 composite outcome measures using confirmatory factor analysis. Statistical and machine learning techniques were applied to these composite outcome measures to evaluate their reliability (internal consistency), validity (concurrent and construct), and efficacy for early detection and progress monitoring of bulbar involvement in ALS.

Results

The composite outcome measures were demonstrated to (1) be internally consistent and structurally valid in measuring the targeted constructs; (2) hold concurrent validity with the existing clinical and functional criteria for bulbar assessment; and (3) outperform the outcome measures obtained from each constituent modality in differentiating individuals with ALS from healthy controls. Moreover, the composite outcome measures combined demonstrated high efficacy for detecting subclinical changes in the targeted constructs, both during the prodromal stage and during the transition from prodromal to symptomatic stages.

Discussion

The findings provided compelling initial evidence for the utility of the multimodal measurement tool for improving early detection and progress monitoring of bulbar involvement in ALS, which have important implications in facilitating timely access to and delivery of optimal clinical care of bulbar dysfunction.

Hierarchical Temporal Structuring of Speech: A Multiscale, Multimodal Framework to Inform the Assessment and Management of Neuromotor Speech Disorder

PURPOSE

Hierarchical temporal structuring of speech is the key to multiscale linguistic information transfer toward effective communication. This study investigated and linked the hierarchical temporal cues of the kinematic and acoustic modalities of natural, unscripted speech in neurologically healthy and impaired speakers.

METHOD

Thirteen individuals with amyotrophic lateral sclerosis (ALS) and 10 age-matched healthy controls performed a story-telling task. The hierarchical temporal structure of the speech stimulus was measured by (a) 26 articulatory-kinematic features characterizing the depth, phase synchronization, and coherence of temporal modulation of the tongue tip, tongue body, lower lip, and jaw, at three hierarchically nested timescales corresponding to prosodic stress, syllables, and onset-rime/phonemes, and (b) 25 acoustic features characterizing the parallel aspects of temporal modulation of five critical-spectral-band envelopes. All features were compared between groups. For each aspect of temporal modulation, the contributions of all articulatory features to the parallel acoustic features were evaluated by group.

RESULTS

Generally consistent disease impacts were identified on the articulatory and acoustic features, manifested by reduced modulation depths of most articulators and critical-spectral-band envelopes, primarily at the timescales of syllables and onset-rime/phonemes. For healthy speakers, the strongest articulatory-acoustic relationships were found for (a) jaw and lip, in modulating stress timing, and (b) tongue tip, in modulating the timing relation between onset-rime/phonemes and syllables. For speakers with ALS, the tongue body, tongue tip, and jaw all showed the greatest contributions to modulating syllable timing.

CONCLUSIONS

The observed disease impacts likely reflect reduced entrainment of speech motor activities to finer-grained linguistic events, presumably due to the dynamic constraints of the neuromuscular system. To accommodate these restrictions, speakers with ALS appear to use their residual articulatory motor capacities to accentuate and convey the perceptually most salient temporal cues underpinned by the syllable-centric parsing mechanism. This adaptive strategy has potential implications in managing neuromotor speech disorders.

A Fine-Grained Temporal Analysis of Multimodal Oral Diadochokinetic Performance to Assess Speech Impairment in Amyotrophic Lateral Sclerosis

PURPOSE

This study used a semiautomated fine-grained temporal analysis to extract features of temporal oral diadochokinetic (DDK) performance across multiple modalities and tasks, from neurologically healthy and impaired individuals secondary to amyotrophic lateral sclerosis (ALS). The aims were to (a) delineate temporal oral DDK deficits relating to the neuromotor pathology of ALS and (b) identify the optimal task-feature combinations to detect speech impairment in ALS.

METHOD

Mandibular myoelectric, kinematic, and acoustic data were acquired from 13 individuals with ALS and 10 healthy controls producing three alternating motion rate tasks and one sequential motion rate task. Twenty-seven features were extracted from the multimodal data, characterizing three temporal constructs: duration/rate, variability, and coordination. The disease impacts on these features were assessed across tasks, and the task eliciting the greatest disease-related change was identified for each feature. Such "optimal" task-feature combinations were fed into logistic regression to differentiate individuals with ALS from healthy controls.

RESULTS

Temporal deficits in ALS were characterized by (a) increased duration and variability and reduced coordination of jaw muscle activities, (b) increased duration and variability and altered temporal symmetry of jaw velocity profile, (c) increased muscle-burst-to-peak-velocity duration, and (d) increased motion-to-voice onset duration. These temporal features were differentially affected across tasks. The optimal task-feature combinations, which were further clustered into three composite factors reflecting temporal variability, coarser-grained duration, and finer-grained duration, differentiated ALS from controls with an F1 score of 0.86 (precision = 1.00, recall = 0.75).

CONCLUSIONS

Temporal oral DDK deficits are likely attributed to a hierarchy of interrelated neurophysiological and biomechanical factors associated with the neuromotor pathology of ALS. These deficits, as assessed crossmodally, provide previously unavailable insights into the multifaceted timing impairment of oromotor performance in ALS. The optimal task-feature combinations targeting these deficits show promise as quantitative markers for (early) detection of speech impairment in ALS.

The Relationship Between Acoustic and Kinematic Vowel Space Areas With and Without Normalization for Speakers With and Without Dysarthria

PURPOSE

Few studies have reported on the vowel space area (VSA) in both acoustic and kinematic domains. This study examined acoustic and kinematic VSAs for speakers with and without dysarthria and evaluated effects of normalization on acoustic and kinematic VSAs and the relationship between these measures.

METHOD

Vowel data from 12 speakers with and without dysarthria, presenting with a range of speech abilities, were examined. The speakers included four speakers with Parkinson's disease (PD), four speakers with brain injury (BI), and four neurotypical (NT) speakers. Speech acoustic and kinematic data were acquired simultaneously using electromagnetic articulography during a passage reading task. Raw and normalized VSAs calculated from corner vowels /i/, /æ/, /ɑ/, and /u/ were evaluated. Normalization was achieved through z score transformations to the acoustic and kinematic data. The effect of normalization on variability within and across groups was evaluated. Regression analysis was used across speakers to assess the association between acoustic and kinematic VSAs for both raw and normalized data.

RESULTS

When evaluating the speakers as three different groups (i.e., PD, BI, and NT), normalization reduced the standard deviations within each group and changed the relative differences in average magnitude between groups. Regression analysis revealed a significant relationship between normalized, but not raw, acoustic and kinematic VSAs, after the exclusion of an outlier speaker.

CONCLUSIONS

Normalization reduces the variability across speakers, within groups, and changes average magnitudes affecting speaker group comparisons. Normalization also influences the correlation between acoustic and kinematic measures. Further investigation of the impact of normalization techniques upon acoustic and kinematic measures is warranted.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.22669747.

Functional Role of Temporal Patterning of Articulation in Speech Production: A Novel Perspective Toward Global Timing-Based Motor Speech Assessment and Rehabilitation

PURPOSE

This study aimed to (a) relate temporal patterning of articulation to functional speech outcomes in neurologically healthy and impaired speakers, (b) identify changes in temporal patterning of articulation in neurologically impaired speakers, and (c) evaluate how these changes can be modulated by speaking rate manipulation.

METHOD

Thirteen individuals with amyotrophic lateral sclerosis (ALS) and 10 neurologically healthy controls read a sentence 3 times, first at their habitual rate and then at a voluntarily slowed rate. Temporal patterning of articulation was assessed by 24 features characterizing the modulation patterns within (intra) and between (inter) four articulators (tongue tip, tongue body, lower lip, and jaw) at three linguistically relevant, hierarchically nested timescales corresponding to stress, syllable, and onset-rime/phoneme. For Aim 1, the features for the habitual rate condition were factorized and correlated with two functional speech outcomes-speech intelligibility and intelligible speaking rate. For Aims 2 and 3, the features were compared between groups and rate conditions, respectiely.

RESULTS

For Aim 1, the modulation features combined were moderately to strongly correlated with intelligibility (R ² = .51-.53) and intelligible speaking rate (R ² = .63-.73). For Aim 2, intra-articulator modulation was impaired in ALS, manifested by moderate-to-large decreases in modulation depth at all timescales and cross-timescale phase synchronization. Interarticulator modulation was relatively unaffected. For Aim 3, voluntary rate reduction improved several intra-articulator modulation features identified as being susceptible to the disease effect in individuals with ALS.

CONCLUSIONS

Disrupted temporal patterning of articulation, presumably reflecting impaired articulatory entrainment to linguistic rhythms, may contribute to functional speech declines in ALS. These impairments tend to be improved through voluntary rate reduction, possibly by reshaping the temporal template of motor plans to better accommodate the disease-related neuromechanical constraints in the articulatory system. These findings shed light on a novel perspective toward global timing-based motor speech assessment and rehabilitation.

Articulatory Underpinnings of Reduced Acoustic-Phonetic Contrasts in Individuals With Amyotrophic Lateral Sclerosis

PURPOSE

The aim of this study is to identify the articulatory underpinnings of the acoustic-phonetic correlates of functional speech decline in individuals with amyotrophic lateral sclerosis (ALS).

METHOD

Thirteen individuals with varying severities of speech impairment secondary to ALS and 10 neurologically healthy controls speakers read 12 minimal word pairs, targeting the contrasts in the height, advancement, and length of vowels; the manner and place of articulation for consonants and consonant cluster; and liquid and glide approximants, 5 times. Sixteen acoustic features were extracted to characterize the phonetic contrasts of these minimal word pairs. These acoustic features were correlated with a functional speech index-intelligible speaking rate-using penalized regression, based on which the contributive features were identified as the acoustic-phonetic correlates of the functional speech outcome. Articulatory contrasts of the minimal word pairs were characterized by a set of dissimilarity indices derived by the dynamic time warping algorithm, which measured the differences in the displacement and velocity trajectories of tongue tip, tongue dorsum, lower lip, and jaw between the minimal word pairs. The contributive articulatory features to the acoustic-phonetic correlates were identified by penalized regression.

RESULTS

A variety of acoustic-phonetic features were identified as contributing to the functional speech outcome, of which the contrasts in vowel height and advancement, [r]-[l], [r]-[w], and initial cluster-singleton were the most affected in individuals with ALS. Differential articulatory underpinnings were identified for these acoustic-phonetic features. Impairments of these articulatory underpinnings, especially of tongue tip and tongue dorsum velocities and tongue tip displacement, were associated with reduced acoustic-phonetic contrasts of the minimal word pairs, in a context-specific manner.

CONCLUSION

The findings established explanatory relationships between articulatory impairment and the acoustic-phonetic profile of functional speech decline in ALS, providing useful information for developing targeted management strategies to improve and prolong functional speech in individuals with ALS.

Relationship between rate-elicited changes in muscular-kinematic control strategies and acoustic performance in individuals with ALS-A multimodal investigation

INTRODUCTION

As a key control variable, duration has been long suspected to mediate the organization of speech motor control strategies, which has management implications for neuromotor speech disorders. This study aimed to experimentally delineate the role of duration in organizing speech motor control in neurologically healthy and impaired speakers using a voluntary speaking rate manipulation paradigm.

METHODS

Thirteen individuals with amyotrophic lateral sclerosis (ALS) and 10 healthy controls performed a sentence reading task three times, first at their habitual rate, then at a slower rate. A multimodal approach combining surface electromyography, kinematic, and acoustic technologies was used to record jaw muscle activities, jaw kinematics, and speech acoustics. Six muscular-kinematic features were extracted and factor-analyzed to characterize the organization of the mandibular control hierarchy. Five acoustic features were extracted, measuring the spectrotemporal properties of the diphthong /ɑɪ/ and the plosives /t/ and /k/.

RESULTS

The muscular-kinematic features converged into two interpretable latent factors, reflecting the level and cohesiveness/flexibility of mandibular control, respectively. Voluntary rate reduction led to a trend toward (1) finer, less cohesive, and more flexible mandibular control, and (2) increased range and decreased transition slope of the diphthong formants, across neurologically healthy and impaired groups. Differential correlations were found between the rate-elicited changes in mandibular control and acoustic performance for neurologically healthy and impaired speakers.

CONCLUSIONS

The results provided empirical evidence for the long-suspected but previously unsubstantiated role of duration in (re)organizing speech motor control strategies. The rate-elicited reorganization of muscular-kinematic control contributed to the acoustic performance of healthy speakers, in ways consistent with theoretical predictions. Such contributions were less consistent in impaired speakers, implying the complex nature of speaking rate reduction in ALS, possibly reflecting an interplay of disease-related constraints and volitional duration control. This information may help to stratify and identify candidates for the rate manipulation therapy.

"You Say Severe, I Say Mild": Toward an Empirical Classification of Dysarthria Severity

PURPOSE

The main purpose of this study was to create an empirical classification system for speech severity in patients with dysarthria secondary to amyotrophic lateral sclerosis (ALS) by exploring the reliability and validity of speech-language pathologists' (SLPs') ratings of dysarthric speech.

METHOD

Ten SLPs listened to speech samples from 52 speakers with ALS and 20 healthy control speakers. SLPs were asked to rate the speech severity of the speakers using five response options: normal, mild, moderate, severe, and profound. Four severity-surrogate measures were also calculated: SLPs transcribed the speech samples for the calculation of speech intelligibility and rated the effort it took to understand the speakers on a visual analog scale. In addition, speaking rate and intelligible speaking rate were calculated for each speaker. Intrarater and interrater reliability were calculated for each measure. We explored the validity of clinician-based severity ratings by comparing them to the severity-surrogate measures. Receiver operating characteristic (ROC) curves were conducted to create optimal cutoff points for defining dysarthria severity categories.

RESULTS

Intrarater and interrater reliability for the clinician-based severity ratings were excellent and were comparable to reliability for the severity-surrogate measures explored. Clinician severity ratings were strongly associated with all severity-surrogate measures, suggesting strong construct validity. We also provided a range of values for each severity-surrogate measure within each severity category based on the cutoff points obtained from the ROC analyses.

CONCLUSIONS

Clinician severity ratings of dysarthric speech are reliable and valid. We discuss the underlying challenges that arise when selecting a stratification measure and offer recommendations for a classification scheme when stratifying patients and research participants into speech severity categories.

Speech intelligibility loss due to amyotrophic lateral sclerosis: the effect of tongue movement reduction on vowel and consonant acoustic features

The purpose of this study was to identify aspects of impaired tongue motor performance that limit the ability to produce distinct speech sounds and contribute to reduced speech intelligibility in individuals with dysarthria secondary to amyotrophic lateral sclerosis (ALS). We analyzed simultaneously recorded tongue kinematic and acoustic data from 22 subjects during three target words (cat, dog, and took). The subjects included 11 participants with ALS and 11 healthy controls from the X-ray microbeam dysarthria database (Westbury, 1994). Novel measures were derived based on the range and speed of relative movement between two quasi-independent regions of the tongue - blade and dorsum - to characterize the global pattern of tongue dynamics. These "whole tongue" measures, along with the range and speed of single tongue regions, were compared across words, groups (ALS vs. control), and measure types (whole tongue vs. tongue blade vs. tongue dorsum). Reduced range and speed of both global and regional tongue movements were found in participants with ALS relative to healthy controls, reflecting impaired tongue motor performance in ALS. The extent of impairment, however, varied across words and measure types. Compared with the regional tongue measures, the whole tongue measures showed more consistent disease-related changes across the target words and were more robust predictors of speech intelligibility. Furthermore, these whole tongue measures were correlated with various word-specific acoustic features associated with intelligibility decline in ALS, suggesting that impaired tongue movement likely contributes to reduced phonetic distinctiveness of both vowels and consonants that underlie speech intelligibility decline in ALS.

Spatiotemporal Control of Articulation During Speech and Speechlike Tasks in Amyotrophic Lateral Sclerosis

Purpose This study examined the articulatory control of speech and speechlike tasks in individuals with amyotrophic lateral sclerosis (ALS) and neurologically healthy individuals with the aim to identify the most useful set of articulatory features and tasks for assessing bulbar motor involvement in ALS. Method Tongue and jaw kinematics were recorded in 12 individuals with bulbar ALS and 10 healthy controls during a speech task and two speechlike tasks (i.e., alternating motion rate [AMR], sequential motion rate [SMR]). Eight articulatory features were derived for each participant per task, including the range, maximum speed, and acceleration time of tongue and jaw movements as well as the coupling and timing between tongue and jaw movements. The effects of task (i.e., AMR, SMR, speech) and group (i.e., ALS, control) on these articulatory features were evaluated. For each feature, the task that yielded the largest difference between the ALS and control groups was identified. The diagnostic efficacy of these task-specific features was assessed using the receiver operating characteristic analysis; the relation of these task-specific features to a well-established bulbar severity index-speaking rate-was determined using Spearman's rank correlation. Results Seven task-specific articulatory features were identified, including (a) tongue and jaw acceleration time during the AMR task, (b) tongue-jaw coupling during the SMR task, and (c) range of tongue movement, maximum tongue and jaw speed, and temporal lag between tongue and jaw movements during the speech task. Among these features, tongue and jaw acceleration time and their temporal lag showed relatively high accuracy (i.e., 0.83-0.95) in differentiating individuals with ALS from healthy controls. Range of tongue movement and maximum tongue and jaw speed showed significant correlations with speaking rate. Conclusion Findings provided preliminary evidence for the utility of task-specific articulatory measurements as a novel quantitative assessment to detect and predict bulbar motor involvement in ALS.

Patterns of Misidentified Vowels in Individuals With Dysarthria Secondary to Amyotrophic Lateral Sclerosis

Purpose The current study examines the pattern of misidentified vowels produced by individuals with dysarthria secondary to amyotrophic lateral sclerosis (ALS). Method Twenty-three individuals with ALS and 22 typical individuals produced 10 monophthongs in an /h/-vowel-/d/ context. One hundred thirty-five listeners completed a forced-choice vowel identification test. Misidentified vowels were examined in terms of the target vowel categories (front-back; low-mid-high) and the direction of misidentification (the directional pattern when the target vowel was misidentified, e.g., misidentification "to a lower vowel"). In addition, acoustic predictors of vowel misidentifications were tested based on log first formant (F1), log second formant, log F1 vowel inherent spectral change, log second formant vowel inherent spectral change, and vowel duration. Results First, high and mid vowels were more frequently misidentified than low vowels for all speaker groups. Second, front and back vowels were misidentified at a similar rate for both the Mild and Severe groups, whereas back vowels were more frequently misidentified than front vowels in typical individuals. Regarding the direction of vowel misidentification, vowel errors were mostly made within the same backness (front-back) category for all groups. In addition, more errors were found toward a lower vowel category than toward a higher vowel category in the Severe group, but not in the Mild group. Overall, log F1 difference was identified as a consistent acoustic predictor of the main vowel misidentification pattern. Conclusion Frequent misidentifications in the vowel height dimension and the acoustic predictor, F1, suggest that limited tongue height control is the major articulatory dysfunction in individuals with ALS. Clinical implications regarding this finding are discussed.

Tongue- and Jaw-Specific Articulatory Changes and Their Acoustic Consequences in Talkers With Dysarthria due to Amyotrophic Lateral Sclerosis: Effects of Loud, Clear, and Slow Speech

Purpose This study aimed to determine how tongue and jaw displacement changes impact acoustic vowel contrast in talkers with amyotrophic lateral sclerosis (ALS) and controls. Method Ten talkers with ALS and 14 controls participated in this study. Loud, clear, and slow speech cues were used to elicit tongue and jaw kinematic as well as acoustic changes. Speech kinematics was recorded using three-dimensional articulography. Independent tongue and jaw displacements were extracted during the diphthong /ai/ in kite. Acoustic distance between diphthong onset and offset in Formant 1-Formant 2 vowel space indexed acoustic vowel contrast. Results In both groups, all three speech modifications elicited increases in jaw displacement (typical < slow < loud < clear). By contrast, only slow speech elicited significantly increased independent tongue displacement in the ALS group (typical = loud = clear < slow), whereas all three speech modifications elicited significantly increased independent tongue displacement in controls (typical < loud < clear = slow). Furthermore, acoustic vowel contrast significantly increased in response to clear and slow speech in the ALS group, whereas all three speech modifications elicited significant increases in acoustic vowel contrast in controls (typical < loud < slow < clear). Finally, only jaw displacements accounted for acoustic vowel contrast gains in the ALS group. In controls, however, independent tongue displacements accounted for increases in vowel acoustic contrast during loud and slow speech, whereas jaw and independent tongue displacements accounted equally for acoustic vowel contrast change during clear speech. Conclusion Kinematic findings suggest that slow speech may be better suited to target independent tongue displacements in talkers with ALS than clear and loud speech. However, given that gains in acoustic vowel contrast were comparable for slow and clear speech cues in these talkers, future research is needed to determine potential differential impacts of slow and clear speech on perceptual measures, such as intelligibility. Finally, findings suggest that acoustic vowel contrast gains are predominantly jaw driven in talkers with ALS. Therefore, the acoustic and perceptual consequences of direct instructions of enhanced jaw movements should be compared to cued speech modification, such as clear and slow speech in these talkers.

Automated Acoustic Analysis of Oral Diadochokinesis to Assess Bulbar Motor Involvement in Amyotrophic Lateral Sclerosis

Purpose The purpose of this article was to validate a novel acoustic analysis of oral diadochokinesis (DDK) in assessing bulbar motor involvement in amyotrophic lateral sclerosis (ALS). Method An automated acoustic DDK analysis was developed, which filtered out the voice features and extracted the envelope of the acoustic waveform reflecting the temporal pattern of syllable repetitions during an oral DDK task (i.e., repetitions of /tɑ/ at the maximum rate on 1 breath). Cycle-to-cycle temporal variability (cTV) of envelope fluctuations and syllable repetition rate (sylRate) were derived from the envelope and validated against 2 kinematic measures, which are tongue movement jitter (movJitter) and alternating tongue movement rate (AMR) during the DDK task, in 16 individuals with bulbar ALS and 18 healthy controls. After the validation, cTV, sylRate, movJitter, and AMR, along with an established clinical speech measure, that is, speaking rate (SR), were compared in their ability to (a) differentiate individuals with ALS from healthy controls and (b) detect early-stage bulbar declines in ALS. Results cTV and sylRate were significantly correlated with movJitter and AMR, respectively, across individuals with ALS and healthy controls, confirming the validity of the acoustic DDK analysis in extracting the temporal DDK pattern. Among all the acoustic and kinematic DDK measures, cTV showed the highest diagnostic accuracy (i.e., 0.87) with 80% sensitivity and 94% specificity in differentiating individuals with ALS from healthy controls, which outperformed the SR measure. Moreover, cTV showed a large increase during the early disease stage, which preceded the decline of SR. Conclusions This study provided preliminary validation of a novel automated acoustic DDK analysis in extracting a useful measure, namely, cTV, for early detection of bulbar ALS. This analysis overcame a major barrier in the existing acoustic DDK analysis, which is continuous voicing between syllables that interferes with syllable structures. This approach has potential clinical applications as a novel bulbar assessment.