Sensorimotor control of vocal pitch and formant frequencies in Parkinson's disease

Increased vowel contrast and intelligibility in connected speech induced by sensorimotor adaptation

Alterations to sensory feedback can drive robust adaptive changes to the production of consonants and vowels, but these changes often have no behavioral relevance or benefit to communication (e.g., making "head" more like "had"). This work aims to align the outcomes of adaptation with changes known to increase speech intelligibility - specifically, adaptations that increase the acoustic contrast between vowels in running speech. To this end, we implemented a vowel centralization feedback perturbation paradigm that pushes all vowels towards the center of vowel space, making them sound less distinct from one another. Speakers across the adult lifespan adapted to the centralization perturbation during sentence production, increasing the global acoustic contrast among vowels and the articulatory excursions for individual vowels. These changes persisted after the perturbation was removed, including after a silent delay, and showed robust transfer to words that were not present in the sentences. Control analyses demonstrated that these effects were unlikely to be due to explicit pronunciation strategies and occurred in the face of increasingly more rapid and less distinct production of familiar sentences. Finally, sentence transcription by crowd-sourced listeners showed that speakers' vowel contrast predicted their baseline intelligibility and that experimentally-induced increases in contrast predicted intelligibility gains. These findings establish the validity of a sensorimotor adaptation paradigm to implicitly increase vowel contrast and intelligibility in connected speech, an outcome that has the potential to enhance rehabilitation in individuals who present with a reduced vowel space due to motor speech disorders, such as the hypokinetic dysarthria associated with Parkinson's disease.

The Accompanying Effect in Responses to Auditory Perturbations: Unconscious Vocal Adjustments to Unperturbed Parameters

PURPOSE

The present study examined whether participants respond to unperturbed parameters while experiencing specific perturbations in auditory feedback. For instance, we aim to determine if speakers adjust voice loudness when only pitch is artificially altered in auditory feedback. This phenomenon is referred to as the "accompanying effect" in the present study.

METHOD

Thirty native Mandarin speakers were asked to sustain the vowel /ɛ/ for 3 s while their auditory feedback underwent single shifts in one of the three distinct ways: pitch shift (±100 cents; coded as PT), loudness shift (±6 dB; coded as LD), or first formant (F1) shift (±100 Hz; coded as FM). Participants were instructed to ignore the perturbations in their auditory feedback. Response types were categorized based on pitch, loudness, and F1 for each individual trial, such as Popp_Lopp_Fopp indicating opposing responses in all three domains.

RESULTS

The accompanying effect appeared 93% of the time. Bayesian Poisson regression models indicate that opposing responses in all three domains (Popp_Lopp_Fopp) were the most prevalent response type across the conditions (PT, LD, and FM). The more frequently used response types exhibited opposing responses and significantly larger response curves than the less frequently used response types. Following responses became more prevalent only when the perturbed stimuli were perceived as voices from someone else (external references), particularly in the FM condition. In terms of isotropy, loudness and F1 tended to change in the same direction rather than loudness and pitch.

CONCLUSION

The presence of the accompanying effect suggests that the motor systems responsible for regulating pitch, loudness, and formants are not entirely independent but rather interconnected to some degree.

A neurocomputational view of the effects of Parkinson's disease on speech production

The purpose of this article is to review the scientific literature concerning speech in Parkinson's disease (PD) with reference to the DIVA/GODIVA neurocomputational modeling framework. Within this theoretical view, the basal ganglia (BG) contribute to several different aspects of speech motor learning and execution. First, the BG are posited to play a role in the initiation and scaling of speech movements. Within the DIVA/GODIVA framework, initiation and scaling are carried out by initiation map nodes in the supplementary motor area acting in concert with the BG. Reduced support of the initiation map from the BG in PD would result in reduced movement intensity as well as susceptibility to early termination of movement. A second proposed role concerns the learning of common speech sequences, such as phoneme sequences comprising words; this view receives support from the animal literature as well as studies identifying speech sequence learning deficits in PD. Third, the BG may play a role in the temporary buffering and sequencing of longer speech utterances such as phrases during conversational speech. Although the literature does not support a critical role for the BG in representing sequence order (since incorrectly ordered speech is not characteristic of PD), the BG are posited to contribute to the scaling of individual movements in the sequence, including increasing movement intensity for emphatic stress on key words. Therapeutic interventions for PD have inconsistent effects on speech. In contrast to dopaminergic treatments, which typically either leave speech unchanged or lead to minor improvements, deep brain stimulation (DBS) can degrade speech in some cases and improve it in others. However, cases of degradation may be due to unintended stimulation of efferent motor projections to the speech articulators. Findings of spared speech after bilateral pallidotomy appear to indicate that any role played by the BG in adult speech must be supplementary rather than mandatory, with the sequential order of well-learned sequences apparently represented elsewhere (e.g., in cortico-cortical projections).

Daily Phonatory Activity of Individuals With Parkinson's Disease

PURPOSE

This study evaluated the amount of phonatory activity of Persons with Parkinson disease (PwPD) compared to adults without Parkinson's disease measured over 3 days. The relationship between the amount of phonatory activity and Voice Handicap Index (VHI) total score was assessed as were differences in voicing activity across 3 days of data collection.

METHODS

Fifteen PwPD receiving dopaminergic medication and fifteen age and sex matched adults without Parkinson's disease completed the VHI and then wore a VocaLog vocal monitor (VM) for 3 consecutive days. From the VM data, the number of 1-second windows with dB sound pressure level > 0 were summed as a measure of phonatory activity (PA) and reported relative to the time the VM was worn (%PA).

RESULTS

The percentage of time the VM was worn did not differ between groups or across days. The PwPD had statistically significantly fewer minutes of PA per day than controls (F = 21.782, P < 0.001) by 54 minutes on average. The %PA also differed significantly (F = 31.825, P < 0.001) with a mean of 11.1% for PwPD and 18.6% for controls. Neither PA nor %PA differed across the 3 days of vocal monitoring. VHI total score was significantly correlated with PA (r = -0.436, P = 0.016) and %PA (r = -0.534, P = 0.002) for all participants.

CONCLUSIONS

The results indicate that PwPD engaged in less verbal communication in their daily environment compared to adults without Parkinson's disease. The findings support reports in the literature indicating that PwPD often have reduced communication participation. Measures such as %PA could serve as a quantifiable metric in future studies assessing communication changes in PwPD as a function of disease progression or therapeutic interventions.

Microstructural white matter changes underlying speech deficits in Parkinson's disease

Speech impairments are one of the common symptoms of individuals with Parkinson's disease (PD). However, little is known about the underlying neuroanatomical structural deficits specifically in the basal ganglia-thalamocortical (BGTC) loop in the speech deficits of PD. Here we investigated white matter differences in PD using probabilistic tractography. Diffusion tensor imaging data were downloaded from the Parkinson's Progression Markers Initiative database. We included three groups of participants: 20 PD individuals with speech deficits, 20 PD individuals without speech deficits, and 20 age- and gender-matched control participants. Overall, PD individuals with speech deficits had higher mean diffusivity in the BGTC pathway in the left hemisphere compared with PD individuals without speech deficits. The present study exhibits that there may be a distinct pathophysiological profile of white matter for speech deficits in PD.

Test-Retest Reliability of Behavioral Assays of Feedforward and Feedback Auditory-Motor Control of Voice and Articulation

PURPOSE

Behavioral assays of feedforward and feedback auditory-motor control of voice and articulation frequently are used to make inferences about underlying neural mechanisms and to study speech development and disorders. However, no studies have examined the test-retest reliability of such measures, which is critical for rigorous study of auditory-motor control. Thus, the purpose of the present study was to assess the reliability of assays of feedforward and feedback control in voice versus articulation domains.

METHOD

Twenty-eight participants (14 cisgender women, 12 cisgender men, one transgender man, one transmasculine/nonbinary) who denied any history of speech, hearing, or neurological impairment were measured for responses to predictable versus unexpected auditory feedback perturbations of vocal (fundamental frequency, fo) and articulatory (first formant, F1) acoustic parameters twice, with 3-6 weeks between sessions. Reliability was measured with intraclass correlations.

RESULTS

Opposite patterns of reliability were observed for fo and F1; fo reflexive responses showed good reliability and fo adaptive responses showed poor reliability, whereas F1 reflexive responses showed poor reliability and F1 adaptive responses showed moderate reliability. However, a criterion-referenced categorical measurement of fo adaptive responses as typical versus atypical showed substantial test-retest agreement.

CONCLUSIONS

Individual responses to some behavioral assays of auditory-motor control of speech should be interpreted with caution, which has implications for several fields of research. Additional research is needed to establish reliable criterion-referenced measures of F1 adaptive responses as well as fo and F1 reflexive responses. Furthermore, the opposite patterns of test-retest reliability observed for voice versus articulation add to growing evidence for differences in underlying neural control mechanisms.

An interpretable model based on graph learning for diagnosis of Parkinson's disease with voice-related EEG

Parkinson's disease (PD) exhibits significant clinical heterogeneity, presenting challenges in the identification of reliable electroencephalogram (EEG) biomarkers. Machine learning techniques have been integrated with resting-state EEG for PD diagnosis, but their practicality is constrained by the interpretable features and the stochastic nature of resting-state EEG. The present study proposes a novel and interpretable deep learning model, graph signal processing-graph convolutional networks (GSP-GCNs), using event-related EEG data obtained from a specific task involving vocal pitch regulation for PD diagnosis. By incorporating both local and global information from single-hop and multi-hop networks, our proposed GSP-GCNs models achieved an averaged classification accuracy of 90.2%, exhibiting a significant improvement of 9.5% over other deep learning models. Moreover, the interpretability analysis revealed discriminative distributions of large-scale EEG networks and topographic map of microstate MS5 learned by our models, primarily located in the left ventral premotor cortex, superior temporal gyrus, and Broca's area that are implicated in PD-related speech disorders, reflecting our GSP-GCN models' ability to provide interpretable insights identifying distinctive EEG biomarkers from large-scale networks. These findings demonstrate the potential of interpretable deep learning models coupled with voice-related EEG signals for distinguishing PD patients from healthy controls with accuracy and elucidating the underlying neurobiological mechanisms.

Impairment of the internal forward model and feedback mechanisms for vocal sensorimotor control in post-stroke aphasia: evidence from directional responses to altered auditory feedback

The present study examined opposing and following vocal responses to altered auditory feedback (AAF) to determine how damage to left-hemisphere brain networks impairs the internal forward model and feedback mechanisms in post-stroke aphasia. Forty-nine subjects with aphasia and sixty age-matched controls performed speech vowel production tasks while their auditory feedback was altered using randomized ± 100 cents upward and downward pitch-shift stimuli. Data analysis revealed that when vocal responses were averaged across all trials (i.e., opposing and following), the overall magnitude of vocal compensation was significantly reduced in the aphasia group compared with controls. In addition, when vocal responses were analyzed separately for opposing and following trials, subjects in the aphasia group showed a significantly lower percentage of opposing and higher percentage of following vocal response trials compared with controls, particularly for the upward pitch-shift stimuli. However, there was no significant difference in the magnitude of opposing and following vocal responses between the two groups. These findings further support previous evidence on the impairment of vocal sensorimotor control in aphasia and provide new insights into the distinctive impact of left-hemisphere stroke on the internal forward model and feedback mechanisms. In this context, we propose that the lower percentage of opposing responses in aphasia may be accounted for by deficits in feedback-dependent mechanisms of audio-vocal integration and motor control. In addition, the higher percentage of following responses may reflect aberrantly increased reliance of the speech system on the internal forward model for generating sensory predictions during vocal error detection and motor control.

Cognitive profile of patients with and without speech impairment in Parkinson's disease

Cognitive functions have been the subject of studies evaluating the pathophysiological mechanism of speech control.

Objective

To compare the groups of patients with and without speech disorders with cognitive assessment, demographic, and clinical data (disease duration, functionality, and motor symptoms).

Methods

Retrospective, cross-sectional study. Patients were evaluated using the Addenbrooke's Cognitive Examination III and neuropsychological tests. The following speech subsystems were analyzed: articulation, phonation, resonance, and prosody, through auditory-perceptual evaluation (based on the Protocol for the Evaluation of Acquired Speech Disorders in Individuals with Parkinson's Disease - PADAF Protocol tests), observing aspects of speech programming and execution. The patients were distributed into three subgroups (normal cognition, mild cognitive impairment, and dementia). After speech evaluation, they were divided into two subgroups (with and without speech disorders).

Results

A total of 150 patients participated in this study, 104 men and 46 women, 63.58 (8.81) years of age, 11.03 (4.00) years of schooling, 6.61 (4.69) years of disease progression, and with the highest proportion of individuals in stage I-II of the Hoehn & Yarh (H&Y) scale (86, or 57.33%). Statistically significant differences were observed between subgroups with and without speech alteration. Worse performance was verified in the Trail Making Test (TMT) TMT-Δ and a tendency of difference in the TMT-B of the subgroup with speech disorders, in addition to worse severity of motor symptoms (H&Y) and cognitive complaints.

Conclusion

Individuals with speech disorders brought more frequent cognitive complaints and impairment below expected in tests assessing executive functions. Future studies, with stratification by type of speech disorder, are necessary to contribute to and validate these results.

Do Not Cut Off Your Tail: A Mega-Analysis of Responses to Auditory Perturbation Experiments

PURPOSE

The practice of removing "following" responses from speech perturbation analyses is increasingly common, despite no clear evidence as to whether these responses represent a unique response type. This study aimed to determine if the distribution of responses to auditory perturbation paradigms represents a bimodal distribution, consisting of two distinct response types, or a unimodal distribution.

METHOD

This mega-analysis pooled data from 22 previous studies to examine the distribution and magnitude of responses to auditory perturbations across four tasks: adaptive pitch, adaptive formant, reflexive pitch, and reflexive formant. Data included at least 150 unique participants for each task, with studies comprising younger adult, older adult, and Parkinson's disease populations. A Silverman's unimodality test followed by a smoothed bootstrap resampling technique was performed for each task to evaluate the number of modes in each distribution. Wilcoxon signed-ranks tests were also performed for each distribution to confirm significant compensation in response to the perturbation.

RESULTS

Modality analyses were not significant (p > .05) for any group or task, indicating unimodal distributions. Our analyses also confirmed compensatory reflexive responses to pitch and formant perturbations across all groups, as well as adaptive responses to sustained formant perturbations. However, analyses of sustained pitch perturbations only revealed evidence of adaptation in studies with younger adults.

CONCLUSION

The demonstration of a clear unimodal distribution across all tasks suggests that following responses do not represent a distinct response pattern, but rather the tail of a unimodal distribution.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24282676.

Premotor cortex is hypoactive during sustained vowel production in individuals with Parkinson's disease and hypophonia

Introduction

Hypophonia is a common feature of Parkinson's disease (PD); however, the contribution of motor cortical activity to reduced phonatory scaling in PD is still not clear.

Methods

In this study, we employed a sustained vowel production task during functional magnetic resonance imaging to compare brain activity between individuals with PD and hypophonia and an older healthy control (OHC) group.

Results

When comparing vowel production versus rest, the PD group showed fewer regions with significant BOLD activity compared to OHCs. Within the motor cortices, both OHC and PD groups showed bilateral activation of the laryngeal/phonatory area (LPA) of the primary motor cortex as well as activation of the supplementary motor area. The OHC group also recruited additional activity in the bilateral trunk motor area and right dorsal premotor cortex (PMd). A voxel-wise comparison of PD and HC groups showed that activity in right PMd was significantly lower in the PD group compared to OHC (p < 0.001, uncorrected). Right PMd activity was positively correlated with maximum phonation time in the PD group and negatively correlated with perceptual severity ratings of loudness and pitch.

Discussion

Our findings suggest that hypoactivation of PMd may be associated with abnormal phonatory control in PD.

Speaker-induced Suppression in EEG during a Naturalistic Reading and Listening Task

Speaking elicits a suppressed neural response when compared with listening to others' speech, a phenomenon known as speaker-induced suppression (SIS). Previous research has focused on investigating SIS at constrained levels of linguistic representation, such as the individual phoneme and word level. Here, we present scalp EEG data from a dual speech perception and production task where participants read sentences aloud then listened to playback of themselves reading those sentences. Playback was separated into immediate repetition of the previous trial and randomized repetition of a former trial to investigate if forward modeling of responses during passive listening suppresses the neural response. Concurrent EMG was recorded to control for movement artifact during speech production. In line with previous research, ERP analyses at the sentence level demonstrated suppression of early auditory components of the EEG for production compared with perception. To evaluate whether linguistic abstractions (in the form of phonological feature tuning) are suppressed during speech production alongside lower-level acoustic information, we fit linear encoding models that predicted scalp EEG based on phonological features, EMG activity, and task condition. We found that phonological features were encoded similarly between production and perception. However, this similarity was only observed when controlling for movement by using the EMG response as an additional regressor. Our results suggest that SIS operates at a sensory representational level and is dissociated from higher order cognitive and linguistic processing that takes place during speech perception and production. We also detail some important considerations when analyzing EEG during continuous speech production.

Vowel production: a potential speech biomarker for early detection of dysarthria in Parkinson's disease

Objectives

Our aim is to detect early, subclinical speech biomarkers of dysarthria in Parkinson's disease (PD), i.e., systematic atypicalities in speech that remain subtle, are not easily detectible by the clinician, so that the patient is labeled "non-dysarthric." Based on promising exploratory work, we examine here whether vowel articulation, as assessed by three acoustic metrics, can be used as early indicator of speech difficulties associated with Parkinson's disease.

Study design

This is a prospective case-control study.

Methods

Sixty-three individuals with PD and 35 without PD (healthy controls-HC) participated in this study. Out of 63 PD patients, 43 had been diagnosed with dysarthria (DPD) and 20 had not (NDPD). Sustained vowels were recorded for each speaker and formant frequencies were measured. The analyses focus on three acoustic metrics: individual vowel triangle areas (tVSA), vowel articulation index (VAI) and the Phi index.

Results

tVSA were found to be significantly smaller for DPD speakers than for HC. The VAI showed significant differences between these two groups, indicating greater centralization and lower vowel contrasts in the DPD speakers with dysarhtria. In addition, DPD and NDPD speakers had lower Phi values, indicating a lower organization of their vowel system compared to the HC. Results also showed that the VAI index was the most efficient to distinguish between DPD and NDPD whereas the Phi index was the best acoustic metric to discriminate NDPD and HC.

Conclusion

This acoustic study identified potential subclinical vowel-related speech biomarkers of dysarthria in speakers with Parkinson's disease who have not been diagnosed with dysarthria.

Continuous theta burst stimulation over right cerebellum for speech impairment in Parkinson's disease: study protocol for a randomized, sham-controlled, clinical trial

Background

Speech impairment is a common symptom of Parkinson's disease (PD) that worsens with disease progression and affects communication and quality of life. Current pharmacological and surgical treatments for PD have inconsistent effects on speech impairment. The cerebellum is an essential part of sensorimotor network that regulates speech production and becomes dysfunctional in PD. Continuous theta-burst stimulation (cTBS) is a non-invasive brain stimulation technique that can modulate the cerebellum and its connections with other brain regions.

Objective

To investigate whether cTBS over the right cerebellum coupled with speech-language therapy (SLT) can improve speech impairment in PD.

Methods

In this randomized controlled trial (RCT), 40 patients with PD will be recruited and assigned to either an experimental group (EG) or a control group (CG). Both groups will receive 10 sessions of standard SLT. The EG will receive real cTBS over the right cerebellum, while the CG will receive sham stimulation. Blinded assessors will evaluate the treatment outcome at three time points: pre-intervention, post-intervention, and at a 12-week follow-up. The primary outcome measures are voice/speech quality and neurobehavioral parameters of auditory-vocal integration. The secondary outcome measures are cognitive function, quality of life, and functional connectivity determined by resting-state functional magnetic resonance imaging (fMRI).

Significance

This trial will provide evidence for the efficacy and safety of cerebellar cTBS for the treatment of speech impairment in PD and shed light on the neural mechanism of this intervention. It will also have implications for other speech impairment attributed to cerebellar dysfunctions.

Clinical trial registration

www.chictr.org.cn, identifier ChiCTR2100050543.

Transcranial direct current stimulation over left dorsolateral prefrontal cortex facilitates auditory-motor integration for vocal pitch regulation

Background

A growing body of literature has implicated the left dorsolateral prefrontal cortex (DLPFC) in the online monitoring of vocal production through auditory feedback. Specifically, disruption of or damage to the left DLPFC leads to exaggerated compensatory vocal responses to altered auditory feedback. It is conceivable that enhancing the cortical excitability of the left DLPFC may produce inhibitory influences on vocal feedback control by reducing vocal compensations.

Methods

We used anodal transcranial direct current stimulation (a-tDCS) to modulate cortical excitability of the left DLPFC and examined its effects on auditory-motor integration for vocal pitch regulation. Seventeen healthy young adults vocalized vowel sounds while hearing their voice pseudo-randomly pitch-shifted by ±50 or ±200 cents, either during (online) or after (offline) receiving active or sham a-tDCS over the left DLPFC.

Results

Active a-tDCS over the left DLPFC led to significantly smaller peak magnitudes and shorter peak times of vocal compensations for pitch perturbations than sham stimulation. In addition, this effect was consistent regardless of the timing of a-tDCS (online or offline stimulation) and the size and direction of the pitch perturbation.

Conclusion

These findings provide the first causal evidence that a-tDCS over the left DLPFC can facilitate auditory-motor integration for compensatory adjustment to errors in vocal output. Reduced and accelerated vocal compensations caused by a-tDCS over left DLPFC support the hypothesis of a top-down neural mechanism that exerts inhibitory control over vocal motor behavior through auditory feedback.

Effects of intensive speech treatment on Mandarin speakers with Parkinson's Disease: A review

BACKGROUND

Benefits of intensive speech treatment have been documented for a range of speech signs in English speakers with Parkinson's Disease (PD). However, the answer to a critical question that whether the same treatment benefits speech variables including intelligibility in Mandarin speakers is still unclear. In order to develop a targeted speech treatment for Mandarin speakers with PD, we reviewed the efficacy of intensive speech treatment to improve vocal loudness and functional communication and discuss possible explanations for efficacy on Mandarin speakers with PD.

METHODS

Literatures about intensive speech treatment for Mandarin speakers with PD were retrieved from PubMed, Web of Science, Embase, China National Knowledge Infrastructure (CNKI), Wanfang and Weipu Database for Chinese Technical Periodicals (VIP) Database. Search strategy was (voice therapy OR speech therapy OR voice treatment OR speech treatment OR voice training OR speech training OR voice rehabilitation OR speech rehabilitation OR Lee Silverman voice treatment OR intensive speech treatment) and (Parkinson's disease) and (Mandarin speakers OR Chinese OR Chinese people).

RESULTS

Five randomized controlled trials were selected and possible explanations for efficacy on individuals with PD are discussed. Further research directions are suggested.

CONCLUSION

The existing evidence from treatment efficacy studies of intensive speech treatment provides support for improving vocal loudness, speech intelligibility, pitch and rate in Mandarin speakers with PD. Our future research will continue to work to conduct a large sample multicenter randomized controlled trial to provide high quality evidence and understand the basic mechanisms accompanying treatment-related change.

Audio-Tokens: A toolbox for rating, sorting and comparing audio samples in the browser

Here we describe a JavaScript toolbox to perform online rating studies with auditory material. The main feature of the toolbox is that audio samples are associated with visual tokens on the screen that control audio playback and can be manipulated depending on the type of rating. This allows the collection of single- and multidimensional feature ratings, as well as categorical and similarity ratings. The toolbox ( github.com/pwdonh/audio_tokens ) can be used via a plugin for the widely used jsPsych, as well as using plain JavaScript for custom applications. We expect the toolbox to be useful in psychological research on speech and music perception, as well as for the curation and annotation of datasets in machine learning.

A causal link between left supplementary motor area and auditory-motor control of vocal production: Evidence by continuous theta burst stimulation

The supplementary motor area (SMA) has been implicated in the feedforward control of speech production. Whether this region is involved in speech motor control through auditory feedback, however, remains uncertain. The present event-related potential (ERP) study examined the role of the left SMA in vocal pitch regulation in a causal manner by combining auditory feedback manipulations and neuronavigated continuous theta bust stimulation (c-TBS). After receiving c-TBS over the left SMA or the control site (vertex), twenty young adults vocalized the vowel sound /u/ while hearing their voice unexpectedly pitch-shifted -50 or -200 cents. Compared to the control stimulation, c-TBS over the left SMA led to decreased vocal compensations for pitch perturbations of -50 and -200 cents. A significant decrease of N1 and P2 responses to -200 cents perturbations was also found when comparing active and control stimulation. Major neural generators of decreased P2 responses included the right-lateralized superior and middle temporal gyrus and angular gyrus. Notably, a significant correlation was found between active-control differences in the vocal compensation and P2 responses for the -200 cents perturbations. These findings provide neurobehavioral evidence for a causal link between the left SMA and auditory-motor integration for vocal pitch regulation, suggesting that the left SMA receives auditory feedback information and mediates vocal compensations for feedback errors in a bottom-up manner.

The left inferior frontal gyrus is causally linked to vocal feedback control: evidence from high-definition transcranial alternating current stimulation

Current models of speech motor control propose a role for the left inferior frontal gyrus (IFG) in feedforward control of speech production. There is evidence, however, that has implicated the functional relevance of the left IFG for the neuromotor processing of vocal feedback errors. The present event-related potential (ERP) study examined whether the left IFG is causally linked to auditory feedback control of vocal production with high-definition transcranial alternating current stimulation (HD-tACS). After receiving active or sham HD-tACS over the left IFG at 6 or 70 Hz, 20 healthy adults vocalized the vowel sounds while hearing their voice unexpectedly pitch-shifted by ±200 cents. The results showed that 6 or 70 Hz HD-tACS over the left IFG led to larger magnitudes and longer latencies of vocal compensations for pitch perturbations paralleled by larger ERP P2 responses than sham HD-tACS. Moreover, there was a lack of frequency specificity that showed no significant differences between 6 and 70 Hz HD-tACS. These findings provide first causal evidence linking the left IFG to vocal pitch regulation, suggesting that the left IFG is an important part of the feedback control network that mediates vocal compensations for auditory feedback errors.

Voice Biofeedback via Bone Conduction Headphones: Effects on Acoustic Voice Parameters and Self-Reported Vocal Effort in Individuals With Voice Disorders

PURPOSE

This study explores sidetone amplification (amplified playback of one's own voice) provided via bone conduction in participants with voice disorders. The effects of bone conduction feedback on acoustic voice parameters and vocal effort ratings are examined.

METHODS

Speech samples of 47 participants with voice disorders were recorded in three auditory feedback conditions: two with sidetone amplification delivered via bone conduction and one condition with no alteration of the feedback. After each task, the participants rated their vocal effort on a visual analog scale. The voice recordings were evaluated by a speech-language pathologist through the GRBAS scale and processed to calculate the within-participant centered sound pressure level (SPL) values, the mean pitch strength (PS), the time dose (Dt%), and cepstral peak prominence smoothed (CPPS). The effects of the feedback conditions on these acoustic parameters and vocal effort ratings were analyzed.

RESULTS

The high sidetone amplification condition resulted in a statistically significant decrease in the within-participant centered SPL values and mean pitch strength across all participants. The feedback conditions had no statistically significant effects on the vocal effort ratings, time dose (Dt%), or CPPS.

CONCLUSIONS

This study provides an evidence that bone conduction sidetone amplification contributes to a consistent adaptation in the within-participant centered SPL values (ΔSPL) in patients with vocal hyperfunction, glottal insufficiency, and organic/neurological laryngeal pathologies compared to conditions with no feedback.

Continuous theta burst stimulation over left supplementary motor area facilitates auditory-vocal integration in individuals with Parkinson’s disease

Accumulating evidence suggests that impairment in auditory-vocal integration characterized by abnormally enhanced vocal compensations for auditory feedback perturbations contributes to hypokinetic dysarthria in Parkinson’s disease (PD). However, treatment of this abnormality remains a challenge. The present study examined whether abnormalities in auditory-motor integration for vocal pitch regulation in PD can be modulated by neuronavigated continuous theta burst stimulation (c-TBS) over the left supplementary motor area (SMA). After receiving active or sham c-TBS over left SMA, 16 individuals with PD vocalized vowel sounds while hearing their own voice unexpectedly pitch-shifted two semitones upward or downward. A group of pairwise-matched healthy participants was recruited as controls. Their vocal responses and event-related potentials (ERPs) were measured and compared across the conditions. The results showed that applying c-TBS over left SMA led to smaller vocal responses paralleled by smaller P1 and P2 responses and larger N1 responses in individuals with PD. Major neural generators of reduced P2 responses were located in the right inferior and medial frontal gyrus, pre- and post-central gyrus, and insula. Moreover, suppressed vocal compensations were predicted by reduced P2 amplitudes and enhanced N1 amplitudes. Notably, abnormally enhanced vocal and P2 responses in individuals with PD were normalized by c-TBS over left SMA when compared to healthy controls. Our results provide the first causal evidence that abnormalities in auditory-motor control of vocal pitch production in PD can be modulated by c-TBS over left SMA, suggesting that it may be a promising non-invasive treatment for speech motor disorders in PD.

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.

Auditory and somatosensory feedback mechanisms of laryngeal and articulatory speech motor control

PURPOSE

Speech production is a complex motor task involving multiple subsystems. The relationships between these subsystems need to be comprehensively investigated to understand the underlying mechanisms of speech production. The goal of this paper is to examine the differential contributions of 1) auditory and somatosensory feedback control mechanisms, and 2) laryngeal and articulatory speech production subsystems on speech motor control at an individual speaker level using altered auditory and somatosensory feedback paradigms.

METHODS

Twenty young adults completed speaking tasks in which sudden and unpredictable auditory and physical perturbations were applied to the laryngeal and articulatory speech production subsystems. Auditory perturbations were applied to laryngeal or articulatory acoustic features of speech. Physical perturbations were applied to the larynx and the jaw. Pearson-product moment correlation coefficients were calculated between 1) auditory and somatosensory reflexive responses to investigate relationships between auditory and somatosensory feedback control mechanisms, and 2) laryngeal and articulatory reflexive responses as well as acuity measures to investigate the relationship between auditory-motor features of laryngeal and articulatory subsystems.

RESULTS

No statistically significant correlations were found concerning the relationships between auditory and somatosensory feedback. No statistically significant correlations were found between auditory-motor features in the laryngeal and articulatory control subsystems.

CONCLUSION

Results suggest that the laryngeal and articulatory speech production subsystems operate with differential auditory and somatosensory feedback control mechanisms. The outcomes suggest that current models of speech motor control should consider decoupling laryngeal and articulatory domains to better model speech motor control processes.

LaDIVA: A neurocomputational model providing laryngeal motor control for speech acquisition and production

Many voice disorders are the result of intricate neural and/or biomechanical impairments that are poorly understood. The limited knowledge of their etiological and pathophysiological mechanisms hampers effective clinical management. Behavioral studies have been used concurrently with computational models to better understand typical and pathological laryngeal motor control. Thus far, however, a unified computational framework that quantitatively integrates physiologically relevant models of phonation with the neural control of speech has not been developed. Here, we introduce LaDIVA, a novel neurocomputational model with physiologically based laryngeal motor control. We combined the DIVA model (an established neural network model of speech motor control) with the extended body-cover model (a physics-based vocal fold model). The resulting integrated model, LaDIVA, was validated by comparing its model simulations with behavioral responses to perturbations of auditory vocal fundamental frequency (fo) feedback in adults with typical speech. LaDIVA demonstrated capability to simulate different modes of laryngeal motor control, ranging from short-term (i.e., reflexive) and long-term (i.e., adaptive) auditory feedback paradigms, to generating prosodic contours in speech. Simulations showed that LaDIVA's laryngeal motor control displays properties of motor equivalence, i.e., LaDIVA could robustly generate compensatory responses to reflexive vocal fo perturbations with varying initial laryngeal muscle activation levels leading to the same output. The model can also generate prosodic contours for studying laryngeal motor control in running speech. LaDIVA can expand the understanding of the physiology of human phonation to enable, for the first time, the investigation of causal effects of neural motor control in the fine structure of the vocal signal.

What Can Altered Auditory Feedback Paradigms Tell Us About Vocal Motor Control in Individuals With Voice Disorders?

Purpose

The goal of this review article is to provide a summary of the progression of altered auditory feedback (AAF) as a method to understand the pathophysiology of voice disorders. This review article focuses on populations with voice disorders that have thus far been studied using AAF, including individuals with Parkinson's disease, cerebellar degeneration, hyperfunctional voice disorders, vocal fold paralysis, and laryngeal dystonia. Studies using AAF have found that individuals with Parkinson's disease, cerebellar degeneration, and laryngeal dystonia have hyperactive auditory feedback responses due to differing underlying causes. In persons with PD, the hyperactivity may be a compensatory mechanism for atypically weak feedforward motor control. In individuals with cerebellar degeneration and laryngeal dystonia, the reasons for hyperactivity remain unknown. Individuals with hyperfunctional voice disorders may have auditory-motor integration deficits, suggesting atypical updating of feedforward motor control.

Conclusions

These findings have the potential to provide critical insights to clinicians in selecting the most effective therapy techniques for individuals with voice disorders. Future collaboration between clinicians and researchers with the shared objective of improving AAF as an ecologically feasible and valid tool for clinical assessment may provide more personalized therapy targets for individuals with voice disorders.

Voice handicap Index in Parkinson's patients: Subthalamic versus globus pallidus deep brain stimulation

PURPOSE

Subthalamic nucleus (STN) and globus pallidus interna (GPI) are the two most common sites for deep brain stimulation (DBS) in people with Parkinson's disease (PWP). Voice impairments are a common symptom of Parkinson's disease and information about voice outcomes with DBS is limited. Most studies in speech-language pathology have focused on STN-DBS and few have examined the effects of GPI-DBS. This was an initial effort to examine the impact of DBS location on Vocal Handicap Index (VHI) scores, which assess the impact of a voice disorder on an individual.

METHOD

Twenty-four gender-matched PWP (12 STN-DBS and 12 GPI-DBS) completed the VHI post-DBS implantation. Two-tailed independent samples t-tests were used to compare each VHI scale score (physical, functional, emotional, total) and patient factors between the two groups.

RESULTS

No significant differences in total or subscale VHI scores were identified between the two DBS groups. A trend toward greater impairment in PWP with GPI-DBS was noted. An association between higher VHI scores and DBS settings was found.

CONCLUSIONS

Studies directly comparing speech outcomes for different DBS targets are lacking. The current findings provide new insights concerning voice outcomes following DBS by adding to the limited literature directly comparing speech outcomes in multiple DBS targets. Limitations and directions for future research are discussed.

Early auditory responses to speech sounds in Parkinson's disease: preliminary data

Parkinson’s disease (PD), as a manifestation of basal ganglia dysfunction, is associated with a number of speech deficits, including reduced voice modulation and vocal output. Interestingly, previous work has shown that participants with PD show an increased feedback-driven motor response to unexpected fundamental frequency perturbations during speech production, and a heightened ability to detect differences in vocal pitch relative to control participants. Here, we explored one possible contributor to these enhanced responses. We recorded the frequency-following auditory brainstem response (FFR) to repetitions of the speech syllable [da] in PD and control participants. Participants with PD displayed a larger amplitude FFR related to the fundamental frequency of speech stimuli relative to the control group. The current preliminary results suggest the dysfunction of the basal ganglia in PD contributes to the early stage of auditory processing and may reflect one component of a broader sensorimotor processing impairment associated with the disease.

Feedback and Feedforward Auditory-Motor Processes for Voice and Articulation in Parkinson's Disease

PURPOSE

Unexpected and sustained manipulations of auditory feedback during speech production result in "reflexive" and "adaptive" responses, which can shed light on feedback and feedforward auditory-motor control processes, respectively. Persons with Parkinson's disease (PwPD) have shown aberrant reflexive and adaptive responses, but responses appear to differ for control of vocal and articulatory features. However, these responses have not been examined for both voice and articulation in the same speakers and with respect to auditory acuity and functional speech outcomes (speech intelligibility and naturalness).

METHOD

Here, 28 PwPD on their typical dopaminergic medication schedule and 28 age-, sex-, and hearing-matched controls completed tasks yielding reflexive and adaptive responses as well as auditory acuity for both vocal and articulatory features.

RESULTS

No group differences were found for any measures of auditory-motor control, conflicting with prior findings in PwPD while off medication. Auditory-motor measures were also compared with listener ratings of speech function: first formant frequency acuity was related to speech intelligibility, whereas adaptive responses to vocal fundamental frequency manipulations were related to speech naturalness.

CONCLUSIONS

These results support that auditory-motor processes for both voice and articulatory features are intact for PwPD receiving medication. This work is also the first to suggest associations between measures of auditory-motor control and speech intelligibility and naturalness.

Cerebellar Continuous Theta Burst Stimulation Facilitates Auditory-Vocal Integration in Spinocerebellar Ataxia

Clinical studies have shown the efficacy of transcranial magnetic stimulation in treating movement disorders in patients with spinocerebellar ataxia (SCA). However, whether similar effects occur for their speech motor disorders remains largely unknown. The present event-related potential study investigated whether and how abnormalities in auditory-vocal integration associated with SCA can be modulated by neuronavigated continuous theta burst stimulation (c-TBS) over the right cerebellum. After receiving active or sham cerebellar c-TBS, 19 patients with SCA were instructed to produce sustained vowels while hearing their voice unexpectedly pitch-shifted by ±200 cents. Behaviorally, active cerebellar c-TBS led to smaller magnitudes of vocal compensations for pitch perturbations than sham stimulation. Parallel modulatory effects were also observed at the cortical level, as reflected by increased P1 and P2 responses but decreased N1 responses elicited by active cerebellar c-TBS. Moreover, smaller magnitudes of vocal compensations were predicted by larger amplitudes of cortical P1 and P2 responses. These findings provide the first neurobehavioral evidence that c-TBS over the right cerebellum produces modulatory effects on abnormal auditory-motor integration for vocal pitch regulation in patients with SCA, offering a starting point for the treatment of speech motor disorders associated with SCA with cerebellar c-TBS.

Intact Correction for Self-Produced Vowel Formant Variability in Individuals With Cerebellar Ataxia Regardless of Auditory Feedback Availability

Purpose Individuals with cerebellar ataxia (CA) caused by cerebellar degeneration exhibit larger reactive compensatory responses to unexpected auditory feedback perturbations than neurobiologically typical speakers, suggesting they may rely more on feedback control during speech. We test this hypothesis by examining variability in unaltered speech. Previous studies of typical speakers have demonstrated a reduction in formant variability (centering) observed during the initial phase of vowel production from vowel onset to vowel midpoint. Centering is hypothesized to reflect feedback-based corrections for self-produced variability and thus may provide a behavioral assay of feedback control in unperturbed speech in the same manner as the compensatory response does for feedback perturbations. Method To comprehensively compare centering in individuals with CA and controls, we examine centering in two vowels (/i/ and /ɛ/) under two contexts (isolated words and connected speech). As a control, we examine speech produced both with and without noise to mask auditory feedback. Results Individuals with CA do not show increased centering compared to age-matched controls, regardless of vowel, context, or masking. Contrary to previous results in neurobiologically typical speakers, centering was not affected by the presence of masking noise in either group. Conclusions The similar magnitude of centering seen with and without masking noise questions whether centering is driven by auditory feedback. However, if centering is at least partially driven by auditory/somatosensory feedback, these results indicate that the larger compensatory response to altered auditory feedback observed in individuals with CA may not reflect typical motor control processes during normal, unaltered speech production.

Speech Intensity Response to Altered Intensity Feedback in Individuals With Parkinson's Disease

Purpose Hypophonia (low speech intensity) is the most common speech symptom experienced by individuals with Parkinson's disease (IWPD). Previous research suggests that, in IWPD, there may be abnormal integration of sensory information for motor production of speech intensity. In the current study, intensity of auditory feedback was systematically manipulated (altered in both positive and negative directions) during sensorimotor conditions that are known to modulate speech intensity in everyday contexts in order to better understand the role of auditory feedback for speech intensity regulation. Method Twenty-six IWPD and 24 neurologically healthy controls were asked to complete the following tasks: converse with the experimenter, start vowel production, and read sentences at a comfortable loudness, while hearing their own speech intensity randomly altered. Altered intensity feedback conditions included 5-, 10-, and 15-dB reductions and increases in the feedback intensity. Speech tasks were completed in no noise and in background noise. Results IWPD displayed a reduced response to the altered intensity feedback compared to control participants. This reduced response was most apparent when participants were speaking in background noise. Specific task-based differences in responses were observed such that the reduced response by IWPD was most pronounced during the conversation task. Conclusions The current study suggests that IWPD have abnormal processing of auditory information for speech intensity regulation, and this disruption particularly impacts their ability to regulate speech intensity in the context of speech tasks with clear communicative goals (i.e., conversational speech) and speaking in background noise.

Responses to Auditory Feedback Manipulations in Speech May Be Affected by Previous Exposure to Auditory Errors

Purpose Speakers use auditory feedback to guide their speech output, although individuals differ in the magnitude of their compensatory response to perceived errors in feedback. Little is known about the factors that contribute to the compensatory response or how fixed or flexible they are within an individual. Here, we test whether manipulating the perceived reliability of auditory feedback modulates speakers' compensation to auditory perturbations, as predicted by optimal models of sensorimotor control. Method Forty participants produced monosyllabic words in two separate sessions, which differed in the auditory feedback given during an initial exposure phase. In the veridical session exposure phase, feedback was normal. In the noisy session exposure phase, small, random formant perturbations were applied, reducing reliability of auditory feedback. In each session, a subsequent test phase introduced larger unpredictable formant perturbations. We assessed whether the magnitude of within-trial compensation for these larger perturbations differed across the two sessions. Results Compensatory responses to downward (though not upward) formant perturbations were larger in the veridical session than the noisy session. However, in post hoc testing, we found the magnitude of this effect is highly dependent on the choice of analysis procedures. Compensation magnitude was not predicted by other production measures, such as formant variability, and was not reliably correlated across sessions. Conclusions Our results, though mixed, provide tentative support that the feedback control system monitors the reliability of sensory feedback. These results must be interpreted cautiously given the potentially limited stability of auditory feedback compensation measures across analysis choices and across sessions. Supplemental Material https://doi.org/10.23641/asha.14167136.

Processing of Degraded Speech in Brain Disorders

The speech we hear every day is typically "degraded" by competing sounds and the idiosyncratic vocal characteristics of individual speakers. While the comprehension of "degraded" speech is normally automatic, it depends on dynamic and adaptive processing across distributed neural networks. This presents the brain with an immense computational challenge, making degraded speech processing vulnerable to a range of brain disorders. Therefore, it is likely to be a sensitive marker of neural circuit dysfunction and an index of retained neural plasticity. Considering experimental methods for studying degraded speech and factors that affect its processing in healthy individuals, we review the evidence for altered degraded speech processing in major neurodegenerative diseases, traumatic brain injury and stroke. We develop a predictive coding framework for understanding deficits of degraded speech processing in these disorders, focussing on the "language-led dementias"-the primary progressive aphasias. We conclude by considering prospects for using degraded speech as a probe of language network pathophysiology, a diagnostic tool and a target for therapeutic intervention.

Neurobehavioral Effects of LSVT® LOUD on Auditory-Vocal Integration in Parkinson's Disease: A Preliminary Study

Individuals with Parkinson's disease (PD) are impaired in auditory-vocal integration, characterized by abnormal compensatory responses to auditory feedback errors during self-monitoring of vocal production. The present study examined whether auditory feedback control of vocal pitch production in PD can benefit from Lee Silverman voice treatment (LSVT® LOUD), a high effort, intensive speech treatment for hypokinetic dysarthria in PD. Before and immediately after LSVT LOUD, 12 individuals with PD were instructed to produce sustained vowel sounds while hearing their voice unexpectedly pitch-shifted by -200 cents. Their vocal responses and event-related potentials (ERPs) to pitch perturbations were measured to assess the treatment outcomes. A group of 12 healthy controls were one-to-one pair matched by age, sex, and language. Individuals with PD exhibited abnormally enhanced vocal and ERP P2 responses to pitch perturbations relative to healthy controls. Successful treatment with LSVT LOUD, however, led to significantly smaller and faster vocal compensations that were accompanied by significantly larger P2 responses. Moreover, improved vocal loudness during passage reading was significantly correlated with reduced vocal compensations for pitch perturbations. These preliminary findings provide the first neurobehavioral evidence for beneficial effects of LSVT LOUD on impaired auditory-vocal integration associated with PD, which may be related to improved laryngeal motor functions and a top-down modulation of the speech motor network by LSVT LOUD.

Speech compensation responses and sensorimotor adaptation to formant feedback perturbations

Control of speech formants is important for the production of distinguishable speech sounds and is achieved with both feedback and learned feedforward control. However, it is unclear whether the learning of feedforward control involves the mechanisms of feedback control. Speakers have been shown to compensate for unpredictable transient mid-utterance perturbations of pitch and loudness feedback, demonstrating online feedback control of these speech features. To determine whether similar feedback control mechanisms exist in the production of formants, responses to unpredictable vowel formant feedback perturbations were examined. Results showed similar within-trial compensatory responses to formant perturbations that were presented at utterance onset and mid-utterance. The relationship between online feedback compensation to unpredictable formant perturbations and sensorimotor adaptation to consistent formant perturbations was further examined. Within-trial online compensation responses were not correlated with across-trial sensorimotor adaptation. A detailed analysis of within-trial time course dynamics across trials during sensorimotor adaptation revealed that across-trial sensorimotor adaptation responses did not result from an incorporation of within-trial compensation response. These findings suggest that online feedback compensation and sensorimotor adaptation are governed by distinct neural mechanisms. These findings have important implications for models of speech motor control in terms of how feedback and feedforward control mechanisms are implemented.

The Relation of Articulatory and Vocal Auditory-Motor Control in Typical Speakers

Purpose The purpose of this study was to explore the relationship between feedback and feedforward control of articulation and voice by measuring reflexive and adaptive responses to first formant (F 1) and fundamental frequency (f o) perturbations. In addition, perception of F 1 and f o perturbation was estimated using passive (listening) and active (speaking) just noticeable difference paradigms to assess the relation of auditory acuity to reflexive and adaptive responses. Method Twenty healthy women produced single words and sustained vowels while the F 1 or f o of their auditory feedback was suddenly and unpredictably perturbed to assess reflexive responses or gradually and predictably perturbed to assess adaptive responses. Results Typical speakers' reflexive responses to sudden perturbation of F 1 were related to their adaptive responses to gradual perturbation of F 1. Specifically, speakers with larger reflexive responses to sudden perturbation of F 1 had larger adaptive responses to gradual perturbation of F 1. Furthermore, their reflexive responses to sudden perturbation of F 1 were associated with their passive auditory acuity to F 1 such that speakers with better auditory acuity to F 1 produced larger reflexive responses to sudden perturbations of F 1. Typical speakers' adaptive responses to gradual perturbation of F 1 were not associated with their auditory acuity to F 1. Speakers' reflexive and adaptive responses to perturbation of f o were not related, nor were their responses related to either measure of auditory acuity to f o. Conclusion These findings indicate that there may be disparate feedback and feedforward control mechanisms for articulatory and vocal error correction based on auditory feedback.

Auditory-Motor Perturbations of Voice Fundamental Frequency: Feedback Delay and Amplification

Purpose Gradual and sudden perturbations of vocal fundamental frequency (f _o), also known as adaptive and reflexive f _o perturbations, are techniques to study the influence of auditory feedback on voice f _o control mechanisms. Previous vocal f _o perturbations have incorporated varied setup-specific feedback delays and amplifications. Here, we investigated the effects of feedback delays (10-100 ms) and amplifications on both adaptive and reflexive f _o perturbation paradigms, encapsulating the variability in equipment-specific delays (3-45 ms) and amplifications utilized in previous experiments. Method Responses to adaptive and reflexive f _o perturbations were recorded in 24 typical speakers for four delay conditions (10, 40, 70, and 100 ms) or three amplification conditions (-10, +5, and +10 dB relative to microphone) in a counterbalanced order. Repeated-measures analyses of variance were carried out on the magnitude of f _o responses to determine the effect of feedback condition. Results There was a statistically significant effect of the level of auditory feedback amplification on the response magnitude during adaptive f _o perturbations, driven by the difference between +10- and -10-dB amplification conditions (hold phase difference: M = 38.3 cents, SD = 51.2 cents; after-effect phase: M = 66.1 cents, SD = 84.6 cents). No other statistically significant effects of condition were found for either paradigm. Conclusions Experimental equipment delays below 100 ms in behavioral paradigms do not affect the results of f _o perturbation paradigms. As there is no statistically significant difference between the response magnitudes elicited by +5- and +10-dB auditory amplification conditions, this study is a confirmation that an auditory feedback amplification of +5 dB relative to microphone is sufficient to elicit robust compensatory responses for f _o perturbation paradigms.

It's About Time: Minimizing Hardware and Software Latencies in Speech Research With Real-Time Auditory Feedback

Purpose Various aspects of speech production related to auditory-motor integration and learning have been examined through auditory feedback perturbation paradigms in which participants' acoustic speech output is experimentally altered and played back via earphones/headphones "in real time." Scientific rigor requires high precision in determining and reporting the involved hardware and software latencies. Many reports in the literature, however, are not consistent with the minimum achievable latency for a given experimental setup. Here, we focus specifically on this methodological issue associated with implementing real-time auditory feedback perturbations, and we offer concrete suggestions for increased reproducibility in this particular line of work. Method Hardware and software latencies as well as total feedback loop latency were measured for formant perturbation studies with the Audapter software. Measurements were conducted for various audio interfaces, desktop and laptop computers, and audio drivers. An approach for lowering Audapter's software latency through nondefault parameter specification was also tested. Results Oft-overlooked hardware-specific latencies were not negligible for some of the tested audio interfaces (adding up to 15 ms). Total feedback loop latencies (including both hardware and software latency) were also generally larger than claimed in the literature. Nondefault parameter values can improve Audapter's own processing latency without negative impact on formant tracking. Conclusions Audio interface selection and software parameter optimization substantially affect total feedback loop latency. Thus, the actual total latency (hardware plus software) needs to be correctly measured and described in all published reports. Future speech research with "real-time" auditory feedback perturbations should increase scientific rigor by minimizing this latency.

Deficits in monitoring self-produced speech in Parkinson's disease

OBJECTIVE

Speech deficits are common in Parkinson's disease, and behavioural findings suggest that the deficits may be due to impaired monitoring of self-produced speech. The neural mechanisms of speech deficits are not well understood. We examined a well-documented electrophysiological correlate of speech self-monitoring in patients with Parkinson's disease and control participants.

METHODS

We measured evoked electroencephalographic responses to self-produced and passively heard sounds (/a/ phonemes) in age-matched controls (N = 18), and Parkinson's disease patients who had minor speech impairment, but reported subjectively experiencing no speech deficits (N = 17).

RESULTS

During speaking, auditory evoked activity 100 ms after phonation (N1 wave) was less suppressed in Parkinson's disease than controls when compared to the activity evoked by passively heard phonemes. This difference between the groups was driven by increased amplitudes to self-produced phonemes, and reduced amplitudes passively heard phonemes in Parkinson's disease.

CONCLUSIONS

The finding indicates that auditory evoked activity is abnormally modulated during speech in Parkinson's patients who do not subjectively notice speech impairment. This mechanism could play a role in producing speech deficits in as the disease progresses.

SIGNIFICANCE

Our study is the first to show abnormal early auditory electrophysiological correlates of monitoring speech in Parkinson's disease patients.

Central auditory processing in parkinsonian disorders: A systematic review

Altered auditory processing has been increasingly recognized as a non-motor feature in parkinsonian disorders. This systematic review provides an overview of behavioral and electrophysiological literature on central auditory processing in patients with Parkinson's disease (PD), multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). A systematic database search was conducted and yielded 88 studies that met the intelligibility criteria. The collected data revealed distinct impairments in a range of central auditory processes in PD, including altered deviance detection of basic auditory features, auditory brainstem processing, auditory gating and selective auditory attention. In contrast to PD, literature on central auditory processing in atypical parkinsonian disorders was relatively scarce, but provided some evidence for impaired central auditory processing in MSA and PSP. The interpretation of these findings is discussed and suggestions for further research are offered.

The Relationship Between Speech Perceptual Discrimination and Speech Production in Parkinson's Disease

Purpose We recently demonstrated that individuals with Parkinson's disease (PD) respond differentially to specific altered auditory feedback parameters during speech production. Participants with PD respond more robustly to pitch and less robustly to formant manipulations compared to control participants. In this study, we investigated whether differences in perceptual processing may in part underlie these compensatory differences in speech production. Methods Pitch and formant feedback manipulations were presented under 2 conditions: production and listening. In the production condition, 15 participants with PD and 15 age- and gender-matched healthy control participants judged whether their own speech output was manipulated in real time. During the listening task, participants judged whether paired tokens of their previously recorded speech samples were the same or different. Results Under listening, 1st formant manipulation discrimination was significantly reduced for the PD group compared to the control group. There was a trend toward better discrimination of pitch in the PD group, but the group difference was not significant. Under the production condition, the ability of participants with PD to identify pitch manipulations was greater than that of the controls. Conclusion The findings suggest perceptual processing differences associated with acoustic parameters of fundamental frequency and 1st formant perturbations in PD. These findings extend our previous results, indicating that different patterns of compensation to pitch and 1st formant shifts may reflect a combination of sensory and motor mechanisms that are differentially influenced by basal ganglia dysfunction.

Engaging the Articulators Enhances Perception of Concordant Visible Speech Movements

Purpose This study aimed to test whether (and how) somatosensory feedback signals from the vocal tract affect concurrent unimodal visual speech perception. Method Participants discriminated pairs of silent visual utterances of vowels under 3 experimental conditions: (a) normal (baseline) and while holding either (b) a bite block or (c) a lip tube in their mouths. To test the specificity of somatosensory-visual interactions during perception, we assessed discrimination of vowel contrasts optically distinguished based on their mandibular (English /ɛ/-/æ/) or labial (English /u/-French /u/) postures. In addition, we assessed perception of each contrast using dynamically articulating videos and static (single-frame) images of each gesture (at vowel midpoint). Results Engaging the jaw selectively facilitated perception of the dynamic gestures optically distinct in terms of jaw height, whereas engaging the lips selectively facilitated perception of the dynamic gestures optically distinct in terms of their degree of lip compression and protrusion. Thus, participants perceived visible speech movements in relation to the configuration and shape of their own vocal tract (and possibly their ability to produce covert vowel production-like movements). In contrast, engaging the articulators had no effect when the speaking faces did not move, suggesting that the somatosensory inputs affected perception of time-varying kinematic information rather than changes in target (movement end point) mouth shapes. Conclusions These findings suggest that orofacial somatosensory inputs associated with speech production prime premotor and somatosensory brain regions involved in the sensorimotor control of speech, thereby facilitating perception of concordant visible speech movements. Supplemental Material https://doi.org/10.23641/asha.9911846.

Research-based Updates in Swallowing and Communication Dysfunction in Parkinson Disease: Implications for Evaluation and Management

PURPOSE

Individuals with Parkinson disease (PD) present with complex and variable symptoms, with recent findings suggesting that the etiology of PD extends beyond the involvement of just the basal ganglia. These symptoms include significant impairments in the speech and swallowing domains, which can greatly affect quality of life and therefore require therapeutic attention. This research-based update reviews the neurophysiological basis for swallowing and speech changes in PD, the effectiveness of various types of treatments, and implications for symptom evaluation and management.

CONCLUSION

The mechanisms responsible for swallowing and speech symptoms in PD remain largely unknown. Dopaminergic medication and deep-brain-stimulation do not provide consistent benefits for these symptoms suggesting a non-dopaminergic network is involved. Importantly, evidence suggests that symptoms of dysphagia and hypokinetic dysarthria may be early indications of PD, so it is critical to investigate the cause of these changes.

Cerebellar contribution to auditory feedback control of speech production: Evidence from patients with spinocerebellar ataxia

The cerebellum has been implicated in the feedforward control of speech production. However, the role of the cerebellum in the feedback control of speech production remains unclear. To address this question, the present event-related potential study examined the behavioral and neural correlates of auditory feedback control of vocal production in patients with spinocerebellar ataxia (SCA) and healthy controls. All participants were instructed to produce sustained vowels while hearing their voice unexpectedly pitch-shifted -200 or -500 cents. The behavioral results revealed significantly larger vocal compensations for pitch perturbations in patients with SCA relative to healthy controls. At the cortical level, patients with SCA exhibited significantly smaller cortical P2 responses that were source localized in the right superior temporal gyrus, primary auditory cortex, and supramarginal gyrus than healthy controls. These findings indicate that reduced brain activity in the right temporal and parietal regions are significant neural contributors to abnormal auditory-motor processing of vocal pitch regulation as a consequence of cerebellar degeneration, which may be related to disrupted reciprocal interactions between the cerebellum and cortical regions that support the top-down modulation of auditory-vocal integration. These differences in behavior and cortical activity between healthy controls and patients with SCA demonstrate that the cerebellum is not only essential for feedforward control but also plays a crucial role in the feedback-based control of speech production.

Pitch Shifting With the Commercially Available Eventide Eclipse: Intended and Unintended Changes to the Speech Signal

Purpose This study details the intended and unintended consequences of pitch shifting with the commercially available Eventide Eclipse. Method Ten vocally healthy participants ( M = 22.0 years; 6 cisgender females, 4 cisgender males) produced a sustained /ɑ/, creating an input signal. This input signal was processed in near real time by the Eventide Eclipse to create an output signal that was either not shifted (0 cents), shifted +100 cents, or shifted -100 cents. Shifts occurred either throughout the entire vocalization or for a 200-ms period after vocal onset. Results Input signals were compared to output signals to examine potential changes. Average pitch-shift magnitudes were within 1 cent of the intended pitch shift. Measured pitch-shift length for intended 200-ms shifts was between 5.9% and 21.7% less than expected, based on the portion of shift selected for measurement. The delay between input and output signals was an average of 11.1 ms. Trials shifted +100 cents had a longer delay than trials shifted -100 or 0 cents. The first 2 formants (F1, F2) shifted in the direction of the pitch shift, with F1 shifting 6.5% and F2 shifting 6.0%. Conclusions The Eventide Eclipse is an accurate pitch-shifting hardware that can be used to explore voice and vocal motor control. The pitch-shifting algorithm shifts all frequencies, resulting in a subsequent change in F1 and F2 during pitch-shifted trials. Researchers using this device should be mindful of stimuli selection to avoid confusion during data interpretation.

Neural correlates of abnormal auditory feedback processing during speech production in Alzheimer's disease

Accurate integration of sensory inputs and motor commands is essential to achieve successful behavioral goals. A robust model of sensorimotor integration is the pitch perturbation response, in which speakers respond rapidly to shifts of the pitch in their auditory feedback. In a previous study, we demonstrated abnormal sensorimotor integration in patients with Alzheimer's disease (AD) with an abnormally enhanced behavioral response to pitch perturbation. Here we examine the neural correlates of the abnormal pitch perturbation response in AD patients, using magnetoencephalographic imaging. The participants phonated the vowel /α/ while a real-time signal processor briefly perturbed the pitch (100 cents, 400 ms) of their auditory feedback. We examined the high-gamma band (65-150 Hz) responses during this task. AD patients showed significantly reduced left prefrontal activity during the early phase of perturbation and increased right middle temporal activity during the later phase of perturbation, compared to controls. Activity in these brain regions significantly correlated with the behavioral response. These results demonstrate that impaired prefrontal modulation of speech-motor-control network and additional recruitment of right temporal regions are significant mediators of aberrant sensorimotor integration in patients with AD. The abnormal neural integration mechanisms signify the contribution of cortical network dysfunction to cognitive and behavioral deficits in AD.

Effect of deep brain stimulation on vocal motor control mechanisms in Parkinson's disease

INTRODUCTION

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for limb motor symptoms in Parkinson's disease (PD); however, its effect on vocal motor function has yielded conflicted and highly variable results. The present study investigated the effects of STN-DBS on the mechanisms of vocal production and motor control.

METHODS

A total of 10 PD subjects with bilateral STN-DBS implantation were tested with DBS ON and OFF while they performed steady vowel vocalizations and received randomized upward or downward pitch-shift stimuli (±100 cents) in their voice auditory feedback.

RESULTS

Data showed that the magnitude of vocal compensation responses to pitch-shift stimuli was significantly attenuated during DBS ON vs. OFF (p = 0.012). This effect was direction-specific and was only observed when subjects raised their voice fundamental frequency (F0) in the opposite direction to downward stimuli (p = 0.019). In addition, we found that voice F0 perturbation (i.e. jitter) was significantly reduced during DBS ON vs. OFF (p = 0.022), and this DBS-induced modulation was positively correlated with the attenuation of vocal compensation responses to downward pitch-shift stimuli (r = +0.57, p = 0.028).

CONCLUSIONS

These findings provide the first data supporting the role of STN in vocal F0 motor control in response to altered auditory feedback. The DBS-induced attenuation of vocal compensation responses may result from increased inhibitory effects of the subcortical hyperdirect (fronto-subthalamic) pathways on the vocal motor cortex, which can help stabilize voice F0 and ameliorate vocal motor symptoms by impeding PD subjects' abnormal (i.e. overshooting) vocal responses to alterations in the auditory feedback.