SimpleDIVA: A 3-parameter model for examining adaptation in speech and voice production

Published versio

Auditory-motor adaptation is reduced in adults who stutter but not in children who stutter

Previous studies have shown that adults who stutter produce smaller corrective motor responses to compensate for unexpected auditory perturbations in comparison to adults who do not stutter, suggesting that stuttering may be associated with deficits in integration of auditory feedback for online speech monitoring. In this study, we examined whether stuttering is also associated with deficiencies in integrating and using discrepancies between expect ed and received auditory feedback to adaptively update motor programs for accurate speech production. Using a sensorimotor adaptation paradigm, we measured adaptive speech responses to auditory formant frequency perturbations in adults and children who stutter and their matched nonstuttering controls. We found that the magnitude of the speech adaptive response for children who stutter did not differ from that of fluent children. However, the adaptation magnitude of adults who stutter in response to formant perturbation was significantly smaller than the adaptation magnitude of adults who do not stutter. Together these results indicate that stuttering is associated with deficits in integrating discrepancies between predicted and received auditory feedback to calibrate the speech production system in adults but not children. This auditory-motor integration deficit thus appears to be a compensatory effect that develops over years of stuttering

Auditory feedback control mechanisms do not contribute to cortical hyperactivity within the voice production network in adductor spasmodic dysphonia

Adductor spasmodic dysphonia (ADSD), the most common form of spasmodic dysphonia, is a debilitating voice disorder characterized by hyperactivity and muscle spasms in the vocal folds during speech. Prior neuroimaging studies have noted excessive brain activity during speech in ADSD participants compared to controls. Speech involves an auditory feedback control mechanism that generates motor commands aimed at eliminating disparities between desired and actual auditory signals. Thus, excessive neural activity in ADSD during speech may reflect, at least in part, increased engagement of the auditory feedback control mechanism as it attempts to correct vocal production errors detected through audition. To test this possibility, functional magnetic resonance imaging was used to identify differences between ADSD participants and age-matched controls in (i) brain activity when producing speech under different auditory feedback conditions, and (ii) resting state functional connectivity within the cortical network responsible for vocalization. The ADSD group had significantly higher activity than the control group during speech (compared to a silent baseline task) in three left-hemisphere cortical regions: ventral Rolandic (sensorimotor) cortex, anterior planum temporale, and posterior superior temporal gyrus/planum temporale. This was true for speech while auditory feedback was masked with noise as well as for speech with normal auditory feedback, indicating that the excess activity was not the result of auditory feedback control mechanisms attempting to correct for perceived voicing errors in ADSD. Furthermore, the ADSD group had significantly higher resting state functional connectivity between sensorimotor and auditory cortical regions within the left hemisphere as well as between the left and right hemispheres, consistent with the view that excessive motor activity frequently co-occurs with increased auditory cortical activity in individuals with ADSD.First author draf

Sensorimotor adaptation to auditory perturbation of speech is facilitated by noninvasive brain stimulation

Repeated exposure to disparity between the motor plan and auditory feedback during speech production results in a proportionate change in the motor system’s response called auditory-motor adaptation. Artificially raising F1 in auditory feedback results in a concomitant decrease in F1 during speech production. Transcranial direct current stimulation (tDCS) can be used to alter neuronal excitability in focal areas of the brain. The present experiment explored the effect of noninvasive brain stimulation applied to the speech premotor cortex on the timing and magnitude of adaptation responses to artificially raised F1 in auditory feedback. Participants (N = 18) completed a speaking task in which they read target words aloud. Participants' speech was processed to raise F1 by 30% and played back to them over headphones in real time. A within-subjects design compared acoustics of participants’ speech while receiving anodal (active) tDCS stimulation versus sham (control) stimulation. Participants' speech showed an increasing magnitude of adaptation of F1 over time during anodal stimulation compared to sham. These results indicate that tDCS can affect behavioral response during auditory-motor adaptation, which may have translational implications for sensorimotor training in speech disorders

Noninvasive neurostimulation of left ventral motor cortex enhances sensorimotor adaptation in speech production

Sensorimotor adaptation¬—enduring changes to motor commands due to sensory feedback—allows speakers to match their articulations to intended speech acoustics. How the brain integrates auditory feedback to modify speech motor commands and what limits the degree of these modifications remain unknown. Here, we investigated the role of speech motor cortex in modifying stored speech motor plans. In a within-subjects design, participants underwent separate sessions of sham and anodal transcranial direct current stimulation (tDCS) over speech motor cortex while speaking and receiving altered auditory feedback of the first formant. Anodal tDCS increased the rate of sensorimotor adaptation for feedback perturbation. Computational modeling of our results using the Directions Into Velocities of Articulators (DIVA) framework of speech production suggested that tDCS primarily affected behavior by increasing the feedforward learning rate. This study demonstrates how focal noninvasive neurostimulation can enhance the integration of auditory feedback into speech motor plans.This research was supported by NIDCD of the NIH under award numbers R03DC014045 to TP, and R01DC002852 to FG. TLS was supported by T90DA032484. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Healt

An Investigation of Compensation and Adaptation to Auditory Perturbations in Individuals With Acquired Apraxia of Speech

Two auditory perturbation experiments were used to investigate the integrity of neural circuits responsible for speech sensorimotor adaptation in acquired apraxia of speech (AOS). This has implications for understanding the nature of AOS as well as normal speech motor control. Two experiments were conducted. In Experiment 1, compensatory responses to unpredictable fundamental frequency (F0) perturbations during vocalization were investigated in healthy older adults and adults with acquired AOS plus aphasia. F0 perturbation involved upward and downward 100-cent shifts versus no shift, in equal proportion, during 2 s vocalizations of the vowel /a/. In Experiment 2, adaptive responses to sustained first formant (F1) perturbations during speech were investigated in healthy older adults, adults with AOS and adults with aphasia only (APH). The F1 protocol involved production of the vowel /ε/ in four consonant-vowel words of Australian English (pear, bear, care, dare), and one control word with a different vowel (paw). An unperturbed Baseline phase was followed by a gradual Ramp to a 30% upward F1 shift stimulating a compensatory response, a Hold phase where the perturbation was repeatedly presented with alternating blocks of masking trials to probe adaptation, and an End phase with masking trials only to measure persistence of any adaptation. AOS participants showed normal compensation to unexpected F0 perturbations, indicating that auditory feedback control of low-level, non-segmental parameters is intact. Furthermore, individuals with AOS displayed an adaptive response to sustained F1 perturbations, but age-matched controls and APH participants did not. These findings suggest that older healthy adults may have less plastic motor programs that resist modification based on sensory feedback, whereas individuals with AOS have less well-established and more malleable motor programs due to damage from stroke

Auditory modulation during speech planning in stuttering and nonstuttering individuals

Thesis (Ph.D.)--University of Washington, 2015Stuttering is associated with atypical structural and functional connectivity among sensorimotor brain areas. However, it remains entirely unknown which specific mechanisms of sensorimotor control are affected by these neurological differences. In the program of research described here, I used a novel experimental paradigm and electroencephalographic (EEG) recordings to study motor-to-sensory interactions during speech movement planning in stuttering versus nonstuttering speakers. Experiment 1 investigated whether stuttering adults are deficient in modulating the auditory system prior to speech initiation. Auditory modulation was examined by recording auditory evoked potentials in response to probe tones presented during movement planning in a delayed-response speaking condition as compared with no-speaking control conditions. Findings indicated that stuttering speakers did not show the modulation of auditory processing (reflected in reduced amplitude of the N1 component) that was observed in nonstuttering speakers. This finding raised the question whether stuttering individuals have problems specifically with generating or evaluating a planning-related efference copy signal that can be used to predict upcoming self-generated sensory inputs or, more generally, with using any available information to make sensory predictions. In Experiment 2, probe tones were therefore delivered while participants anticipated either self-producing speech or hearing their own pre-recorded speech played back and in a control condition without auditory input. Results showed that auditory modulation differed between stuttering and normally fluent adults in both conditions with predictable auditory input. Experiment 3 was designed to start exploring the functional significance of pre-speech auditory modulation in general, and the functional implications of stuttering speakers' lack of modulation. Participants in this experiment completed a sensorimotor adaptation task with formant-shifted auditory feedback, and the results served to estimate each speaker's reliance on auditory feedback. In a separate session, pre-speech auditory modulation was again assessed by means of probe tones, but this time N1 modulation relative to a no-speaking control condition was quantified both in a condition that allowed typical reliance on auditory feedback (non-delayed auditory feedback; NAF) and in a condition that did not allow reliance on auditory feedback (delayed auditory feedback; DAF). Results revealed that (a) stuttering speakers showed only limited adaptation to formant-shifted auditory feedback; (b) for nonstuttering speakers, DAF caused the amount of pre-speech auditory modulation to be reduced whereas for stuttering speakers, DAF enhanced pre-speech auditory modulation; and (c) across the two groups, there was a relationship between the effect of DAF on pre-speech auditory modulation and reliance on auditory feedback during the adaptation task. These studies demonstrate that stuttering individuals have difficulties with using auditory predictions--both those related to active movement planning and those related to input that is not a consequence of one's own actions--to prime this sensory system with critical importance for speech production. Moreover, stuttering individuals showed not only a lack of modulation of the auditory system under normal speaking conditions (NAF) but also a lower reliance on auditory feedback as revealed here during a sensorimotor adaptation task with formant-shifted auditory feedback. Overall, findings suggest that stuttering is associated with deficits in auditory-motor integration, and that the auditory system may be not appropriately modulated for its role in online feedback control during speech production. I speculate that the inability to use predictive information for appropriately priming task-relevant sensory systems for their role in monitoring articulatory movements may lead to unnecessary and disruptive attempts at correcting ongoing movements. These maladaptive "repairs" may contribute to the fluency breakdowns that form the primary symptoms of stuttering