Douglas M. Shiller

Sensorimotor integration for speech motor learning involves the inferior parietal cortex.

Sensorimotor integration is important for motor learning. The inferior parietal lobe, through its connections with the frontal lobe and cerebellum, has been associated with multisensory integration and sensorimotor adaptation for motor behaviors other than speech. In the present study, the contribution of the inferior parietal cortex to speech motor learning was evaluated using repetitive transcranial magnetic stimulation (rTMS) prior to a speech motor adaptation task. Subjects’ auditory feedback was altered in a manner consistent with the auditory consequences of an unintended change in tongue position during speech production, and adaptation performance was used to evaluate sensorimotor plasticity and short‐term learning. Prior to the feedback alteration, rTMS or sham stimulation was applied over the left supramarginal gyrus (SMG). Subjects who underwent the sham stimulation exhibited a robust adaptive response to the feedback alteration whereas subjects who underwent rTMS exhibited a diminished adaptive response. The results suggest that the inferior parietal region, in and around SMG, plays a role in sensorimotor adaptation for speech. The interconnections of the inferior parietal cortex with inferior frontal cortex, cerebellum and primary sensory areas suggest that this region may be an important component in learning and adapting sensorimotor patterns for speech.

Sensorimotor adaptation of speech in Parkinson's disease

The basal ganglia are involved in establishing motor plans for a wide range of behaviors. Parkinsons disease (PD) is a manifestation of basal ganglia dysfunction associated with a deficit in sensorimotor integration and difficulty in acquiring new motor sequences, thereby affecting motor learning. Previous studies of sensorimotor integration and sensorimotor adaptation in PD have focused on limb movements using visual and force‐field alterations. Here, we report the results from a sensorimotor adaptation experiment investigating the ability of PD patients to make speech motor adjustments to a constant and predictable auditory feedback manipulation. Participants produced speech while their auditory feedback was altered and maintained in a manner consistent with a change in tongue position. The degree of adaptation was associated with the severity of motor symptoms. The patients with PD exhibited adaptation to the induced sensory error; however, the degree of adaptation was reduced compared with healthy, age‐matched control participants. The reduced capacity to adapt to a change in auditory feedback is consistent with reduced gain in the sensorimotor system for speech and with previous studies demonstrating limitations in the adaptation of limb movements after changes in visual feedback among patients with PD.

Plasticity in the Human Speech Motor System Drives Changes in Speech Perception

Recent studies of human speech motor learning suggest that learning is accompanied by changes in auditory perception. But what drives the perceptual change? Is it a consequence of changes in the motor system? Or is it a result of sensory inflow during learning? Here, subjects participated in a speech motor-learning task involving adaptation to altered auditory feedback and they were subsequently tested for perceptual change. In two separate experiments, involving two different auditory perceptual continua, we show that changes in the speech motor system that accompany learning drive changes in auditory speech perception. Specifically, we obtained changes in speech perception when adaptation to altered auditory feedback led to speech production that fell into the phonetic range of the speech perceptual tests. However, a similar change in perception was not observed when the auditory feedback that subjects received during learning fell into the phonetic range of the perceptual tests. This indicates that the central motor outflow associated with vocal sensorimotor adaptation drives changes to the perceptual classification of speech sounds.

Auditory-Perceptual Learning Improves Speech Motor Adaptation in Children

Auditory feedback plays an important role in childrens speech development by providing the child with information about speech outcomes that is used to learn and fine-tune speech motor plans. The use of auditory feedback in speech motor learning has been extensively studied in adults by examining oral motor responses to manipulations of auditory feedback during speech production. Children are also capable of adapting speech motor patterns to perceived changes in auditory feedback; however, it is not known whether their capacity for motor learning is limited by immature auditory-perceptual abilities. Here, the link between speech perceptual ability and the capacity for motor learning was explored in two groups of 5- to 7-year-old children who underwent a period of auditory perceptual training followed by tests of speech motor adaptation to altered auditory feedback. One group received perceptual training on a speech acoustic property relevant to the motor task while a control group received perceptual training on an irrelevant speech contrast. Learned perceptual improvements led to an enhancement in speech motor adaptation (proportional to the perceptual change) only for the experimental group. The results indicate that childrens ability to perceive relevant speech acoustic properties has a direct influence on their capacity for sensory-based speech motor adaptation.

Feel What You Say: An Auditory Effect on Somatosensory Perception

In the present study, we demonstrate an audiotactile effect in which amplitude modulation of auditory feedback during voiced speech induces a throbbing sensation over the lip and laryngeal regions. Control tasks coupled with the examination of speech acoustic parameters allow us to rule out the possibility that the effect may have been due to cognitive factors or motor compensatory effects. We interpret the effect as reflecting the tight interplay between auditory and tactile modalities during vocal production.

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

BACKGROUNDnAuditory feedback reflects information on multiple speech parameters including fundamental frequency (pitch) and formant properties. Inducing auditory errors in these acoustic parameters during speech production has been used to examine the manner in which auditory feedback is integrated with ongoing speech motor processes. This integration has been shown to be impaired in disorders such as Parkinsons disease (PD), in which individuals exhibit difficulty adjusting to altered sensory-motor relationships. The current investigation examines whether such sensorimotor impairments affect fundamental frequency and formant parameters of speech differentially.nnnMETHODSnWe employed a sensorimotor compensation paradigm to investigate the mechanisms underlying the control of vocal pitch and formant parameters. Individuals with PD and age-matched controls prolonged a speech vowel in the context of a word while the fundamental or first formant frequency of their auditory feedback was altered unexpectedly on random trials, using two magnitudes of perturbation.nnnRESULTSnCompared with age-matched controls, individuals with PD exhibited a larger compensatory response to fundamental frequency perturbations, in particular in response to the smaller magnitude alteration. In contrast, the group with PD showed reduced compensation to first formant frequency perturbations.nnnCONCLUSIONSnThe results demonstrate that the neural processing impairment of PD differentially affects the processing of auditory feedback for the control of fundamental and formant frequency. The heightened modulation of fundamental frequency in response to auditory perturbations may reflect a change in sensory weighting due to somatosensory deficits associated with the larynx, while the reduced ability to modulate vowel formants may result from impaired activation of the oral articulatory musculature.

Short-Term Visual Deprivation Improves the Perception of Harmonicity

Neuroimaging studies have shown that the perception of auditory stimuli involves occipital cortical regions traditionally associated with visual processing, even in the absence of any overt visual component to the task. Analogous behavioral evidence of an interaction between visual and auditory processing during purely auditory tasks comes from studies of short-term visual deprivation on the perception of auditory cues, however, the results of such studies remain equivocal. Although some data have suggested that visual deprivation significantly increases loudness and pitch discrimination and reduces spatial localization inaccuracies, it is still unclear whether such improvement extends to the perception of spectrally complex cues, such as those involved in speech and music perception. We present data demonstrating that a 90-min period of visual deprivation causes a transient improvement in the perception of harmonicity: a spectrally complex cue that plays a key role in music and speech perception. The results provide clear behavioral evidence supporting a role for the visual system in the processing of complex auditory stimuli, even in the absence of any visual component to the task.

Sensorimotor adaptation of whole-body postural control

The aim of the present study was to examine the modification of postural symmetry during quiet standing using a sensorimotor adaptation paradigm. A group of neurologically typical adult participants performed a visually guided mediolateral (left-right) weight shifting task requiring precise adjustments in body orientation. During one phase of the task, the visual feedback of center of pressure (COP) was systematically biased toward the left or the right, requiring an adjustment in posture to compensate. COP during quiet standing without visual feedback was examined prior to and immediately following the sensorimotor adaptation procedure, in order to observe whether compensatory adjustments in postural control resulting from the visual-feedback manipulation would transfer to the control of whole-body COP during quiet standing. Results showed that the sensorimotor adaptation procedure induced a small but reliable compensatory change in the stance of participants, resulting in a change in postural symmetry and control that was found to persist even after normal visual feedback was restored.

Enhancing speech adaptation to a palatal perturbation using ultrasound visual biofeedback

Prior clinical studies suggest that visual biofeedback of the tongue (e.g., ultrasound) may enhance the treatment of speech disorders, but outcomes have been mixed, likely due to variability in both the clinical profiles of participants and the way in which treatments have been carried out. Understanding the true potential of this clinical tool requires a clearer sense of how visual biofeedback interacts with speech motor control. Here, we present a novel experimental approach that mimics the conditions of clinical treatment for speech disorders while maintaining a high level of consistency and control over the speech-learning task. The procedure involves altering the vocal tract of typically developing talkers using a palatal prosthesis to perturb /s/-production in combination with the controlled application of ultrasound biofeedback. As participants practice and improve their speech, changes in articulatory movements are examined using acoustic and kinematic measures. The present study compared a control group (nu2009=u200910) receiving only auditory feedback during speech practice with a group receiving visual biofeedback (nu2009=u200910). Results indicate an effect of biofeedback, in particular in the retention of learned motor patterns, indicating that talkers integrate real-time visual feedback of tongue movement into the sensorimotor processes driving speech adaptation.Prior clinical studies suggest that visual biofeedback of the tongue (e.g., ultrasound) may enhance the treatment of speech disorders, but outcomes have been mixed, likely due to variability in both the clinical profiles of participants and the way in which treatments have been carried out. Understanding the true potential of this clinical tool requires a clearer sense of how visual biofeedback interacts with speech motor control. Here, we present a novel experimental approach that mimics the conditions of clinical treatment for speech disorders while maintaining a high level of consistency and control over the speech-learning task. The procedure involves altering the vocal tract of typically developing talkers using a palatal prosthesis to perturb /s/-production in combination with the controlled application of ultrasound biofeedback. As participants practice and improve their speech, changes in articulatory movements are examined using acoustic and kinematic measures. The present study compared a contro...

Speech adaptation to palatal perturbation: Evidence for sensorimotor reorganization across the workspace

It has recently been shown that talkers are capable of simultaneously adapting multiple vowels to an alteration of auditory feedback during the production of complex, variable sentences [1]. The present study extends this work by examining adaptation to a more complex, physical alteration of the speech motor system (palatal prosthesis) that impacts both auditory and somatosensory feedback. Acoustic and kinematic measures (electromagnetic articulography of the tongue) were used to assess the initial impact of the perturbation on a range of vowels and consonants, as well as learned changes following 20 minutes of practice producing variable sentences with the prosthesis in place. Kinematic analyses revealed robust, systematic perturbation and motor learning effects across all speech sounds, indicating that talkers are capable of rapid adaptation in the production of multiple sounds across the articulatory workspace following a physical alteration of the vocal apparatus.