Articulatory and segmental performance in children with and without speech disorder: A multiple case pilot study.

This multiple case pilot study explored how nonword imitation influences articulatory and segmental performance in children with and without speech disorder. Eight children, ages 4- to 8-years-old, participated, including two children with childhood apraxia of speech (CAS), four children with phonological disorder (PD), and two children with typical development (TD). Tokens included two complexity types and were presented in random order. Minimal feedback was provided and nonwords were never associated with a referent. Kinematic and transcription data were analysed to examine articulatory variability, segmental accuracy, and segmental variability in session 1 and session 5. Descriptive statistics, percent change, effect sizes, and Pearson correlations are reported. In session 1, the two participants with CAS showed high articulatory variability, low segmental accuracy, and high segmental variability compared to the participants with PD and TD. By session 5, both participants with CAS, two with PD, and one with TD showed increased articulatory variability in the lowest complexity nonword. Segmental accuracy remained low and variability remained high for the two participants with CAS in session 5, whereas several participants with PD and TD showed improved segmental performance. Articulatory and segmental variability were not significantly correlated. The results of this study suggest that motor practice with minimal feedback and no assignment of a lexical referent can instantiate positive changes to segmental performance for children without apraxia. Positive changes to segmental performance are not necessarily related to increased articulatory control; these two processing levels can show distinct and disparate learning trajectories.

A case for the role of memory consolidation in speech-motor learning.

This review will explore the role of memory consolidation in speech-motor learning. Existing frameworks of speech-motor control account for the protracted time course of building the speech-motor representation. These perspectives converge on the speech-motor representation as a multimodal unit that is comprised of auditory, motor, and linguistic information. Less is known regarding the memory mechanisms that support the emergence of a generalized speech-motor unit from instances of speech production. Here, we consider the broader learning and memory consolidation literature and how it may apply to speech-motor learning. We discuss findings from relevant domains on the stabilization, enhancement, and generalization of learned information. Based on this literature, we provide our predictions for the division of labor between conscious and unconscious memory systems in speech-motor learning, and the subsequent effects of time and sleep to memory consolidation. We identify both the methodological challenges, as well as the practical importance, of advancing this work empirically. This discussion provides a foundation for building a memory-based framework for speech-motor learning.

Motor sequence learning in children with recovered and persistent developmental stuttering: preliminary findings.

PURPOSE: Previous studies have associated developmental stuttering with difficulty learning new motor skills. We investigated non-speech motor sequence learning in children with persistent developmental stuttering (CWS), children who have recovered from developmental stuttering (CRS) and typically developing controls (CON). METHODS: Over the course of two days, participants completed the Multi-Finger Sequencing Task, consisting of repeated trials of a10-element sequence, interspersed with trials of random sequences of the same length. We evaluated motor sequence learning using accuracy and response synchrony, a timing measure for evaluation of sequencing timing. We examined error types as well as recognition and recall of the repeated sequences. RESULTS: CWS demonstrated lower performance accuracy than CON and CRS on the first day of the finger tapping experiment but improved to the performance level of CON and CRS on the second day. Response synchrony showed no overall difference among CWS, CRS and CON. Learning scores of repeated sequences did not differ from learning scores of random sequences in CWS, CRS and CON. CON and CRS demonstrated an adaptive strategy to response errors, whereas CWS maintained a high percentage of corrected errors for both days. CONCLUSIONS: Our study examined non-speech sequence learning across CWS, CRS and CON. Our preliminary findings support the idea that developmental stuttering is not associated with sequence learning per se but rather with general fine motor performance difficulties.

Recalibration of auditory perception of speech due to orofacial somatosensory inputs during speech motor adaptation.

Speech motor control and learning rely on both somatosensory and auditory inputs. Somatosensory inputs associated with speech production can also affect the process of auditory perception of speech, and the somatosensory-auditory interaction may play a fundamental role in auditory perception of speech. In this report, we show that the somatosensory system contributes to perceptual recalibration, separate from its role in motor function. Subjects participated in speech motor adaptation to altered auditory feedback. Auditory perception of speech was assessed in phonemic identification tests before and after speech adaptation. To investigate a role of the somatosensory system in motor adaptation and subsequent perceptual change, we applied orofacial skin stretch in either a backward or forward direction during the auditory feedback alteration as a somatosensory modulation. We found that the somatosensory modulation did not affect the amount of adaptation at the end of training, although it changed the rate of adaptation. However, the perception following speech adaptation was altered depending on the direction of the somatosensory modulation. Somatosensory inflow rather than motor outflow thus drives changes to auditory perception of speech following speech adaptation, suggesting that somatosensory inputs play an important role in tuning of perceptual system.NEW & NOTEWORTHY This article reports that the somatosensory system works not equally with the motor system, but predominantly in the calibration of auditory perception of speech by speech production.

Successful auditory motor adaptation requires task-relevant auditory errors.

When we produce speech movements, we also predict the auditory consequences of the movements. We use discrepancies between our predictions and incoming auditory information to modify our future movements (adapt). Although auditory errors are crucial for speech motor learning, not all perceived auditory errors are consequences of our own actions. Therefore, the brain needs to evaluate the relevance of perceived auditory errors. In this study, we examined error assessment processes involved in auditory motor adaptation by systematically manipulating the correspondence between speech motor outputs and their auditory consequences during speaking. Participants (n = 30) produced speech while they received perturbed auditory feedback (e.g., produced "head" but heard a word that sounded like "had"). In one condition, auditory errors were related to participants' productions (task-relevant errors). In another condition, auditory errors were defined by the experimenter and had no correspondence with participants' speech output (task-irrelevant errors). We found that the extent of adaptation and error sensitivity (derived from a state-space model) were greater in the condition with task-relevant auditory errors compared with those in the condition with task-irrelevant auditory errors. Additionally, participants with smaller perceptual targets (derived from a categorical perception task) adapted more to auditory perturbations, and participants with larger perceptual targets adapted less. Similarly, participants with smaller perceptual targets were more sensitive to errors in the condition with task-relevant auditory errors. Together, our results highlight the intricate mechanisms, involving both perception and production systems, that the brain uses to optimally integrate auditory errors for successful speech motor learning.NEW & NOTEWORTHY Feedback monitoring is essential for accurate speech production. By providing empirical results and a computational framework, we show that 1) the brain evaluates relevance of auditory errors and responds more to relevant errors, and 2) smaller perceptual targets are associated with more sensitivity to errors and more auditory motor adaptation.

Changes in movement transitions across a practice period in childhood apraxia of speech.

This study examined changes in speech motor control across a movement transition between sounds within a motor learning task in children with apraxia of speech (CAS) and typical development (TD). It was investigated whether oral articulator movement was refined with practice and whether practice gains generalized to words not included in the practice session. A total of 16 children (ages 5-6) with CAS (n = 8) and TD (n = 8) participated in this study. Novel and real word tokens were produced at three time points. Kinematic data was collected using facial motion tracking at each time point. Children completed a practice session following baseline data collection session that integrated motor learning principles. Three tokens were included in the practice session and the remaining stimuli assessed carryover of practice gains. Kinematic data was then collected immediately following practice and 3 days later. Kinematic analyses were conducted on the movement gesture for the first syllable of each word. Narrow transcription analyses examined speech production accuracy. Children in the CAS group displayed increased consonant and vowel accuracy only for the practised tokens. Adjustments to spatial control and movement variability were observed in the CAS group, though only for practised words. Children in the TD group altered spatial and temporal domains of movement and variability across both practised and non-practised tokens. Interestingly, the CAS group displayed a pattern of increased displacement along with decreased variability, which was not observed in the TD group. The degree to which these findings reflect facilitative or maladaptive changes are discussed. Results are also interpreted in relation to vowel properties, novel/real word status and variable practice of novel and real words.

Is There an Interaction between Task Complexity and Practice Variability in Speech-Motor learning?

BACKGROUND: Prior studies have investigated the influence of principles of motor learning (PMLs) on speech-motor learning. However, the interactive effect of different PMLs on speech-motor learning remains unknown. PURPOSE: This study is aimed at investigating the interaction of 2 PMLs, that is, practice variability and task complexity and their influence on speech-motor learning. METHOD: Forty healthy individuals (aged 18-30 years) were randomly and equally allocated to 2 groups where they had to either practice a simple (simple group) or a complex phrase (complex group). Two levels of practice variability (constant and variable) were considered in training participants in simple and complex groups. Participants practiced 50 practice trials of either complex or simple phrase during the first 2 days. At the end of training on each day, participants produced 10 trials of the phrase they practiced without feedback. On the third day, participants returned for a delayed retention test. The participant utterances on all the 3 days were recorded for later analysis. RESULTS: Data analysis revealed that there was no major effect of practice condition, and there was no interaction of task complexity and practice condition. However, there was an interaction between data collection points and complexity. CONCLUSION: The findings suggest that irrespective of the complexity of the to-be-learned speech task, there is no preponderance of variable over constant practice, which contradicts the findings of the non-speech-motor learning literature.

Learning trajectories for speech motor performance in children with specific language impairment.

UNLABELLED: Children with specific language impairment (SLI) often perform below expected levels, including on tests of motor skill and in learning tasks, particularly procedural learning. In this experiment we examined the possibility that children with SLI might also have a motor learning deficit. Twelve children with SLI and thirteen children with typical development (TD) produced complex nonwords in an imitation task. Productions were collected across three blocks, with the first and second blocks on the same day and the third block one week later. Children's lip movements while producing the nonwords were recorded using an Optotrak camera system. Movements were then analyzed for production duration and stability. Movement analyses indicated that both groups of children produced shorter productions in later blocks (corroborated by an acoustic analysis), and the rate of change was comparable for the TD and SLI groups. A nonsignificant trend for more stable productions was also observed in both groups. SLI is regularly accompanied by a motor deficit, and this study does not dispute that. However, children with SLI learned to make more efficient productions at a rate similar to their peers with TD, revealing some modification of the motor deficit associated with SLI. LEARNING OUTCOMES: The reader will learn about deficits commonly associated with specific language impairment (SLI) that often occur alongside the hallmark language deficit. The authors present an experiment showing that children with SLI improved speech motor performance at a similar rate compared to typically developing children. The implication is that speech motor learning is not impaired in children with SLI.

Redistribution of neural phase coherence reflects establishment of feedforward map in speech motor adaptation.

Despite recent progress in our understanding of sensorimotor integration in speech learning, a comprehensive framework to investigate its neural basis is lacking at behaviorally relevant timescales. Structural and functional imaging studies in humans have helped us identify brain networks that support speech but fail to capture the precise spatiotemporal coordination within the networks that takes place during speech learning. Here we use neuronal oscillations to investigate interactions within speech motor networks in a paradigm of speech motor adaptation under altered feedback with continuous recording of EEG in which subjects adapted to the real-time auditory perturbation of a target vowel sound. As subjects adapted to the task, concurrent changes were observed in the theta-gamma phase coherence during speech planning at several distinct scalp regions that is consistent with the establishment of a feedforward map. In particular, there was an increase in coherence over the central region and a decrease over the fronto-temporal regions, revealing a redistribution of coherence over an interacting network of brain regions that could be a general feature of error-based motor learning in general. Our findings have implications for understanding the neural basis of speech motor learning and could elucidate how transient breakdown of neuronal communication within speech networks relates to speech disorders.

Precise feedback control underlies sensorimotor learning in speech.

Acquiring the skill of speaking in another language, or for that matter a child's learning to talk, does not follow a single recipe. People learn by variable amounts. A major component of speech learnability seems to be sensing precise feedback errors to correct subsequent utterances that help maintain speech goals. We have tested this idea in a speech motor learning paradigm under altered auditory feedback, in which subjects repeated a word while their auditory feedback was changed online. Subjects learned the task to variable degrees, with some simply failing to learn. We assessed feedback contribution by computing one-lag covariance between formant trajectories of the current feedback and the following utterance that was found to be a significant predictor of learning. Our findings rely on a novel use of information-rich formant trajectories in evaluating speech motor learning and argue for their relevance in auditory speech goals of vowel sounds.

Sensorimotor adaptation of speech in Parkinson's disease.

The basal ganglia are involved in establishing motor plans for a wide range of behaviors. Parkinson's 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.