Speech Motor Control Processes Research Articles

Effects of speech rate modifications on phonatory acoustic outcomes in Parkinson's disease.

Speech rate reduction is a global speech therapy approach for speech deficits in Parkinson's disease (PD) that has the potential to result in changes across multiple speech subsystems. While the overall goal of rate reduction is usually improvements in speech intelligibility, not all people with PD benefit from this approach. Speech rate is often targeted as a means of improving articulatory precision, though less is known about rate-induced changes in other speech subsystems that could help or hinder communication. The purpose of this study was to quantify phonatory changes associated with speech rate modification across a broad range of speech rates from very slow to very fast in talkers with and without PD. Four speaker groups participated: younger and older healthy controls, and people with PD with and without deep brain stimulation of the subthalamic nucleus (STN-DBS). Talkers read aloud standardized sentences at 7 speech rates elicited using magnitude production: habitual, three slower rates, and three faster rates. Acoustic measures of speech intensity, cepstral peak prominence, and fundamental frequency were measured as a function of speech rate and group. Overall, slower rates of speech were associated with differential effects on phonation across the four groups. While all talkers spoke at a lower pitch in slow speech, younger talkers showed increases in speech intensity and cepstral peak prominence, while talkers with PD and STN-DBS showed the reverse pattern. Talkers with PD without STN-DBS and older healthy controls behaved in between these two extremes. At faster rates, all groups uniformly demonstrated increases in cepstral peak prominence. While speech rate reductions are intended to promote positive changes in articulation to compensate for speech deficits in dysarthria, the present results highlight that undesirable changes may be invoked across other subsystems, such as at the laryngeal level. In particular, talkers with STN-DBS, who often demonstrate speech deterioration following DBS surgery, demonstrated more phonatory detriments at slowed speech rates. Findings have implications for speech rate candidacy considerations and speech motor control processes in PD.

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

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. 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. 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. 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.

A Contribution to the Role of the Claustrum in Speech Motor Control Processes

A Contribution to the Role of the Claustrum in Speech Motor Control Processes

The effect of emotion on articulation rate in persistence and recovery of childhood stuttering

PurposeThis study investigated the possible association of emotional processes and articulation rate in pre-school age children who stutter and persist (persisting), children who stutter and recover (recovered) and children who do not stutter (nonstuttering). MethodsThe participants were ten persisting, ten recovered, and ten nonstuttering children between the ages of 3–5 years; who were classified as persisting, recovered, or nonstuttering approximately 2–2.5 years after the experimental testing took place. The children were exposed to three emotionally-arousing video clips (baseline, positive and negative) and produced a narrative based on a text-free storybook following each video clip. From the audio-recordings of these narratives, individual utterances were transcribed and articulation rates were calculated. ResultsResults indicated that persisting children exhibited significantly slower articulation rates following the negative emotion condition, unlike recovered and nonstuttering children whose articulation rates were not affected by either of the two emotion-inducing conditions. Moreover, all stuttering children displayed faster rates during fluent compared to stuttered speech; however, the recovered children were significantly faster than the persisting children during fluent speech. ConclusionNegative emotion plays a detrimental role on the speech-motor control processes of children who persist, whereas children who eventually recover seem to exhibit a relatively more stable and mature speech-motor system. This suggests that complex interactions between speech-motor and emotional processes are at play in stuttering recovery and persistency; and articulation rates following negative emotion or during stuttered versus fluent speech might be considered as potential factors to prospectively predict persistence and recovery from stuttering.

Speech motor planning and execution deficits in early childhood stuttering.

BackgroundFive to eight percent of preschool children develop stuttering, a speech disorder with clearly observable, hallmark symptoms: sound repetitions, prolongations, and blocks. While the speech motor processes underlying stuttering have been widely documented in adults, few studies to date have assessed the speech motor dynamics of stuttering near its onset. We assessed fundamental characteristics of speech movements in preschool children who stutter and their fluent peers to determine if atypical speech motor characteristics described for adults are early features of the disorder or arise later in the development of chronic stuttering.MethodsOrofacial movement data were recorded from 58 children who stutter and 43 children who do not stutter aged 4;0 to 5;11 (years; months) in a sentence production task. For single speech movements and multiple speech movement sequences, we computed displacement amplitude, velocity, and duration. For the phrase level movement sequence, we computed an index of articulation coordination consistency for repeated productions of the sentence.ResultsBoys who stutter, but not girls, produced speech with reduced amplitudes and velocities of articulatory movement. All children produced speech with similar durations. Boys, particularly the boys who stuttered, had more variable patterns of articulatory coordination compared to girls.ConclusionsThis study is the first to demonstrate sex-specific differences in speech motor control processes between preschool boys and girls who are stuttering. The sex-specific lag in speech motor development in many boys who stutter likely has significant implications for the dramatically different recovery rates between male and female preschoolers who stutter. Further, our findings document that atypical speech motor development is an early feature of stuttering.

Defining Speech and Language Fluency Profiles in Children with and without Family History of Stuttering, before and after the Onset of Stuttering: Preliminary Findings

Current research indicates that the onset, recovery and persistence of stuttering stem from a number of complex factors and their interaction with speech motor control processes. The use of non-speech and quasi-speech tasks have helped to increase the understanding of speech production processes involved with stuttering, however results from such studies are somewhat inconsistent and do not reflect natural speaking contexts. It is often difficult to ascertain the direction of causality of findings. This experiment investigated familial history as a risk factor for the onset of stuttering and whether changes in speech and language fluency profiles associated with stuttering are a cause or consequence of stuttering. Eighteen young children participated in this experiment to investigate the onset and developmental aspects of early stuttering across four data sessions collected three months apart. The first data session was prior to the onset of any stuttering. This allowed for investigation of the relevant risk factors associated with the onset of stuttering, and speech production development associated with and without stuttering. A number of detailed speech production measures were gathered to comprise the speech and fluency profiles. To explore the way in which speech motor control and linguistic planning processes interact, the set of collected speech measures targeted both processes. Together, the measures reflect the multidimensional aspect of fluency and dynamic processes of speech production. A novel approach for the investigation of pauses in speech was adopted (Kirsner, Dunn, & Hird, 2003) in conjunction with common measures of speech and language production (Systematic Analysis of Language Transcripts: SALT, Miller, 2008). Nine children with a positive family history of stuttering and nine age and gender matched children without positive family history of stuttering participated. Children were aged between 21 to 48 months at the first data session and aged between 30 and 57 months when the study ended. Speech and language fluency profiles were determined through natural speaking contexts; conversation and play sessions with a parent and the examiner. During the study five children were diagnosed with stuttering but familial history was not found to be a significant predictor for the onset of stuttering. This was likely due to the small sample size available. Syllables Spoken per Second, a measure of articulation rate, was found to be a significant predictor for stuttering onset. However, this result was inconclusive as it could also be explained by group differences in age. Prior to any stuttering onset, the speech and language fluency profiles of children who started stuttering was comparable to that of children who continued to typically develop. However, soon after stuttering onset, the results showed an early impact of stuttering on speech production. The preliminary findings demonstrate that changes in speech production measures occurred as a consequence of stuttering.

Language and motor abilities of preschool children who stutter: Evidence from behavioral and kinematic indices of nonword repetition performance

Stuttering is a disorder of speech production that typically arises in the preschool years, and many accounts of its onset and development implicate language and motor processes as critical underlying factors. There have, however, been very few studies of speech motor control processes in preschool children who stutter. Hearing novel nonwords and reproducing them engages multiple neural networks, including those involved in phonological analysis and storage and speech motor programming and execution. We used this task to explore speech motor and language abilities of 31 children aged 4–5years who were diagnosed as stuttering. We also used sensitive and specific standardized tests of speech and language abilities to determine which of the children who stutter had concomitant language and/or phonological disorders. Approximately half of our sample of stuttering children had language and/or phonological disorders. As previous investigations would suggest, the stuttering children with concomitant language or speech sound disorders produced significantly more errors on the nonword repetition task compared to typically developing children. In contrast, the children who were diagnosed as stuttering, but who had normal speech sound and language abilities, performed the nonword repetition task with equal accuracy compared to their normally fluent peers. Analyses of interarticulator motions during accurate and fluent productions of the nonwords revealed that the children who stutter (without concomitant disorders) showed higher variability in oral motor coordination indices. These results provide new evidence that preschool children diagnosed as stuttering lag their typically developing peers in maturation of speech motor control processes.Educational objectives: The reader will be able to: (a) discuss why performance on nonword repetition tasks has been investigated in children who stutter; (b) discuss why children who stutter in the current study had a higher incidence of concomitant language deficits compared to several other studies; (c) describe how performance differed on a nonword repetition test between children who stutter who do and do not have concomitant speech or language deficits; (d) make a general statement about speech motor control for nonword production in children who stutter compared to controls.

Do We Have a “Mental Syllabary” in the Brain? An fMRI Study

The present study combines functional magnetic resonance imaging (fMRI) and reaction time (RT) measurements to further elucidate the influence of syllable frequency and complexity on speech motor control processes, i.e., overt reading of pseudowords. Tying in with a recent fMRI-study of our group we focused on the concept of a mental syllabary housing syllable sized ready-made motor plans for high- (HF), but not low-frequency (LF) syllables. The RT-analysis disclosed a frequency effect weakened by a simultaneous complexity effect for HF-syllables. In contrast, the fMRI data revealed no effect of syllable frequency, but point to an impact of syllable structure: Compared with CV-items, syllables with a complex onset (CCV) yielded higher hemodynamic activation in motor "execution" areas (left sensorimotor cortex, right inferior cerebellum), which is at least partially compatible with our previous study. We discuss the role of the syllable in speech motor control.

Linguistic complexity, speech production, and comprehension in Parkinson's disease: behavioral and physiological indices.

To investigate the effects of increased syntactic complexity and utterance length demands on speech production and comprehension in individuals with Parkinson's disease (PD) using behavioral and physiological measures. Speech response latency, interarticulatory coordinative consistency, accuracy of speech production, and response latency and accuracy on a receptive language task were analyzed in 16 individuals with PD and 16 matched control participants. Individuals with PD had higher oral motor coordination variability, took a longer time to initiate speech, and made more errors on the speaking task compared with the control group. They also received lower scores on the 2 complex conditions of the receptive language task. Increased length and syntactic complexity negatively affected performance in both groups of speakers. These findings provide a novel window into the speech deficits associated with PD by examining performance on longer, sentence-level utterances in contrast to earlier investigations of single-word or nonword productions. Speech motor control processes and language comprehension were adversely affected in the majority of our participants with mild to moderate PD compared to the control group. Finally, increased syntactic complexity and sentence length affected both the healthy aging and PD groups' speech production performance at the behavioral and kinematic levels.

Effects of jaw perturbation on cortical activity during speech production

Functional magnetic resonance imaging (fMRI) was used to investigate cortical activation caused by introducing a perturbation to the jaw during speech. The DIVA model of speech production [e.g., Guenther and Ghosh (2003), Proceedings of the ICPhS. Barcelona, ICPhS Committee] predicts that jaw perturbation will cause a mismatch between learned target (expected) sensations and actual sensory inputs in higher-order somatosensory cortical areas in the supramarginal gyrus, and that this mismatch will drive compensatory activations of motor cortical areas. To test this hypothesis, we performed an fMRI experiment in which articulation of pseudo-words was perturbed by the rapid inflation of a small, stiff balloon held between the subjects molars. The perturbation condition occurred pseudo-randomly on 1/7 of the trials. After controlling for brain activation due to normal speech production (no perturbation) and due to the sensation of balloon inflation alone (no production), two regions responded preferentially to the perturbed speech condition: one region along the boundary of the angular gyrus and posterior supramarginal gyrus in inferior parietal cortex, and another in the ventral posterior inferior frontal gyrus extending into the frontal operculum and anterior insula. These results provide evidence for the type of speech motor control processes hypothesized by the DIVA model.

Development of functional synergies for speech motor coordination in childhood and adolescence.

Adults produce rapid, interleaved sequences of speech sounds by controlling the relative motions in time and space of the oral articulators. The control and coordination of these effectors appear to be automatic, effortless, and usually error free. If speech production is viewed within the framework of classical motor control theories, we can infer that adults have organized functional synergies (consistent patterns of activation of muscle collectives) that act as stable subunits. In this study, the development of these stable functional synergies is examined. Motion of the upper lip, lower lip, and jaw was recorded during sentence production in 180 children and adults (aged 4-22 years). Two indices of oral motor coordination were computed, which reflect the degree of trial-to-trial consistency in intereffector relationships and thus the stability of the underlying functional synergies. Major findings are: (a) The time course of development for speech motor coordination is protracted, (b) speech motor control processes are not adultlike until after age 14 years for both females and males, (c) boys (until age 5 years) show a slower maturational course of speech motor development, and (d) late childhood (the 7- to 12-year period) is characterized by a plateau in the development of these coordinative synergies for speech production. We posit that multiple factors are likely to contribute to the protracted development of oral motor coordination for speech, including maturation of components of the motor system itself and maturation of the brain subsystems for language processing.

Speech movements do not scale by orofacial structure size.

The potential role of a size-scaling principle in orofacial movements for speech was examined by using between-group (adults vs. 5-yr-old children) as well as within-group correlational analyses. Movements of the lower lip and jaw were recorded during speech production, and anthropometric measures of orofacial structures were made. Adult women produced speech movements of equal amplitude and velocity to those of adult men. The children produced speech movement amplitudes equal to those of adults, but they had significantly lower peak velocities of orofacial movement. Thus we found no evidence supporting a size-scaling principle for orofacial speech movements. Young children have a relatively large-amplitude, low-velocity movement strategy for speech production compared with young adults. This strategy may reflect the need for more time to plan speech movement sequences and an increased reliance on sensory feedback as young children develop speech motor control processes.

Articulatory movements in adolescents: evidence for protracted development of speech motor control processes.

In order to contribute to a more comprehensive model of speech motor development, we examined the movement trajectories of the upper lip, lower lip, and jaw to determine (a) if there are changes in articulatory motor control in late adolescence; (b) if there are sex differences during this developmental period, perhaps related to differences in craniofacial growth rates; (c) if control of jaw motion is adultlike earlier than control of the upper and lower lip; and (d) if control of spatial and temporal aspects of articulatory movement co-develop in adolescence. Participants were 12-, 14-, and 16-year-olds, and young adults (mean age 21.2 years), with 15 males and 15 females per group. A measure reflecting spatiotemporal consistency in trajectory formation for repeated productions of a phrase was calculated for the upper lip, lower lip, and jaw movements. Overall trajectory variability was higher for adolescents compared to young adults. Jaw trajectories were less variable than upper lip or lower lip trajectories, but all effectors showed parallel decreases in variability as age increased, suggesting that control of jaw movement does not reach adult performance before control of the lips. Separate temporal and spatial measures revealed that adolescents had significantly longer movement durations, lower velocities, smaller displacements, and greater variability on these measures than young adults. There were no sex differences on any measure examined, suggesting that peripheral growth factors do not account for this protracted developmental time course. These results provide initial evidence of significant changes in speech motor control processes during adolescence.

Alterations in lip and jaw kinematics as a function of speech rate

Manipulation of speech rate provides a means for examining variations in articulatory kinematics with natural alterations in speech motor timing. Such rate studies have been popular, based upon expected insights into underlying speech motor control processes. However, results from prior work on kinematic variations with speech rate have been equivocal. The divergent findings may be due to task differences, the few subjects studied in each experiment, and/or limitations in the number of task repetitions. In this context, each of ten normal subjects produced syllable repetition sequences and sentences with relatively large numbers of repetitions for each. Multiple measures of lip and jaw kinematics were applied, including some previously shown to be particularly revealing in studies of locomotion, arm, and hand movements. Findings indicated previously unreported speech rate‐related variations in peak velocity‐amplitude ratios, syllable‐to‐syllable magnitude and timing, vowel‐consonant versus consonant‐vowel...