This study uses ultrasound to image onset velar stop consonant articulation in words. By examining tongue body placement, the extent of velar closure variation across vowel contexts provides for the measurement of anticipatory coarticulation while productions within the same vowel context provide measurement of extent of token-to-token variation. Articulate Assistant Advanced 2.0 software was used to semi-automatically generate midsagittal tongue contours at the initial point of maximum velar closure and was used to fit each contour to a curved spline. Patterns of lingual coarticulation and measures of speech motor stability, based on curve-to-curve distance (Zharkova, Hewlett, & Hardcastle, 2011), are investigated to compare the speech of typically fluent speakers to the speech of people who stutter. Anticipatory coarticulation can be interpreted as a quantitative measure indicating the maturity of the speech motor system and its planning abilities. Token-to-token variability is examined from multiple velar vowel productions within the same vowel context, describing the accuracy of control, or stability, of velar closure gestures. Measures for both speaking groups are examined across the lifespan at stages during speech development, maturation, and aging. Results indicate an overall age effect, interpreted as refinement, with increased speech stability and progressively more segmental (less coarticulated) productions across the lifespan. A tendency toward decreased stability and more coarticulated speech was found for younger people who stutter, but this difference was small and absent among older adults. Outcomes of this study suggest the articulatory maturation trajectories of people who stutter may be delayed, but overall maturation of the speech mechanism is evident by older adulthood for typically fluent speakers and those who stutter. Applications to intervention are discussed in closing.

The event related potential (ERP) technique is enjoying widespread application in neurophysiological research due to its fine temporal resolution. Of relevance to this study are ERPs related to voluntary movements. The precision with which movement related processes could be recorded using the ERP technique was demonstrated by Gilden, Vaughan and Costa (1966) and Kutas and Donchin (1974, 1977, and 1980) who found that the readiness potential (RP) immediately preceding hand movement was larger over the hemisphere contralateral to the responding hand. Given that left hemisphere controls right hand movements and vice versa, their findings confirmed that the lateralized readiness potential (LRP) is an index of motor preparation. It has been well established that electrodes from the left precentral site (C3) and from the right precentral site (C4) can capture LRPs, and that the motor cortex is the major generator of this component. In the speech domain, researchers recording ERPs related to motor preparation have often considered pre-determined electrode sites (e.g., F3, F4, C3, C4, Cz) assuming that their proximity to motor areas on the cortex enables capturing of specific activity from those areas [F3 close to Broca’s area, Cz close to Supplementary motor area (SMA), C3 to left motor strip, C4 to right motor strip]. A consistent finding has been that the RP preceding speech is greatest at the central electrode sites, which has been attributed to SMA and motor cortex activity. Studying speech production related ERPs at predetermined set of electrodes might not suffice for two reasons: (1) unlike simple finger movement, speaking is a fine motor skill requiring coordination of multiple systems (e.g., respiratory system, phonatory system, articulatory system) and muscles, and (2) the far-field nature of the ERP recording technique often results in spatial and temporal overlap of components. To overcome these challenges, this study considered multichannel recordings and principal component analysis (PCA). Twenty three healthy participants completed a simple hand motor task (pressing a button with the right index finger and another button using the left index finger based on the color of a stimulus frame displayed on a computer screen), and a speech task (saying “pool” or withholding the response based on the color of the frame). The purpose of including a hand motor task was to verify that neural activity specific to motor preparation was detectable in participants when a well-established condition for the elicitation of LRPs was utilized. Both stimulus-locked and response-locked ERPs from 21 right handed participants (11 females and 10 males) were studied. Interhemispheric difference wave analysis and PCA revealed left hemisphere lateralization of the potential (i.e., the LRP) immediately preceding right hand movements, similar to previous studies. The LRP specific to left hand movements (non-dominant hand), however, showed bihemispheric distribution. Results from the speech motor task confirmed that overlapping components affect interpretation of ERPs related to speech production if just central electrode sites are considered. Two ERP components emerged from the multichannel PCA as distinguishing between the speaking and no speaking condition: a posterior negative component and a left lateralized positive component. The morphology of the posterior negative component and significant moderate correlation of its amplitude with the mean reaction time suggest that this component is a possible index of speech motor preparation. Further research is required to determine whether the left-lateralized component reflects a process mediated by the speech dominant hemisphere (left). In addition to demonstrating the usefulness of multichannel recordings and PCA in ERP investigations, the study provides several methodological guidelines for capturing ERPs related to speech production.

There is a rich literature demonstrating that adults who stutter (AWS) demonstrate atypical functional brain activity during speech production. These differences can be characterized by increased activity in the right inferior frontal gyrus and premotor regions and decreased activity in the left inferior frontal gyrus, premotor area, and bilaterally in the superior temporal gyrus. The process of speech production requires motor movements first be planned and then executed. However, few studies have examined activity related to speech-motor planning independently from speech-motor execution. Additionally, due to methodological limitations, few investigations have examined functional brain activity in children who stutter (CWS). We hypothesized that AWS and CWS would demonstrate atypical brain activity related to both speech-motor planning and execution. Using Near Infrared Spectroscopy (fNIRS), we measured the change in oxygenated hemoglobin concentration (HbO) during speech-motor planning (repetition of nonwords with three repeated or different syllables) and speech-motor execution (covert/overt naming). Results indicated that both AWS and CWS demonstrated cortical activity that was atypical during speech-motor planning processes in the right inferior frontal gyrus and atypical speech-motor execution processes in the left inferior frontal gyrus. Deactivations in the left inferior frontal gyrus may reflect inefficient feedforward mechanisms for speech production. Inefficient feedforward mechanisms will likely result in more variable movements, for which larger feedback correction signals will be necessary. Overactivations in the right inferior frontal gyrus may reflect this increased correction. Additionally, AWS demonstrated atypical speech-motor planning activity in the right middle frontal gyrus, potentially related to the production of prosody. These results are presented within a theoretical framework of two competing theories of stuttering.

No description available.

The present study examined the divided attention effects of three non-speech tasks on concurrent speech motor performance. These tasks targeted linguistic, cognitive, and manual motor activity. Participants included 60 healthy adults separated into three different age groups of twenty participants each: college-age (20s), middle-aged (40s), and older adults (60s). Each participant completed a speech task once in isolation and once concurrently with each of the three non-speech tasks: a semantic decision task, a quantitative comparison task, and a manual motor task. The non-speech tasks were also performed in isolation. The speech task involved repeating a target phrase each time a beep sounded, for a total of fourteen repetitions. Dependent measures for speech were derived from lip kinematic recordings from a head-mounted strain gauge system. Dependent measures for the other tasks included timed response counts and accuracy rates. Results indicated significant divided attention effects, impacting speech and nonspeech measures in the linguistic and cognitive conditions, and impacting speech measures in the manual motor condition. A significant age effect for utterance duration was also found, as well as a divided attention interaction with age for cognitive task accuracy. The results add to what is known about bidirectional interference between speech and other concurrent tasks, as well as age effects on speech motor control.

Ce travail de thèse étudie la production de la parole à l'âge de 4 ans, en comparaison avec l'adulte, sous l'angle du contrôle moteur. Un intérêt particulier a été porté à deux indices : la variabilité liée à la répétition de voyelles isolées et la coarticulation anticipatoire intra et extra-syllabique dans le cadre de la production de séquences de type V1-C-V2. Des données acoustiques et articulatoires ont été enregistrées via l'échographie linguale et le dispositif HOCUS. Les données acoustiques ont été analysées pour 20 enfants et 10 adultes et les données articulatoires ont été analysées pour 6 de ces enfants et 2 de ces adultes. En accord avec de nombreuses études de la littérature, la variabilité liée à la répétition est plus importante chez les enfants que chez les adultes. Une forte anticipation de V2 dans la réalisation de V1 a été observée pour tous les adultes. Chez les enfants, cette anticipation n'est pas systématique, et lorsqu'elle est observée, elle est d'amplitude plus faible que chez les adultes. Ainsi, seulement 5 enfants parmi les 20 étudiés montrent des signes d'anticipation, majoritairement dans la dimension antéropostérieure, manifestée dans l'espace acoustique par la dimension F2. La coarticulation anticipatoire intra-syllabique semble également être d'amplitude plus faible chez les enfants. Enfin, les gestes de parole des enfants sont plus lents que ceux des adultes. Dans leur ensemble, ces résultats sont interprétés comme la preuve de l'immaturité du système moteur pour la production de la parole chez l'enfant, selon deux perspectives : des patrons moteurs insuffisamment stables pour la production de gestes vocaliques et un manque d'efficacité dans l'anticipation les gestes futurs lors de la production d'une séquence de sons de parole. Selon une perspective empruntée aux théories du contrôle moteur optimal, nous proposons que la coarticulation anticipatoire repose sur l'usage de modèles internes, représentations sensori-motrices du système moteur de la parole dans le système nerveux central, et que son amplitude reflète la maturation progressive de ces représentations sensori-motrices à mesure que la production de la parole se développe. / This thesis work investigates speech production in 4-year-old children, in comparison with adults, from a speech motor control perspective. It focuses on two indices: measures of token-to-token variability in the production of isolated vowels and on anticipatory intra and extra-syllabic coarticulation within V1-C-V2 sequences. Acoustic and articulatory data were recorded thanks to ultrasound tongue imaging within the HOCUS system. Acoustic data from 20 children and 10 adults have been analyzed. Ultrasound data have been analyzed from a subset of these participants: 6 children and 2 adults. In agreement with former studies, token-to-token variability was greater in children than in adults. Strong anticipation of V2 in V1 realization was found in all adults. In children, anticipation was not systematic, and when observed, it was of smaller amplitude than in adults. In more details, only 5 children among the 20 studied showed a small amount of anticipation, mainly along the antero-posterior dimension, manifested in the acoustic F2 dimension. Anticipatory intra-syllabic coarticulation also seems to be of smaller amplitude in children than in adults. Last, children's speech gestures are slower than those of adults. These results are interpreted as evidence for the immaturity of children's speech motor control from two perspectives: insufficiently stable motor control patterns for vowel production, and a lack of effectiveness in anticipating forthcoming gestures. In line with theories of optimal motor control, we assume that anticipatory coarticulation is based on the use of internal models, i.e. sensori-motor representations of the speech production apparatus in the central nervous system, and that the amplitude of anticipatory coarticulation reflects the increasing maturation of these sensori-motor representations as speech develops.

Ce travail exploite un modèle biomécanique de la production de la parole comme sujet de référence pour étudier plusieurs phénomènes liés à l'adaptabilité et à la stabilité du contrôle moteur de la parole, en particulier l'équivalence motrice et le contrôle postural.La première partie de cette thèse s’intéresse au phénomène de l'équivalence motrice. L'équivalence motrice est une caractéristique essentielle du contrôle moteur de la parole, car les locuteurs doivent s'adapter constamment à des contextes phonétiques toujours différents et à conditions variables de production de la parole. Le concept de « Uncontrolled Manifold » (UCM) offre un cadre théorique pour comprendre les mécanismes sous-jacents à l'équivalence motrice : il propose de représenter la coordination entre les variables de contrôle moteur en deux sous-espaces séparés, un dans lequel tout changement des variables de contrôle affectent la sortie et un autre dans lequel ces changements n'influencent aucunement la sortie.Ce concept est développé et étudié pour la production de la parole en utilisant un modèle biomécanique 2D du conduit vocal. D'abord, une représentation des UCM linéarisées basée sur des matrices de projection orthogonale est proposée. Les UCM de différentes configurations du conduit vocal des 10 voyelles orales françaises sont ensuite caractérisées en étudiant les réponses aux perturbations de leurs commandes. On étudie alors si chaque catégorie phonétique, telle que les phonèmes, les voyelles antérieures/postérieures, ou les voyelles arrondies/non-arrondies, peut être caractérisée par une UCM unique ou si les UCM varient considérablement entre les différents représentants de chacune de ces classes. On a constaté que les UCM linéarisées, celles qui sont spécifiquement calculées pour chaque configuration du conduit vocal, mais aussi celles, plus globales, des classes phonétiques, permettent une réponse efficace aux perturbations des commandes. Cela suggère que des stratégies équivalentes d'équivalence motrice peuvent être mises en œuvre dans chacune de ces classes et que les UCM en fournissent des caractérisations exploitables. Des suggestions sont faites pour de futurs travaux pour déterminer quelles classes pourraient être utilisées dans la pratique.La deuxième partie étudie dans quelle mesure le contrôle postural de la langue exploit des mécanismes passifs - tels que les propriétés mécaniques et élastiques intrinsèques de la langue- ou des réflexes à faible latence - comme le réflexe d’étirement.Une perturbation en force a été appliquée au modèle biomécanique 2D, dans laquelle la langue est tirée vers l'avant par une force exercée sur le corps de la langue à l'aide d'un robot relié à la partie supérieure de la lame de la langue. Les simulations ont été comparées à des données expérimentales recueillies au Gipsa-lab dans des conditions similaires.Cette perturbation a été simulée avec différentes valeurs du paramètre qui dans le modèle module le feedback induit par l’étirement des fibres musculaires. Les résultats ont montré un effet de rebond dans les mouvements de la langue suite à la perturbation qui est imputable au mécanisme réflexe. Étant donné qu'un rebond similaire est observé dans les données expérimentales sur des sujets humains, ce résultat suggère qu’un mécanisme réflexe joue un rôle significatif dans la stabilité posturale de la langue. Les caractéristiques temporelles de ce réflexe ont été analysées et il s’avère que la précision du modèle est insuffisante pour tirer des conclusions sur l'origine, corticale ou spinale, de ce réflexe. Des pistes pour de futures études expérimentales sont proposées. / This work makes use of a biomechanical model of speech production as a reference subject to address several phenomena related to the adaptability and stability of speech motor control, namely motor equivalence and postural stability. The first part of this thesis is related to the phenomenon of motor equivalence. Motor equivalence is a key feature of speech motor control, since speakers must constantly adapt to various phonetic contexts and speaking conditions. The Uncontrolled Manifold (UCM) idea offers a theoretical framework for considering motor equivalence in which coordination among motor control variables is separated into two subspaces, one in which changes in control variables modify the output and another one in which these changes do not influence the output.This concept is developed and investigated for speech production using a 2D biomechanical model. First, a representation of the linearized UCM based on orthogonal projection matrices is proposed. The UCMs of various vocal tract configurations of the 10 French oral vowels are then characterized using their command perturbation responses. It is then investigated whether each phonetic class such as phonemes, front/back vowels, rounded/un-rounded vowels can be characterized by a unique UCM, or whether the UCMs vary significantly across representatives of these different classes. It was found that linearized UCMs, especially those that are specifically computed for each configuration, but also across many of the phonetic classes allow for a command perturbation response that is effective. This suggests that similar motor equivalence strategies can be implemented within each of these classes and that UCMs provide a valid characterization of an equivalence strategy. Further work is suggested to elaborate which classes might be used in practice.The second part addresses the question of the degree to which postural control of the tongue is accomplished through passive mechanisms - such as the mechanical and elastic properties of the tongue itself - or through short-latency reflexes - such as the stretch reflex.A specific external force perturbation, was applied to the 2D biomechanical model , namely one in which the tongue is pulled anteriorly using specific force profile exerted on the tongue body using a force effector attached to the superior part of the tongue blade. Simulation results were compared to experimental data collected at Gipsa-lab under similar conditions.This perturbation was simulated with various values of the model's parameter modulating the reflex strength (feedback gain). The results showed that a perturbation rebound seen in simulated data is due to a reflex mechanism. Since a compatible rebound is seen in data from human subjects, this can be taken as evidence of a reflex mechanism being involved in postural stability of the tongue. The time course of the mechanisms of this reflex, including the generation of force and the movement of the tongue, were analyzed and it was determined that the precision of the model was insufficient to make any conclusions on the origin of this reflex (whether cortical or brainstem). Still, numerous experimental directions are proposed.

Research examining bilinguals who stutter (BWS) is limited; in particular there are few studies that have considered examining features of speech motor control in BWS. The present study was designed to examine features of speech motor control in bilingual speakers of Mandarin and English. Speech motor control was examined through the acoustic analysis of speaking rate, voice onset time (VOT) and stuttering adaptation. Participants ranged from age between 9 and 27 years. Upon completion of a language dominance questionnaire, two BWS participants were found to be English dominant and three were Mandarin dominant. Each BWS participant was matched to age/sex matched control participants (BWNS). Results for the BWS participants found more stuttering in the less dominant language based on a measure of percentage of syllables stuttered. All of the BWS participants demonstrated stuttering adaptation and there was no significant difference in the amount of adaptation for Mandarin and English. There was no difference found between BWS and BWNS for speaking rate and VOT. In spite of the similarity between BWS and BWNS, speaking rate in Mandarin appeared to be faster compared to English. These findings suggest that speech motor control in BWS and BWNS are similar and current application of these findings to the clinical setting is discussed.

The present study is the first to examine the effect of first versus second language (L1 versus L2) speech production on specific temporal parameters of speech in bilingual speakers with neurogenic speech disorders. Three persons with apraxia of speech (AOS), three with phonemic paraphasia (PP) and five normal speaking participants were included as subjects in the study. Subjects were required to read phonemically similar L1 and L2 target utterances in a carrier phrase, five times each, at a normal and fast speaking rate, respectively. This rendered four speaking contexts that included speech production in L1 at either a normal (L1NR) or fast speaking rate (L1FR) and speech production in L2 at either a normal (L2NR) or fast speaking rate (L2FR). Acoustic analysis of on-target productions involved measurement of utterance onset duration, vowel duration, utterance duration and voice onset time. Results revealed that in normal speakers, speech production in L2 results in greater token-to-token variability than in L1. However, token-to-token variability in the experimental subjects did not tend to increase whilst speaking in L2, most probably because these subjects generally decreased their speaking rate in this context, resulting in more consistent production. The subjects with AOS and PP seemed to be influenced by the increased processing demands of speaking in L2 to a greater extent than the normal speakers, in that they more frequently experienced difficulty with durational adjustments (decreasing duration in the fast speaking rate) in L2 than in L1. Furthermore, the subjects with AOS or PP also exhibited a greater extent of durational adjustment in L1 than in L2. The durations of most of the subjects with either AOS or PP tended to differ from those of the normal group to a greater extent in L2FR that was hypothesized to be the most demanding speaking context for these subjects. The longer than normal durations and greater than normal token-to-token variability in the subjects with either AOS or PP imply the presence of a motor control deficit. The extent of the motor control deficit appears to be more severe in AOS than in PP as is evident from the finding that the subjects with AOS generally exhibited longer durations and greater token-to-token variability than the subjects with PP. The pattern of breakdown in respect of different parameters and utterance groups also differed between subjects with AOS and PP. The nature of the disorder in AOS and PP thus appears to be both quantitatively and qualitatively different. Regarding measurement of the different temporal parameters, voice onset time appears to be less subject to the influence of L2 than the other measured temporal parameters. The results of this study imply that bilingual AOS is as much a reality as bilingual aphasia. Furthermore, the results underscore the importance of taking contextual factors, specifically L1 versus L2, into account when compiling assessment and treatment procedures for persons with either AOS or PP, since speech production in L2 appears to be motorically more difficult than in L1 for persons with neurogenic involvement. The significance of the results is discussed with reference to the influence of speech production in L2 on temporal control and the underlying nature of AOS and PP with regard to theories of speech sensorimotor control. Copyright / Dissertation (DPhil (Communication Pathology))--University of Pretoria, 2004. / Speech-Language Pathology and Audiology / unrestricted