Dissertations / Theses on the topic 'Sensorimotor control of speech'

Pour s'adapter aux imprévus lors de la production de la parole, le système moteur intègre les informations sensorielles (ex. le retour auditif), et bénéficie du groupement rythmique, qui est caractérisé par la prosodie. Cependant, le système sensorimoteur d'un locuteur traite différemment les événements acoustiques relatifs à sa propre voix par rapport à ceux d'autrui. Cette thèse vise à examiner la flexibilité de la production de la parole en analysant le rôle organisateur de la prosodie et la sensation subjective d'un locuteur sur le contrôle de sa voix (c.-à-d. le sens d'agentivité relatif à sa voix).Des expériences des perturbations du retour auditif ont été menées chez des locutrices francophones. Avec le retour auditif retardé (DAF), la différence de durée entre les voyelles accentuées et non accentuées s'est accrue, soulignant une plus grande flexibilité durant la production des accents. De plus, le DAF a induit une réorganisation du rythme de la parole avec un renforcement du groupement syllabique. Avec un décalage continu de la fréquence fondamentale (f0) du retour auditif, la majorité des locutrices ont aligné leur f0 sur celle modifiée du retour auditif, suggérant que leur système sensorimoteur aurait traité la voix perçue comme une entrée externe. La présence simultanée du DAF et d'un décalage de la f0 a entraîné une réduction des effets du DAF par rapport à la condition sans décalage de la f0. Cette observation suggère une réduction du sens d'agentivité relatif à la voix chez les locutrices, ainsi qu’une interaction entre l'organisation rythmique et le sens d’agentivité dans les processus sensorimoteurs de production de la parole
To adapt to unforeseen circumstances during speech production, the motor system integrates sensory information (e.g., auditory feedback) and benefits from rhythmic grouping, which is characterized by prosody. However, a speaker's sensorimotor system processes acoustic events related to their own voice differently from those of others. This thesis aims to examine the flexibility of speech production by analyzing the organizing role of both prosody and a speaker's subjective sensation of control over his voice (i.e., the sense of agency related to his voice).Experiments of auditory feedback perturbations were conducted with French-speaking female speakers. With delayed auditory feedback (DAF), the duration difference between accented and unaccented vowels increased, highlighting greater flexibility during accent production. Furthermore, DAF induced a reorganization of speech rhythm with enhanced syllabic grouping. With a constant shift in the fundamental frequency (f0) of auditory feedback, the majority of female speakers aligned their f0 with the modified auditory feedback, suggesting that their sensorimotor system processed the perceived voice as an external input. The simultaneous presence of DAF and an f0 shift resulted in a reduction of DAF effects compared to the condition without an f0 shift. This observation suggests a reduction in the sense of agency related to the voice among female speakers, as well as an interaction between rhythmic organization and sense of agency in sensorimotor processes of speech production

The thesis deals with two extreme end of speech perception in cognitive neuroscience. On its one end it deals with single isolated person brain responses to acoustic stimulus and missing articulatory cues, and on the other end it explores the neural mechanisms emerging while speech is embedded in a true conversational interaction. Studying these two extremities requires the use of relatively different methodological approaches. In fact, the first approach has seen the consolidation of a wide variety of experimental designs and analytical methods. Otherwise, the investigation of speech brain processes during a conversation is still in its early infancy and several technical and methodological challenges still needs to be solved. In the present thesis, I will present one EEG study using a classical attentive speech listening task, analyzed by using recent methodological advancement explicitly looking at the neural entrainment to speech oscillatory properties. Then, I will report on the work I did to design a robust speech-based interactive task, to extract acoustic and articulatory indexes of interaction, as well as the neural EEG correlates of its word-level dynamics. All in all, this work suggests that motor processes play a critical role both in attentive speech listening and in guiding mutual speech accomodation. In fact, the motor system, on one hand reconstruct information that are missing in the sensory domain and on the other hand drives our implicit tendency to adapt our speech production to the conversational partner and the interactive dynamics.

The multisensory nature of speech, and in particular, the modulatory influence of one’s own articulators during speech processing, is well established in adults. However, the origins of the sensorimotor influence on auditory speech perception are largely unknown, and require the examination of a population in which a link between speech perception and speech production is not well-defined; by studying preverbal infant speech perception, such early links can be characterized. Across three experimental chapters, I provide evidence that articulatory information selectively affects the perception of speech sounds in preverbal infants, using both neuroimaging and behavioral measures. In Chapter 2, I use a looking time procedure to show that in 6-month-old infants, articulatory information can impede the perception of a consonant contrast when the related articulator is selectively impaired. In Chapter 3, I use the high-amplitude suck (HAS) procedure to show that neonates are able to discriminate and exhibit memory for the vowels /u/ and /i/; however, the information from the infants’ articulators (a rounded lip shape) seems to only marginally affect behavior during the learning of these vowel sounds. In Chapter 4, I co-register HAS with a neuroimaging technique – Near Infrared Spectroscopy (NIRS) – and identify underlying neural networks in newborn infants that are sensitive to the sensorimotor-auditory match, in that the vowel which matches the lip shape (/u/) is processed differently than the vowel that is not related to the lip shape (/i/). Together, the experiments reported in this dissertation suggest that even before infants gain control over their articulators and speak their first words, their sensorimotor systems are interacting with their perceptual systems as they process auditory speech information.
Arts, Faculty of
Psychology, Department of
Graduate

LES CARTES SENSORIMOTRICES DE LA PAROLE : Corrélats neurocognitifs et couplage fonctionnel des systèmes de perception et de production des voyelles du Français --- La parole est construite sur un jeu de correspondances entre représentations sensorielles et articulatoires, notamment lors de l'acquisition du langage les premières années de vie. Par l'utilisation de l'imagerie par résonance magnétique fonctionelle, l'objectif premier de nos travaux était de déterminer, chez l'adulte, un possible couplage fonctionnel des systèmes de perception et de production des voyelles du Français, considérées comme unités élémentaires de la parole. En parallèle, nos travaux devaient permettre de clarifier les structures cérébrales liées au contrôle moteur orofacial de mouvements simples supralaryngés et, à l'aide de la technique de stimulation magnétique transcrânienne, de déterminer une possible implication causale des régions sensorielles et motrices lors de la perception de la parole. Nos travaux ont permis de souligner l'implication des régions sensorielles et motrices aussi bien lors de la réalisation des gestes orofaciaux que lors de la production et de la perception des voyelles. La mise en évidence d'un effet d'adaptation pour ces régions motrices, auditives et somatosensorielles lors de l'écoute ou de la réalisation répétée d'une même voyelle ou d'un même geste suggère de plus l'existence de boucles sensorimotrices communes, impliquées dans des mécanismes adaptatifs de contrôle en ligne des gestes de parole perçus et produits. Enfin, nous avons pu démontrer le rôle causal et fonctionnel des régions sensorielles et motrices de la voie dorsale lors de la catégorisation de sons de parole. Pris ensemble, nos travaux soulignent la nature distribuée sensorimotrice des représentations cérébrales des unités de parole. Mots clés: perception et production de la parole, voyelles, contrôle moteur orofacial, interactions sensorimotrices, représentations et cartes neurocognitives, IRMf, TMS.

There have been many recent advances in the simulation of biologically realistic systems, but controlling these systems remains a challenge. In this thesis, we focus on methods for learning to control these systems without prior knowledge of the dynamics of the system or its environment. We present two algorithms. The first, designed for quasistatic systems, combines Gaussian process regression and stochastic gradient descent. By testing on a model of the human mid-face, we show that this combined method gives better control accuracy than either regression or gradient descent alone, and improves the efficiency of the optimization routine. The second addresses the trajectory-tracking problem for dynamical systems. Our method automatically learns the relationship between muscle activations and resulting movements. We also incorporate passive dynamics compensation and propose a novel gain-scheduling algorithm. Experiments performed on a model of the human index finger demonstrate that each component we add to the control formulation improves performance of fingertip precision tasks.
Science, Faculty of
Computer Science, Department of
Graduate

Maintaining upright stance involves a time-critical process in which the central nervous system monitors postural orientation and modulates muscle activity accordingly. Visual, vestibular and somatosensory systems detect body motion that the balance controller utilizes to update standing control. The time delays between motor output and the resulting sensory feedback are expected and likely accommodated for. Consequently, we perceive whole-body movement as being a consequence of our own actions. Balance control, however, also involves processes that do not rely on conscious perception, allowing us to maintain standing balance almost effortlessly. Recent studies have demonstrated that both the perception and vestibular control of balance are modulated when sensory signals of whole-body movement do not match self-generated ankle torques. The aim of this thesis was to explore the temporal properties of the sensorimotor loops driving the perception and vestibular control of standing balance. Using a robotic balance simulator, experimentally-induced time delays were introduced between human participant’s ankle-produced torques and body movement. The first experiment used a psychophysical design to determine what delay is needed for humans to perceive a change in balance control. All participants were able to perceive a 300 ms delay with 100% success, with an average 69% correct threshold of 155 ms. In the second experiment, participants were exposed to a virtual vestibular perturbation while they balanced their body at different induced delays. Vestibular-evoked muscle responses attenuated with increasing loop delays, falling to amplitudes 84% smaller than baseline when a 500 ms delay was introduced between the produced torques and body movement. This is the first study to explore the time domain relationship between sensory and motor signals in standing, and the results reveal and describe temporal constraints of the sensorimotor control of balance. The present findings will act as springboard for studying postural control mechanisms in the future, encouraging the use of this robotic simulator to alter sensorimotor relationships during ongoing balance control. Using interventions like induced delays, we can decipher the natural processes that govern posture, and explore the adaptability and plasticity of these systems.
Education, Faculty of
Graduate

Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Kinesiology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Postural control during standing and walking is an inherently unstable task requiring the interaction of various biomechanical, sensory, and neurophysiological mechanisms to shape stable patterns of whole-body coordination that are able to counteract postural disequilibrium. This thesis focused on the examination of central aspects of the functional roles of these mechanisms and the modes of interaction between them. A further aim was to determine the conditions of dynamic stability for healthy standing and walking performance as well as for certain balance and gait disorders. By studying movement fluctuations in the walking pattern it could be demonstrated that dynamic stability during walking depends on gait speed and is differentially regulated for the medio-lateral and the fore-aft walking planes. Stability control in the fore-aft walking plane exhibits attractor dynamics typical for a dynamical system. Accordingly, the most stable pattern of movement coordination in terms of minimal fluctuations in the order parameter (i.e., the relative phase between the two oscillating legs) can be observed at the attractor of self-paced walking. Critical fluctuations occur at increasingly non-preferred speeds, indicating a loss of dynamic gait stability close to the speed boundaries of the walking mode. Moreover, stability control during slow walking is critically dependent on sensory feedback control, whereas dynamic stability during fast walking relies mainly on the smooth operation of cerebellar pacemaker regions. Disturbances of sensory and cerebellar locomotor control in certain gait disorders could be further linked to a loss of dynamic gait stability, in particular an increased risk of falls. Furthermore, this thesis examined alterations in the sensorimotor postural control scheme that may trigger the experience of subjective imbalance and vertigo in the conditions of phobic postural vertigo and visual height intolerance. Both conditions are characterized by an inadequate mode of balance regulation featuring increased levels of open-loop balance control and a precipitate integration of closed-loop sensory feedback into the postural control scheme. This inadequate balance control strategy is accompanied by a stiffening of the anti-gravity musculature and is elicited by specific influences of attention and sensory feedback control. The findings of this thesis contribute to the understanding of central sensorimotor mechanisms involved in the control of dynamic postural stability during standing and walking. They further provide relevant information for the differential diagnosis and fall risk estimation of certain balance and gait disorders.

The brain coordinates a continuous coupling between perception and action in the presence of uncertainty and incomplete knowledge about the world. This mapping is enabled by control policies and motor learning can be perceived as the update of such policies on the basis of improving performance given some task objectives. Despite substantial progress in computational sensorimotor control and empirical approaches to motor adaptation, to date it remains unclear how the brain learns motor control policies while updating its internal model of the world. In light of this challenge, we propose here a computational framework, which employs error-based learning and exploits the brain’s inherent link between forward models and feedback control to compute dynamically updated policies. The framework merges optimal feedback control (OFC) policy learning with a steady system identification of task dynamics so as to explain behavior in complex object manipulation tasks. Its formalization encompasses our empirical findings that action is learned and generalised both with regard to a body-based and an object-based frame of reference. Importantly, our approach predicts successfully how the brain makes continuous decisions for the generation of complex trajectories in an experimental paradigm of unfamiliar task conditions. A complementary method proposes an expansion of the motor learning perspective at the level of policy optimisation to the level of policy exploration. It employs computational analysis to reverse engineer and subsequently assess the control process in a whole body manipulation paradigm. Another contribution of this thesis is to associate motor psychophysics and computational motor control to their underlying neural foundation; a link which calls for further advancement in motor neuroscience and can inform our theoretical insight to sensorimotor processes in a context of physiological constraints. To this end, we design, build and test an fMRI-compatible haptic object manipulation system to relate closed-loop motor control studies to neurophysiology. The system is clinically adjusted and employed to host a naturalistic object manipulation paradigm on healthy human subjects and Friedreich’s ataxia patients. We present methodology that elicits neuroimaging correlates of sensorimotor control and learning and extracts longitudinal neurobehavioral markers of disease progression (i.e. neurodegeneration). Our findings enhance the understanding of sensorimotor control and learning mechanisms that underlie complex motor tasks. They furthermore provide a unified methodological platform to bridge the divide between behavior, computation and neural implementation with promising clinical and technological implications (e.g. diagnostics, robotics, BMI).

This thesis investigates information-theoretic tools for detecting and describing causal influences in embodied agents. It presents an analysis of philosophical and statistical approaches to causation, and in particular focuses on causal Bayes nets and transfer entropy. It argues for a novel perspective that explicitly incorporates the epistemological role of information as a tool for inference. This approach clarifies and resolves some of the known problems associated with such methods. Here it is argued, through a series of experiments, mathematical results and some philosophical accounts, that universally applicable measures of causal influence strength are unlikely to exist. Instead, the focus should be on the role that information-theoretic tools can play in inferential tests for causal relationships in embodied agents particularly, and dynamical systems in general. This thesis details how these two approaches differ. Following directly from these arguments, the thesis proposes a concept of “hidden” information transfer to describe situations where causal influences passing through a chain of variables may be more easily detected at the end-points than at intermediate nodes. This is described using theoretical examples, and also appears in the information dynamics of computer-simulated and real robots developed herein. Practical examples include some minimal models of agent-environment systems, but also a novel complete system for generating locomotion gait patterns using a biologically-inspired decentralized architecture on a walking robotic hexapod.

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 150-159).
This thesis builds on previous efforts to develop tactile speech-reception aids for the hearing-impaired. Whereas conventional hearing aids mainly amplify acoustic signals, tactile speech aids convert acoustic information into a form perceptible via the sense of touch. By facilitating visual speechreading and providing sensory feedback for vocal control, tactile speech aids may substantially enhance speech communication abilities in the absence of useful hearing. Research for this thesis consisted of several lines of work. First, tactual detection and temporal order discrimination by congenitally deaf adults were examined, in order to assess the practicability of encoding acoustic speech information as temporal relationships among tactual stimuli. Temporal resolution among most congenitally deaf subjects was deemed adequate for reception of tactually-encoded speech cues. Tactual offset-order discrimination thresholds substantially exceeded those measured for onset-order, underscoring fundamental differences between stimulus masking dynamics in the somatosensory and auditory systems. Next, a tactual speech transduction scheme was designed with the aim of extending the amount of articulatory information conveyed by an earlier vocoder-type tactile speech display strategy. The novel transduction scheme derives relative amplitude cues from three frequency-filtered speech bands, preserving the cross-channel timing information required for consonant voicing discriminations, while retaining low-frequency modulations that distinguish voiced and aperiodic signal components. Additionally, a sensorimotor training approach ("directed babbling") was developed with the goal of facilitating tactile speech acquisition through frequent vocal imitation of visuo-tactile speech stimuli and attention to tactual feedback from one's own vocalizations. A final study evaluated the utility of the tactile speech display in resolving ambiguities among visually presented consonants, following either standard or enhanced sensorimotor training. Profoundly deaf and normal-hearing participants trained to exploit tactually-presented acoustic information in conjunction with visual speechreading to facilitate consonant identification in the absence of semantic context. Results indicate that the present transduction scheme can enhance reception of consonant manner and voicing information and facilitate identification of syllableinitial and syllable-final consonants. The sensorimotor training strategy proved selectively advantageous for subjects demonstrating more gradual tactual speech acquisition. Simple, low-cost tactile devices may prove suitable for widespread distribution in developing countries, where hearing aids and cochlear implants remain unaffordable for most severely and profoundly deaf individuals. They have the potential to enhance verbal communication with minimal need for clinical intervention.
by Theodore M. Moallem.
Ph.D.

Chemotaxis is a powerful paradigm to study how sensory stimulations drive orientation behaviors in an organism. Drosophila larvae navigate odor gradients by controlling the duration of runs and the direction of turns. A turn is preceded by lateral head sweeps (“casts”) that sample the stimulus from the surroundings. In addition, larvae correct their course towards the odor source during runs, a phenomenon called “weathervaning”. Peristaltic waves that propagate along the body axis drive forward run events. We showed that the peristaltic wave cycle acts as a natural unit of movement and sets a physical constraint on the amount of reorientation achieved during runs. Moreover, head-casts are strictly observed within the bounds of the peristaltic cycle that can be categorized into either runcasts or stop-casts based on the presence or absence of the peristaltic wave respectively. Integrating behavioral experiments and extracellular electrophysiological recordings from the olfactory sensory neurons (OSNs), we observed a remarkable ability of larva to sense, to process and to act at short timescales of head-casts. In particular, we found that the larval sensorimotor system is able to modulate the amplitude of stop-casts based on the changes in the OSN firing rate during casts. Finally, integrating models for OSN activity, peristaltic locomotion, and behavioral quantification, we built an agent-based model that recapitulates essential aspects of larval chemotactic behavior. Overall, our findings provide a new formalism to study larval sensorimotor control. Additionally, we developed a high spatiotemporal resolution larval tracker with an ability to detect and precisely stimulate individual sensory organs. The tracker is highly effective tool to discern neural basis of behaviors occurring at short timescales in Drosophila larvae and other model systems.
La quimiotaxis es un poderoso paradigma para estudiar en un organismo comportamientos de orientación derivados de estímulos sensoriales. La larva de la Drosophila navega por gradientes de olor gracias al control de la duración y la dirección de sus giros. El giro va precedido por barridos laterales de la cabeza (“head-casts”) que muestrean estímulos de los alrededores de la larva. Además, las larvas corrigen su trayectoria en dirección a la fuente de olor, un fenómeno llamado “weathervaning”. Movimientos peristálticos que se propagan por el eje del cuerpo conducen a carreras (runs) hacia adelante. Demostramos que los ciclos de ondas peristálticas actúan como unidades naturales del movimiento y establecen un límite físico en cuanto a la cantidad de reorientaciones conseguidas en una carrera. Además, los “head-casts” sólo se observan en los límites de los ciclos peristálticos que pueden ser categorizados en “run-cast” o “stopcast” basándonos en la presencia o ausencia de ondas peristálticas respectivamente. Asimismo, hemos descubierto que la magnitud del “stop-cast” es mayor al encontrarse con un estímulo positivo y menor al detectar un cambio negativo. Combinando experimentos de comportamiento y registros de electrofisiología extracelulares en neuronas sensoriales del olfato (OSNs), hemos observado una remarcable habilidad en la larva para sentir, procesar y actuar en escalas a corto tiempo durante los “head-casts”. Combinando un modelo para la actividad de OSN, un modelo para la locomoción peristáltica, y la cuantificación del comportamiento, hemos construido un modelo “agent-based” que recapitula aspectos esenciales del comportamiento quimiotáctico de la larva. En general, nuestro estudio aporta un nuevo formalismo para estudiar el control sensomotor de la larva. De la misma manera, hemos desarrollado un rastreador de larvas espacio-temporal de alta resolución con habilidad para detectar y estimular con precisión órganos sensoriales. El rastreador nos permite investigar el papel del muestreo activo y el olfato estéreo en transformaciones sensomotoras durante la quimiotaxis de la larva.

To survive and effectively interact with the environment, human sensorimotor control system collects sensory information and acts based on the state of the world. Human behavior can be considered and studied at discrete time or continuous time. For the former, human makes discrete categorical decisions when presented with different alternative choices (e.g. choose Left or Right at an intersection). For the later, humans plan and execute continuous movements when instructed to perform a motor task (e.g. drive to a destination). In this dissertation we examine human behavior at both levels. Part I focuses on understanding decision-making at discrete time using Bayesian Models. We start by investigating the influence of environmental statistics in a saccadic visual search ask, in which we use a dynamic belief model to describe subjects' learning process of the environment statistics cross-trials. Then we look at a special effect of decision- making, the sequential effect, and apply the dynamic belief model to explain subjects' cross-trial learning and a drift diffusion model to explain their within-trial decision- making process. Part II focuses on examining motor control at continuous time using Optimal Control Theory. We start by investigating the objective functions in oculomotor control (saccadic eye movement, smooth pursuit, and applications in eye-hand coordination) with an infomax model. Then we apply inverse optimal control model to study impaired motor behavior in depressed individuals. In particular, we present a framework based on optimal control theory, which can distinguish the effects of sensorimotor speed, goal setting and motivational factors in goal-directed motor tasks. Finally, we propose to use facial expression as another measure of the emotional state in depressed individuals, which can be used to provide further understanding of the behavior and model parameters estimated from the proposed inverse framework.

Mental practice (MP) is the cognitive rehearsal of a task in the absence of overt physical movements. It has been shown that MP allows performance improvements in various tasks, but little is known about the effectiveness of different strategies of MP and about the exact sensorimotor mechanisms that underlie this improvement. Several strategies of MP are here investigated in relation to the practice outcome. In particular, in the context of music performance, it is shown that pitch imagery is strongly associated with better performance, regardless of the specific nature of the musical task. Conversely, structural/formal analysis appears to be important for music memorization, and motor imagery for fine motor control. In terms of sensorimotor outcomes of the practice, it is shown that MP results in improvements of movement velocity, movement anticipation and coarticulation. Additional experiments from force-field learning paradigm show that MP can also result in changes of somatosensory perception. Results are discussed in the context of the simulation theories of motor control.

Suite à une lésion (ex: blessure médullaire, accident vasculaire cérébral) ou une maladie neurodégénérative (ex: maladie de Parkinson), le système nerveux central humain peut être sujet à de multiples déficiences sensori-motrices menant à des handicaps plus ou moins lourds au cours du temps.Face aux méthodes thérapeutiques classiques, la stimulation électrique fonctionnelle (SEF) des muscles préservés permet de restaurer le mouvement et de fournir une assistance afin d’améliorer la condition des personnes atteintes et de faciliter leur réadaptation fonctionnelle.De nombreuses problématiques intrinsèques à la complexité du système musculo-squelettique et aux contraintes technologiques rendent néanmoins difficile la démocratisation de solutions de stimulation électro-fonctionnelle en dépit d’avancées majeures dans le domaine.Visant à favoriser l’utilisabilité et l’adaptabilité de telles solutions, cette thèse s’appuie sur un réseau de capteurs/actionneurs génériques embarqués sur le sujet, afin d’utiliser la connaissance issue de l’observation et l’analyse du mouvement pathologique des membres inférieurs pour étudier et valider expérimentalement de nouvelles solutions de commande de la SEF à travers une approche orientée-patient
The human central nervous system (CNS) can be subject to multiple dysfunctions. Potentially due to physical lesions (e.g.: spinal cord injuries, hemorrhagic or ischemic stroke) or to neurodegenerative disorders (e.g.: Parkinson’s disease), these deficiencies often result in major functional impairments throughout the years.As an alternative to usual therapeutic approaches, functional electrical stimulation (FES) of preserved muscles enables to assist individuals in executing functional movements in order to improve their daily life condition or to help enhancing rehabilitation process.Despite major technological advances in rehabilitation engineering, the complexity of the musculoskeletal system and the technological constraints associated have led to a very slow acceptance of neurorehabilitation technologies.To promote usability and adaptability, several approaches and algorithms were studied through this thesis and were experimentally validated in different clinical and pathological contexts, using low-cost wearable sensors combined to programmable stimulators to assess and control motion through a patient-centered approach

My thesis focuses on describing novel functional connectivity properties of the sensorimotor system that are of potential interest in the field of brain-machine interface. In particular, I have investigated how the connectivity changes as a consequence of either pathologic conditions or spontaneous fluctuations of the brain's internal state. An ad-hoc electronic device has been developed to implement the appropriate experimental settings. First, the functional communication among sensorimotor primary nodes was investigated in multiple sclerosis patients afflicted by persistent fatigue. I selected this condition, for which there is no effective pharmacological treatment, since existing literature links this type of fatigue to the motor control system. In this study, electroencephalographic (EEG) and electromyographic (EMG) traces were acquired together with the pressure exerted on a bulb during an isometric hand grip. The results showed a higher frequency connection between central and peripheral nervous systems (CMC) and an overcorrection of the exerted movement in fatigued multiple sclerosis patients. In fact, even though any fatigue-dependent brain and muscular oscillatory activity alterations were absent, their connectivity worked at higher frequencies as fatigue increased, explaining 67% of the fatigue scale (MFIS) variance (p=.002). In other terms, the functional communication within the central-peripheral nervous systems, namely involving primary sensorimotor areas, was sensitive to tiny alterations in neural connectivity leading to fatigue, well before the appearance of impairments in single nodes of the network. The second study was about connectivity intended as propagation of information and studied in dependence on spontaneous fluctuations of the sensorimotor system triggered by an external stimulus. Knowledge of the propagation mechanisms and of their changes is essential to extract significant information from single trials. The EEG traces were acquired during transcranial magnetic stimulation (TMS) to yield to a deeper knowledge about the response to an external stimulation while the cortico-spinal system passes through different states. The results showed that spontaneous increases of the excitation of the node originating the transmission within the hand control network gave rise to dynamic recruitment patterns with opposite behaviors, weaker in homotopic and parietal circuits, stronger in frontal ones. As probed by TMS, this behavior indicates that the effective connectivity within bilateral circuits orchestrating hand control are dynamically modulated in time even in resting state. The third investigation assessed the plastic changes in the sensorimotor system after stroke induced by 3 months of robotic rehabilitation in chronic phase. A functional source extraction procedure was applied on the acquired EEG data, enabling the investigation of the functional connectivity between homologous areas in the resting state. The most significant result was that the clinical ameliorations were associated to a ‘normalization’ of the functional connectivity between homologous areas. In fact, the brain connectivity did not necessarily increase or decrease, but it settled within a ‘physiological’ range of connectivity. These studies strengthen our knowledge about the behavioral role of the functional connectivity among neuronal networks’ nodes, which will be essential in future developments of enhanced rehabilitative interventions, including brain-machine interfaces. The presented research also moves the definition of new indices of clinical state evaluation relevant for compensating interventions, a step forward.

This thesis describes a model of speech timing, predicting at the syllable level, with sensitivity to rhythmic factors at the foot level, that predicts segmental durations by a process of accommodation into the higher-level timing framework. The model is based on analyses of two large databases of British English speech; one illustrating the range of prosodic variation in the language, the other illustrating segmental duration characteristics in various phonetic environments. Designed for a speech synthesis application, the model also has relevance to linguistic and phonetic theory, and shows that phonological specification of prosodic variation is independent of the phonetic realisation of segmental duration. It also shows, using normalisation of phone-specific timing characteristics, that lengthening of segments within the syllable is of three kinds: prominence-related, applying more to onset segments; boundary-related, applying more to coda segments; and rhythm/rate-related, being more uniform across all component segments. In this model, durations are first predicted at the level of the syllable from consideration of the number of component segments, the nature of the rhyme, and the three types of lengthening. The segmental durations are then constrained to sum to this value by determining an appropriate uniform quantile of their individual distributions. Segmental distributions define the range of likely durations each might show under a given set of conditions; their parameters are predicted from broad-class features of place and manner of articulation, factored for position in the syllable, clustering, stress, and finality. Two parameters determine the segmental duration . pdfs, assuming a Gamma distribution, and one parameter determines the quantile within that pdf to predict the duration of any segment in a given prosodic context. In experimental tests, each level produced durations that closely fitted the data of four speakers of British English, and showed performance rates higher than a comparable model predicting exclusively at the level of the segment.

Human sensorimotor control is remarkably adept at utilising contextual information to learn and recall systematic sensorimotor transformations. Here, we investigate the motor representations that underlie such learning, and examine how motor memories acquired based on different contextual information interact. Using a novel three-dimensional robotic manipulandum, the 3BOT, we examined the spatial transfer of learning across various movement directions in a 3D environment, while human subjects performed reaching movements under velocity-dependent force field. The obtained pattern of generalisation suggested that the representation of dynamic learning was most likely defined in a target-based, rather than an extrinsic, coordinate system. We further examined how motor memories interact when subjects adapt to force fields applied in orthogonal dimensions. We found that, unlike opposing fields, learning two spatially orthogonal force fields led to the formation of separate motor memories, which neither interfered with nor facilitated each other. Moreover, we demonstrated a novel, more general aspect of the spontaneous recovery phenomenon using a two-dimensional force field task: when subjects learned two orthogonal force fields consecutively, in the following phase of clamped error feedback, the expression of adaptation spontaneously rotated from the direction of the second force field, towards the direction of the first force field. Finally, we examined the interaction of sensorimotor memories formed based on separate contextual information. Subjects performed reciprocating reaching and object manipulation tasks under two alternating contexts (movement directions), while we manipulated the dynamics of the task in each context separately. The results suggested that separate motor memories were formed for the dynamics of the task in different contexts, and that these motor memories interacted by sharing error signals to enhance learning. Importantly, the extent of interaction was not fixed between the context-dependent motor memories, but adaptively changed according to the task dynamics to potentially improve overall performance. Together, our experimental and theoretical results add to the understanding of mechanisms that underlie sensorimotor learning, and the way these mechanisms interact under various tasks and different dynamics.

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed March 3, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 237-245).

Study 1: Development of a comprehensive performance testing protocol for competitive surfers Purpose: Appropriate and valid testing protocols for evaluating the physical performances of surfing athletes is not well refined. The purpose of this project was to develop, refine, and evaluate a testing protocol for use with elite surfers, including measures of anthropometry, strength and power, and endurance. Methods: After pilot testing and consultation with athletes, coaches and sport scientists, a specific suite of tests was developed. Forty-four competitive junior surfers (16.2±1.3 years, 166.3±7.3 cm, 57.9±8.5 kg) participated in this study involving a within-day repeated measures analysis, using an Elite Junior Group of 22 international competitors (EJG), to establish reliability of the measures. To reflect validity of the testing measures, a comparison of performance results was then undertaken between the EJG and an age-matched Competitive Junior Group of 22 nationally competitive surfers (CJG). Results: Percent Typical Error of Measurement (%TEM) for primary variables gained from the assessments ranged from 1.1-3.0%, with intra-class correlation coefficients ranging from 0.96- 0.99. One-way analysis of variance revealed that the EJG had lower skinfolds (p=0.005, d=0.9) compared to the CJG, despite no difference in stature (p=0.102) or body mass (p=0.827). The EJG were faster in 15 m sprint-paddle velocity (pd=1.3), had higher lower-body isometric peak force (p=0.04, d=0.7), and superior endurance paddling velocity (p=0.008, d=0.9). Conclusions: The relatively low %TEM of these tests in this population allows for high sensitivity to detect change. The results of this study suggest that competitively superior junior surfers are leaner, and possess superior strength, paddling power, and paddling endurance. Study 2: Comparison of physical capacities between non-selected and selected elite male competitive surfers for the national team Purpose: The purpose of this study was to determine whether a previously validated performance testing protocol for competitive surfers was able to differentiate between Australian elite junior surfers selected (S) to the national team, and those not selected (NS). Methods: Thirty-two elite male competitive junior surfers were divided into two groups (S=16; NS=16). The mean age, stature, body mass, sum of 7 skinfolds and lean body mass ratio (mean ± SD) were 16.17 ± 1.26 y, 173.40 ± 5.30 cm, 62.35 ± 7.40 kg, 41.74 ± 10.82 mm, 1.54 ± 0.35 for the S athletes and 16.13 ± 1.02 y, 170.56 ± 6.6 cm; 61.46 ± 10.10 kg; 49.25 ± 13.04 mm; 1.31 ± 0.30 for the NS athletes. Power (countermovement jump; CMJ), strength (isometric mid-thigh pull), 15 m sprint paddling, and 400 m endurance paddling was measured. Results: There were significant (p ≤ 0.05) differences between the S and NS athletes for relative vertical jump peak force (p=0.01, d=0.9), CMJ height (p=0.01, d=0.9), time to 5, 10, and 15 m sprint paddle, sprint paddle peak velocity (p=0.03, d=0.8; PV), time to 400 m (p=0.04, d=0.7) and endurance paddling velocity (p=0.05, d=0.7). Conclusions: All performance variables, particularly CMJ height, time to 5, 10, and 15 m sprint paddle, sprint paddle PV, time to 400 m and endurance paddling velocity can effectively discriminate between S and NS competitive surfers and this may be important for athlete profiling and training program design. Study 3: The development and evaluation of a drop and stick method to assess landing skills in various levels of competitive surfers The purpose of this study was to develop and evaluate a drop and stick (DS) test method and to assess dynamic postural control in senior elite (SE), junior elite (JE), and junior development (JD) surfers. Nine SE, 22 JE, and 17 JD competitive surfers participated in the study. The athletes completed five drop and stick trials barefoot from a pre-determined box height (0.5 m). The lowest and highest time to stabilisation (TTS) trials were discarded, and the average of the remaining trials were used for analysis. The SE group demonstrated excellent single measures repeatability (ICC=0.90) for TTS, whereas the JE and JD demonstrated good single measures repeatability (ICC 0.82 and 0.88, respectively). In regards to relative peak landing force (rPLF), SE demonstrated poor single measures reliability compared to JE and JD groups. TTS for SE (0.69 ± 0.13 s) group was significantly (p=0.04) lower than the JD (0.85 ± 0.25 s). There were no significant (p=0.41) differences in the TTS between SE (0.69 ± 0.13 s) and JE (0.75 ± 0.16 s) groups or between the JE and JD groups (p=0.09). rPLF for SE (2.7 ± 0.4 body mass; BM) group was significantly lower than the JE (3.8 ± 1.3 BM) and JD (4.0 ± 1.1 BM), with no significant (p=0.63) difference among the JE and JD groups. A possible benchmark approach for practitioners would be to use TTS and rPLF as a qualitative measure of dynamic postural control using a reference scale to discriminate amongst groups. Study 4: Effects of stable and unstable resistance training on strength, power, and sensorimotor abilities in adolescent surfers The purpose of this study was to investigate two different resistance-training interventions (unstable or stable) on strength, power, and sensorimotor abilities in adolescent surfers. Ten competitive female and male high school surfers were assessed before and after each of 2 x 7-week training intervention, using a within-subjects cross-over study design. Results for strength revealed no condition by time interaction or main effect for condition. However, there was a significant main effect for time, with significant strength gains post-training. There was a significant condition by time interaction for power exhibited as a significant decrease from pre- to post-training in the unstable condition, while the stable condition approached significant improvement. These results suggest that unstable and stable resistance training are equally effective in developing strength in previously untrained competitive surfers, but with little effect on sensorimotor abilities. However, unstable training is inferior for the development of lower body power in this population. Study 5: Effect of four weeks detraining on power, strength, and sensorimotor ability of adolescent surfers The purpose of this study was to investigate the effect of four weeks of detraining on power, strength, and sensorimotor ability in adolescent surfers. Nineteen adolescent surfers with an overall mean age, mass, and stature (mean ± SD) of 14.1 ± 1.6 y, 54.0 ± 10.8 kg and 165.1 ± 9.0 cm, respectively, volunteered to participate in four weeks of detraining (surfing participation maintained but resistance training ceased) following seven weeks of periodized resistance training. Power (vertical jump height; VJH), maximal isometric strength (isometric mid-thigh pull; IMTP), and sensorimotor ability (time to stabilization during a drop and stick (DS); TTS) pre-test results were determined from the conclusion (post-test) of the first seven-week training block while post-test results were measured at the start (pre-test) of a second seven-week training block. Four weeks of detraining significantly decreased the following variables: VJH by -5.26%, (p = 0.037, d = -0.40), vertical jump peak velocity by -3.73% (p = 0.001, d = -0.51), maximal isometric strength by -5.5%, (p = 0.012, d = -0.21), and relative maximal isometric strength by -7.27% (p = 0.003, d = -0.47). Furthermore, sensorimotor ability worsened, as assessed by TTS, with a significant increase of 61.36% (p = 0.004, d = 0.99), indicating athletes took longer to stabilize from a dynamic landing task. This demonstrates that surfing, in the absence of resistance training, is not a sufficient training stimulus to maintain physical characteristics. Adolescent surfers with a relatively low training age should avoid cessation of resistance training and strive to maintain consistent resistance training in conjunction with surf training in order to avoid negative decrements in physical characteristics that are associated with surfing performance.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (leaf 16).
This research continues the work begun by Sungho Jo and Steve G. Massaquoi on modeling human walking and upright balance. The model of human neurological control of balance and gait generation put forward by Jo and Massaquoi in "A model ofcerebrocerebello-spoinomuscular interaction in the sagittal control of human walking" and executed in MATLAB Simulink/SimMechanics. This model has been used to determine the feed-forward command sequences for the generation of walking and running gaits. Furthermore, two feedback circuits controlling the center of mass relative to the swing leg and the composted leg angle of the simulated model were added. These provide a basis for a wider control of disturbances in order to implement running. This work helps forward the long-term goals of the MIT Sensorimotor Control Group--creating a control model of the neurological circuitry responsible for governing human balance and locomotion and testing that model by using it to control a bipedal robot. The results of this research help to prove the validity of the cerebrocerebello-spinomuscular control model developed by Jo and Massaquoi and point positively towards the introduction of the running of the control model on a physical robot.
by Ellen Cappo.
S.B.

This research is motivated by the benefits that knowledge regarding early development in infants may provide to different fields of science. In particular, early sensorimotor exploration behaviors are studied in the framework of developmental robotics. The main objective is about understanding the role of motor constraint awareness and imitative behaviors during sensorimotor exploration. Particular emphasis is placed on prelinguistic vocal development because during this stage infants start to master the motor systems that will later allow them to pronounce their first words. Previous works have demonstrated that goal-directed intrinsically motivated sensorimotor exploration is an essential element for sensorimotor control learning. Moreover, evidence coming from biological sciences strongly suggests that knowledge acquisition is shaped by the environment in which an agent is embedded and the embodiment of the agent itself, including developmental processes that shape what can be learned and when. In this dissertation, we firstly provide a collection of theoretical evidence that supports the relevance of our study. Starting from concepts of cognitive and developmental sciences, we arrived al the conclusion that spoken language, i.e., early \/ocal development, must be studied asan embodied and situated phenomena. Considering a synthetic approach allow us to use robots and realistic simulators as artifacts to study natural cognitive phenomena. In this work, we adopta toy example to test our cognitive architectures and a speech synthesizer that mimics the mechanisms by which humans produce speech. Next, we introduce a mechanism to endow embodied agents with motor constraint awareness. lntrinsic motivation has been studied as an importan! element to explain the emergence of structured developmental stages during early vocal development. However, previous studies failed to acknowledge the constraints imposed by the embodiment and situatedness, al sensory, motor, cognitive and social levels. We assume that during the onset of sensorimotor exploratory behaviors, motor constraints are unknown to the developmental agent. Thus, the agent must discover and learn during exploration what !hose motor constraints are. The agent is endowed with a somesthetic system based on tactile information. This system generales a sensor signal indicating if a motor configuration was reached or not. This information is later used to create a somesthetic model to predict constraint violations. Finally, we propase to include social reinforcement during exploration. Sorne works studying early vocal development have shown that environmental speech shapes the sensory space explored during babbling. More generally, imitative behaviors have been demonstrated to be crucial for early development in children as they constraint the search space.during sensorimotor exploration. Therefore, based on early interactions of infants and caregivers we proposed an imitative mechanism to reinforce intrinsically motivated sensorimotor exploration with relevan! sensory units. Thus, we modified the constraints aware sensorimotor exploration architecture to include a social instructor, expert in sensor units relevant to communication, which interacts with the developmental agent. lnteraction occurs when the learner production is ·enough' similar to one relevan! to communication. In that case, the instructor perceives this similitude and reformulates with the relevan! sensor unit. When the learner perceives an utterance by the instructor, it attempts to imitate it. In general, our results suggest that somesthetic senses and social reinforcement contribute to achieving better results during intrinsically motivated exploration. Achieving lest redundant exploration, decreasing exploration and evaluation errors, as well as showing a clearer picture of developmental transitions.
La motivación principal de este trabajo es la magnitud que las contribuciones al conocimiento en relación al desarrollo infantil pueden aportar a diferentes campos de la ciencia. Particularmente, este trabajo se enfoca en el estudio de los comportamientos de autoexploración sensorimotora en un marco robótico e inspirado en el campo de la psicología del desarrollo. Nuestro objetivo principal es entender el papel que juegan las restricciones motoras y los reflejos imitativos durante la exploración espontánea observada en infantes. Así mismo, este trabajo hace especial énfasis en el desarrollo vocal-auditivo en infantes, que les provee con las herramientas que les permitirán producir sus primeras palabras. Trabajos anteriores han demostrado que los comportamientos de autoexploración sensorimotora en niños, la cual ocurre en gran medida por motivaciones intrínsecas, es un elemento importante para aprender a controlar su cuerpo con tal de alcanzar estados sensoriales específicos. Además, evidencia obtenida de estudios biológicos sugiere tajantemente que la adquisición de conocimiento es regulada por el ambiente en el cual un agente cognitivo se desenvuelve y por el cuerpo del agente per se. Incluso, los procesos de desarrollo que ocurren a nivel físico, cognitivo y social también regulan que es aprendido y cuando esto es aprendido. La primera parte de este trabajo provee al lector con la evidencia teórica y práctica que demuestran la relevancia de esta investigación. Recorriendo conceptos que van desde las ciencias cognitivas y del desarrollo, llegamos a la conclusión de que el lenguaje, y por tanto el habla, deben ser estudiados como fenómenos cognitivos que requieren un cuerpo físico y además un ambiente propicio para su existencia. En la actualidad los sistemas robóticos, reales y simulados, pueden ser considerados como elementos para el estudio de los fenómenos cognitivos naturales. En este trabajo consideramos un ejemplo simple para probar las arquitecturas cognitivas que proponemos, y posteriormente utilizamos dichas arquitecturas con un sintetizador de voz similar al mecanismo humano de producción del habla. Como primera contribución de este trabajo proponemos introducir un mecanismo para construir robots capaces de considerar sus propias restricciones motoras durante la etapa de autoexploración sensorimotora. Ciertos mecanismos de motivación intrínseca para exploración sensorimotora han sido estudiados como posibles conductores de las trayectorias de desarrollo observadas durante el desarrollo temprano del habla. Sin embargo, en previos estudios no se consideró o que este desarrollo está a delimitado por restricciones debido al ambiente, al cuerpo físico, y a las capacidades sensoriales, motoras y cognitivas. En nuestra arquitectura, asumimos que un agente artificial no cuenta con conocimiento de sus limitantes motoras, y por tanto debe descubrirlas durante la etapa de autoexploración. Para tal efecto, el agente es proveído de un sistema somatosensorial que le indica cuando una configuración motora viola las restricciones impuestas por el propio cuerpo. Finalmente, como segunda parte de nuestra contribución proponemos incluir un mecanismo para reforzar el aprendizaje durante la autoexploración. Estudios anteriores demostraron que el ambiente lingüístico en que se desarrolla un infante, o un agente artificial, condiciona sus producciones vocales durante la autoexploración o balbuceo. En este trabajo nos enfocamos en el estudio de episodios de imitación que ocurren durante el desarrollo temprano de un agente. Basados en estudios sobre la interacción entre madres e hijos durante la etapa pre lingüística, proponemos un mecanismo para reforzar el aprendizaje durante la autoexploración con unidades sensoriales relevantes. Entonces, a partir de la arquitectura con autoconocimiento de restricciones motores, construimos una arquitectura que incluye un instructor experto en control sensorimotor. Las interacciones entre el aprendiz y el experto ocurren cuando el aprendiz produce una unidad sensorial relevante para la comunicación durante la autoexploración. En este caso, el experto percibe esta similitud y responde reformulando la producción del aprendiz como la unidad relevante. Cuando el aprendiz percibe una acción del experto, inmediatamente intenta imitarlo. Los resultados presentados en este trabajo sugieren que, los sistemas somatosensoriales, y el reforzamiento social contribuyen a lograr mejores resultados durante la etapa de autoexploración sensorimotora motivada intrínsecamente. En este sentido, se logra una exploración menos redundante, los errores de exploración y evaluación disminuyen, y por último se obtiene una imagen más nítida de las transiciones entre etapas del desarrollo.
La motivació principal d'aquest treball és la magnitud que les contribucions al coneixement en relació al desenvolupament infantil poden aportar a diferents camps de la ciència. Particularment, aquest treball s'enfoca en l'estudi dels comportaments d’autoexploració sensorimotora en un marc robòtic i inspirat en el camp de la psicologia del desenvolupament. El nostre objectiu principal és entendre el paper que juguen les restriccions motores i els reflexos imitatius durant l’exploració espontània observada en infants. Així mateix, aquest treball fa especial èmfasi en el desenvolupament vocal-auditiu en infants, que els proveeix amb les eines que els permetran produir les seves primeres paraules. Treballs anteriors han demostrat que els comportaments d'autoexploració sensorimotora en nens, la qual ocorre en gran mesura per motivacions intrínseques, és un element important per aprendre a controlar el seu cos per tal d'assolir estats sensorials específics. A més, evidencies obtingudes d'estudis biològics suggereixen que l’adquisició de coneixement és regulada per l'ambient en el qual un agent cognitiu es desenvolupa i pel cos de l'agent per se. Fins i tot, els processos de desenvolupament que ocorren a nivell físic, cognitiu i social també regulen què és après i quan això ès après. La primera part d'aquest treball proveeix el lector amb les evidencies teòrica i pràctica que demostren la rellevància d'aquesta investigació. Recorrent conceptes que van des de les ciències cognitives i del desenvolupament, vam arribar a la conclusió que el llenguatge, i per tant la parla, han de ser estudiats com a fenòmens cognitius que requereixen un cos físic i a més un ambient propici per a la seva existència. En l'actualitat els sistemes robòtics, reals i simulats, poden ser considerats com a elements per a l'estudi dels fenòmens cognitius naturals. En aquest treball considerem un exemple simple per provar les arquitectures cognitives que proposem, i posteriorment utilitzem aquestes arquitectures amb un sintetitzador de veu similar al mecanisme humà de producció de la parla. Com a primera contribució d'aquest treball proposem introduir un mecanisme per construir robots capaços de considerar les seves pròpies restriccions motores durant l'etapa d'autoexploració sensorimotora. Certs mecanismes de motivació intrínseca per exploració sensorimotora han estat estudiats com a possibles conductors de les trajectòries de desenvolupament observades durant el desenvolupament primerenc de la parla. No obstant això, en previs estudis no es va considerar que aquest desenvolupament és delimitat per restriccions a causa de l'ambient, el cos físic, i les capacitats sensorials, motores i cognitives. A la nostra arquitectura, assumim que un agent artificial no compta amb coneixement dels seus limitants motors, i per tant ha de descobrir-los durant l'etapa d'autoexploració. Per a tal efecte, l'agent és proveït d'un sistema somatosensorial que li indica quan una configuració motora viola les restriccions imposades pel propi cos. Finalment, com a segona part de la nostra contribució proposem incloure un mecanisme per reforçar l'aprenentatge durant l'autoexploració. Estudis anteriors han demostrat que l'ambient lingüísticstic en què es desenvolupa un infant, o un agent artificial, condiciona les seves produccions vocals durant l'autoexploració o balboteig. En aquest treball ens enfoquem en l'estudi d'episodis d’imitació que ocorren durant el desenvolupament primerenc d'un agent. Basats en estudis sobre la interacció entre mares i fills durant l'etapa prelingüística, proposem un mecanisme per reforçar l'aprenentatge durant l'autoexploració amb unitats sensorials rellevants. Aleshores, a partir de l'arquitectura amb autoconeixement de restriccions motors, vam construir una arquitectura que inclou un instructor expert en control sensorimotor. Les interaccions entre l'aprenent i l'expert, ocorren quan una producció sensorial de l'aprenent durant l'autoexploració és similar a una unitat sensorial rellevant per a la comunicació. En aquest cas, l'expert percep aquesta similitud i respon reformulant la producció de l'aprenent com la unitat rellevant. Quan l'aprenent percep una acció de l'expert, immediatament intenta imitar-lo. Els resultats presentats en aquest treball suggereixen que els sistemes somatosensorials i el reforçament social contribueixen a aconseguir millors resultats durant l'etapa d'autoexploració sensorimotora motivada intrínsecament. En aquest sentit, s'aconsegueix una exploració menys redundant, els errors d’exploració i avaluació disminueixen, i finalment s’obté una imatge més nítida de les transicions entre etapes del desenvolupament

The human shoulder complex relies on the sensorimotor system to maintain stability. The sensorimotor system includes sensory feedback, control of the central nervous system and motor output. Exercise is considered an important part of shoulder rehabilitation and sports training to help improve control of the sensorimotor system. However, few studies have investigated the effect of exercise on the sensorimotor system. The first study of this dissertation explored the central control of the deltoid and rotator cuff (infraspinatus). Although both the deltoid and infraspinatus contribute to shoulder abduction, the results from this study showed that the modulation of their corticospinal excitability was affected differently by elevation angle. This could be explained by the fact that they play different roles at the shoulder: the deltoid is a prime mover while the infraspinatus is a stabilizer. The second study of this dissertation investigated scapular proprioception, which has not been assessed in previous studies. The findings of this study demonstrated that joint position sense errors of the overall shoulder joint mainly came from the glenohumeral joint. Scapular proprioception may need to be tested separately in addition to overall shoulder proprioception. In the third study, the effect of the exercise on shoulder sensorimotor system was investigated by measuring shoulder kinematics, shoulder joint position sense and cortical excitability before and after a four-week exercise training program. This protocol included strengthening and neuromuscular exercises targeting rotator cuff and scapular muscles. After the training protocol, although strength increased overall, the only observed sensorimotor adaptations were a decrease in upper trapezius activation and a decrease in the corticospinal excitability of the supraspinatus. There were no changes in other key parameters. Exercises focusing on specific muscles, combined with low-intensity closed-chain exercises, were not found to improve shoulder joint position sense or scapular kinematics. Combined with the findings of the decrease in corticospinal excitability of the supraspinatus and no change in muscle activity of the rotator cuff, it appears that while the exercises increased rotator cuff strength, these gains did not transfer to an increase in muscle activation during motion. This dissertation includes previously published co-authored material.

The reactive control of fingertip forces maintaining grasp stability was examined in man during a prehensile task. Blindfolded subjects used the precision grip between the tips of index finger and thumb to restrain an object that was subjected to unpredictable load forces. These were delivered tangential to the parallel grip surfaces of the object. Load forces, grip forces (perpendicular to the grip surfaces) and position of the object were recorded.Subjects automatically adjusted the grip forces to loads of various amplitudes and rates. Thereby they maintained a reliable safety margin against frictional slips without using excessive grip forces. A rapid rise in grip force lasting about 0.2 s was triggered after a short delay following the onset of a sustained ramp load increase. This 'catch-up' response caused a quick restoration of an adequate grip:load force ratio that prevented frictional slips. If the ramp load continued to increase after the catchup response, the grip force also increased in parallel with the load change in a 'tracking' manner. Consequently, during the hold phases of 'ramp-and-hold' loads, the employed grip forces were approximately proportional to the load amplitude. Sensory information about the rate of change of the load force parametrically scaled the 'catchup' and 'tracking' responses.Following anesthetic block of sensory input from the digits, the grip responses were both delayed and attenuated or even abolished. To compensate for these impairments, subjects had to voluntarily maintain exceedingly high grip forces to prevent the object from slipping. The grip control improved slightly during hand and forearm support conditions that allowed marked wrist movements to occur in response to the loading. This indicates that signals from receptors in muscles, joints or skin areas proximal to the digits can to some extent be used to adjust grip forces during impaired digital sensibility. In contrast, these signals had only minor influence on the control during normal digital sensibility.Grip responses to loads delivered in various directions revealed that the load direction, in relation to gravity and to the hand's geometry, represents intrinsic task variables in the automatic processes that maintain a stable grasp. The load direction influenced both the response latencies and the magnitudes of the grip responses. The response latencies were shortest for loads in directions that were the most critical with regard to the consequences of frictional slippage, i.e., loads directed away from the palm or in the direction of gravity. Recordings of signals in cutaneous afferents innervating the finger tips demonstrated that these effects on the response latencies depended on differences in the time needed by the central nervous system to implement the motor responses. The short latencies in the most ‘criticar load directions may reflect the preparation of a default response, while additional central processing would be needed to execute the response to loads in other directions. Adjustments to local frictional anisotropies at the digit-object interface largely explained the magnitude effects.In conclusion, grip responses are automatically adjusted to the current loading condition during unpredictable loading of a hand held object. Subjects call up a previously acquired sensorimotor transform that supports grasp stability by preventing both object slippage and excessive grip forces. Cutaneous sensory information about tangential forces and frictional conditions at the digit-object interface is used to initiate and scale the grip responses to the current loading conditions, largely in a predictive manner.

Diss. (sammanfattning) Umeå : Umeå universitet, 1995, Härtill 5 uppsatser

digitalisering@umu

The aim of this thesis is to further our understanding of the processes which control the sequencing of phonemes as we speak: this is an example of what is commonly known as the serial order problem. Such a process is apparent in normal speech and also from the existence of a class of speech errors known as sound movement errors, where sounds are anticipated (spoken too soon), perseverated (repeated again later), or exchanged (the sounds are transposed). I argue that this process is temporally governed, that is, the serial ordering mechanism is restricted to processing sounds that are close together in time. This is in conflict with frame-based accounts (e.g. Dell, 1986; Lapointe & Dell, 1979), serial buffer accounts (Shattuck-Hufnagel, 1979) and associative chaining theories (Wickelgren, 1969). An analysis of sound movement errors from Harley and MacAndrew's (1995) corpus shows how temporal processing bears on the production of speech sounds by the temporal constraint observed in the pattern of errors, and I suggest an appropriate computational model of this process. Specifically, I show how parallel temporal processing in an oscillator-based model can account for the movement of sounds in speech. Similar predictions were made by the model to the pattern of movement errors actually observed in speech error corpora. This has been demonstrated without recourse to an assumption of frame and slot structures. The OSCillator-based Associative REcall (OSCAR) model, on the other hand, is able to account for these effects and other positional effects, providing support for a temporal based theory of serial control.

Purpose/Hypothesis: Mal de Debarquement Syndrome (MdDS) is a rare condition in which those afflicted perceive a chronic rocking or swaying sensation, often relieved when in motion and symptomatic when still. Etiology is uncertain; therefore, treatment options are limited. While there is reported success with medication, optokinetic stimulation or transcutaneous magnetic stimulation, there is no single treatment that works for all patients. This retrospective chart review investigated rehabilitation outcomes following sensorimotor, multi-axis, rotational (SMART) training to address MdDS symptoms. Number of Subjects: Forty-nine Materials and Methods: Forty-nine patients participated in 10-20 sessions of SMART training, with integrated use of a visual targeting system and physical therapy. Between sessions, patients were instructed to perform mindfulness breathing, relaxation and grounding techniques. Pre- and post-training Dizziness Handicap Inventory (DHI), 4-item Dynamic Gait Index (DGI), and computerized posturography including Sensory Organization Test (SOT) were assessed. Subjective change following rehabilitation was tracked at discharge, 5 weeks, 3 months, 6 months and 1 year post-training. Results: Mean age (SD) of patients was 52.9 (12.6) years with the majority (n=47) being female. Mean time from onset of symptoms (SD) was 50.8 (87.8) months suggesting chronic symptoms. At discharge, 42 of 49 patients reported improvements, with nearly half (n=24, 48.9%) of all patients reporting marked or moderate improvement in symptoms; whereas, 14 (28.6%) reported minimal improvement in symptoms. Based on paired t-tests, all outcome measures – DHI, MdDS severity Visual Analog Scale (VAS), Motion VAS, 4-item DGI, and SOT - improved significantly (p < 0.001) from initial evaluation to discharge. Several personal factors were associated with rehabilitation outcomes based on bivariate correlations. With some variation, patients sustaining improvements at 1 week post-discharge, generally continued to sustain at 5 weeks, 3 months, 6 months and 1 year. Conclusions: SMART training plus physical therapy resulted in improved performance outcomes and in significant reduction or resolution in MdDS symptoms. This study provides early evidence that this method of training has promising potential to aid in the management or recovery of MdDS. Clinical Relevance: MdDS is disorder with no specific cure. Treatment is limited. SMART training may serve as an effective outcome to reduce or resolve symptoms associated with MdDS.