Head position signal is crucial for preparing reaching movements because it contributes to specifying the position of body and target in space and relative to each other. However, it is unclear whether sensory information pertaining head position is used to control the movement after movement onset. In this study, nineteen participants performed discrete reaches towards a virtual target while neck vibration was randomly applied before and/or during the movement or not at all. The main dependent variable was the directional bias of the reaching finger. Neck vibration induced early leftward or late rightward trajectory biases. It appears that participants interpreted the sensed head shift as a target or an eye-in-head motion, which can be explained by individual differences in the use of reference frames. Nevertheless, body-centered and head-centered frames of reference appear to be important for the early and late stages of a goal-directed movement, respectively.

Movement of different body segments is an essential component for the control of postural stability. Notably, balance impairment has been reported in individuals with chronic low back pain. Various impairments that are likely to affect postural control have been reported in this population, including proprioceptive deficits and altered control of movement at the lumbopelvic region. Although little is known about how movement of the lumbar spine contributes to postural control, spinal movement is likely to be part of the movement strategy when the multisegmental nature of the human body configuration is taken into consideration. The overall objective of this thesis was to investigate the changes in postural stability in individuals with chronic LBP, and the association with altered movement control at the lumbar spine. The control of postural stability was examined with different postural challenges while standing on either a flat surface or a short base. A short base was used to force the subjects to use a “hip strategy”; movement at the lumbopelvic region for postural correction. Kinematics of different body segments including the lumbar spine and hip were recorded to study the movement of the lumbopelvic region. In addition, ground reaction force data were collected with a force platform system to examine postural adjustments during various postural tasks. The studies showed that people with chronic low back pain have difficulty maintaining stance, with increased risk of overbalancing when standing on a short base without any perturbation. Altered motion of the lumbar spine was evident during both expected and unexpected postural perturbations, which indicated impairment of both anticipatory and feedback control of lumbar motion in individuals with chronic low back pain. In addition, subjects took longer to regain postural stability and made more postural adjustments during the recovery period after expected and unexpected perturbations. Together, the studies suggested significant contribution of changes in lumbar motion to postural impairment in people with chronic low back pain. In summary, these findings provide further evidence that spinal movement plays a critical role in the maintenance of postural stability, and altered control of movement affects the quality of postural control in individuals with chronic low back pain.

La proprioception permet de fournir des informations spatio-temporelles pour calibrer un espace moteur, ajuster la trajectoire des mouvements, l'équilibre, la direction des mouvements, et la coordination intermembres et multiarticulaires. Nous prenons à partir des récepteurs sensoriels une information liée à la vitesse du geste, à sa direction, à son amplitude et à son orientation. Bien que les muscles soient définis comme étant les récepteurs sensoriels contribuant principalement à fournir une information proprioceptive, les récepteurs cutanés avec l'étirement de la peau au cours du mouvement montrent des capacités à fournir une information redondante aux récepteurs musculaires. Cependant au regard de la contribution des récepteurs musculaires, le poids attribué aux informations cutanées est relativement faible hormis dans des situations précises où la contribution des récepteurs musculaires est altérée comme en situation de fatigue musculaire ou minimisée comme lors de l'évaluation du sens de la position articulaire. Le champ de la médecine sportive suggère que les différents supports de prévention des traumatismes améliorent l'acuité proprioceptive par une stimulation des récepteurs cutanés. Il reste néanmoins quelques points à éclaircir, en particulier comment pouvons nous stimuler la peau ? Au cours de trois expérimentations, nous avons testé deux moyens, la pression et les forces de cisaillement pour améliorer l'acuité proprioceptive. Dans l'ensemble nos résultats montrent une amélioration de la pertinence des informations cutanées par une diminution de l'incertitude dans le choix de la position articulaire ce traduisant par une amélioration de la précision de nos mouvements. Cette amélioration est indépendante du niveau de pression et serait en lien avec la création de force de cisaillement là où la peau s'étire le plus avec le mouvement. / Proprioception can provide spatiotemporal information for calibrating a motor space, adjust the trajectory of movement, balance, direction of movement, and coordination and Inter multiarticulaires. We take from the sensory receptors of information related to the speed of movement, its leadership, its amplitude and its direction. Although the muscles are defined as sensory receptors contributing primarily to provide information proprioceptive receptors in the skin of the tethering of the skin during movement show a capacity to provide redundant information to muscle receptors. However, in view of the contribution of muscle receptors, the weight given to information skin is relatively low except in specific situations where the contribution of muscle receptors is altered as experiencing muscle fatigue or minimized as in the evaluation of the meaning of joint position. The field of sports medicine suggests that different media Injury Prevention im prove proprioceptive acuity by stimulation of cutaneous receptors. It remains to clarify some points, especially how can we stimulate the skin? In three experiments, we tested two methods, pressure and shear forces to improve proprioceptive acuity. Overall our results show an improvement in the adequacy of the information skin by reducing the uncertainty in the choice of this joint position resulting in improved accuracy of our movements. This improvement is independent of pressure level and be linked with the creation of shear force where the skin stretches over with the movement.

NUNES, Rubens Fernandes. Uma representação flexível de controladores para animação fisicamente realista de personagens virtuais. 2006. 102 f. Dissertação (Mestrado em ciência da computação)- Universidade Federal do Ceará, Fortaleza-CE, 2006. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-07-12T17:05:38Z No. of bitstreams: 1 2006_dis_rfnunes.pdf: 4755244 bytes, checksum: 609de3a4c10e34fbdedc62d4f883917c (MD5) / Approved for entry into archive by Rocilda Sales (rocilda@ufc.br) on 2016-07-21T16:13:17Z (GMT) No. of bitstreams: 1 2006_dis_rfnunes.pdf: 4755244 bytes, checksum: 609de3a4c10e34fbdedc62d4f883917c (MD5) / Made available in DSpace on 2016-07-21T16:13:17Z (GMT). No. of bitstreams: 1 2006_dis_rfnunes.pdf: 4755244 bytes, checksum: 609de3a4c10e34fbdedc62d4f883917c (MD5) Previous issue date: 2006 / We propose an improved representation of controllers which uses high-level sensors and possess a general and intuitive structure that offers the animator several types of parameters to manipulate. This structure, with the feedback signals provided by its sensors, allows that several state machines act simultaneously on the model, or in a subset of its actuators. It also permits that procedures with general instructions, in accordance with a specified motion, be defined during its design phase and be adequately associated with it by the animator, in order to be automatically executed by the controller during the dynamic simulation. / Neste trabalho, é proposta uma representação de controladores que utiliza sensores de alto nível e tem uma estrutura geral e intuitiva que disponibiliza vários tipos de parâmetros para o animador. Essa estrutura permite, de acordo com a retroalimentação de seus sensores, que várias máquinas de estados atuem simultaneamente no modelo, ou em subconjuntos de seus atuadores. Também permite que, durante seu projeto, procedimentos com instruções gerais, de acordo com o movimento desejado, possam ser definidos e adequadamente associados a ela pelo animador, para serem executados automaticamente pelo controlador durante a simulação dinâmica.

L’objectif du présent travail de thèse est d’étudier les mécanismes de pondération des informations visuelles et somatosensorielles dans le contrôle du mouvement volontaire visuoguidé de la main lorsque les retours sensoriels de ces deux canaux véhiculent des informations spatiales congruentes ou incongruentes. Une incongruence entre les informations visuelles et somatosensorielles peut-être crée expérimentalement en décalant l’environnement visuel perçu des participants. Dans une telle situation, les participants devaient suivre les contours d’une forme géométrique irrégulière avec un stylet sur une tablette graphique. L’activité cérébrale des régions visuelles, somatosensorielles et pariétales postérieures a été enregistrée en électroencéphalographie, et quantifiée par la mesure de l’amplitude de potentiels évoqués visuels [Etude 1] et de la puissance des bandes de fréquences alpha (8-12 Hz), beta (15-25 Hz) et gamma (50-80 Hz) [Etudes 2 et 3]. Nous avons ainsi montré que le mouvement visuoguidé entraînait une augmentation de l’activité au niveau des aires corticales visuelles, et que le contrôle du mouvement en situation d’incongruence induisait une augmentation supplémentaire de l’excitabilité des cortex visuels, somatosensoriels et pariétaux postérieurs. Ces modulations reflèteraient des mécanismes de pondération du traitement de ces entrées sensorielles dans le but de s’adapter à cette situation. Plus généralement, nos résultats soutiennent l’idée que notre système nerveux est en mesure de moduler localement son activité en fonction de la pertinence du traitement des informations pour répondre aux exigences imposées par le contexte. / The goal of our doctoral research was to investigate the weighting of these sensory inputs in conditions under which they provided either congruent or incongruent information about hand motion. A visuo-somatosensory incongruence can be induced experimentally by shifting the visual feedback of the environment. We asked participants to follow precisely the outline of an irregular shape with a stylus on a digitizing tablet. Brain activity was recorded with an electroencephalographic device, and quantified by measuring visual evoked potentials amplitudes [Study 1], and the power in the alpha (8-12 Hz), beta (15- 25 Hz) and gamma (50-80 Hz) frequency-bands [Studies 2 and 3]. We first evidenced that visually-guided hand movements increased the sensitivity to visual inputs of a large cortical network. Moreover, we showed that controlling movement in a situation with an incongruence between visual and somatosensory input led to a further increase of visual, somatosensory and posterior-parietal cortical excitability. We suggest that these modulations reflect sensory weighting mechanisms in order to attempt to adapt to the sensory incongruence. Interestingly, in the somatosensory areas, we found that the sensory incongruent condition led to a reduction of gamma power, suggesting a reduced integration of somatosensory inputs for controlling movements. Taken together, our findings are in line with the existence of a general sensory gain control mechanism driven by the state of adaptation of the sensorimotor system in a given sensory context. More generally, our results argue for the idea that sensory processing is function of the context-dependent relevance of the sensory inputs.

Examination of goal-directed aiming tasks has revealed that rapid, discrete human action is amendable to online control. This control affords humans a margin of error in movement planning and execution as well as a means of acquiring their goals when the body and/or the environment are extrinsically perturbed. For over a century, the models of online movement control that have best described the trajectories and outcomes of goal-directed reaches hold that these movements are composed of two distinct components. The first component moves the limb from its resting position towards the target. The second component is a corrective movement that is formed on the basis of a visual referencing of the moving limb and target positions. As such, the temporal and spatial characteristics of these discrete movement changes have been attributed to the limits of visual information processing. Furthermore, the absence of any discrete movement changes in the portions of movements outside of the temporal and spatial limits of vision led many investigators to conclude that first component impulses are ballistic and uncontrollable. However, recent studies involving environmental perturbation and within-subject trial-to-trial spatial variability analyses have evidenced that initial impulses are privy to online control. Because the corrections made early in movement impulses occur quicker than purely afferent visual information can be processed this form of control has been attributed to the use of forward anticipatory processes. The four studies presented here examine the nature of initial impulse control through kinematic analyses of reaches made to targets against various combinations of limb, target, and environment perturbations. This was done in order to evaluate anticipatory control's relationship with visually-regulated control and the relative influence the two processes have on the movement trajectory and performance outcome. The first study examined target-directed reaches made against illusory moving background and target relocation perturbations. The results showed the presence of early anticipatory and late visually-regulated control. Non-interactive main effects of the two perturbations on outcome accuracy revealed that the processes operate independently. The second study tested the applicability of an air discharging stylus as a tool for perturbing reach velocities. The results showed that the stylus effectively perturbed limb velocity and highlighted the presence of a limb forwarding response to either an advancing or hindering perturbation. The findings evidence the non-specific nature of anticipatory control responses. The third study examined reaches made against combinations of actual limb velocity and target position perturbations. The interactive effect of the two perturbations on reach trajectories and outcome accuracy indicated that the perturbations were salient enough to prompt parallel operation of the two control processes. Again, the control of initial movement portions was highlighted by non-specific responses to the perturbations. The fourth study examined reaches made against combinations of illusory and actual perturbations to both the anticipatory and visually-regulated control processes. Interestingly, performers withheld responses to the illusory perturbation unless they were also responding to an actual perturbation. This finding suggests that anticipatory control responses are biased during movement preparation. Furthermore, combined illusory and actual perturbations to target position had interactive effects on visually regulated control. Overall, the studies evidence that target-directed movements are mediated by two modes of control. There is an anticipatory mode of control that operates continuously and, given that reaches are made within the spatial and temporal limits of visual processing, there is also a feedback driven discrete mode of control that overlaps with the continuous mode. / Thesis / Doctor of Philosophy (PhD)

No description available.

SUMMARY SUBJECT MATTER OF THE THESIS: Physical exercise influence on voluntary movement control. AIM OF THE THESIS: Assessment of various motivation physical exercise on voluntary movements control in women. The investigated individuals were divided into two groups: group of aerobics and group of local exercises. The Group or aerobics was composed of 51 women with 2 or 3 weekly classes of aerobics (average age 21,6 ±0,4 years, body weight index 20,7 ±0,3 kg/m²).). The group of local exercises consisted of 18 women with 2-3 Pilates health improvement classes (average age 20,9 +/-0,3, body weight index 21,5 ±0,5 kg/m²). METHODS: The computer aided platform “LIBRA” was employed for the investigation in order to determine proprioception. Both the groups were examined twice: before and after physical exercises. The examination was carried out in three positions: by standing on frontal plane, sitting on frontal plane and sitting on saggital plane. For movement control evaluation the following measurements were taken: extension area, extension time, recovery time, which were measured in standard units as well as global instability assessment in scores (0-10). RESULTS: The group of aerobics showed significant changes in most of the parameters under test within the second testing (after physical exercises). While in making assessments for the effect of local exercises on movement control, a significant reduction of extension time and global instability assessment in sitting... [to full text]

No description available.

Human movements are remarkably adaptive, such that we are capable of completing movements in a novel environment with similar accuracy to those performed in a typical environment. Our ability to perform in these environments involves accurate processing of sensory feedback for online and offline control. These processes of control have been widely studied for well learned actions, but not for actions in a novel visuomotor environment. In two experiments, we examined control processes underlying reaches when participants were first introduced to a visuomotor rotation (Experiment 1) and then following visuomotor adaptation (Experiment 2). All participants completed 150 reach training trials when (1) a cursor accurately represented their hand motion (i.e., aligned cursor) and (2) a cursor was rotated 45 degrees clockwise relative to their hand motion (i.e., rotated cursor). In Experiment 1, we sought to determine if the control processes underlying movements in typical and novel visuomotor conditions were comparable. Participants (n = 16) received either continuous visual feedback or terminal visual feedback regarding movement endpoint during reach training. Analyses revealed that participants were able to demonstrate similar outcomes (i.e., movement time and endpoint errors) regardless of visual or cursor feedback, but also demonstrated more offline control (i.e., took more time planning and were less consistent in initiating their movements) when reaching with a rotated cursor compared to an aligned cursor, even at the end of training. Together, the results suggest a greater contribution of offline control processes and less effective online corrective processes when reaching in a novel environment compared to when reaching in a typical environment. In attempt to promote online corrective processes, participants (n = 16) in Experiment 2 first completed the training trials with continuous visual feedback and then completed an additional 45 reaches under (1) slow movement time (i.e., Slow MT: 800-1000 ms) and (2) fast movement time (i.e., Fast MT: 400-500ms) constraints. Results showed a shift to online control (i.e., greater endpoint accuracy) when reaching with an aligned and rotated cursor, when sufficiently more time was provided (i.e., Slow MT). Specifically, participants were able to more effectively utilize visual feedback for online control under the Slow MT constraint compared to when reaching quickly (i.e., Fast MT). Together, these experiments demonstrate a flexibility in control processes underlying reaches with rotated visual feedback of the hand. In that reaches first engage in offline control processes during adaptation to a visuomotor rotation, and then shift to online corrective processes following visuomotor adaptation.