46 research outputs found
Control of Leg Movements Driven by EMG Activity of Shoulder Muscles
Get PDFDuring human walking, there exists a functional neural coupling between arms and legs, and between cervical and lumbosacral pattern generators. Here, we present a novel approach for associating the electromyographic (EMG) activity from upper limb muscles with leg kinematics. Our methodology takes advantage of the high involvement of shoulder muscles in most locomotor-related movements and of the natural co-ordination between arms and legs. Nine healthy subjects were asked to walk at different constant and variable speeds (3-5 km/h), while EMG activity of shoulder (deltoid) muscles and the kinematics of walking were recorded. To ensure a high level of EMG activity in deltoid, the subjects performed slightly larger arm swinging than they usually do. The temporal structure of the burst-like EMG activity was used to predict the spatiotemporal kinematic pattern of the forthcoming step. A comparison of actual and predicted stride leg kinematics showed a high degree of correspondence (r > 0.9). This algorithm has been also implemented in pilot experiments for controlling avatar walking in a virtual reality setup and an exoskeleton during over-ground stepping. The proposed approach may have important implications for the design of human-machine interfaces and neuroprosthetic technologies such as those of assistive lower limb exoskeletons
Analyse et représentation du mouvement du membre supérieur de l'homme
No full textSince antiquity, humans have attempted to reproduce their own movements as demonstrated by multitudes of artistic expressions. The recognition of action has been the object of many studies since the discovery of mirror neurons both in humans and monkeys, suggesting a resonance of action observation in the central nervous system. However these mechanisms are controversial and few studies have attempted to define the movement characteristics that are important for action recognition. This work was based on the analysis of human kinematic characteristics. The first aim was to define important variables for action and the second was to compare them to variables implicated in action recognition by an observer. In the methodological part, we developed a method of 3D reconstruction from electromagnetic recordings carried out with a restricted number of sensors. This method allows the study of 3D hand displacements as well as the configuration of the whole arm. Moreover, it allows the creation of a display made up of points or a stick diagram. The experimental part was based upon a protocol in which participants were asked to reach, grasp and lift cylindrical objects onto a target placed 18cm above the support surface. The visual appearance of the different objects was identical but the weight varied. In the first experiment, we studied the kinematic characteristics of the endpoint. When the weight of the object could be anticipated, the kinematics of the majority of the variables were invariant across the different weights. When the objects were presented randomly and the weight could therefore not be anticipated, these invariant characteristics disappeared. We found that when the object was heavier, the duration of the grasp increased and the acceleration during the lift decreased. This experiment was also carried with a deafferented patient. This revealed the importance of proprioceptive information in the regulation of the kinematics of action. A computational model of the effect of the weight on the movement characteristics in the different conditions of anticipation and proprioceptive feedback was developed in order to better understand the mechanisms behind the variations observed. In the second study we analysed the mechanisms which allow the weight of an object to be judged during observation of its lifting (observers saw either a recording of their own movements or those of another person). In the two visual conditions (working point or stick diagram), we observed that the response of the participants was correlated with the weight of the objects. Acceleration during the lift phase had the highest correlation with the subjects responses. In other words, the higher the acceleration, the lower the perceived weight of the object. The variability of the responses suggested that observers do not use other variables which also vary with the weight, neither do they base judgement on maximal height, which may be misleading. This might suggest that the response is not due to a mirror resonance. Acceleration during lifting seems to be specific to the weight during action even when anticipation is not possible. Moreover, it is particularly important for the visual judgement of the intrinsic properties of objects. Overall, these results show that kinematic analysis, when coupled with models, is a useful tool to increase understanding of the mechanisms of human motor control and action recognition. The methodology used (electromagnetic sensors and a kinematic model) could also allow a richer graphic environment to be created (an avatar, for example) so that experimental conditions can be altered, particularly for the study of action recognition (changing the view point, for example). The perspectives seem to be numerous in the field of rehabilitation as well as for virtual reality (or augmented reality) or for fun or educational purposesL homme tente depuis l antiquité de reproduire ses propres mouvements comme en témoignent de multiples expressions artistiques. La reconnaissance de l action a donné lieu à de nombreux travaux récents depuis l observation de neurones miroirs chez le singe et chez l homme ce qui suggère une résonance automatique de l action d autrui dans le système nerveux central de l observateur. Mais ces mécanismes demeurent discutés et très peu d études se sont attachées à définir quelles sont les caractéristiques particulières du mouvement qui sont importantes pour la reconnaissance de l action. Ce travail de thèse repose sur l analyse des caractéristiques cinématiques du mouvement humain d une part pour définir les variables importantes pour l exécution de l action et d autre part pour les comparer aux variables impliquées dans l observation et la reconnaissance de l action par un tiers. Dans une partie méthodologique nous avons contribué à développer une méthode de reconstruction tridimensionnelle à partir d enregistrements électromagnétiques effectués avec un nombre restreints de capteurs. Cette méthode permet l étude du déplacement 3D de la main et de la configuration articulaire du membre supérieur et l affichage de façon simplifiée sous forme de points ou de diagrammes en bâtons. D un point de vue expérimental, nous avons choisi comme action prototype la préhension et nous nous sommes basés sur un protocole où les sujets devaient atteindre et transporter des objets cylindriques, visuellement identiques mais de différents poids, vers une cible placée en hauteur (étagère). Dans une première expérience nous avons étudié les caractéristiques cinématiques du point de travail (main et objet) pendant l action. Nous avons observé que dans une condition où le poids de l objet pouvait être anticipé, la plupart des variables cinématique étudiées étaient invariantes par rapport au poids. Cette propriété n est toutefois pas conservée lorsque les poids sont présentés au hasard et où donc les effets d anticipation sont inexistants. Lorsque le poids est plus élevé, la durée de la saisie augmente et l accélération du mouvement de soulèvement diminue. Cette expérience a également été menée avec une personne présentant une déafférentation ce qui a montré l importance des informations proprioceptives dans la régulation de la cinématique de l action. L effet du poids sur le mouvement a été modélisé dans différentes conditions d anticipation et de retour proprioceptif pour mieux comprendre l origine des variations observées. Dans une deuxième expérience nous avons analysé les mécanismes permettant le jugement perceptif de différents poids chez des observateurs lorsqu ils visualisent des actions de préhension (un enregistrement de leurs propres mouvements ou ceux d autrui). Dans les deux conditions visuelles (affichage du point de travail ou du diagramme en bâtons), nous avons observé que la réponse des participants était corrélée au poids réel, ce qui montre une bonne capacité de reconnaissance des actions. L accélération durant le soulèvement (dès le décollement de l objet jusqu au pic de vitesse) était l indice le plus corrélé à la réponse des sujets. En d autres termes plus l accélération était importante plus le poids parait léger. L analyse de la variabilité des réponses a montré que les observateurs n utilisaient pas les autres variables qui varient de façon régulière avec le poids, ou se fiaient de façon erronée à la hauteur maximum du mouvement. Ce qui suggère que la réponse n est pas uniquement due à une résonance en miroir. L accélération du mouvement apparaît donc comme une variable caractéristique du poids de l objet pendant l action, même lorsque l anticipation de poids est possible. De plus elle est particulièrement importante pour effectuer un jugement perceptif des caractéristiques intrinsèques de l objet. Au total, ces résultats montrent l intérêt de l analyse cinématique couplée à la modélisation pour mieux comprendre les mécanismes du contrôle moteur humain et de la reconnaissance de l action La méthodologie développée (capteurs électromagnétiques et modèle cinématique) devrait permettre ultérieurement d enrichir l affichage graphique (par exemple par un avatar) pour varier les conditions expérimentales pour la reconnaissance de l action (étudier l effet du point de vue par exemple). Les perspectives semblent nombreuses dans le domaine de la rééducation et dans le domaine des systèmes de réalité virtuelle ou augmentée dans un but ludique ou éducatif.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
From Spinal Central Pattern Generators to Cortical Network: Integrated BCI for Walking Rehabilitation
Get PDFSuccess in locomotor rehabilitation programs can be improved with the use of brain-computer interfaces (BCIs). Although a wealth of research has demonstrated that locomotion is largely controlled by spinal mechanisms, the brain is of utmost importance in monitoring locomotor patterns and therefore contains information regarding central pattern generation functioning. In addition, there is also a tight coordination between the upper and lower limbs, which can also be useful in controlling locomotion. The current paper critically investigates different approaches that are applicable to this field: the use of electroencephalogram (EEG), upper limb electromyogram (EMG), or a hybrid of the two neurophysiological signals to control assistive exoskeletons used in locomotion based on programmable central pattern generators (PCPGs) or dynamic recurrent neural networks (DRNNs). Plantar surface tactile stimulation devices combined with virtual reality may provide the sensation of walking while in a supine position for use of training brain signals generated during locomotion. These methods may exploit mechanisms of brain plasticity and assist in the neurorehabilitation of gait in a variety of clinical conditions, including stroke, spinal trauma, multiple sclerosis, and cerebral palsy
Perceptual Weight Judgments When Viewing One's Own and others' Movements under Minimalist Conditions of Visual Presentation
No full text Across five experiments, we investigated the parameters involved in the observation and in the execution of the action of lifting an object. The observers were shown minimal information on movements, consisting of either the working-point displacement only (ie two points representing the hand and object) or additional configural information on the kinematics of the trunk, shoulder, arm, forearm, and hand, joined by a stick diagram. Furthermore, displays showed either a participant's own movements or those of another person, when different weights were lifted. The participants' task was to estimate the weight of the lifted objects. The results revealed that, although overall performance was not dependent on the visual conditions (working point versus stick diagram) or ownership conditions (self versus other), the kinematic cues used to perform the task differed as a function of these conditions. In addition, the kinematic parameters relevant for action observation did not match those relevant for action execution. This was confirmed in experiments by using artificially altered movement samples, where the variations in critical kinematic variables were manipulated separately or in combination. We discuss the implications of these results for the roles of motor simulation and visual analysis in action observation. </jats:p
Etude du couplage audio-moteur chez des sujets valides par un système de capture du mouvement électromagnétique.
No full textLes systèmes de capture électromagnétique permettent d'enregistrer des positions et des orientations dans l'espace tridimensionnel au cours du temps. Nous avons développé un système de réalité virtuelle purement auditif couplant les mouvements de la main et de la tête à un générateur sonore tridimensionnel (OpenAl). Lors de l'expérience, le but du sujet est d'attraper une source sonore fixe. Le son est perçu par des « oreilles virtuelles » placées soit sur la main (mode main) soit sur la tête (mode tête). Les variations sonores perçues par le sujet sont sensibles à la position et l'orientation des « oreilles virtuelles ». Les résultats préliminaires montrent que lors de l'expérience en mode main le sujet produit plus de mouvements exploratoires. De plus, le pourcentage de réussite en mode main est plus important qu'en mode tête. La réussite dépend également de la position 3D des cibles : elle est plus grande pour les cibles basses et lointaines en mode main et pour les cibles hautes et proches en mode tête. Cette étude préliminaire a permis de démontrer dans un premier temps la faisabilité de ce type de protocole. La réussite semble dépendre de la capacité à explorer l'espace c'est à dire à améliorer ses entrées sensorielles. Dans cette étude la capture et l'analyse du mouvement sont appliquées à l'enrichissement de l'environnement d'action dans le cadre de la rééducation
EMG patterns during assisted walking in the exoskeleton
Get PDFNeuroprosthetic technology and robotic exoskeletons are being developed to facilitate stepping, reduce muscle efforts and promote motor recovery. Nevertheless, the guidance forces of an exoskeleton may influence the sensory inputs, sensorimotor interactions and resulting muscle activity patterns during stepping. The aim of this study was to report the muscle activation patterns in a sample of intact and injured subjects while walking with a robotic exoskeleton and, in particular, to quantify the level of muscle activity during assisted gait. We recorded electromyographic (EMG) activity of different leg and arm muscles during overground walking in an exoskeleton in six healthy individuals and four spinal cord injury (SCI) participants. In SCI patients, EMG activity of the upper limb muscles was augmented while activation of leg muscles was typically small. Contrary to our expectations, however, in neurologically intact subjects, EMG activity of leg muscles was similar or even larger during exoskeleton-assisted walking compared to normal overground walking. In addition, significant variations in the EMG waveforms were found across different walking conditions. The most variable pattern was observed in the hamstring muscles. Overall, the results are consistent with a non-linear reorganization of the locomotor output when using the robotic stepping devices. The findings may contribute to our understanding of human-machine interactions and adaptation of locomotor activity patterns
Modeling Human Walk by PCPG for Lower Limb Neuroprosthesis Control
No full textIn this paper, we propose an original and biologically-inspired leg prosthesis control system. We demonstrate that human walk periodic patterns can be modeled by a Programmable Central Pattern Generator (PCPG) algorithm. Assuming that high-level commands reflecting the user's intention (such as accelerate, decelerate or stop) - and optionally, with their associated confidence level - are available, we show that the PCPG can generate an output signal directly exploitable to control the prosthesis actuators at different desired walking speeds in a smooth way. Thanks to an adequate tuning of the PCPG parameters relying on realistic human walk kinematics, such a prosthesis would undoubtedly increase the comfort of the patient. In this study, we modeled the kinematics of foot angle of elevation of seven subjects walking on a treadmill at 10 different speeds. The method we used to modify at best the PCPG parameters is presented. We found that a low-level order polynomial interpolation of the PCPG parameters as a function of speed provides good similarity indices between real walk and generated patterns at different speeds. This proves the relevancy of our approach and paves the way for numerous applications of human walk rehabilitation. Additionally, results suggest that walk would be advantageously modeled by two PCPGs
Direct kinematic modeling of the upper limb during trunk-assisted reaching.
No full textInternational audienceThe study proposes a rigid-body biomechanical model of the trunk and whole upper limb including scapula and the test of this model with a kinematic method using a six-dimensional (6-D) electromagnetic motion capture (mocap) device. Large unconstrained natural trunk-assisted reaching movements were recorded in 7 healthy subjects. The 3-D positions of anatomical landmarks were measured and then compared to their estimation given by the biomechanical chain fed with joint angles (the direct kinematics). Thus, the prediction errors was attributed to the different joints and to the different simplifications introduced in the model. Large (approx. 4 cm) end-point prediction errors at the level of the hand were reduced (to approx. 2 cm) if translations of the scapula were taken into account. As a whole, the 6-D mocap seems to give accurate results, except for prono-supination. The direct kinematic model could be used as a virtual mannequin for other applications, such as computer animation or clinical and ergonomical evaluations
Performance of the Emotiv Epoc headset for P300-based applications
No full textBackground: For two decades, EEG-based Brain-Computer Interface (BCI) systems have been widely studied in research labs. Now, researchers want to consider out-of-the-lab applications and make this technology available to everybody. However, medical-grade EEG recording devices are still much too expensive for end-users, especially disabled people. Therefore, several low-cost alternatives have appeared on the market. The Emotiv Epoc headset is one of them. Although some previous work showed this device could suit the customer's needs in terms of performance, no quantitative classification-based assessments compared to a medical system are available.Methods: This paper aims at statistically comparing a medical-grade system, the ANT device, and the Emotiv Epoc headset by determining their respective performances in a P300 BCI using the same electrodes. On top of that, a review of previous Emotiv studies and a discussion on practical considerations regarding both systems are proposed. Nine healthy subjects participated in this experiment during which the ANT and the Emotiv systems are used in two different conditions: sitting on a chair and walking on a treadmill at constant speed.Results: The Emotiv headset performs significantly worse than the medical device; observed effect sizes vary from medium to large. The Emotiv headset has higher relative operational and maintenance costs than its medical-grade competitor.Conclusions: Although this low-cost headset is able to record EEG data in a satisfying manner, it should only be chosen for non critical applications such as games, communication systems, etc. For rehabilitation or prosthesis control, this lack of reliability may lead to serious consequences. For research purposes, the medical system should be chosen except if a lot of trials are available or when the Signal-to-Noise Ratio is high. This also suggests that the design of a specific low-cost EEG recording system for critical applications and research is still required. © 2013 Duvinage et al. licensee BioMed Central Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
