Analyse et représentation du mouvement du membre supérieur de l'homme

Since 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

Etude du couplage audio-moteur chez des sujets valides par un système de capture du mouvement électromagnétique.

Les 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

Des oreilles sur la main : atteindre des cibles dans un espace tridimensionnel avec un système audio-moteur

International audienc

Ears on the hand: reaching 3D audio targets

We studied the ability of right-handed participants to reach 3D audio targets with their right hand. Our immersive audio environment was based on the OpenAL library and Fastrak magnetic sensors for motion capture. Participants listen the target through a “virtual” listener linked to a sensor fixed either on the head or on the hand. We compare three experimental conditions in which the virtual listener is on the head, on the left hand, and on the right hand (that reach the target). We show that (1) participants are able to learn the task but (2) with a low success rate and high durations, (3) the individual levels of performance are very variable, (4) the best performances are achieved when the listener is on the right hand. Consequently, we concluded that our participants were able to learn to locate 3D audio sources even if their ears are transposed on their hand, but we found of behavioral differences between the three experimental conditions

Ears on the hand: reaching 3D audio targets

We studied the ability of right-handed participants to reach 3D audio targets with their right hand. Our immersive audio environment was based on the OpenAL library and Fastrak magnetic sensors for motion capture. Participants listen the target through a “virtual” listener linked to a sensor fixed either on the head or on the hand. We compare three experimental conditions in which the virtual listener is on the head, on the left hand, and on the right hand (that reach the target). We show that (1) participants are able to learn the task but (2) with a low success rate and high durations, (3) the individual levels of performance are very variable, (4) the best performances are achieved when the listener is on the right hand. Consequently, we concluded that our participants were able to learn to locate 3D audio sources even if their ears are transposed on their hand, but we found of behavioral differences between the three experimental conditions

Performance of the Emotiv Epoc headset for P300-based applications

Background: 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

Neural rhythmic symphony of human walking observation: Upside-down and uncoordinated condition on cortical theta, Alpha, Beta and gamma oscillations

Biological motion observation has been recognized to produce dynamic change in sensorimotor activation according to the observed kinematics. Physical plausibility of the spatial-kinematic relationship of human movement may play a major role in the top-down processing of human motion recognition. Here, we investigated the time course of scalp activation during observation of human gait in order to extract and use it on future integrated brain-computer interface using virtual reality (VR). We analyzed event related potentials (ERP), the event related spectral perturbation (ERSP) and the inter-trial coherence (ITC) from high-density EEG recording during video display onset (-200-600 ms) and the steady state visual evoked potentials (SSVEP) inside the video of human walking 3D-animation in three conditions: Normal; Upside-down (inverted images); and Uncoordinated (pseudo-randomly mixed images). We found that early visual evoked response P120 was decreased in Upside-down condition. The N170 and P300b amplitudes were decreased in Uncoordinated condition. In Upside-down and Uncoordinated conditions, we found decreased alpha power and theta phase-locking. As regards gamma oscillation, power was increased during the Upside-down animation and decreased during the Uncoordinated animation. An SSVEP-like response oscillating at about 10 Hz was also described showing that the oscillating pattern is enhanced 300 ms after the heel strike event only in the Normal but not in the Upside-down condition. Our results are consistent with most of previous point-light display studies, further supporting possible use of virtual reality for neurofeedback applications.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Oscillations in the human brain during walking execution, imagination and observation

Gait is an essential human activity which organizes many functional and cognitive behaviors. The biomechanical constraints of bipedalism implicating a permanent control of balance during gait are taken into account by a complex dialog between the cortical, subcortical and spinal networks. This networking is largely based on oscillatory coding, including changes in spectral power and phase-locking of ongoing neural activity in theta, alpha, beta and gamma frequency bands. This coding is specifically modulated in actual gait execution and representation, as well as in contexts of gait observation or imagination. A main challenge in integrative neuroscience oscillatory activity analysis is to disentangle the brain oscillations devoted to gait control. In addition to neuroimaging approaches, which have highlighted the structural components of an extended network, dynamic high-density EEG gives non-invasive access to functioning of this network. Here we revisit the neurophysiological foundations of behavior-related EEG in the light of current neuropsychological theoretic frameworks. We review different EEG rhythms emerging in the most informative paradigms relating to human gait and implications for rehabilitation strategies.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A subjective assessment of a P300 BCI system for lower-limb rehabilitation purposes

Recent research has shown that a P300 system can be used while walking without requiring any specific gait-related artifact removal techniques. Also, standard EEG-based Brain-Computer Interfaces (BCI) have not been really assessed for lower limb rehabilitation/prosthesis. Therefore, this paper gives a first baseline estimation (for future BCI comparisons) of the subjective and objective performances of a four-state P300 BCI plus a non-control state for lower-limb rehabilitation purposes. To assess usability and workload, the System Usability Scale and the NASA Task Load Index questionnaires were administered to five healthy subjects after performing a real-time treadmill speed control. Results show that the P300 BCI approach could suit fitness and rehabilitation applications, whereas prosthesis control, which suffers from a low reactivity, appears too sensitive for risky and crowded areas. © 2012 IEEE.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

A strategy of faster movements used by elderly humans to lift objects of increasing weight in ecological context

It is not known whether, during the course of aging, changes occur in the motor strategies used by the CNS for lifting objects of different weights. Here, we analyzed the kinematics of object-lifting in two different healthy groups (young and elderly people) plus one well-known deafferented patient (GL). The task was to reach and lift onto a shelf an opaque cylindrical object with changing weight. The movements of the hand and object were recorded with electromagnetic sensors. In an ecological context (i.e. no instruction was given about movement speed), we found that younger participants, elderly people and GL did not all move at the same speed and that, surprisingly, elder people are faster. We also observed that the lifting trajectories were constant for both the elderly and the deafferented patient while younger participants raised their hand higher when the object weighed more. It appears that, depending on age and on available proprioceptive information, the CNS uses different strategies of lifting. We suggest that elder people tend to optimize their feedforward control in order to compensate for less functional afferent feedback, perhaps to optimize movement time and energy expenditure at the expense of high precision. In the case of complete loss of proprioceptive input, however, compensation follows a different strategy as suggested by GL's behavior who moved more slowly compared to both our younger and older participants.SCOPUS: ar.jinfo:eu-repo/semantics/publishe