Visual control of posture: The role of motion parallax and cognitive processes

The thesis investigates visual control of posture in man, in particular the role of visual motion parallax. The moving room paradigm, which simulates self-motion, was used in most experiments. In the first series of experiments the effects of room motion in the presence or absence of a foreground fixation target were investigated. Directionally specific postural responses opposite to background motion were observed when subjects were fixating the foreground target. Neither induced motion, ocular convergence nor binocular vision were sufficient to evoke such responses. It was concluded that such postural response and more generally postural control could be influenced by motion parallax. In experiments carried out in a normal stationary room, it was found that the motion parallax a subject generates during spontaneous body sway is used by the visuo-motor system to control body oscillations. The parallax-based effect was, however, limited to low frequency components of body sway (0.75 Hz). The influence of cognitive processes in visuo-postural control was also investigated. It was found that the predictability of the forthcoming displacement of a moving visual scene helped observers distinguish visual flow due to self-motion from that due to object-motion and therefore inhibit postural readjustments induced by object motion. The visual control of posture in patients with congenital nystagmus, who show involuntary movement of the eyes at a frequency of 3-5 Hz, was also investigated. It was found that, in the moving room paradigm, these patients were able to use motion parallax to control slow reorientation of the body as do control subjects. In contrast, during spontaneous body sway in a 3 dimensional environment they were not able to control rapid oscillations of the body (> 0.5Hz). These findings suggest that in congenital nystagmus, visual control of posture is restricted by low frequency sampling of the visual scene (foveation periods). They also suggest that although motion parallax is a dynamic cue, it can be used to control slow body re-orientation on the basis of solely discrete visual samples

Fake hand in movement: Visual motion cues from the rubber hand are processed for kinesthesia

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La «pierre du Midi» à Lyon et à Vienne à l'époque gallo-romaine : utilisation, chronologie et provenance

The " pierre du Midi " in the roman towns of Lyon and Vienne : utilisation, chronology and origin. The " pierre du Midi " (biodetritic miocene limestone) was one of the most important calcareous ashlar of the roman cities along the Rhone's valley. The story of the quarrying of this material, hitherto identified in some buildings of Lyon, is now better known thanks to the archaeological evidence from new excavations, in the towns of Lyon, Saint-Romain-en-Gal (Rhône) and Vienne (Isère). The present article deals both with archaeology and geology. A survey of the roman buildings where the " pierre du Midi " was found, revels how and were this material was used, from the end of the 1st century B.C. to the 3rd century A.D. The geological study deals with the problem of the origin of this stone, by basin on paleontological and lithological criteria. As several facies were used, we suggest several possible origins, among all the outcrops quarried in the Rhône valley. The results of this interdisciplinary work open on economic and historic fields : evolution of the building materials supplying, planning of the lines of communication, exploitation of the regional ressources, linked to the roman town development.La «pierre du Midi» (calcaire biodétritique miocène) occupe une place de choix parmi les pierres de taille calcaires de Lyon et de Vienne antiques. L'histoire de l'exploitation de ce matériau déjà identifié dans quelques monuments lyonnais s'éclaire d'un jour nouveau grâce aux recherches entreprises depuis quelques années sur les matériaux des constructions antiques, en relation avec les fouilles urbaines récentes de Lyon, Vienne et Saint-Romain-en-Gal. Notre approche est à la fois archéologique et géologique : en dressant un inventaire aussi exhaustif que possible des constructions où fut mise en œuvre la «pierre du Midi», l'étude archéologique révèle les modalités de son utilisation et de sa chronologie de la fin du Ier siècle avant J.-C. au IIIe siècle après. L'étude géologique cherche à résoudre le problème de la provenance de ce matériau en se basant sur des critères paléontologiques et lithologiques. Plusieurs faciès lithologiques ont été utilisés, ce qui conduit à proposer plusieurs provenances possibles parmi toutes les carrières recensées le long de la vallée du Rhône. Les résultats de ce travail interdisciplinaire débouchent en outre sur des questions économiques et historiques : évolution de l'approvisionnement en matériaux de construction, aménagement des voies de communication, mise en valeur des ressources régionales liée aux rythmes du développement urbain antique...Philippe Michel, Savay-Guerraz Hugues. La «pierre du Midi» à Lyon et à Vienne à l'époque gallo-romaine : utilisation, chronologie et provenance. In: Bulletin mensuel de la Société linnéenne de Lyon, 58ᵉ année, n°5, mai 1989. pp. 141-172

Integration of visual and proprioceptive afferents in kinesthesia.

International audienceProprioceptive signals are of prime importance in kinesthesia. However, in conditions of visuo-proprioceptive conflicts, strong visual-evoked biases can be observed. In three experiments, we parsed the interaction between visual and proprioceptive afferents using the 'mirror box' paradigm. Participants' left arm, the image of which was reflected in a mirror, was passively moved into flexion/extension or remained static. In Experiment 1 proprioceptive afferents of the unseen static right arm were masked with diffuse arm vibration. In Experiments 2 and 3, afferent signals were enhanced by muscle vibration of biceps or triceps stretch receptors. Illusory arm movements were evaluated with subjective reports and matching adjustments. Results revealed that participants did not experience kinesthetic illusions when the mirror reflected the image of a static arm while proprioceptive afferents conveyed signals of a moving arm (Experiment 2). In this specific case, vision apparently contributed much more strongly to the final percept than proprioceptive signals. However, in most circumstances, the percept reflected integration of both afferent signals (Experiments 1-3). For instance, when both sensory channels conveyed signals of arm displacement but in the opposite direction, kinesthetic illusions occurred but were either proprioceptively (vibration illusion) or visually driven (mirror illusion), according to individual sensorial preferences (Experiments 2 and 3). These results indicate that kinesthesia is the product of cooperative integration processes in which the final percept strongly depends on the experimental conditions as well as sensorial preferences. The observed changes in the relative contribution of each input across experimental conditions likely reflect reliability-dependent weights

Trying to move your unseen static arm modulates visually-evoked kinesthetic illusion

Although kinesthesia is known to largely depend on afferent inflow, recent data suggest that central signals originating from volitional control (efferent outflow) could also be involved and interact with the former to build up a coherent percept. Evidence derives from both clinical and experimental observations where vision, which is of primary importance in kinesthesia, was systematically precluded. The purpose of the present experiment was to assess the role of volitional effort in kinesthesia when visual information is available. Participants (n=20) produced isometric contraction (10-20% of maximal voluntary force) of their right arm while their left arm, which image was reflected in a mirror, either was passively moved into flexion/extension by a motorized manipulandum, or remained static. The contraction of the right arm was either congruent with or opposite to the passive displacements of the left arm. Results revealed that in most trials, kinesthetic illusions were visually driven, and their occurrence and intensity were modulated by whether volitional effort was congruent or not with visual signals. These results confirm the impact of volitional effort in kinesthesia and demonstrate for the first time that these signals interact with visual afferents to offer a coherent and unified percept

Distorsion de la représentation du corps chez l'adolescente souffrant d’anorexie mentale

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What's left of the mirror illusion when the mirror can no longer be seen? Bilateral integration of proprioceptive afferents!

International audienceRecent data suggest that manipulating the muscle afferents of one arm affects both ipsilateral and contralateral perceptual estimates. Here, we used the mirror paradigm to study the bimanual integration of kinesthetic muscle afferents. The reflection of a moving hand in a mirror positioned in the sagittal plane creates an illusion of symmetrical bimanual movement. Although vision clearly has a role in kinesthesia, its role in the mirror illusion might have been overestimated. Conversely, the role of bimanual integration of muscle afferents might have been underestimated. We hypothesized that muscle-proprioceptive afferents of the passively displaced arm (the image of which was reflected in the mirror) are involved in this illusion. We evoked in 19 healthy adult participants the mirror illusion by displacing passively their left arm, the image of which was reflected in the mirror. Once participants experienced the illusion that their hidden right arm was moving, we then either occluded their view of the mirror (using occlusive glasses) and/or prevent the passive left arm displacement. Participants' illusion characteristics (duration and kinematic) under these conditions were compared with classical mirror illusion (without visual occlusion). We found that as long as the arm was still moving, the kinesthetic illusion decayed slowly after visual occlusion. These findings suggest that the mirror illusion results from the combination of visuo-proprioceptive signals from the two arms and is not purely visual in origin. Our findings also support the more general concept whereby proprioceptive afferents are integrated bilaterally for the purpose of kinesthesia during bimanual tasks

Postural challenge and adaptation to vibration-induced disturbances.

International audienceThe described experiment investigated whether adaptation to successive Achilles tendon vibration depends on the postural challenge. In phase 1, thirty-six participants were divided into three groups, each with a different postural challenge. After being blindfolded, participants received 15 trials of Achilles tendon vibration (10 s-90 Hz) while standing upright in either a free-standing condition (FS group), a light finger touch condition (LFT group), or a restrained-standing condition (RS group) in which a dorsal stand prevented body displacement. In phase 2, all participants were freely standing and received 15 additional trials of vibration. Antero-posterior trunk tilt was measured at the level of the trunk (C7). Although there were limited postural readjustments in LFT, adaptation was observed in phase 1 in both FS and LFT groups. In phase 2, the evoked postural displacement was greater in the RS group than in the other two groups. We concluded that although the absence of any postural challenge concomitant to the sensory stimulation prevented adaptation to occur, a minimal challenge was sufficient

French Project PLUSPAC : development of a hydrogen storage unit for an optimisation of stationary fuel cell systems - safety of metal hybrides

International audienceOne of the objectives of the French project PLUSPAC (Local Production and hydrogen Storage Unit for an optimisation of Fuel Cell stationary systems), coordinated by the Energy Research Centre of Veolia Environment is to evaluate the performances of hydrogen storage in metal hydrides for the energetic optimisation of a stationary fuel cell system. INERIS was in charge to assess the safety of metal hydrides as a storage mean. As very few information is available regarding the safety of intermetallic compounds developed within PLUSPAC project, experimental tests have been performed so as to get information about the reactivity of the powder (reaction with air, with water, thermal decomposition). Tests have been performed on activated (15 and 30 cycles) and no activated powders, and also on an other intermetallic compound, which is supposed to be reactive. Nevertheless, none of the tests have shown any adverse reaction, neither with air, nor with water, nor when exposed to high temperatures. Today, it appears that metal hydrides tested have a safe behaviour when exposed to air, water and high temperatures. Further tests would be necessary to investigate other materials