Bayesian Action-Perception loop modeling: Application to trajectory generation and recognition using internal motor simulation

International audienceThis paper is about modeling perception-action loops and, more precisely, the study of the influence of motor knowledge during perception tasks. We use the Bayesian Action-Perception (BAP) model, which deals with the sensorimotor loop involved in reading and writing cursive isolated letters and includes an internal simulation of movement loop. By using this probabilistic model we simulate letter recognition, both with and without internal motor simulation. Comparison of their performance yields an experimental prediction, which we set forth

Effects of attentional focus on postural sway in children and adults

The present study examined, in children aged 4-11 and in adults, the postural control modifications when attention was oriented voluntary on postural sway. Since (1) there are less attentional resources in children than in adults, (2) the selective attention processing improves with age, i.e., children use a different strategy to focus their attention than adults, and (3) adults' postural stability decreases when attention is focused on postural sway, we hypothesized that postural stability was less affected in children than in adults when attention was focused on postural sway. Fourty four children aged 4- to 11-year-old and 11 adults participated in the experiments. The postural control task was executed in a Romberg position. Two experimental conditions were presented to the subjects, (1) to look at a video on a TV screen without instruction about the posture, and (2) to fixate a cross placed at the center of the TV screen with the instruction to remain as stable as possible. Postural performance was measured by means of a force platform. Results from this study (1) confirmed a non-monotonic improvement of postural stability during the ontogenetic period without reaching the adults' level at the age of 11, (2) suggested that children, aged 4-11, are able to focus their attention on the control of posture, and (3) showed that the automatic control of posture increases postural stability since the age of 4

Neuroscience of Bodily Self-Consciousness

We review recent research about human subjectivity and self-consciousness that has focused on cognitive psychology and neuroimaging of bodily self-consciousness. Multidisciplinary research on the fields of neurology, cognitive neuroscience and virtual reality opens new avenues to investigate brain mechanisms underlying a fundamental sense of the bodily self. Clinical evidence for the implication of right temporo-parietal junction for bodily self-consciousness has received support by studies in which virtual-reality based own body illusions are evoked in healthy participants to study the underlying processes. A series of experiments will be reviewed in which it was shown that the experiences of self-location, self-identification and the first-person perspective can be manipulated experimentally and rely on the integration of multisensory stimuli (touch, vision, proprioception, vestibular information). Specific protocols are available to predictably influence the different aspects of bodily self consciousness. We predict that the understanding of fundamental brain mechanisms of bodily self-consciousness will lead to unprecedented empirical insights that are of broad relevance for science, virtual reality, engineering, the humanities, as well as medicine and psychotherapy

The lasting effects of spike insoles on postural control in the elderly

The purpose of the present study was to explore the lasting effects of a tactile sensitivity enhancement induced by spike insoles on the control of stance in the elderly. Healthy elderly subjects (n = 19, mean age = 68.8) and young adults (n = 17, mean age = 24.3) were instructed to stand or to walk for 5 minutes with sandals equipped with spike insoles. Postural control was evaluated four times during unperturbed stance: (1) before putting on the sandals equipped with spike insoles, (2) 5 minutes after standing or walking with them, (3) immediately after placing thin, smooth, and flexible insoles (no spike insoles) into the sandals to avoid the cutaneous contact with the spikes, and (4) after a sitting rest of 5 minutes with the no spike insoles. Sway parameters such as surface area, mean speed and root mean square were recorded. The present results suggest that (1) whatever the session (i.e. standing or walking) and the population, the artificial sensory message elicited by the spikes improved postural sway and, (2) the elderly were particularly perturbed when the tactile sensitivity enhancement device was removed. Whatever the age, the enriched sensory context provided by this tactile sensitivity enhancement device led to a better postural control; its suppression entailed a reweighting of the plantar cutaneous information. The difficulty that the elderly had to adjust the relative contribution of the different inputs probably reflected their poorer central integrative mechanisms for the reconfiguration of the postural set. A reduced peripheral sensitivity may also explain these postural deficits

Leg muscle vibration modulates bodily self-consciousness: integration of proprioceptive, visual, and tactile signals

Behavioral studies have used visuo-tactile conflicts between a participant's body and a visually presented fake or virtual body to investigate the importance of bodily perception for self-consciousness (bodily self-consciousness). Illusory self-identification with a fake body and changes in tactile processing--modulation of visuo-tactile cross-modal congruency effects (CCEs)--were reported in previous findings. Although proprioceptive signals are deemed important for bodily self-consciousness, their contribution to the representation of the full body has not been studied. Here we investigated whether and how self-identification and tactile processing (CCE magnitude) could be modified by altering proprioceptive signals with 80-Hz vibrations at the legs. Participants made elevation judgments of tactile cues (while ignoring nearby lights) during synchronous and asynchronous stroking of a seen fake body. We found that proprioceptive signals during vibrations altered the magnitude of self-identification and mislocalization of touch (CCE) in a synchrony-dependent fashion: we observed an increase of self-identification and CCE magnitude during asynchronous stroking. In a second control experiment we studied whether proprioceptive signals per se, or those from the lower limbs in particular, were essential for these changes. We applied vibrations at the upper limbs (which provide no information about the position of the participant's body in space) and in this case observed no modulation of bodily self-consciousness or tactile perception. These data link proprioceptive signals from the legs that are conveyed through the dorsal column-medial lemniscal pathway to bodily self-consciousness. We discuss their integration with bodily signals from vision and touch for full-body representations

L'estimation kinesthésique des distances : études comportementales et analyse probabiliste

National audienceThe purpose of the present paper is to review studies examining the estimation of distances on the basis of kinesthetic cues. In this kind of task, blindfolded participant explores a path (target distance) with one arm-hand system and reproduces later its distance with the same arm-hand system. The analysis of data shows the estimations depend on three types of factor : 1) the geometrical cues ; 2) the force cues ; and 3) the cognitive factors. Moreover, the analysis about the different variables used by researchers to measure the performance shows that the different types of errors - constant, absolute and variable errors- have been processed either conjointly or independently. By casting these error measures in the probabilistic modeling framework, we show that none of these is inherently more adequate than the others; they differ in the underlying, implicit hypotheses they assume. Discussing the relevance of these error measures thus amounts to discussing the validity of these hypotheses, which fortunately, could be assessed experimentally.Cette revue critique concerne les processus psychologiques par lesquels nous estimons des distances en utilisant les indices kinesthésiques en l'absence d'informations visuelles. Le paradigme expérimental utilisé par les chercheurs consiste à demander à des sujets (sous occlusion visuelle momentanée) d'explorer avec le système bras-main une distance cible et puis de la reproduire avec la même main. L'analyse des données de la littérature scientifique montre que l'estimation kinesthésique des distances dépend de trois types de facteurs : 1) les indices géométriques, 2) les indices de force et 3) les facteurs cognitifs. De plus, l'analyse des mesures utilisées par les chercheurs pour quantifier cette estimation révèle que les différents types de mesure -l'erreur constante, l'erreur variable et l'erreur absolue- sont traités soit conjointement soit indépendamment. En replaçant ces mesures dans le cadre d'une analyse probabiliste, il apparaît qu'aucune de ces dernières n'est intrinsèquement meilleure que les autres. En réalité, elles font des hypothèses implicites différentes. Discuter de la pertinence de ces mesures d'erreurs revient donc à discuter de la validité de ces hypothèses sous-jacentes, ce qui, heureusement, peut être examiné expérimentalement

Contribution des afférences tactiles plantaires au maintien de l'équilibre. Effets du port de semelles à picots sur le contrôle postural quasi-statique et la sensibilité cutanée plantaire de la personne âgée.

The prevention of falls in elderly is a major focus of medical research. Although the mechanisms underlying the effect of aging on the postural control system are varied and complex, impaired sensory function is likely to be an important contributing factor to the deterioration in postural balance and may increase the likelihood of falling. Age-related loss of cutaneous sensation, in particular, is pervasive, and appears to correlate with impaired postural control. As the feet interface directly with the ground, cutaneous cues provide relevant information about the support surface properties, and about the body position in reference to verticality. The purpose of this study was to explore the effects of a mechanical stimulation of the plantar mechanoreceptors, by means of spikes within the footwear insole, on postural stability. Our results provide evidence that applying a mechanical stimulation reduce, to some extent, postural sway in most of the young adults, the elderly and the patients with diabetic neuropathy. The benefits are not correlated with the cutaneous sensitivity or the initial postural performances of the subject. There was also a significant inter-individual variability. The enriched sensory context provided by the spikes is an original method of stimulation that may be appropriated for subjects with balance problems. This stimulation may reproduce, to some extent, the effects of a massage without requiring a systematic therapeutic intervention. Further research is needed to find the best compromise between the duration, the intensity, the frequency of the stimulation and the comfort of the insoles.La prévention des chutes chez les personnes âgées constitue aujourd'hui un objectif prioritaire en matière de santé publique. Bien que les mécanismes associés au vieillissement soient complexes et variables selon les individus, la détérioration des fonctions sensorielles semble être un des facteurs majeurs de la dégradation du contrôle postural. Cette diminution des performances posturales augmente la probabilité de chute. L'altération de la sensibilité cutanée qui apparaît avec l'âge est, en particulier, à l'origine de problèmes d'équilibre. Compte tenu de leur localisation à l'interface du corps et du support podal, les capteurs tactiles plantaires fournissent des informations très pertinentes sur les oscillations du corps par rapport à la verticale. Dans le cadre de ce travail de thèse, nous nous sommes particulièrement intéressés aux effets d'une stimulation mécanique de la sole plantaire par le port de semelles à picots. Nos travaux ont mis en évidence que ce type de stimulation améliore dans certaines conditions la stabilité posturale chez les jeunes, chez les personnes âgées saines ou atteintes d'une neuropathie diabétique. Les bénéfices observés ne sont ni corrélés à la sensibilité cutanée plantaire, ni aux performances posturales initiales du sujet et varient selon les individus. L'enrichissement du contexte sensoriel apporté par les picots pourrait constituer une méthode de stimulation originale et particulièrement appropriée pour les personnes qui présentent des problèmes d'équilibre. Elle permettrait de reproduire dans une certaine mesure les effets bénéfiques d'un massage de la sole plantaire, ce qui éviterait ainsi l'intervention systématique d'un thérapeute. Les perspectives de ce travail sont nombreuses et nous permettront de déterminer le meilleur compromis en termes de durée, d'intensité, de fréquence de stimulation et de confort afin de pouvoir quantifier plus précisément la stimulation optimale