Designing for physically disabled users: benefits from human motion capture – a case study

International audiencePurpose: The present study aimed to improve the design of an interface that may help disabled children to play a musical instrument. The main point is to integrate human motion capture in the design process. Method: The participant performed 20 pointing movements toward four selected locations. A three one-way analysis of variance (ANOVA) was performed in order to determine the most efficient input location. For each button position, we compared (1) the reaction time (RT), (2) the movement time (MT), and (3) the spatial variability of the movements. Results: According to the results obtained for RT and MT, one position was the most efficient button location in order to produce efficient movements. Conclusions: As the case study showed, combining the 3D motion capture system and the statistical analysis led to help the designers their design methodology and crucial choices

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

Proxemics models for human-aware navigation in robotics: Grounding interaction and personal space models in experimental data from psychology

International audienceIn order to navigate in a social environment, a robot must be aware of social spaces, which include proximity and interaction-based constraints. Previous models of interaction and personal spaces have been inspired by studies in social psychology but not systematically grounded and validated with respect to experimental data. We propose to implement personal and interaction space models in order to replicate a classical psychology experiment. Our robotic simulations can thus be compared with experimental data from humans. Thanks to this comparison, we first show the validity of our models, examine the necessity of the interaction and personal spaces and discuss their geometric shape. Our experiments suggest that human-like robotic behavior can be obtained by using only correctly calibrated personal spaces (i.e., without explicit representation of interaction spaces and therefore, without the need to detect interactions between humans in the environment)

The Action Constraints of an Object Increase Distance Estimation in Extrapersonal Space

This study investigated the role of action constraints related to an object as regards allocentric distance estimation in extrapersonal space. In two experiments conducted in both real and virtual environments, participants intending to push a trolley had to estimate its distance from a target situated in front of them. The trolley was either empty (i.e., light) or loaded with books (i.e., heavy). The results showed that the estimated distances were larger for the heavy trolley than for the light one, and that the actual distance between the participants and the trolley moderated this effect. This data suggests that the potential mobility of an object used as a reference affects distance estimation in extrapersonal space. According to embodied perception theories, our results show that people perceive space in terms of constraints related to their potential actions

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

Haptic guidance improves the visuo-manual tracking of trajectories

BACKGROUND: Learning to perform new movements is usually achieved by following visual demonstrations. Haptic guidance by a force feedback device is a recent and original technology which provides additional proprioceptive cues during visuo-motor learning tasks. The effects of two types of haptic guidances-control in position (HGP) or in force (HGF)-on visuo-manual tracking ("following") of trajectories are still under debate. METHODOLOGY/PRINCIPALS FINDINGS: Three training techniques of haptic guidance (HGP, HGF or control condition, NHG, without haptic guidance) were evaluated in two experiments. Movements produced by adults were assessed in terms of shapes (dynamic time warping) and kinematics criteria (number of velocity peaks and mean velocity) before and after the training sessions. CONCLUSION/SIGNIFICANCE: These results show that the addition of haptic information, probably encoded in force coordinates, play a crucial role on the visuo-manual tracking of new trajectories

How actions constrain the visual perception of space

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Planification et contrôle de la trajectoire d'un mouvement d'atteinte de cible (influence des contraintes visuelles)

La production de mouvements d'atteinte de cible, qu'il s'agisse de pointage de cibles ou de saisie d'objets, soulève la question des processus permettant la transformation d'une intention motrice en un mouvement réel. Ce traitement implique une phase de spécification de la trajectoire permettant au segment distal d'atteindre la cible. Si l'existence de cette phase de planification est généralement admise, l'espace dans lequel les commandes motrices sont définies continue d'être un objet de discussion. Une première théorie postule que la planification des mouvements est réalisée sur la base de leurs effets externes en spécifiant une trajectoire spatiale du segment distal dans l'espace des tâches. Un autre courant, en revanche, postule que les commandes motrices seraient définies dans l'espace articulaire, la trajectoire effectuée par la main n'étant que la conséquence du mouvement planifié. Le but de ce travail est de montrer qu'une contrainte visuelle peut modifier l'espace dans lequel les commandes motrices sont spécifiées. Une première expérience a donc consisté à comparer la production de mouvements de pointage effectués dans des situations de contrôle visuel direct et indirect (contrôle vidéo-assisté). Les mouvements étaient effectués vers des cibles placées à différentes excentricités (20, 40, 60 et 80 deg) et pouvaient être physiquement contraints (2D) ou non contraints (3D). Lorsque le mouvement est contraint, les trajectoires de la main tendent à être rectilignes quels que soient l'excentricité de la cible et le type de contrôle visuel. Des résultats différents sont observés pour les mouvements non contraints. En effet, en situation de vision directe la courbure de la trajectoire augmente selon l'excentricité de la cible alors qu'elle reste rectiligne dans la situation de vision indirecte. Une seconde expérience a consisté à analyser, dans des conditions similaires, un mouvement de saisie. Malgré les fortes contraintes bio-mécaniques pesant sur ce type de mouvement, on observe également une tendance à produire des trajectoires rectilignes en situation de vision indirecte. Le même résultat est observé lors d'une expérience destinée à analyser l'effet d'un biais directionnel (rotation de 45 degrés). L'ensemble de ce travail indique qu'un contrôle visuel indirect contraint le système moteur à planifier le mouvement dans l'espace des tâches, ce qui démontre, par là même, le caractère non exclusif des modes de représentation des commandes motrices.In goal-directed movements, the way motor intentions are transformed into motor commands raises the question of defining the mechanisms responsible for the hand trajectory formation. A large set of data led to the conclusion that goal-directed movements are encoded as a displacement along a given pre-established trajectory. According to some theories, the motor system selects a given trajectory in task space and then, transforms this path into a pattern of joint covariations. Whereas according to another view, the path taken by the hand in the external world is the result of a trajectory specified at the joint level. The goal of the present work is to show that trajectory planning can be influenced by a visual constraint. In a first experiment we compared movements carried out either under a direct or a remote visual control (use a video system). Movements aimed at targets placed at different eccentricities and were either constrained (i.e., two dimensional movements) or unconstrained (i.e., three dimensional movements). Results revealed that trajectories of constrained movements were nearly straight whatever the eccentricity of the target and the type of visual control. However, a different pattern was revealed for unconstrained movements: Under direct vision, the trajectory curvature increased as the eccentricity of the target augmented, whereas under indirect vision, trajectories remained nearly straight whatever the eccentricity of the target. In a second experiment, grasping movements were analysed in a similar situation. Despite the biomechanical constraints that weigh upon such movements, subjects tended to produce straight trajectories in the indirect visual feedback situation. Similar results were observed in motor adaptation to a directional bias imposed by a 45 degree rotation of the remote visual feedback (Third experiment). Taken together, these results suggest that movements controlled through a remote visual feedback are planned in task space and therefore show that motor commands are represented differently as a function of the demands of the task.GRENOBLE2/3-BU Droit/Lettres (384212101) / SudocSudocFranceF

Effets des points d’inflexion sur les estimations des distances euclidiennes dans une tâche manuelle d’intégration de trajets

The kinaesthetic perception of Euclidean distance: Effect of inflexion points This study used a manual tracking task to investigate the processes that underlie the estimate of Euclidean distances (ED) on the basis of kinaesthetic cues. In this kind of task, blindfolded adults traced straight and curvilinear paths with one finger and estimated, later, the ED between the starting and ending points. Previous results suggested that errors in the estimations of ED would be related to both the presence of inflection points in paths and the size of the workspace explored. This experiment examined the effect of the number of inflection points (2, 4 or 6) included in curved paths on two ED (7,5 cm or 22,5 cm) estimations. For the small paths, errors increased when the paths included at least two inflection points regardless of the number inflection points. For larger paths, the ED estimations were independent of the number of inflection points. These findings suggest that the presence of inflection points in curved paths may explain the detour effect observed in a reduced portion of space.RÉSUMÉ Cette étude a pour but de mieux comprendre les processus impliqués dans l’estimation des distances euclidiennes (DE) à partir des signaux kinesthésiques dans une tâche manuelle d’intégration de trajets. Dans ce type de tâche, les sujets doivent explorer des trajets rectilignes et curvilignes à l’aide de leur index et estimer, par la suite, la DE entre le point de départ et d’arrivée. Certaines études observent que, par rapport à la simple reproduction d’un trajet rectiligne, les erreurs d’estimation de cette DE s’amplifient au fur et à mesure que la longueur du trajet curviligne augmente. Le but de cette expérience est de montrer que cet «effet de détour» est expliqué plutôt par la présence de points d’inflexion le long du trajet curviligne que par l’augmentation de sa longueur. Pour cela, nous avons testé la capacité à estimer deux DE (7,5 cm et 22,5 cm) après l’exploration de trajets curvilignes deux fois plus longs dans lesquels le nombre de points d’inflexion pouvait varier (2, 4 ou 6). Les résultats montrent un effet de détour uniquement pour la DE de 7,5 cm, incluant 2, 4 ou 6 points d’inflexion. Ces résultats montrent que l’effet de détour n’est pas lié à la longueur des trajets curvilignes mais à leur géométrie, et plus précisément, à la présence d’au moins 2 points d’inflexion regroupés dans une partie restreinte de l’espace de travail.Gentaz Edouard, Faineteau Henry, Palluel-Germain Richard. Effets des points d’inflexion sur les estimations des distances euclidiennes dans une tâche manuelle d’intégration de trajets. In: L'année psychologique. 2008 vol. 108, n°1. pp. 3-14

Mirror exposure following visual body-size adaptation does not affect own body image

Prolonged visual exposure to large bodies produces a thinning aftereffect on subsequently seen bodies, and vice versa. This visual adaptation effect could contribute to the link between media exposure and body shape misperception. Indeed, people exposed to thin bodies in the media, who experience fattening aftereffects, may internalize the distorted image of their body they see in the mirror. This preregistered study tested this internalization hypothesis by exposing 196 young women to an obese adaptor before showing them their reflection in the mirror, or to a control condition. Then, we used a psychophysical task to measure the effects of this procedure on perceptual judgements about their own body size, relative to another body and to the control mirror exposure condition. We found moderate evidence against the hypothesized self-specific effects of mirror exposure on perceptual judgements. Our work strengthens the idea that body size adaptation affects the perception of test stimuli rather than the participants' own body image. We discuss recent studies which may provide an alternative framework to study media-related distortions of perceptual body image