Le travail de thèse exposé dans ce manuscrit s'intéresse à la simulation d'un mouvement de manipulation d'objet, plus particulièrement à la saisie suivie de la rotation d'une sphère selon un axe fixe. Le but ici est, à partir d'une analyse de mouvements réels, d'être capable de proposer un algorithme de simulation reproduisant des mouvements comparables aux données expérimentales, en fournissant en entrée le moins d'informations possibles et en essayant d'introduire de la variabilité dans le mouvement simulé. 12 sujets volontaires ont participé à l'expérimentation. Nous leur avons demandé de saisir et de tourner une sphère de 60mm de diamètre avec des amplitudes allant de 45° à 360°, dans les deux sens. L'analyse de ces données expérimentales, complétée par des simulations de l'effet des limites articulaires sur le mouvement nous ont permis d'étudier plusieurs hypothèses sur le contrôle de mouvement telles que l'hypothèse de confort final (« end-state comfort ») et le principe de travail minimum. Une des conclusions majeures est que l'anticipation posturale au moment de saisie semble être expliquée davantage par le confort en fin de mouvement qu'au moment de saisie. Basé sur ces observations, nous proposons un algorithme de simulation avec pour nouveautés la prise en compte de l'espace de mouvements admissibles par les limites articulaires ainsi que l'introduction de la variabilité au choix de la posture de saisie. Les premiers résultats semblent être en accord en grande partie avec les observations expérimentales donnant une base de travail pour aller vers des outils de simulation se rapprochant de plus en plus vers un comportement "humain" / The thesis work presented in this manuscript focuses on the simulation of an handling motion, more specifically on the grasp followed by the rotation of a sphere along a fixed single axis. The aim here is, from the analysis of actual motions, to be able to propose an simulation algorithm reproducing motions comparable to experimental data, with the less input as possible and trying to introduce some variability into the simulated motion. 12 volunteers participated to the experiment. Subjects were asked to grasp and turn a sphere of 60mm of diameter. Amplitudes of rotations were ranged from 45° to 360°, in both directions. Experimental data analysis, completed with some simulations of the effect of joint limits on motion, allowed us to investigate several motion control hypothesis as the end-state comfort hypothesis or the minimum work principle. One of the main conclusions is that postural anticipation when grasping seems to be more explained by the comfort at the end of the motion than when grasping. Based on these observations, we proposed a simulation algorithm being original by the way of how it takes into account possible motions allowed by joint limits and by the introduction of variability into the simulated grasp posture. The first results seem to follow most part of the experimental observations giving a strong basis to go towards simulation tools that will come closer to a “human” behavior

There is considerable evidence to suggest that object affordances (see Gibson, 1966) can serve to moderate volitional responses by “priming” the visuomotor system toward certain actions (e.g., Tucker & Ellis, 1998). Typically, these studies assume that shorter voluntary reaction time latencies reflect more efficient movement planning. Questions remain however, as to whether object affordances offer the same motor priming benefits in situations where the temporal window to initiate motor action precludes volitional movements (e.g., during an unexpected balance perturbation). The efficiency of balance reactions to a perturbation is dependent upon the ability for the motor system to generate short latency actions at the onset of instability. Due to the rapid nature of these actions, they are suggested to be regulated by information received prior to the perturbation. In this study, participants sat in a custom-built chair that delivered posterior perturbations and, on each trial, were presented with two of three types of stimuli within their reach (two graspable poles that varied in orientation and a flat non-graspable control). They were instructed to reach and grasp one of the poles at the moment of perturbation so as to mitigate the tilt. To assess cortical activity that may be indicative of motor planning in response to the perception of object affordances, changes in oxyhemoglobin (oxy-Hb) in the right and left premotor cortices were measured using a continuous wave fNIRS system. Results revealed a significant increase (F= 4.62, p= .043) in oxy-Hb in the right and left hemisphere (M = .023 µM) in response to objects that afford an optimal form of grasping action (mitigating excessive supination or pronation of the hand), compared to when no grasping opportunity was present (M = -.051 µM). These results suggest that affordances may be used to prime the system in the event of a balance threat. / Thesis / Master of Science (MSc)