Évaluation de l'impact de la modification du retour visuel présenté par un égo-avatar temps réel sur la cinématique de la marche

Abstract

In recent years, virtual reality (VR) has found many uses in physical and motor rehabilitation. This democratization of VR is due, in part, to the fact that equipment is more and more available and affordable. This growing popularity is also linked to the fact that it is possible to place users in a fully controllable virtual environment (VE). VR makes it, using a selfavatar, to replace the users’s visualization of their body and thus to provide a visual feedback allowing the participants to observe their own movements performed by their virtual double. This self-avatar can accurately replicate the user’s movements, or these movements can be modified in real time. When a user is exposed to a modified visual feedback provided by a self-avatar in a static situation, proprioceptive and physical drift are induced. It has yet to be determined if those observations are also possible in a dynamic condition such as walking. The objective of this study is to quantify the kinematic, kinetic and spatiotemporal variations in gait of the participants when the movement of the lower limb of their self-avatar is manipulated. More precisely, when the hip flexion angle of the avatar is increased by 30 °. In this study, ten participants were evaluated. They had to walk on a treadmill instrumented with force platforms while observing their self-avatar from a first-person perspective (as if they were looking themselves in a virtual mirror) and from a third-person perspective (as if they were following themselves and if they were looking themselves from a profile perspective). The selected parameters were compared between the different conditions in order to determine if the participant changes his gait in order to follow his self-avatar. It is interesting to note that several parameters (kinematic, kinetic and spatiotemporal) are modified when the participant is exposed to his self-avatar that is accurately following his movement. The effect of the system latency and exposure to unusual visual feedback are explored as possible explanations. When the self-avatar is modulated, an increase in the vertical force on the ground at the time of heel strike is observed. The modulation algorithm chosen to modify the kinematics of the leg of the avatar produces a hip flexion of greater amplitude over an unchanged period of time. The speed of the leg of the self-avatar is thus visibly increased. Since the initial hypothesis is that participants will attempt to follow the movement of their self-avatars, an increase in the vertical displacement velocity of the participant's foot could be at the origin of the observed kinetic change. A modulation algorithm generating a more natural and better targeted movement could allow to have a more significant impact on the participants' movement characteristics and would be an interesting clinical tool in a gait rehabilitation context.

Date	21 Dec 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	David Labbé (Supervisor) & Rachid Aissaoui (Co-supervisor)