Influence of visual, vestibular and proprioceptive feedbacks on spatial orientation

The perception of gravity, although unconscious, is omnipresent in our daily life and plays a key role in our movements and interactions with the environment. Gravity perception relies on a multisensory integration based on 3 sources of information: visual, vestibular and proprioceptive, each weighted according to its reliability. The aim of this master thesis is to better understand the influence of these three sources of information on the estimation of the true gravitational vertical. To do so, two experiments were designed using a virtual reality (VR) headset to induce a visual bias and a tilting chair to induce a vestibular bias. In the two experiments, subjects were asked to align a stick in the VR environment with what they believed to be the gravitational vertical in the real world. The first experiment focused on both visual and vestibular biases in the sagittal plane, using three different orientations of the VR environment: aligned with the subject, or tilted backward/forward; and three body orientations: tilted forward/backward or not. The second experiment focused on visual and vestibular biases in the frontal plane, with three different orientations of the VR environment: aligned with the subject or tilted leftward/rightward; and two orientations of the head: tilted or not. The trends in the results of the first experiment were not very marked. We observed that the orientation of the virtual environment had an effect on the SVV's results, and that this influence was different depending on the orientation of the body. Body orientation, on the other hand, had no influence on the SVV. Under all conditions, a forward bias was observed, which contrasts with previous studies. On the other hand, the second experiment shows clear patterns consistent with previous studies. We observe significant effects of the visual conditions and of the vestibular conditions, and there is also a significant interaction between them. We observed a bias in the direction of the VR environment and a bias in the direction of the head. Although imperfect, our results bring new insights on the influence of visual and vestibular biases on the perception of gravity using VR technologies.