The perception of self-motion draws on inputs from the visual, vestibular and proprioceptive systems. Decades of behavioural research has shed light on constructs such as multisensory weighting, heading perception, and sensory thresholds, that are involved in self-motion perception. Despite the abundance of knowledge generated by behavioural studies, there is a clear lack of research exploring the neural processes associated with full-body, multisensory self-motion perception in humans. Much of what is known about the neural correlates of self-motion perception comes from either the animal literature, or from human neuroimaging studies only administering visual self-motion stimuli. The goal of this thesis was to bridge the gap between understanding the behavioural correlates of full-body self-motion perception, and the underlying neural processes of the human brain. We used a high-fidelity motion simulator to manipulate the interaction of the visual and vestibular systems to gain insights into cognitive processes related to self-motion perception. The present line of research demonstrated that theta, alpha and beta oscillations are the underlying electrophysiological oscillations associated with self-motion perception. Specifically, the three empirical chapters combine to contribute two main findings to our understanding of self-motion perception. First, the beta band is an index of visual-vestibular weighting. We demonstrated that beta event-related synchronization power is associated with visual weighting bias, and beta event-related desynchronization power is associated with vestibular weighting bias. Second, the theta band is associated with direction processing, regardless of whether direction information is provided through the visual or vestibular system. This research is the first of its kind and has opened the door for future research to further develop our understanding of biomarkers related to self-motion perception. / Dissertation / Doctor of Philosophy (PhD) / As we move through the environment, either by walking, or operating a vehicle, our senses collect many different kinds of information that allow us to perceive factors such as, how fast we are moving, which direction we are headed in, or how other objects are moving around us. Many of our senses take in very different information, for example, the vestibular system processes information about our head movements, while our visual system processes information about incoming light waves. Despite how different all of this self-motion information can be, we still manage to have one smooth perception of our bodies moving through the environment. This smooth perception of self-motion is due to our senses sharing information with one another, which is called multisensory integration. Two of the most important senses for collecting information about self-motion are the visual and vestibular systems. To this point, very little is known about the biological processes in the brain while the visual and vestibular systems integrate information about self-motion. Understanding this process is limited because until recently, we have not had the technology or the methodology to adequately record the brain while physically moving people in a virtual environment. Our team developed a ground-breaking set of methodologies to solve this issue, and discovered key insights into brainwave patterns that take place in order for us to perceive ourselves in motion. There were two critical insights from our line of research. First, we identified a specific brainwave frequency (beta oscillations) that indexes integration between the visual and vestibular systems. Second, we demonstrated another brainwave frequency (theta oscillation) that is associated with perceiving which direction we are headed in, regardless of which sense this direction information is coming from. Our research lays the foundation for our understanding of biological processes of self-motion perception and can be applied to diagnosing vestibular disorders or improving pilot simulator training.

Lorsqu’ils explorent leur environnement, les humains comme les autres animaux ont la capacité d’utiliser de nombreuses sources d’information afin d’estimer la distance qu’ils parcourent. Le flux optique est un indice important dans la perception de la distance parcourue. De plus, il a été montré que l’ajout d’un point de vue oscillant à une simulation visuelle de mouvement propre vers l’avant modulait cette perception. A travers ce travail, nous nous sommes intéressés à tester si la perception de la distance parcourue était également affectée par un point de vue oscillant, mimant de manière plus ou moins fidèle les mouvements de la tête lors de la marche. Dans six premières expériences, il était demandé aux participants stationnaires, confrontés à un flux optique simulant leur propre mouvement vers l’avant, d’indiquer quand ils pensaient avoir atteint la position d’une cible distante initialement perçue. Une expérience subséquentes s'est intéressée à déterminer si l’absence de ces oscillations jouait un rôle important dans l’estimation de la distance parcourue lorsqu’ils marchaient sur un tapis roulant. Enfin, dans une dernière expérience nous avons développé une mesure dynamique de la distance parcourue à travers l’utilisation d’une tâche demandant aux participants de pointer continuellement la position d’une cible distante initialement perçue. Dans l’ensemble, nos résultats montrent qu’un point de vue oscillant joue un rôle important dans la perception visuelle du mouvement propre et que de nombreux paramètres semblent être impliqués dans ce processus, incluant les informations visuelles et proprioceptives mais également l’aspect écologique de la marche naturelle. / When exploring their environment, humans and other animals have the ability to use many sources of information to estimate the distance they travel. Several studies have shown that optic flow is a significant cue to perceive distance travelled. Furthermore, it was found that adding various viewpoint oscillations to a purely translational optic flow, simulating forward self-motion, modulated this perception. In a series of experiments, we tested whether the perception of distance travelled was also affected by viewpoint oscillation, similar to head motion during natural walking. A first series of experiments, participants were exposed to an immersive optic flow simulating forward self-motion and they were asked to indicate when they thought they had reached the remembered position of a previously seen target. Two further experiments aimed to test whether the idiosyncrasy of viewpoint oscillations affects the perception of distance travelled in stationary observers and whether the absence of their own viewpoint oscillation played an important role in subjects’ estimates, while they were walking on a treadmill. And finally, in a last experiment we tried to develop a dynamic measure of distance travelled to a previously seen target, with a continuous pointing task method. Overall, our results show that viewpoint oscillations play an important role in visual self-motion perception and that several parameters (including visual information, proprioceptive information and ecological aspects of natural walking) seem to be involved in this process.