Your space or mine? : Mapping self in time

Peer reviewedPublisher PD

The Role of Perspective in Mental Time Travel

Recent years have seen accumulating evidence for the proposition that people process time by mapping it onto a linear spatial representation and automatically “project” themselves on an imagined mental time line. Here, we ask whether people can adopt the temporal perspective of another person when travelling through time. To elucidate similarities and differences between time travelling from one’s own perspective or from the perspective of another person, we asked participants to mentally project themselves or someone else (i.e., a coexperimenter) to different time points. Three basic properties of mental time travel were manipulated: temporal location (i.e., where in time the travel originates: past, present, and future), motion direction (either backwards or forwards), and temporal duration (i.e., the distance to travel: one, three, or five years). We found that time travels originating in the present lasted longer in the self- than in the other-perspective. Moreover, for self-perspective, but not for other-perspective, time was differently scaled depending on where in time the travel originated. In contrast, when considering the direction and the duration of time travelling, no dissimilarities between the self- and the other-perspective emerged. These results suggest that self- and other-projection, despite some differences, share important similarities in structure

Visuo-vestibular mechanisms of bodily self-consciousness

Bodily self-consciousness is linked to multisensory integration and is particularly dependent on vestibular perception providing the brain with the main sensory cues about body motion and location in space. Vestibular and visual inputs are permanently balanced and integrated to encode the most optimal representation of the external world and of the observer in the central nervous system. Vection, an illusory self-motion experience induced only by visual stimuli, illustrates the fact that the visual and the vestibular systems share common neural underpinnings and a similar phenomenology. Optokinetic stimulation inducing vection and direct vestibular stimulation induce whole-body motion sensations that can be used to explore multisensory interactions. A failure in visuo-vestibular integration, artificially induced by the methods of cognitive psychology or in pathological conditions, has also been reported to altered own body perception and bodily self-consciousness. The respective contributions of the vestibular and visual systems to bodily self-consciousness amongst other polymodal sensory mechanisms, and the neural correlates of visuo-vestibular convergence, should be better understood. We first performed a neuroimaging study of brain regions where optokinetic and vestibular stimuli converge, using 7T functional magnetic resonance imaging in individual subjects. We identified three main regions of convergence: (1) the depth of supramarginal gyrus or retroinsular cortex, (2) the surface of supramarginal gyrus at the temporo-parietal junction, (3) and the posterior part of middle temporal gyrus and superior temporal sulcus. Then, we aimed to induce the embodiment of an external fake rubber hand through visuo-tactile conflict - the so-called rubber hand illusion paradigm, and studied how this integration is modulated by vection. Subjects experiencing vection in the direction of the rubber hand mislocalised the position of their real hand towards the rubber hand indicating that visuo-vestibular stimuli can enhance visuo-tactile integration. We also investigated if visuo-proprioceptive and tactile integration in peripersonal space could be dynamically updated based on the congruency of visual and proprioceptive feedback. A pair of rubber hands or feet provided visual feedback. Fake and real limbs were crossed or uncrossed. We showed that sensory cues were integrated in peripersonal space, dynamically reshaped but only for hands. Finally, we investigated a rare case of an illusory own body perception in an epileptic patient suffering from multiple daily disembodiments during seizures. Seizures were associated to a focal cortical microdysplasia juxtaposed to a developmental venous anomaly in the left angular gyrus, a brain region known to be important for visuo-vestibular integration and bodily self-consciousness. Our results characterize the inferior parietal lobule as a crucial structure in merging visual, vestibular, tactile and proprioceptive inputs, allowing the emergence of the global and unified experience of being âI.â Multisensory body representation can be reshaped transiently using visual and vestibular signals or in relation to a medical condition affecting the temporo-parietal junction. The integration of visual and vestibular signals, aims to adapt dynamically our internal representations to constant changes occurring in our environment

Software techniques for improving head mounted displays to create comfortable user experiences in virtual reality

Head Mounted Displays (HMDs) allow users to experience Virtual Reality (VR) with a great level of immersion. Advancements in hardware technologies have led to a reduction in cost of producing good quality VR HMDs bringing them out from research labs to consumer markets. However, the current generation of HMDs suffer from a few fundamental problems that can deter their widespread adoption. For this thesis, we explored two techniques to overcome some of the challenges of experiencing VR when using HMDs. When experiencing VR with HMDs strapped to your head, even simple physical tasks like drinking a beverage can be difficult and awkward. We explored mixed reality renderings that selectively incorporate the physical world into the virtual world for interactions with physical objects. We conducted a user study comparing four rendering techniques that balance immersion in the virtual world with ease of interaction with the physical world. Users of VR systems often experience vection, the perception of self-motion in the absence of any physical movement. While vection helps to improve presence in VR, it often leads to a form of motion sickness called cybersickness. Prior work has discovered that changing vection (changing the perceived speed or moving direction) causes more severe cybersickness than steady vection (walking at a constant speed or in a constant direction). Based on this idea, we tried to reduce cybersickness caused by character movements in a First Person Shooter (FPS) game in VR. We propose Rotation Blurring (RB), uniformly blurring the screen during rotational movements to reduce cybersickness. We performed a user study to evaluate the impact of RB in reducing cybersickness and found that RB led to an overall reduction in sickness levels of the participants and delayed its onset. Participants who experienced acute levels of cybersickness benefited significantly from this technique

Larger Head Displacement to Optic Flow Presented in the Lower Visual Field

Optic flow that simulates self-motion often produces postural adjustment. Although literature has suggested that human postural control depends largely on visual inputs from the lower field in the environment, effects of the vertical location of optic flow on postural responses are not well investigated. Here, we examined whether optic flow presented in the lower visual field produces stronger responses than optic flow in the upper visual field. Either expanding or contracting optic flow was presented in upper, lower, or full visual fields through an Oculus Rift head-mounted display. Head displacement and vection strength were measured. Results showed larger head displacement under the optic flow presentation in the full visual field and the lower visual field than the upper visual field, during early period of presentation of the contracting optic flow. Vection was strongest in the full visual field and weakest in the upper visual field. Our findings of lower field superiority in head displacement and vection support the notion that ecologically relevant information has a particularly important role in human postural control and self-motion perception

Le rôle de l'intégration vestibulo-visuelle au sein du contrôle postural debout

Lors de ce projet de maîtrise, la contribution de l’intégration de l’information visuelle et vestibulaire sur le contrôle postural debout a été investiguée chez une population jeune et saine. Huit sujets (4 hommes; 4 femmes) furent soumis à diverses combinaisons de stimulation vestibulaire galvanique (SVG) et de stimulation optocinétique (rotation d’un nuage de point dans le plan frontal; SOC) impliquant 2 conditions visuelles (vision non-perturbée, nO; SOC droite, OS) et à 3 conditions vestibulaires (absence de stimulation, nG; SVG droite, GR; SVG gauche, GL). Ainsi, les 6 conditions expérimentales furent: absence de stimulation sensorielle (nG_nO), stimulation sensorielle indépendante (nG_OS, GR_nO and GL_nO) et combinée (GR_OS and GL_OS). Les mouvements angulaires de la tête et du tronc ainsi que du centre de pression (CoP) furent principalement évalués. Lors des conditions indépendantes de SVG (GR_nO et GL_nO), les résultats démontrent un déplacement de la tête, du tronc et du CoP en direction de l’anode. La nG_OS entraîne un déplacement angulaire comparable de la tête et du tronc vers la droite. La somme algébrique des réponses aux stimulations indépendantes (nG_OS et GR_nO) n’était pas significativement différente des résultats des stimulations combinées dans la même direction. Par ailleurs, la somme algébrique des stimulations nG_OS et GL_nO ne différait pas des stimulations combinées (GL_OS) ou de l’absence de stimulation (nG_nO). Finalement, les stimulations vestibulaires et visuelles ont entraîné une réponse posturale différente au niveau du CoP et les informations vestibulaires et visuelles semblent s’additionner de façon linéaire

The effects of rotating the self out of the body in the full virtual body ownership illusion

It has been shown that it is possible to induce a strong illusion that a virtual body (VB) is one's own body. However, the relative influence of a first-person-perspective (1PP) view of the VB and spatial coincidence of the real body and VB remains unclear. We demonstrate a method that permits separation of these two factors. It provides a 1PP view of a VB, supporting visuomotor synchrony between real body and VB movements, but where the entire scene including the body is rotated 15° upwards through the axis connecting the eyes, so that the VB and real body are coincident only through this axis. In a within-subjects study that compared this 15° rotation with a 0° rotation condition, participants reported only slightly diminished levels of perceived ownership of the VB in the rotated condition and did not detect the rotation of the scene. These results indicate that strong spatial coincidence of the virtual and real bodies is not necessary for a full-body ownership illusion. The rotation method used, similar to the effects of vertical prisms, did not produce significant negative side-effects, thus providing a useful methodology for further investigations of body ownership

Circular, linear, and curvilinear vection in a large-screen virtual environment with floor projection

Vection is defined as the compelling sensation of illusory self-motion elicited by a moving sensory, usually visual, stimulus. This paper presents collected introspective data, user discomfort and perceived speed data for the experience of linear, circular, and curvilinear vection in a large-screen, immersive, virtual environment. As a first step we evaluated the effectiveness of a floor projection on the perception of vection for four trajectories: linear forward, linear backward, circular left, and circular right. The floor projection, which considerably extended the field of view, was found to significantly improve the introspective measures of linear, but not circular, vection experienced in a photo-realistic three-dimensional town. In a second study we investigated the differences between 12 different motion trajectories on the illusion of self-motion. In this study we found that linear translations to the left and right are perceived as the least convincing, while linear down is perceived as the most convincing of the linear trajectories. Second, we found that while linear forward vection is not perceived to be very convincing, curvilinear forward vection is reported to be as convincing as circular vection. In a third and final experiment we investigated the perceived speed for all different trajectories and acquired data based on simulator sickness questionnaires to compute a discomfort factor associated with each type of trajectory. Considering our experimental results, we offer suggestions for increasing the sense of self-motion in simulators and VE applications, specifically to increase the number of curvilinear trajectories (as opposed to linear ones) and, if possible, add floor projection in order to improve the illusory sense of self-motion

Circular, Linear, and Curvilinear Vection in a Large-screen Virtual Environment with Floor Projection

Vection is defined as the compelling sensation of illusory self- motion elicited by a moving sensory, usually visual, stimulus. This paper presents collected introspective data on the experience of linear, circular, and curvilinear vection. We evaluate the differences between twelve different trajectories and the influence of the floor projection on the illusion of self-motion. All of the simulated self- motions examined are of a constant velocity, except for a brief simulated initial acceleration. First, we find that linear translations to the left and right are perceived as the least convincing, while linear down is perceived as the most convincing of the linear trajectories. Second, we find that the floor projection significantly improves the introspective measures of linear vection experienced in a photorealistic three-dimensional town. Finally, we find that while linear forward vection is not perceived to be very convincing, curvilinear forward vection is reported to be as convincing as circular vection. Considering our experimental results, our suggestions for simulators and VE applications where vection is desirable is to increase the number of curvilinear trajectories (as opposed to linear ones) and, if possible, add floor projection in order to improve the illusory sense of self-motion