Jean-Marie Normand

Extending body space in immersive virtual reality: a very long arm illusion

Recent studies have shown that a fake body part can be incorporated into human body representation through synchronous multisensory stimulation on the fake and corresponding real body part – the most famous example being the Rubber Hand Illusion. However, the extent to which gross asymmetries in the fake body can be assimilated remains unknown. Participants experienced, through a head-tracked stereo head-mounted display a virtual body coincident with their real body. There were 5 conditions in a between-groups experiment, with 10 participants per condition. In all conditions there was visuo-motor congruence between the real and virtual dominant arm. In an Incongruent condition (I), where the virtual arm length was equal to the real length, there was visuo-tactile incongruence. In four Congruent conditions there was visuo-tactile congruence, but the virtual arm lengths were either equal to (C1), double (C2), triple (C3) or quadruple (C4) the real ones. Questionnaire scores and defensive withdrawal movements in response to a threat showed that the overall level of ownership was high in both C1 and I, and there was no significant difference between these conditions. Additionally, participants experienced ownership over the virtual arm up to three times the length of the real one, and less strongly at four times the length. The illusion did decline, however, with the length of the virtual arm. In the C2–C4 conditions although a measure of proprioceptive drift positively correlated with virtual arm length, there was no correlation between the drift and ownership of the virtual arm, suggesting different underlying mechanisms between ownership and drift. Overall, these findings extend and enrich previous results that multisensory and sensorimotor information can reconstruct our perception of the body shape, size and symmetry even when this is not consistent with normal body proportions.

Camera Control in Computer Graphics

Recent progress in modelling, animation and rendering means that rich, high fidelity virtual worlds are found in many interactive graphics applications. However, the viewers experience of a 3D world is dependent on the nature of the virtual cinematography, in particular, the camera position, orientation and motion in relation to the elements of the scene and the action. Camera control encompasses viewpoint computation, motion planning and editing. We present a range of computer graphics applications and draw on insights from cinematographic practice in identifying their different requirements with regard to camera control. The nature of the camera control problem varies depending on these requirements, which range from augmented manual control (semi‐automatic) in interactive applications, to fully automated approaches. We review the full range of solution techniques from constraint‐based to optimization‐based approaches, and conclude with an examination of occlusion management and expressiveness in the context of declarative approaches to camera control.

Multisensory stimulation can induce an illusion of larger belly size in immersive virtual reality.

Background Body change illusions have been of great interest in recent years for the understanding of how the brain represents the body. Appropriate multisensory stimulation can induce an illusion of ownership over a rubber or virtual arm, simple types of out-of-the-body experiences, and even ownership with respect to an alternate whole body. Here we use immersive virtual reality to investigate whether the illusion of a dramatic increase in belly size can be induced in males through (a) first person perspective position (b) synchronous visual-motor correlation between real and virtual arm movements, and (c) self-induced synchronous visual-tactile stimulation in the stomach area. Methodology Twenty two participants entered into a virtual reality (VR) delivered through a stereo head-tracked wide field-of-view head-mounted display. They saw from a first person perspective a virtual body substituting their own that had an inflated belly. For four minutes they repeatedly prodded their real belly with a rod that had a virtual counterpart that they saw in the VR. There was a synchronous condition where their prodding movements were synchronous with what they felt and saw and an asynchronous condition where this was not the case. The experiment was repeated twice for each participant in counter-balanced order. Responses were measured by questionnaire, and also a comparison of before and after self-estimates of belly size produced by direct visual manipulation of the virtual body seen from the first person perspective. Conclusions The results show that first person perspective of a virtual body that substitutes for the own body in virtual reality, together with synchronous multisensory stimulation can temporarily produce changes in body representation towards the larger belly size. This was demonstrated by (a) questionnaire results, (b) the difference between the self-estimated belly size, judged from a first person perspective, after and before the experimental manipulation, and (c) significant positive correlations between these two measures. We discuss this result in the general context of body ownership illusions, and suggest applications including treatment for body size distortion illnesses.

How to Build an Embodiment Lab: Achieving Body Representation Illusions in Virtual Reality

Advances in computer graphics algorithms and virtual reality (VR) systems, together with the reduction in cost of associated equipment, have led scientists to consider VR as a useful tool for conducting experimental studies in fields such as neuroscience and experimental psychology. In particular virtual body ownership, where the feeling of ownership over a virtual body is elicited in the participant, has become a useful tool in the study of body representation, in cognitive neuroscience and psychology, concerned with how the brain represents the body. Although VR has been shown to be a useful tool for exploring body ownership illusions, integrating the various technologies necessary for such a system can be daunting. In this paper we discuss the technical infrastructure necessary to achieve virtual embodiment. We describe a basic VR system and how it may be used for this purpose, and then extend this system with the introduction of real-time motion capture, a simple haptics system and the integration of physiological and brain electrical activity recordings.

Virtual camera planning: a survey

Modelling, animation and rendering has dominated research computer graphics yielding increasingly rich and realistic virtual worlds. The complexity, richness and quality of the virtual worlds are viewed through a single media that is a virtual camera. In order to properly convey information, whether related to the characters in a scene, the aesthetics of the composition or the emotional impact of the lighting, particular attention must be given to how the camera is positioned and moved. This paper presents an overview of automated camera planning techniques. After analyzing the requirements with respect to shot properties, we review the solution techniques and present a broad classification of existing approaches. We identify the principal shortcomings of existing techniques and propose a set of objectives for research into automated camera planning.

Moments of the characteristic polynomial in the three ensembles of random matrices

Moments of the characteristic polynomial of a random matrix taken from any of the three ensembles, orthogonal, unitary or symplectic, are given either as a determinant or a Pfaffian or as a sum of determinants. For Gaussian ensembles, on comparing two expressions of the same moment one obtains two remarkable identities, one between an n×n determinant and an m×m determinant and another between the Pfaffian of a 2n×2n anti-symmetric matrix and a sum of m×m determinants.

A Semantic Space Partitioning Approach to Virtual Camera Composition

In this paper, we present a semantic space partitioning (SSP) approach to the virtual camera composition problem. Virtual camera composition (VCC) consists in positioning a camera in a virtual world, such that the resulting image satises a set of visual cinematographic properties. Whereas most related works concentrate on numerically computing a unique camera position satisfying the problem, we offer to isolate identical possible solutions in 3D volumes with respect to their visual properties, and to propose them to the user. We introduce the notion of semantic volumes as an extension of visual aspects to characterize, compute and manipulate distinct solution sets. Our approach relies on (1) a space partitioning process derived from a study of possible camera locations w.r.t. to the objects in the scene and (2) local search numerical techniques to compute good representatives of each volume. This work is motivated by the lack of VCC tools in 3D software and the will to integrate cinematographic semantics in the description, solving and interaction processes. Experimental results illustrate the suitability of our approach for identifying and providing distinct solution sets. Furthermore, the exploitation of the semantic volumes lays the groundwork for natural and efcient user interaction by providing knowledge and reasoning on possible classes of solutions.

Probability density of the determinant of a random Hermitian matrix

The probability density function for the determinant of a nn random Hermitian matrix taken from the Gaussian unitary ensemble is calculated. It is found to be a Meijer G- function or a linear combination of two Meijer G-functions, depending on the parity of n. The integer moments of this probability density are also given.

Real time whole body motion mapping for avatars and robots

We describe a system that allows for controlling different robots and avatars from a real time motion stream. The underlying problem is that motion data from tracking systems is usually represented differently to the motion data required to drive an avatar or a robot: there may be different joints, motion may be represented by absolute joint positions and rotations or by a root position, bone lengths and relative rotations in the skeletal hierarchy. Our system resolves these issues by remapping in real time the tracked motion so that the avatar or robot performs motions that are visually close to those of the tracked person. The mapping can also be reconfigured interactively at run-time. We demonstrate the effectiveness of our system by case studies in which a tracked person is embodied as an avatar in immersive virtual reality or as a robot in a remote location. We show this with a variety of tracking systems, humanoid avatars and robots.

Beaming into the Rat World: Enabling Real-Time Interaction between Rat and Human Each at Their Own Scale

Immersive virtual reality (IVR) typically generates the illusion in participants that they are in the displayed virtual scene where they can experience and interact in events as if they were really happening. Teleoperator (TO) systems place people at a remote physical destination embodied as a robotic device, and where typically participants have the sensation of being at the destination, with the ability to interact with entities there. In this paper, we show how to combine IVR and TO to allow a new class of application. The participant in the IVR is represented in the destination by a physical robot (TO) and simultaneously the remote place and entities within it are represented to the participant in the IVR. Hence, the IVR participant has a normal virtual reality experience, but where his or her actions and behaviour control the remote robot and can therefore have physical consequences. Here, we show how such a system can be deployed to allow a human and a rat to operate together, but the human interacting with the rat on a human scale, and the rat interacting with the human on the rat scale. The human is represented in a rat arena by a small robot that is slaved to the human’s movements, whereas the tracked rat is represented to the human in the virtual reality by a humanoid avatar. We describe the system and also a study that was designed to test whether humans can successfully play a game with the rat. The results show that the system functioned well and that the humans were able to interact with the rat to fulfil the tasks of the game. This system opens up the possibility of new applications in the life sciences involving participant observation of and interaction with animals but at human scale.