The use of PC based VR in clinical medicine: the VREPAR projects

Virtual reality (VR) is an emerging technology that alters the way individuals interact with computers: a 3D computer-generated environment in which a person can move about and interact as if he actually was inside it. Given to the high computational power required to create virtual environments, these are usually developed on expensive high-end workstations. However, the significant advances in PC hardware that have been made over the last three years, are making PC-based VR a possible solution for clinical assessment and therapy. VREPAR - Virtual Reality Environments for Psychoneurophysiological Assessment and Rehabilitation - are two European Community funded projects (Telematics for health - HC 1053/HC 1055 - http://www.psicologia.net) that are trying to develop a modular PC-based virtual reality system for the medical market. The paper describes the rationale of the developed modules and the preliminary results obtained.

Gaze angle: a possible mechanism of visual stress in virtual reality headsets

It is known that some Virtual Reality (VR) head-mounted displays (HMDs) can cause temporary deficits in binocular vision. On the other hand, the precise mechanism by which visual stress occurs is unclear. This paper is concerned with a potential source of visual stress that has not been previously considered with regard to VR systems: inappropriate vertical gaze angle. As vertical gaze angle is raised or lowered the 'effort' required of the binocular system also changes. The extent to which changes in vertical gaze angle alter the demands placed upon the vergence eye movement system was explored. The results suggested that visual stress may depend, in part, on vertical gaze angle. The proximity of the display screens within an HMD means that a VR headset should be in the correct vertical location for any individual user. This factor may explain some previous empirical results and has important implications for headset design. Fortuitously, a reasonably simple solution exists.

Aftereffects and sense of presence in virtual environments: formulation of a research and development agenda

This report represents a committee summary of the current state of knowledge regarding aftereffects and sense of presence in virtual environments (VEs). The work presented in this article, and the proposed research agenda, are the result of a special session that was set up in the framework of the Seventh International Conference on Human Computer Interaction. Recommendations were made by the committee regarding research needs in aftereffects and sense of presence, and, where possible, priorities were suggested. The research needs were structured in terms of the short, medium, and long term and, if followed, should lead toward the effective use of VE technology. The 2 most critical research issues identified were (a) standardization and use of measurement approaches for aftereffects and (b) identification and prioritization of sensorimotor discordances that drive aftereffects. Identification of aftereffects countermeasures (i.e., techniques to assist users in readily transitioning between the real and virtual worlds), reduction of system response latencies, and improvements in tracking technology were also thought to be of critical importance.

Virtual reality environments for psycho-neuro-physiological assessment and rehabilitation

Virtual Reality Environments for Psychoneurophysiological Assessment and Rehabilitation-is an European Community funded project (Telematics for health-HC 1053 http:/(/)www.etho.be/ht_projects/vrepar/) whose aim is: to develop a PC based virtual reality system (PC-VRS) for the medical market that can be marketed at a price which is accessible to its possible end-users (hospitals, universities and research centres) and which would have the modular, connectability and interoperability characteristics that the existing systems lack; to develop three hardware/software modules for the application of the PC VRS in psychoneurophysiological assessment and rehabilitation. The chosen development areas are eating disorders (bulimia, anorexia and obesity), movement disorders (Parkinson's disease and torsion dystonia) and stroke disorders (unilateral neglect and hemiparesis). This paper presents the rationale of the different approaches and the methodology used.

Relation between velocity and curvature in movement: equivalence and divergence between a power law and a minimum-jerk model

Unconstrained hand movements typically display a decrease in hand speed around highly curved sections of a trajectory. It has been suggested that this relation between tangential velocity and radius of curvature conforms to a one-third power law. We demonstrate that a one-third power law can be explained by models taking account of trajectory costs such as a minimum-jerk model. Data were analyzed from 6 subjects performing elliptical drawing movements of varying eccentricities. Conformity to the one-third power law in the average was obtained but is shown to be artifactual. It is demonstrated that asymmetric velocity profiles may result in consistent departures from a one-third power law but that such differences may be masked by inappropriate analysis procedures. We introduce a modification to the original minimum-jerk model by replacing the assumption of a Newtonian point-mass with a visco-elastic body. Simulations with the modified model identify a basis for asymmetry of velocity profiles and thereby predict departures from a one-third law commensurate with the empirical findings.