A Theoretical Approach of the Design and Evaluation of a Virtual Reality Device

The majority of virtual reality researches mainly tackle the problems of modeling and digitalization of the virtual world. On interfacing man and the virtual world, few studies analyze theoretically these problems, with introduction of new concepts and new methods: behavioral interfaces, three levels of immersion and interaction (sensorimotor, mental and functional), the mental immersion based on the schemas, the behavioral software assistance In this article, we propose a theoretical and pragmatic approach for the design and the evaluation of a virtual reality device, with two examples: the virtual reality training on infrastructures railway and the study of the behavior of consumer in a virtual store. 1 Theoretical approach of virtual reality 1.1. Bases of reality virtual We expose different levels of definitions which enable to clarify the field of virtual reality, by separating its finality from its functional and technical definitions. 1.1.1. Definitions of virtual reality The finality of virtual reality is to allow one or several people to do sensorimotor, and thus mental, experiments in an artificial world, which is either imaginary, or a simulation of some aspects of the real world. The fields of the real world, which must be simulated, are to be determined during the stage of design. This initial stage is fundamental and must be explicitly analyzed. The principal error is that the designer seeks the greatest "degree of realism" (limited in practice by technical and economic constraints) without worrying to know precisely the fields of the reality which the application requires. It is absurd to wish the behavior of the virtual world entirely identical of the real world is absurd. If we want to make a " virtual " reality, it is with an aim of modifying some fields of the " true " reality. For example: training of people in a virtual world in order to avoid real risks to them, studying a future product which is thus not materialized yet, etc. But if a simulation represents only part of reality, virtual reality also enables to simulate differently some physical phenomena, " the realism " going beyond " true " reality: physical, invisible phenomena by the human senses (radioactivity, infra-reds, etc.) can be virtually represented. the images of the objects in boundary representation can be more comprehensible. Virtual Reality (VR) can be also exploited to represent concepts, structures and symbolic entities, associated with the simulated real world. Those allow the user to have a better mental representation of its environment. The functional definition enables us to specify the field of the VR applications: with his own perception of reality, man discerns the concepts of time and space on which he