Tuning of the Level of Presence (LOP)

One of the goals and defining characteristics of virtual reality systems is to create “presence”, that is, to leave the user with the feeling of having been (or having done something) “in” the virtual environment as much as possible. While there has been much research work focused on identifying different factors that affect presence, it is still not clear how to effectively combine these results to create a content with high presence with respect to a given hardware setup, limited computing resource, and content dynamics. Along this line of thinking, this paper proposes for the concept of “Level of Presence (LOP)”, analogous to the “Level of Detail”, in which we attempt to select a set of “computational” presence elements and their levels to maximize their “contribution” toward the overall presence subject to system resources and possibly other constraints. Such an optimization scheme would require a reasonable characterization of the computational costs and a sufficient knowledge of the relative merits of various presence elements. While much research still remain to find a general model of presence, we made an attempt to apply the LOP concept to the VR system design for a particular application, a virtual fish tank. We selected two possibly important presence elements, the FOV and the simulation level of detail, and quantified their costs in terms of the required computation time. Then, we ran a simple experiment to quantify the relative benefits (or contribution toward the overall presence) of those two presence factors. For this particular application, it was found that providing more lifelike fish movements, for instance, incurred needlessly expensive computations compared to the amount of increased benefit. Based on the result, the virtual fish tank was configured for maximum presence while meeting various conditions including the required frame rate and content requirement (e.g. fixed number of fishes).