Using the perceptually oriented approach to optimize spatial presence ego-motion simulation

This chapter is concerned with the perception and simulation of ego-motion in virtual environments, and how spatial presence and other higher cognitive and top-down factors can contribute to improve the illusion of ego-motion in virtual reality (VR). In the real world, we are used to being able to move around freely and interact with our environment in a natural and effortless manner. Current VR technology does, however, not yet allow for natural, real-life-like interaction between the user and the virtual environment. One crucial shortcoming in current VR is the insufficient and often unconvincing simulation of ego-motion, which frequently causes disorientation, unease, and motion sickness. We posit that a realistic perception of ego-motion in VR is a fundamental constituent for spatial presence and vice versa. Thus, by improving both spatial presence and ego-motion perception in VR, we aim to eventually enable performance levels in VR similar to the real world for basic tasks, e.g., spatial orientation and distance perception, which are currently very problematic cases. Users frequently get lost easily in VR while navigating, and simulated distances appear to be compressed and underestimated compared to the real world (Witmer & Sadowski, 1998; Chance, Gaunet, Beall, & Loomis, 1998; Creem-Regehr, Willemsen, Gooch, and Thompson, 2003; Knapp, 1999; Thompson, Willemsen, Gooch, Creem-Regehr, Loomis, & Beall, 2004, Stanney, 2002). The overall goal of the EU-funded project on “Perceptually Oriented Ego-Motion Simulation” (POEMS-IST-2001-39223, see www.poems-project.info) has been to take first steps towards establishing a lean and elegant ego-motion simulation paradigm to achieve convincing ego-motion perception and effective ego-motion simulation in VR, without (or while hardly) moving the user physically. The ultimate goal is to achieve cost-efficient, ego-motion simulation that enables compelling perception of self-motion and quick, intuitive, and robust spatial orientation while travelling in VR, with performance similar to the real world. The POEMS approach to tackle this goal was to concentrate on perceptual aspects and task-specific effectiveness rather than aiming for perfect physical realism (see Section 2). This approach focuses on multi-modal stimulation of our senses, where vision, auditory information, and vibrations let users perceive that they are moving in space. Furthermore, top-down or high-level phenomena like spatial presence and reference frames are utilized to improve the effectiveness of ego-motion simulation. It is well-known that quite compelling ego-motion illusions can occur both in the real world and in VR. Hence, the investigation of such ego-motion illusions in VR was used as a starting point for improving self-motion simulations in VR. Spatial presence and immersion occupy an important role in this context, as they are expected to be an essential factor in enabling robust and effortless spatial orientation and task performance. Furthermore, according to our current spatial orientation framework (von der Heyde & Riecke, 2002, Riecke & von der Heyde, 2002), we propose that spatial presence and immersion are necessary prerequisites for quick, robust, and effortless spatial orientation behaviour and also for automatic spatial updating in particular. Thus, increasing spatial presence and immersion would in turn be expected to increase the overall convincingness and perceived realism of the simulation, bringing us one step closer to our ultimate goal of real world-like interaction with and navigation through the virtual environment. In our psychophysical experiments, the observed data suggest a direct relation between spatial presence and the strength of the self-motion illusion in VR: Experimental data from two ego-motion perception experiments will be reported in more detail in Section 3 and 4, where a systematic link between spatial presence ratings and ego-motion perception responses was observed. This finding is important, both from an applied perspective of self-motion simulation, and for our understanding of presence and of self-motion perception.