A necessary part of developing effective and realistic Virtual Reality (VR) simulations is emulating perceptual sensations that occur to humans in corresponding natural environments. VR users are often seated and unable to freely move through the virtual world, therefore necessitating other means to simulate and perceive self-movement. One approach to tackle this challenge is to induce embodied illusions of self-motion ("vection") in stationary observers, typically by providing moving visual stimuli on a wide field-of-view display. While numerous stimulus parameters have been shown to affect vection [see Riecke, 2011 for a review], there is little research investigating how the type of display itself might contribute. Here, we compared the vection-inducing potential as well as user experience and usability of two common displays for large-field stimulation: A passive stereoscopic projection setup and a 3D television with shutter glasses. Uncovering differences in vection between these displays would contribute to the theoretical understanding of vection and the potential relevance of different display properties, and guide the development of more immersive and effective VR setups. From a practical standpoint, this study helps to determine whether the more expensive projection system provides a benefit over the more accessible and affordable 3D television.

Can self-motion perception in virtual reality (VR) be enhanced by providing affordable, user-powered minimal motion cueing? To investigate this, we compared the effect of different interaction and motion paradigms on onset latency and intensity of self-motion illusions ("vection") induced by curvilinear locomotion in projection-based VR. Participants either passively observed the simulation or had to actively follow pre-defined trajectories of different curvature in a simple virtual scene. Visual-only locomotion (either passive or with joystick control) was compared to locomotion controlled by a modified Gyroxus gaming chair, where leaning forwards and sideways (±10cm) controlled simulated translations and rotations, respectively, using a velocity control paradigm similar to a joystick. In the active visual+chair motion condition, participants controlled the chair motion and resulting virtual locomotion themselves, without the need for external actuation. In the passive visual+chair motion condition, the experimenter did this. Self-motion intensity was increased in the visual+chair motion conditions as compared visual-only motion, corroborating the benefit of simple motion cueing. Surprisingly, however, active control reduced the occurrence of vection and increased vection onset latencies, especially in the chair motion condition. This might be related to the reduced intuitiveness and controllability observed for the active chair motion as compared to the joystick condition. Together, findings suggest that simple user-initiated motion cueing can in principle provide an affordable means of increasing self-motion simulation fidelity in VR. However, usability and controllability issues of the gaming chair used might have counteracted the benefit of such motion cueing, and suggests ways to improve the interaction paradigm.

When we locomote through real or virtual environments, self-to-object relationships constantly change. Nevertheless, in real environments we effortlessly maintain an ongoing awareness of roughly where we are with respect to our immediate surrounds, even in the absence of any direct perceptual support (e.g., in darkness or with eyes closed). In virtual environments, however, we tend to get lost far more easily. Why is that? Research suggests that physical motion cues are critical in facilitating this “automatic spatial updating” of the self-to-surround relationships during perspective changes. However, allowing for full physical motion in VR is costly and often unfeasible. Here, we demonstrated for the first time that the mere illusion of self-motion (“circular vection”) can provide a similar benefit as actual self-motion: While blindfolded, participants were asked to imagine facing new perspectives in a well-learned room, and point to previously-learned objects. As expected, this task was difficult when participants could not physically rotate to the instructed perspective. Performance was significantly improved, however, when they perceived illusory self-rotation to the novel perspective (even though they did not physically move). This circular vection was induced by a combination of rotating sound fields (“auditory vection”) and biomechanical vection from stepping along a carrousel-like rotating floor platter. In summary, illusory self-motion was shown to indeed facilitate perspective switches and thus spatial orientation. These findings have important implications for both our understanding of human spatial cognition and the design of more effective yet affordable VR simulators. In fact, it might ultimately enable us to relax the need for physical motion in VR by intelligently utilizing self-motion illusions.

Most virtual reality simulators have a serious flaw: Users tend to get easily lost and disoriented as they navigate. According to the prevailing opinion, this is because of the lack of actual physical motion to match the visually simulated motion: E.g., using HMD-based VR, Klatzky et al. [1] showed that participants failed to update visually simulated rotations unless they were accompanied by physical rotation of the observer, even if passive. If we use more naturalistic environments (but no salient landmarks) instead of just optic flow, would physical motion cues still be needed to prevent disorientation? To address this question, we used a paradigm inspired by Klatzky et al.: After visually displayed passive movements along curved streets in a city environment, participants were asked to point back to where they started. In half of the trials the visually displayed turns were accompanied by a matching physical rotation. Results showed that adding physical motion cues did not improve pointing performance. This suggests that physical motions might be less important to prevent disorientation if visuals are naturalistic enough. Furthermore, unexpectedly two participants consistently failed to update the visually simulated heading changes, even when they were accompanied by physical rotations. This suggests that physical motion cues do not necessarily improve spatial orientation ability in VR (by inducing obligatory spatial updating). These findings have noteworthy implications for the design of effective motion simulators.

The use of vection, the illusion of self-movement, has recently been explored as a novel way to immerse observers in mediated environments through illusory yet compelling self-motion without physically moving. This provides advantages over existing systems that employ costly, cumbersome, and potentially hazardous motion platforms, which are often surprisingly inadequate to provide life-like motion experiences. This study investigates whether spatialized sound rotating around the stationary, blindfolded listener can facilitate biomechanical vection, the illusion of self-rotation induced by stepping along a rotating floor plate. For the first time, integrating simple auditory and biomechanical cues for turning in place evoked convincing circular vection. In an auditory baseline condition, participants experienced only spatialized auditory cues. In a purely biomechanical condition, seated participants stepped along sideways on a rotating plate while listening to mono masking sounds. Scores of the bi-modal condition (binaural+biomechanical cues) exceeded the sum of both single cue conditions, which may imply super-additive or synergistic effects.

Sound fields rotating around stationary blindfolded listeners sometimes elicit auditory circular vection, the illusion that the listener is physically rotating. Experiment 1 investigated whether auditory circular vection depends on participants' situational awareness of “movability,” that is, whether they sense/know that actual motion is possible or not. While previous studies often seated participants on movable chairs to suspend the disbelief of self-motion, it has never been investigated whether this does, in fact, facilitate auditory vection. To this end, 23 blindfolded participants were seated on a hammock chair with their feet either on solid ground (“movement impossible”) or suspended (“movement possible”) while listening to individualized binaural recordings of two sound sources rotating synchronously at 60°/s. Although participants never physically moved, situational awareness of movability facilitated auditory vection. Moreover, adding slight vibrations like the ones resulting from actual chair rotation increased the frequency and intensity of vection. Experiment 2 extended these findings and showed that nonindividualized binaural recordings were as effective in inducing auditory circular vection as individualized recordings. These results have important implications both for our theoretical understanding of self-motion perception and for the applied field of self-motion simulations, where vibrations, nonindividualized binaural sound, and the cognitive/perceptual framework of movability can typically be provided at minimal cost and effort.