A fundamental principle of virtual reality is the crafting of illusion which immerses and guides users. In contrast to the ample work on visual illusions and VR, auditory illusions remain relatively understudied. We are particularly interested in how VR can leverage auditory stimuli to manipulate user movement and perception of movement. Here we conduct trials to study how the sounds of footsteps can be manipulated to give the impression of upwards or downwards incline during walking, and how this compares to visual stimuli. We do so by crafting Shepard tone imbued footstep sounds which exploit the cross-modal correspondence between auditory pitch and elevation. We found that while our chosen visual stimuli were considerably more powerful, our footstep sounds still shifted the perception of movement direction, including when they contradicted the direction of visual stimuli. This study opens new research possibilities on how other auditory illusions can influence movement. The Shepard footsteps themselves have direct application in environments where the user must explore the vertical dimension of a 3D space.

Standard virtual reality (VR) controllers often provide limited tactile feedback, which can detract from player immersion and the seamlessness of interactions diminishing the overall experience. This paper evaluates MUHI - a Multi-Use Haptic Interface, which is a novel passive haptic tool designed to enhance player experience by convincingly simulating multiple virtual tools through its distinct physical handles. These tools are central to a series of playable mini-games embedded within a narrative-driven, redirected walking (RDW) based VR experience. The experience incorporates the RDW related drift, such that the temporarily stationary physical prop MUHI can represent various virtual tools in different parts of the virtual environment. The core investigation focuses on how integrating tangible, tool-based interactions via MUHI into these minigames enhances the game experience and immersive qualities, potentially concealing the RDW resets incidentally. A user study (N=17) compared the experience of playing the VR game with MUHI against a standard VR controller. Results demonstrate that MUHI significantly enhanced user enjoyment and increased reported presence scores. These findings suggest that specialized passive haptic interfaces like MUHI can substantially improve player engagement and the overall experience in VR applications, particularly by making core game mechanics, including those designed to mask RDW resets, more interactive and compelling.

Augmented Virtuality integrates physical content into virtual environments, but the occlusion of physical by virtual content is a challenge. This unwanted occlusion may disrupt user interactions with physical devices and compromise safety and usability. This paper investigates two resolution strategies to address this issue: Redirected Walking, which subtly adjusts the user’s movement to maintain physical-virtual alignment, and Automatic Teleport Rotation, which realigns the virtual environment during travel. A user study set in a virtual forest demonstrates that both methods effectively reduce occlusion. While in our testbed, Automatic Teleport Rotation achieves higher occlusion resolution, it is suspected to increase cybersickness compared to the less intrusive Redirected Walking approach.

Several redirected walking techniques have been introduced and analyzed in recent years, while the main focus was on manipulations in horizontal directions, in particular, by means of curvature, rotation, and translation gains. However, less research has been conducted on the manipulation of vertical movements and its possible use as a redirection technique. Actually, vertical movements are fundamentally important, e.g., for remotely steering a drone using a virtual reality headset.In this paper, we explored vertical gains, a novel redirection technique, which enables us to purposefully manipulate the mapping of the user’s physical vertical movements to movements in the virtual space and the remote space. This approach allows natural and more active physical control of a real drone. To demonstrate the usability of vertical gains, we implemented a telepresence drone and vertical redirection techniques for stretching and crouching actions using common VR devices. We conducted two user studies to investigate the effective manipulation ranges and its usability: one study using a virtual environment (VE), and one using a camera stream from a telepresence drone. The results revealed that our technique could manipulate a users vertical movement without her/his noticing.

Redirected walking (RDW) enables virtual reality (VR) users to explore large virtual environments (VE) in confined tracking spaces by guiding users on different paths in the real world than in the VE. However, so far, spaces larger than typical room-scale setups of 5m × 5m are still required to allow infinitely straight walking, i. e., to prevent a subjective mismatch between real and virtual paths. This mismatch could in theory be reduced by interacting with the underlying brain activity. Transcranial direct-current stimulation (tDCS) presents a simply method able to modify ongoing cortical activity and excitability levels. Hence, this approach provides enormous potential to widen detection thresholds for RDW, and consequently reduce the above mentioned space requirements. In this paper, we conducted a psychophysical experiment using tDCS to evaluate detection thresholds for RDW gains. In the stimulation conditon 1.25 mA cathodal tDCS were applid over the prefrontal cortex (AF4 with Pz for the return current) for 20 minutes. TDCS failed to exert a significant overall effect on detection thresholds. However, for the highest gain only, path deviance was significantly modified by tDCS. In addition, subjectively reported disorientation was significantly lower during the tDCS as compared to the sham condition. Along the same line, oculomotor cyber sickness symptoms after the session were significantly decreased compared to baseline in tDCS, while there was no significant effect in sham. This work presents the first use of tDCS during virtual walking which provides new vistas for future research in the area of neurostimulation in VR.

Redirected walking (RDW) allows virtual reality (VR) users to walk infinitely while staying inside a finite physical space through subtle shifts (gains) of the scene to redirect them back inside the volume. All prior approaches measure the feasibility of RDW techniques based on if the user perceives the manipulation, leading to rather small applicable gains. However, we treat RDW as an interaction technique and therefore use visually perceivable gains instead of using the perception of manipulation. We revisited prior experiments with focus on applied gains and additionally tested higher gains on the basis of applicability in a user study. We found that users accept curvature gains up to 20°/m, which reduces the necessary physical volume down to approximately 6x6m for virtually walking infinitely straight ahead. Our findings strife to rethink the usage of redirection from being unperceived to being applicable and natural.

Redirected walking allows users to explore immersive virtual environments by real walking even when the physical tracking space is limited. Redirected walking is usually implemented via translation gains, rotation gains, and curvature gains, while previous research was focused on identifying detection thresholds for such manipulations. To our knowledge, all previous experiments were conducted without a visual self-representation of the user in the virtual environment, in particular, without showing the user's feet. In this paper, we address the question if the virtual self-representation of the user's feet changes the detection thresholds for translation gains. Furthermore, we consider the influence of the holisticness of the visual stimulus, i. e., the type of virtual environment. Therefore, we conducted an experiment to identify detection thresholds for translation gains under three different conditions: (i) without visible virtual feet and (ii) with visible virtual feet both in a high fidelity visually rich virtual environment, and (iii) with visible virtual feet in a low cue virtual environment. The results revealed the range of detection thresholds for translations gains, which cannot be detected by the user when the feet are visible. Furthermore, the results show a significant difference between the two types of environment. Our findings suggest that the virtual environment is more important for manipulation detection than the visual self-representation of the user's feet.

Real walking in virtual reality (VR) is a promising locomotion technique since it offers multi-modal feedback to the user. Unfortunately, the virtual environment (VE) is limited by the available space in the physical world. So far, several techniques were developed to overcome this problem, e. g. redirected walking (RDW) and the use of impossible spaces. RDW subtly manipulates the viewpoint of the user to reorient her walking direction. Impossible spaces are based on subtle changes of the VE to reuse the same physical space for different virtual spaces. In this research demonstration, we show how these two approaches of redirected walking and impossible spaces can be combined. In particular, for our implementation we focus on the use of curved corridors that benefits both methods.

Immersive computer-generated environments (aka virtual reality, VR ) are limited by the physical space around them, e.g., enabling natural walking in VR is only possible by perceptually-inspired locomotion techniques such as redirected walking (RDW). We introduce a completely new approach to imperceptible position and orientation redirection that takes advantage of the fact that even healthy humans are functionally blind for circa ten percent of the time under normal circumstances due to motor processes preventing light from reaching the retina (such as eye blinks) or perceptual processes suppressing degraded visual information (such as blink-induced suppression). During such periods of missing visual input, change blindness occurs, which denotes the inability to perceive a visual change such as the motion of an object or self-motion of the observer. We show that this phenomenon can be exploited in VR by synchronizing the computer graphics rendering system with the human visual processes for imperceptible camera movements, in particular to implement position and orientation redirection. We analyzed human sensitivity to such visual changes with detection thresholds, which revealed that commercial off-the-shelf eye trackers and head-mounted displays suffice to translate a user by circa 4 -- 9 cm and rotate the user by circa 2 -- 5 degrees in any direction, which could be accumulated each time the user blinks. Moreover, we show the potential for RDW, whose performance could be improved by approximately 50% when using our technique.

Telepresence systems have the potential to overcome limits and distance constraints of the real-world by enabling people to remotely visit and interact with each other. However, current telepresence systems usually lack natural ways of supporting interaction and exploration of remote environments (REs). In particular, single webcams for capturing the RE provide only a limited illusion of spatial presence, and movement control of mobile platforms in today's telepresence systems are often restricted to simple interaction devices. One of the main challenges of telepresence systems is to allow users to explore a RE in an immersive, intuitive and natural way, e.g., by real walking in the user's local environment (LE), and thus controlling motions of the robot platform in the RE. However, the LE in which the user's motions are tracked usually provides a much smaller interaction space than the RE. In this context, redirected walking (RDW) is a very suitable approach to solve this problem. However, so far there is no previous work, which explored if and how RDW can be used in video-based 360° telepresence systems. In this article, we conducted two psychophysical experiments in which we have quantified how much humans can be unknowingly redirected on virtual paths in the RE, which are different from the physical paths that they actually walk in the LE. Experiment 1 introduces a discrimination task between local and remote translations, and in Experiment 2 we analyzed the discrimination between local and remote rotations. In Experiment 1 participants performed straightforward translations in the LE that were mapped to straightforward translations in the RE shown as 360° videos, which were manipulated by different gains. Then, participants had to estimate if the remotely perceived translation was faster or slower than the actual physically performed translation. Similarly, in Experiment 2 participants performed rotations in the LE that were mapped to the virtual rotations in a 360° video-based RE to which we applied different gains. Again, participants had to estimate whether the remotely perceived rotation was smaller or larger than the actual physically performed rotation. Our results show that participants are not able to reliably discriminate the difference between physical motion in the LE and the virtual motion from the 360° video RE when virtual translations are down-scaled by 5.8% and up-scaled by 9.7%, and virtual rotations are about 12.3% less or 9.2% more than the corresponding physical rotations in the LE.

Our study investigates the effects of (non-)isometric mappings between physical movements and virtual motions in the virtual environment (VE) on walking biomechanics of older adults. Three primary domains (pace, base of support and phase) of spatio-temporal and temporo-phasic parameters were used to evaluate gait performance. Our results show similar results in pace and phasic domains when older adults walk in the VE in the isometric mapping condition compared to the corresponding parameters in the real world. We found significant differences in base of support for our user group between walking in the VE and real world. For non-isometric mappings we found an increased divergence of gait parameters in all domains correlating with the up-or down-scaled velocity of visual self-motion feedback.

Redirected walking (RDW) promises to allow near-natural walking in an infinitely large virtual environment (VE) by subtle manipulations of the virtual camera. Previous experiments showed that a physical radius of at least 22 meters is required for undetectable RDW. However, we found that it is possible to decrease this radius and to apply RDW to room-scale VR, i. e., up to approximately 5m × 5m. This is done by using curved paths in the Ve instead of straight paths, and by coupling them together in a way that enables continuous walking. Furthermore, the corresponding paths in the real world are laid out in a way that fits perfectly into room-scale VR. In this research demo, users can experience RDW in a room-scale head-mounted display VR setup and explore a VE of approximately 25m × 25m.

Walking constitutes the predominant form of self-propelled movement from one geographic location to another in our real world. Likewise, walking in virtual environments (VEs) is an essential part of a users experience in many application domains requiring a high degree of interactivity. However, researchers and practitioners often observe that basic implementations of virtual walking, in which head-tracked movements are mapped isometrically to a VE are not estimated as entirely natural. Instead, users estimate a virtual walking velocity as more natural when it is slightly increased compared to the users physical body movement. In this article, we investigate the effects of such nonisometric mappings between physical movements and virtual motions in the VE on walking velocity and biomechanics of the gait cycle. Therefore, we performed an experiment in which we measured and analyzed parameters of the biomechanics of walking under conditions with isometric as well as nonisometric mappings. Our results show significant differences in most gait parameters when walking in the VE in the isometric mapping condition compared to the corresponding parameters in the real world. For nonisometric mappings we found an increased divergence of gait parameters depending on the velocity of visual self-motion feedback. The results revealed a symmetrical effect of gait detriments for up- or down-scaled virtual velocities, which we discuss in the scope of the previous findings.

Redirected walking (RDW) promises to allow near-natural walking in an infinitely large virtual environment (VE) by subtle manipulations of the virtual camera. Previous experiments analyzed the human sensitivity to RDW manipulations by focusing on the worst-case scenario, in which users walk perfectly straight ahead in the VE, whereas they are redirected on a circular path in the real world. The results showed that a physical radius of at least 22 meters is required for undetectable RDW. However, users do not always walk exactly straight in a VE. So far, it has not been investigated how much a physical path can be bent in situations in which users walk a virtual curved path instead of a straight one. Such curved walking paths can be often observed, for example, when users walk on virtual trails, through bent corridors, or when circling around obstacles. In such situations the question is not, whether or not the physical path can be bent, but how much the bending of the physical path may vary from the bending of the virtual path. In this article, we analyze this question and present redirection by means of bending gains that describe the discrepancy between the bending of curved paths in the real and virtual environment. Furthermore, we report the psychophysical experiments in which we analyzed the human sensitivity to these gains. The results reveal encouragingly wider detection thresholds than for straightforward walking. Based on our findings, we discuss the potential of curved walking and present a first approach to leverage bent paths in a way that can provide undetectable RDW manipulations even in room-scale VR.

Current developments in the field of user interface (UI) technologies as well as robotic systems provide enormous potential to reshape the future of human-robot interaction (HRI) and collaboration. However, the design of reliable, intuitive and comfortable user interfaces is a challenging task. In this paper, we focus on one important aspect of such interfaces, i.e., teleoperation. We explain how to setup a heterogeneous, extendible and immersive system for controlling a distant robotic system via the network. Therefore, we exploit current technologies from the area of virtual reality (VR) and the Unity3D game engine in order to provide natural user interfaces for teleoperation. Regarding robot control, we use the well-known robot operating system (ROS) and apply its freely available modular components. The contribution of this work lies in the implementation of a flexible immersive grasping control system using a network layer (ROSbridge) between Unity3D and ROS for arbitary robotic hardware.

It is known for decades that users tend to significantly underestimate or overestimate distances or speed in immersive virtual environments (IVEs) compared to corresponding judgments in the real world. Although several factors have been identified in the past that could explain small portions of this effect, the main causes of these perceptual discrepancies still remain elusive. One of the factors that has received less attention in the literature is the amount of blur presented in the visual imagery, for example, when using a head-mounted display (HMD).