As the use of Head-Mounted Displays in moving vehicles increases, passengers can immerse themselves in visual experiences independent of their physical environment. However, interaction methods are susceptible to physical motion, leading to input errors and reduced task performance. This work investigates the impact of G-forces, vibrations, and unpredictable maneuvers on 3D interaction methods. We conducted a field study with 24 participants in both stationary and moving vehicles to examine the effects of vehicle motion on four interaction methods: (1) Gaze&Pinch, (2) DirectTouch, (3) Handray, and (4) HeadGaze. Participants performed selections in a Fitts' Law task. Our findings reveal a significant effect of vehicle motion on interaction accuracy and duration across the tested combinations of Interaction Method x Road Type x Curve Type. We found a significant impact of movement on throughput, error rate, and perceived workload. Finally, we propose future research considerations and recommendations on interaction methods during vehicle movement.

In pursuit of hand redirection techniques that are ever more tailored to human perception, we propose the first algorithm for hand redirection in virtual reality that makes use of saccades, i.e., fast ballistic eye movements that are accompanied by the perceptual phenomenon of change blindness. Our technique combines the previously proposed approaches of gradual hand warping and blink-suppressed hand redirection with the novel approach of saccadic redirection in one unified yet simple algorithm. We compare three variants of the proposed Saccadic & Blink-Suppressed Hand Redirection (SBHR) technique with the conventional approach to redirection in a psychophysical study (N = 25). Our results highlight the great potential of our proposed technique for comfortable redirection by showing that SBHR allows for significantly greater magnitudes of unnoticeable redirection while being perceived as significantly less intrusive and less noticeable than commonly employed techniques that only use gradual hand warping.

As more and more virtual reality (VR) headsets support eye tracking, recent techniques started to use eye blinks to induce unnoticeable manipulations to the virtual environment, e.g., to redirect users’ actions. However, to exploit their full potential, more control over users’ blinking behavior in VR is required. To this end, we propose a set of reflex-based blink triggers that are suited specifically for VR. In accordance with blink-based techniques for redirection, we formulate (i) effectiveness, (ii) efficiency, (iii) reliability, and (iv) unobtrusiveness as central requirements for successful triggers. We implement the soft- and hardware-based methods and compare the four most promising approaches in a user study. Our results highlight the pros and cons of the tested triggers, and show those based on the menace, corneal, and dazzle reflexes to perform best. From these results, we derive recommendations that help choosing suitable blink triggers for VR applications.

Rendering haptic feedback for interactions with virtual objects is an essential part of effective virtual reality experiences. In this work, we explore providing haptic feedback for rotational manipulations, e.g., through knobs. We propose the use of a Pseudo-Haptic technique alongside a physical proxy knob to simulate various physical resistances. In a psychophysical experiment with 20 participants, we found that designers can introduce unnoticeable offsets between real and virtual rotations of the knob, and we report the corresponding detection thresholds. Based on these, we present the Pseudo-Haptic Resistance technique to convey physical resistance while applying only unnoticeable pseudo-haptic manipulation. Additionally, we provide a first model of how C/D gains correspond to physical resistance perceived during object rotation, and outline how our results can be translated to other rotational manipulations. Finally, we present two example use cases that demonstrate the versatility and power of our approach.

Handheld virtual reality (VR) controllers enable users to manipulate virtual objects in VR but do not convey a virtual object's weight. This hinders users from effectively experiencing lighter and heavier objects. While previous work explored either hardware-based interfaces or software-based pseudo-haptics, in this paper, we combine two techniques to improve the virtual weight perception in VR. By adapting the trigger resistance of the VR controller when grasping a virtual object and manipulating the control-display (C/D) ratio during lifting, we create a continuous weight sensation. In a psychophysical study (N=29), we compared our combined approach against the individual rendering techniques. Our results show that participants were significantly more sensitive towards smaller weight differences in the combined weight simulations compared to the individual methods. Additionally, participants were also able to determine weight differences significantly faster with both cues present compared to the single pseudo-haptic technique. While all three techniques were generally valued to be effective, the combined approach was favoured the most. Our findings demonstrate the meaningful benefit of combining physical and virtual techniques for virtual weight rendering over previously proposed methods.

While consumer-grade virtual reality (VR) hardware can deliver immersive audiovisual experiences, these systems often lack the ability to display realistic haptic feedback, or incorporate cost-efficient vibrotactile actuators with very limited abilities to provide tactile feedback. To overcome these limitations, we introduce an approach based on audio-based vibrotactile actuators. Due to their wide frequency response and multiple resonant frequencies, they can provide more tactile details. In our implementation, every VR interaction uses standard audio clips to provide simultaneous auditory and tactile feedback, as well as coupled realistic physics simulations for the visual feedback. We evaluate our approach to assess the benefits on the user’s experience regarding various interaction scenarios in VR, comparing our approach to a simulated fixed-frequency actuator as a baseline. The results confirmed the benefits of our approach in terms of user preference, perceived realism, comfort, sense of agency, and texture perception. Furthermore, multimodal feedback resulted in the best user experience.

Raycasting-based interaction techniques are widely used for object selection in immersive environments. Despite their intuitive use, they come with challenges due to small or far away objects, hand tremor, and tracking inaccuracies. Previous adaptations for raycasting, such as directly snapping the ray to the closest target, extruding the ray to a cone, or multi-step selection techniques, require additional time for users to become familiar with them. To address these issues, we propose three assistive techniques in which the visible selection ray is subtly redirected towards a target, with a proximity and gain based increase in the redirection amount. In a user study (N = 26), we compared these redirection techniques with a baseline condition based on a Fitts’ law task and collected performance measures as well as comprehensive subjective feedback. The results indicate that the three redirection techniques are significantly faster and have higher effective throughput than the baseline condition. Participants retained a high sense of agency with all redirection techniques and reported significantly lower total workload compared to the baseline. The majority of participants preferred selection with assistive ray redirection and perceived it as not distracting or intrusive. Our findings support that assistive redirected raycasting techniques can improve object selection performance and user experience in virtual environments.

On the way towards novel hand redirection (HR) techniques that make use of change blindness, the next step is to take advantage of saccades for hiding body warping. A prerequisite for saccadic HR algorithms, however, is to know how much the user’s virtual hand can unnoticeably be offset during saccadic suppression. We contribute this knowledge by conducting a psychophysical experiment, which lays the ground for upcoming HR techniques by exploring the perceptual detection thresholds (DTs) of hand offset injected during saccades. Our findings highlight the pivotal role of saccade direction for unnoticeable hand jumps, and reveal that most offset goes unnoticed when the saccade and hand move in opposite directions. Based on the gathered perceptual data, we derived a model that considers the angle between saccade and hand offset direction to predict the DTs of saccadic hand jumps.

We propose a novel open-source software toolkit to support researchers in the domains of human-computer interaction (HCI) and virtual reality (VR) in conducting psychophysical experiments. Our toolkit is designed to work with the widely-used Unity engine and is implemented in C# and Python. With the toolkit, researchers can easily set up, run, and analyze experiments to find perceptual detection thresholds using the adaptive weighted up/down method, also known as the staircase procedure. Besides being straightforward to integrate in Unity projects, the toolkit automatically stores experiment results, features a live plotter that visualizes answers in real time, and offers scripts that help researchers analyze the gathered data using statistical tests.

The coupling between perception and action has seldom been explored in sophisticated motor behaviour such as 3D pointing. In this study, we investigated how 3D pointing accuracy, measured by a depth estimation task, could be affected by the target appearing in different visual eccentricities. Specifically, we manipulated the visual eccentricity of the target and its depth in virtual reality. Participants wore a head-mounted-display with an integrated eye-tracker and docked a cursor into a target. We adopted a within-participants factorial design with three variables. The first variable is Eccentricity: the location of the target on one of five horizontal eccentricities (left far periphery, left near periphery, foveal, right near periphery and right far periphery). The second variable is Depth at three levels and the third variable is Feedback Loop with two levels: open/closed. Eccentricity is refactored into Motion Correspondence between the starting location of the cursor and the target location with four levels: periphery to fovea, fovea to periphery, periphery to periphery, fovea to fovea. The results showed that the pointing accuracy is modulated mainly by the target locations rather than the initial locations of the effector (hand). Visible feedback during pointing improved performance.

We introduce VR Strider, a novel locomotion user interface (LUI) for seated virtual reality (VR) experiences, which maps cycling biomechanics of the user's legs to virtual walking movements. The core idea is to translate the motion of pedaling on a mini exercise bike to a corresponding walking animation of a virtual avatar while providing audio-based tactile feedback on virtual ground contacts. We conducted an experiment to evaluate the LUI and our novel anchor-turning rotation control method regarding task performance, spatial cognition, VR sickness, sense of presence, usability and comfort in a path-integration task. The results show that VR Strider has a significant positive effect on the participants' angular and distance estimation, sense of presence and feeling of comfort compared to other established locomotion techniques, such as teleportation and joystick-based navigation. A confirmatory study further indicates the necessity of synchronized avatar animations for virtual vehicles that rely on pedalling.

Balance training has been shown to be effective in reducing risks of falling, which is a major concern for older adults. Usually, exercise programs are individually prescribed and monitored by physiotherapeutic or medical experts. Unfortunately, supervision and motivation of older adults during home-based exercises cannot be provided on a large scale, in particular, considering an ageing population. Augmented reality (AR) in combination with virtual coaches could provide a reasonable solution to this challenge.

We report on findings from two focus groups for designing an application for balance training at home with an augmented reality virtual coach. Following a User-Centered Design approach, we performed two focus groups with older adults at the early stages of development. Focus group participants were shown a prototype using a Meta 2 head mounted display. Their movements were tracked using a Kinect 2. The virtual coach gave balance training instructions and demonstrated their correct performance. Results suggest that, given the trade-offs of traditional health care, older adults are positive towards using an AR coach for their balance training.

Interaction tasks in virtual reality (VR) such as three-dimensional (3D) selection or manipulation of objects often suffer from reduced performance due to missing or different feedback provided by VR systems than during corresponding realworld interactions. Vibrotactile and auditory feedback have been suggested as additional perceptual cues complementing the visual channel to improve interaction in VR. However, it has rarely been shown that multimodal feedback improves performance or reduces errors during 3D object selection. Only little research has been conducted in the area of proximity-based multimodal feedback, in which stimulus intensities depend on spatiotemporal relations between input device and the virtual target object. In this paper, we analyzed the effects of unimodal and bimodal feedback provided through the visual, auditory and tactile modalities, while users perform 3D object selections in VEs, by comparing both binary and continuous proximity-based feedback. We conducted a Fitts' Law experiment and evaluated the different feedback approaches. The results show that the feedback types affect ballistic and correction phases of the selection movement, and significantly influence the user performance.