Topic models help digital humanists explore large archives, but their outputs are sparse word lists that still require expert interpretation. Large language models (LLMs) can draft topic interpretations, yet their usefulness for end users and exploratory sensemaking remains unclear. We report a feasibility study on a German twentieth-century cultural heritage archive, Ortslinien (OL). Using BERTopic, we identified recurring topics and produced three German interpretations per topic: a peer-proofread digital humanities (DH) expert baseline, GPT-4o, and LLaMA-3. In an online survey (N = 111), participants rated interpretations on coherence, relevance to top words, informativeness, readability, interpretive value, and theme, and ranked the best overall match. GPT-4o led on most dimensions, while the human expert outperformed LLaMA-3 on interpretive value; disciplinary background moderated several judgments. We discuss implications for designing human–AI co-interpretation workflows for scalable, user-facing archive exploration.

Exergames promise enjoyable physical activity through gameplay, yet players often face barriers that undermine engagement, safety, and retention. To date, knowledge about which barriers are encountered by end-users of commercial exergames and which mitigation strategies are used is limited. To address this gap, we conducted an online survey with 174 participants and provide a comprehensive organization of 60 reported barriers across six categories: physical, mental, social, environmental, technological, and game design. Key barriers include space limitations, social discomfort, addictive gameplay, and injuries. Our analysis reveals that while players try to mitigate barriers through ad-hoc strategies, issues like embarrassment, addiction, and harassment remain difficult to overcome. These findings highlight the need for more adaptive game designs, including dynamic spatial adjustments, personalized pacing mechanisms, and supportive social features. This work advances the understanding of exergame barriers and their impact and offers actionable insights for designing more inclusive and resilient movement-based games.

Exergames combine motivating game elements with bodily movement to encourage physical activity. However, onboarding players to perform correct movements remains a challenge, especially in virtual reality (VR) environments where safety and performance are critical. Drawing inspiration from sports training and learning sciences, we contrast two onboarding approaches: (i) trial-and-error and (ii) observational learning via a novel self-model tutorial. In this tutorial, players temporarily lose agency and observe their own avatar performing the movements, leveraging VR’s unique affordances for embodied experiences. To explore which of these two approaches yields a better performance and player experience, we conducted a between-participants study (N = 60), comparing them against a baseline condition without a tutorial. Our findings show that the self-model tutorial not only improves players’ performance but also increases the perceived ease of control and progress feedback. We discuss tradeoffs and implications for the design of future onboarding experiences in VR exergames.

Intelligent assistants (IAs) in virtual reality (VR) environments offer novel ways of interaction between humans and artificial intelligence (AI). Human-like conversational abilities change the way we interact with AI. In human communication, multimodal referential interaction, such as using eye gaze or pointing with deictic expressions, or by using descriptive speech, is essential for achieving a shared understanding of the space surrounding the interaction partners. By facilitating efficient and intuitive referential interaction among users and IAs, user engagement and overall effectiveness could be enhanced.This paper compares three referential interaction methods in VR to determine user preferences: (i) verbal communication, (ii) gaze, and (iii) pointing. We conducted a user study with 39 participants in VR, where information about scene objects had to be gathered using these different referential interaction methods. The results reveal that gaze performed well in terms of performance (both time and number of prompts) and usability measures (as assessed by the UEQ and NASA-TLX). While verbal interaction was less physically straining than pointing, it required greater mental effort. Although there were no significant differences in the overall preferences, a qualitative analysis indicated differences in individual inclination. Enriching the referential methods with feedback and enabling multimodal interactions are promising methods to improve usability and decrease task load further.

Recent advances in generative AI have accelerated the deployment of virtual celebrity agents for commercial endorsements. However, little is known about how their visual style and vocal type, especially when these characteristics are generated via advanced AI reconstruction or voice cloning techniques, affect user trust, perceived realism, familiarity, and social presence. We extracted a representative clip of Sheldon Cooper from The Big Bang Theory as a baseline and generated multiple Sheldon virtual agents that varied in visual style (hand-sculpted, AI-reconstructed, or non-stylized) and vocal type (cloned or synthesized). A 3 × 2 within-subjects experiment (N = 30) revealed that visual style significantly affected user trust, perceived realism, familiarity, and social presence, while vocal type affected only perceived realism and familiarity. Comparisons between the virtual agents and the video baseline confirmed that even cutting-edge 3D modeling still differs significantly from authentic video representations. Behavioral data indicate that the relationship between interpersonal-distance variations and trust levels is not a simple linear one. These findings provide actionable guidance for designers leveraging generative AI to create trustworthy virtual avatars or agents and delineate new research avenues for virtual celebrity agents.

Redirected walking (RDW) alters the relationship between physical locomotion and visual feedback to guide users along virtual paths that vary from their real-world trajectories. Over time these changes can lead to adaptation of the user and produce novel sensorimotor settings that users might retain across sessions and apply directly once they enter virtual reality (VR). Although short-term adaptation to altered sensorimotor contingencies is well established, it remains unclear whether such adaptation is retained across multiple days. We investigated long-term retention of RDW adaptation by repeatedly exposing ten participants to a fixed rightward curvature gain of π /30 across nine sessions over two weeks. Each session consisted of 200 walking repetitions with gain applied. Adaptation was assessed before and after each session using blind walking and a pointing task. Moreover, perceptual detection thresholds for curvature gains were measured before the first session (Baseline), a day after the ninth session (Final), and once in-between before the 5th adaptation session. Results showed clear retention of adapted locomotor behavior: during blind walking at the beginning of the sessions, when instructed to walk straight, participants consistently exhibited curved trajectories, which indicates that newly acquired sensorimotor contingencies can be retained over days and are immediately available upon re-entering VR. At the same time, pointing accuracy remained stable throughout the experiment and detection thresholds showed no consistent changes across sessions. In summary, our study provides evidence that adaptation to altered sensorimotor contingencies in VR can be retained across multiple sessions and days and can be available as soon as the user enters VR. This may be useful for many scenarios in which users repeatedly use VR tools over a long period of time. The complete data set, all supplemental materials and the preprint of the manuscript are available at https://osf.io/z973w.

Although immersive technologies hold enormous potential for enhancing sports training, existing systems encounter notable limitations. While fully immersive virtual reality (VR) systems can address constraints of physical training setups such as limited space or equipment, full VR environments often lack rich, realistic, and multisensory feedback often required for effective sports training. To address this gap, this work investigates skill-based sport training, particularly, golf putting, across the reality-virtuality continuum. We implemented a mixed reality (MR) putting simulator that combines real equipment (putter and golf ball) with a virtual training environment. Three training conditions were realized: (i) real-world putting, constrained by limited physical space; (ii) a VR putting, in which a real putter and ball are used but represented virtually within the virtual environment (VE); (iii) an augmented virtuality (AV) putting, which reveals the real putter, ball, and users' limbs through a localized video-passthrough window, aiming to preserve users' sense of embodiment and presence while enabling simulation of an unlimited putting area. We conducted a pilot within-subjects experiment with 36 participants and found that the AV condition improved immediate putting performance, reduced task load, reduced perceived motion sickness, and increased user preference compared to the VR condition, while user's sense of presence remained comparable to VR training. These findings indicate that AV offers a pragmatic "sweet spot" on the virtuality continuum, balancing the tradeoff between sensory fidelity and training flexibility, offering valuable design insights for immersive sports training systems.

Interaction between humans and virtual agents is becoming increasingly prevalent. This research investigates the influence of virtual agents on users' opinions within a virtual stand-up comedy club setting, focusing on the socio-psychological mechanisms of emotional contagion and group conformity. We aimed to combine these two areas in a novel study approach. To this end, we designed and conducted an exploratory pilot study in which participants ($\mathrm{N}=20$) rated the funniness of jokes in VR, under varying conditions of virtual agent laughter (absence, medium intensity, strong intensity). Our analysis shows a significant positive linear effect on the log odds of higher funniness ratings when virtual agents exhibit laughter. Moreover, our study shows that this effect is mainly due to emotional contagion processes, individual differences in susceptibility to group conformity, and the interaction of both concepts, showing that emotional contagion happens only when the individual susceptibility to group conformity is high. The results offer valuable insights into the social impact of VR environments and the potential of virtual agents to shape user perception and opinion.

Figure 1: Illustration of familiarity in intelligent virtual agents: (A) picture of real human, (B) the familiar agent created from it, and (C) the unfamiliar agent created from a non-existent person with similar visual appearance, such as hairstyle, skin color, eyes color, or clothes.

Conversational Virtual Agents (CVAs) offer a promising approach for enhancing user task performance in Mixed Reality (MR) environments. This paper explores the integration of a CVA into an MR application designed to assist in solving a 2D physical puzzle, offering enhanced spatial cognitive capabilities. Using the CVA classification architecture and the MiRAS (Mixed Reality Agents) Cube Taxonomy, we developed an MR system with a state-aware assistant to guide users in a puzzle-solving task only when requested. The primary research question is whether or not the CVA needs to be embodied. We conducted a study with 34 participants to investigate the influence of Voice-only and Embodied CVAs on puzzle-solving performance, user interactions with the assistant, the assistant’s social presence, overall system cognitive workload, and users’ perceptions of future system use. Both modalities showed equivalent outcomes regarding the number of position- and orientation-related queries, perceived usability, message and affective understanding, performance, frustration, and usefulness. However, results showed that Voice-only CVA significantly enhanced task efficiency: participants completed puzzles more quickly and accurately, reporting lower effort than in the Embodied condition. These findings suggest that Voice-only CVAs may be more effective for tasks like puzzle solving, where auditory guidance alone appears sufficient to support better performance.

In virtual reality (VR), using the hands instead of controllers has enormous potential for intuitive user interactions, e.g., direct grasping, touching, or moving virtual objects. In this context, the realism of the hands plays an important role in the body ownership illusion and the user’s feeling of presence. Yet, most applications use generic 3D hand models, so they do not include individual user characteristics, like wrinkles, moles, or skin features. In this work, we present a pipeline to include fully articulated, photorealistic, fully tracked hand scans for VR applications. Our pipeline captures photos of the hand from different perspectives simultaneously using a customized hand scanner. Using open-source photogrammetry software, a rigged 3D model of the hand is created and integrated into a Unity application. At last, we provide practitioners and researchers with a fast and easy way to integrate a user’s real hands into a VR application. Finally, we present guidelines for generating a fully articulated, personalized virtual hand model within 30 minutes from a set of 2D images.

Fidelity describes how closely a replication resembles the original. It can be helpful to analyze how faithful interactions in virtual reality (VR) are to a reference interaction. In prior research, fidelity has been restricted to the simulation of reality—also called realism. Our definition includes other reference interactions, such as superpowers or fiction. Interaction fidelity is a multilayered concept. Unfortunately, different aspects of fidelity have either not been distinguished in scientific discourse or referred to with inconsistent terminology. Therefore, we present the Interaction Fidelity Model (IntFi Model). Based on the human-computer interaction loop, it systematically covers all stages of VR interactions. The conceptual model establishes a clear structure and precise definitions of eight distinct components. As a communication tool, it helps teams to understand and discuss fidelity in VR. It was reviewed through workshops with fourteen VR experts. We provide guidelines, diverse examples, and educational material to apply the IntFi Model universally to any VR experience and propose foundational research opportunities.

Insufficient physical activity is a major challenge in our aging society. Although exergames can provide enjoyable exercise opportunities for older adults, it remains unclear which display technology is best suited to reach this goal. This paper compares two popular exergame technologies with different immersion levels: (i) a virtual reality head-mounted display (VR-HMD) and (ii) the ExerCube, a commercial projection-based system. We conducted a within-participants study ( N =34) with older adults to evaluate player experience, presence, cybersickness, game performance, and physical exertion. Both display types provided a comparably high player experience and physical exertion that can benefit older adults’ physical well-being. The VR-HMD offered superior presence, while the ExerCube led to higher performance and physical activity. Our findings advance the understanding of how different exergame technologies affect older adults’ experiences. We present research and design implications to guide the future development of age-appropriate exergames.

The locomotion and interaction of multi-user groups are critical components of social virtual reality (VR), where users collaboratively navigate shared spaces defined by their relationships. As metaverse and social VR platforms evolve, safeguarding group spatial integrity becomes paramount. While teleportation-widely adopted for efficient navigation-enhances communication, it risks unintended intrusion into group spaces, compromising privacy and security. This paper presents two novel negotiated user-to-group teleportation techniques, paired with dynamic zone computation methods, to address these challenges. Our approach enables guest users to join groups through spatially aware teleportation, mediated by real-time negotiation. The negotiation interaction process is designed to facilitate users to negotiate teleportation locations efficiently and smoothly. To validate our techniques, we conducted a user study with 36 participants in a VR art museum environment, where they performed collaborative social-tour tasks. The findings demonstrate that our techniques significantly enhance group privacy protection, effectively support user-to-group negotiation of teleportation joining requirements, and alleviate anxiety associated with unwanted proximity within social VR groups.

Many people struggle to exercise regularly, raising the risk of serious health-related issues. Extended reality (XR) exergames address these hurdles by combining physical exercises with enjoyable, immersive gameplay. While a growing body of research explores XR exergames, no previous review has structured this rapidly expanding research landscape. We conducted a scoping review of the current state of XR exergame research to (i) provide a structured overview, (ii) highlight trends, and (iii) uncover knowledge gaps. After identifying 1318 papers in human-computer interaction and medical databases, we ultimately included 186 papers in our analysis. We provide a quantitative and qualitative summary of XR exergame research, showing current trends and potential future considerations. Finally, we provide a taxonomy of XR exergames to help future design and methodological investigation and reporting.

The increasing relevance of artificial intelligence (AI) agents for people’s everyday professional and private lives leads to a great need for identifying efficient and user-friendly modalities for human-agent interaction. Such interaction usually takes place via text or voice. While chatbots and voice assistants each rely on only one modality, the focus of this paper is on asymmetric modality combinations. A user study was conducted in the context of information retrieval, and different input and output modalities were evaluated in a 2 × 2 within-subject design. It was found that efficient modality combinations are not always preferred and that usability factors, such as user control, have a greater influence on preference. For example, the combination of voice input and text output can prove to be very efficient, but at the same time be less preferred due to weaknesses in the user experience. Pure text-based interaction was found to be the preferred combination as it ensures a high degree of control and freedom for the user. Dialog-based applications for information retrieval should therefore use the text modality as a basis and supplement this with voice-based input and output options.

We introduce Reality Fusion, a novel robot teleoperation system that localizes, streams, projects, and merges a typical onboard depth sensor with a photorealistic, high resolution, high framerate, and wide FoV rendering of the complex remote environment represented as 3D Gaussian splats (3DGS). Our framework enables robust egocentric and exocentric robot teleoperation in immersive VR, with the 3DGS effectively extending spatial information of a depth sensor with limited FoV and balancing the trade-off between data streaming costs and data visual quality. We evaluated our framework through a user study with 24 participants, which revealed that Reality Fusion leads to significantly better user performance, situation awareness, and user preferences. To support further research and development, we provide an open-source implementation with an easy-to-replicate custom-made telepresence robot, a high-performance virtual reality 3DGS renderer, and an immersive robot control package.1

Uncertainty cues are inherent in natural human interaction, as they signal to communication partners how much they can rely on conveyed information. Humans subconsciously provide such signals both verbally (e.g., through expressions such as “maybe’’ or “I think’’) and non-verbally (e.g., by diverting their gaze). In contrast, artificial intelligence (AI)-based services and machine learning (ML) models such as ChatGPT usually do not disclose the reliability of answers to their users.

Previous work suggests that the mere visual perception of disease cues displayed in 2D videos or photos can proactively enhance mucosal immune responses even without actual pathogen exposure. In this paper, we present the first immersive immunological experiment, which investigates if social interactions with virtual agents in virtual reality (VR) can lead to a mucosal immune response, in particular, a proactive release of secretory immunoglobin A(sIgA) in saliva. Therefore, we simulated a virtual bus stop scenario of enhanced airborne contagion risk in which participants were required to closely approach and establish eye contact with ten agents in two conditions. In the first (i.e., contagion) condition, seven of the ten agents sneezed directly before smiling or at predefined intervals. The second (i.e., control) condition used the same agents but without sneezes. We tested 70 healthy participants in a between-subjects design, measured changes in salivary sIgA, as well as subjectively perceived disgust and contagion risk, and assessed their sense of presence and cybersickness in the VE. We found that sIgA secretion increased in both scenarios, while in the control scenario, this increase also correlated with the perceived involvement and sense of presence in the VE. This suggests that the intimate social interactions with virtual agents were sufficient to trigger increased sIgA secretion regardless of sneezing. Hence, VR can be used to provoke proactive immune responses in laboratory experiments.

Redirected walking is a locomotion technique that allows users to naturally walk through large immersive virtual environments (IVEs) by guiding them on paths that might vary from the paths they walk in the real world. While this technique enables the exploration of larger spaces in the IVE via natural walking, previous work has shown that it induces extra cognitive load for the users. On the other hand, previous research has shown that exposure to virtual nature environments can restore users’ diminished attentional capacities and lead to enhanced cognitive performances. Therefore, the aim of this paper is to investigate if the environment in which the user is redirected has the potential to reduce its cognitive demands. For this purpose, we conducted an experiment with 28 participants, who performed a spatial working memory task (i.e., 2-back test) while walking and being redirected with different gains in two different IVEs (i.e., (i) forest and (ii) urban). The results of frequentist and Bayesian analysis are consistent and provide evidence against an effect of the type of IVE on detection thresholds as well as cognitive and locomotion performances. Therefore, redirected walking is robust to the variation of the IVEs tested in this experiment. The results partly challenge previous research findings and, therefore, require future work in this direction.

In modern spatial computing devices, users are confronted with diverse methods for object selection, including eye gaze (cf. Apple Vision Pro), hand gestures (cf. Microsoft HoloLens 2), touch gestures (cf. Google Glass Enterprise Edition 2), and external controllers (cf. Magic Leap 2). Although there are a plethora of empirical studies on which selection techniques perform best, a common limiting factor stems from the partly artificial setups. These typically exclude practical influences such as visual distraction.

Immersive virtual reality (VR) exergames blend playful environments with physical activities. In such games, providing continuous cues, i.e., real-time indications of how the movements are being performed, can guide players and improve the execution of movements. However, research about how continuous cues impact player performance and experience in VR exergames remains sparse. To this end, we conducted a within-participants study (N=32) with four conditions: (i) no, (ii) audio, (iii) visual, and (iv) audiovisual cueing. The results show that both unimodal and bimodal cueing improve the player experience without causing cybersickness, while bimodal cueing improves pose accuracy. We provide three main design implications for VR exergames: (i) considering the granularity of cues, (ii) exploring different continuous cue designs, and (iii) underlining the use of continuous cues in other immersive experiences.

Enabled by the latest achievements in artificial intelligence (AI), computer graphics as well as virtual, augmented, and mixed reality (VR/AR/MR), virtual agents are increasingly resembling humans in both their appearance and intelligent behavior. This results in enormous potential for agents to support users in their daily lives, for example in customer service, healthcare, education or the envisioned all-encompassing metaverse. Today's technology would allow users to customize their conversation partners in the metaverse - as opposed to reality - according to their preferences, potentially improving the user experience. On the other hand, there is little research on how reshaping the head of a communication partner might affect the immediate interaction with them. In this paper, we investigate the user requirements for and the effects of agent customization. In a two-stage user study ($N=30$), we collected both self-reported evaluations (e.g., intrinsic motivation) and interaction metrics (e.g., interaction duration and number of tried out items) for the process of agent customization itself as well as data on how users perceived the subsequent human-agent interaction in VR. Our results indicate that users only wish to have full customization for agents in their personal social circle, while for general services, a selection or even a definite assignment of pre-configured agents is sufficient. When customization is offered, attributes such as gender, clothing or hair are subjectively more relevant to users than facial features such as skin or eye color. Although the customization of human interaction partners is beyond our control, customization of virtual agents significantly increases perceived social presence as well as rapport and trust. Further findings on user motivation and agent diversity are discussed in the paper.

Several advanced redirected walking techniques have been proposed in recent years to improve natural walking in virtual environments. One active and important research challenge of redirected walking focuses on the alignment of virtual and physical environments by redirection gains. If both environments are aligned, physical objects appear at the same positions as their virtual counterparts. When a user arrives at such a virtual object, she can touch the corresponding physical object providing passive haptic feedback. When multiple transferable virtual or physical target positions exist, the alignment can exploit multiple options, but the process requires more complicated solutions. In this paper, we study the problem of virtual-physical environmental alignment at multiple transferable target positions, and introduce a novel reinforcement learning-based redirected walking method. We design a novel comprehensive reward function that dynamically determines virtual-physical target matching and updates virtual target weights for reward computation. We evaluate our method through various simulated experiments as well as real user tests. The results show that our method obtains less physical distance error for environmental alignment and requires fewer resets than state-of-the-art techniques.

Traveling between scenes has become a major requirement for navigation in numerous virtual reality (VR) social platforms and game applications, allowing users to efficiently explore multiple virtual environments (VEs). To facilitate scene transition, prevalent techniques such as instant teleportation and virtual portals have been extensively adopted. However, these techniques exhibit limitations when there is a need for frequent travel between separate VEs, particularly within indoor environments, resulting in low efficiency. In this article, we first analyze the design rationale for a novel navigation method supporting efficient travel between virtual indoor scenes. Based on the analysis, we introduce the SceneFusion technique that fuses separate virtual rooms into an integrated environment. SceneFusion enables users to perceive rich visual information from both rooms simultaneously, achieving high visual continuity and spatial awareness. While existing teleportation techniques passively transport users, SceneFusion allows users to actively access the fused environment using short-range locomotion techniques. User experiments confirmed that SceneFusion outperforms instant teleportation and virtual portal techniques in terms of efficiency, workload, and preference for both single-user exploration and multi-user collaboration tasks in separate VEs. Thus, SceneFusion presents an effective solution for seamless traveling between virtual indoor scenes.

Virtual Reality (VR) exergames can increase engagement in and motivation for physical activities. Most VR exergames focus on the upper body because many VR setups only track the users’ heads and hands. To become a serious alternative to existing exercise programs, VR exergames must provide a balanced workout and train the lower limbs, too. To address this issue, we built a VR exergame focused on vertical jump training to explore full-body exercise applications. To create a safe and effective training, nine domain experts participated in our prototype design. Our mixed-methods study confirms that the jump-centered exercises provided a worthy challenge and positive player experience, indicating long-term retention. Based on our findings, we present five design implications to guide future work: avoid an unintended forward drift, consider technical constraints, address safety concerns in full-body VR exergames, incorporate rhythmic elements with fluent movement patterns, adapt difficulty to players’ fitness progression status.

Consumer social virtual reality (VR) applications have recently started to enable social interactions at a distance. Yet it is still relatively unknown if and to what extent such applications provide meaningful social experiences in cases where in-person leisure activities are not feasible. To explore this, we developed a custom social VR application and conducted an exploratory lab study with 25 dyads in which we compared an in-person and a virtual version of a co-located multiplayer scenario. Our mixed-methods analysis revealed that both scenarios created a socially rich atmosphere and strengthened the social closeness between players. However, the lack of facial animations, limited body language, and a low field of view led to VR’s main social experiential limitations: a reduced mutual awareness and emotional understanding compared to the in-person scenario. We derive implications for social VR design and research as well as game user research.

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.

Real-time detection of saccades is of major interest for many applications in human-computer interaction and mixed reality. However, due to relatively low update rates and high latencies of current commercially available eye trackers, gaze events are typically detected after they occur with some delay. This limits interaction scenarios such as intent-based gaze interaction, redirected walking, or gaze forecasting.

Augmented Reality (AR) technology has been widely investigated to support various navigation tasks, including initial approaches that suggest its potential use on ships. For maritime navigation, skippers use a variety of information displayed on a ship’s bridge. However, the constant shift of focus between this information and the outside view of the ship might pose cognitive as well as safety challenges. Here, AR could facilitate the navigation of ships by overlaying the real-world view with spatially anchored visual navigation aids. Despite this potential, previous work mainly presents conceptual approaches, technical tests, or user studies performed in ship simulators only.In this paper, we evaluate an AR-based assistance system in the actual real-world water environment, where technical issues and varying physical conditions could influence the system’s usability. In collaboration with hydrographic experts following a user-centered design approach, a functional AR system was developed that virtually displays navigation aids on the water surface. In a field study, ten skippers used the system to navigate a ship along a path through a port area. We assessed the accuracy, perceived workload, and user experience of participants. In addition, qualitative feedback was thematically analyzed to retrieve insights about the skippers’ attitude regarding using AR on actual ships. We report lessons learned about aspects such as ergonomics, perceived safety challenges, as well as envisioned further use cases and extended data integration.

Medical virtual agents (VAs) hold great potential to support patients in achieving their health goals, especially at times or in regions where the demand for physiological and psychological therapy exceeds the capacity of medical services. To create an accepted complement to on-site diagnosis, treatment, and counseling, it is critical to understand the impact of factors such as the agent’s visual representation, behavior, and responsibilities on creating a trustworthy human-agent relationship. To gain insights into these factors, we conducted a systematic literature review including 59 papers on embodied VAs in the medical domain. Our review focused on the application fields and the role of VAs in medicine, as well as the technology used to display them. Using thematic analysis, we discuss our findings in terms of user preferences, as well as potentials and barriers faced in the interaction with medical VAs. Concerning the visual representation, the users’ wish for customization in terms of appearance and communication modalities was pointed out. It was also important that the agent’s information builds up on trustworthy sources, that they are motivating and adapted to the users’ knowledge. Finally, our results identify research gaps, in particular regarding the technological implementation and the use of artificial intelligence.

Recent advancements in Neural Radiance Fields (NeRF) provide enormous potential for a wide range of Mixed Reality (MR) applications. However, the applicability of NeRF to real-time MR systems is still largely limited by the rendering performance of NeRF. In this paper, we present a novel approach for Variable Rate Shading for Neural Radiance Fields (VRS-NeRF). In contrast to previous techniques, our approach does not require training multiple neural networks or re-training of already existing ones, but instead utilizes the raytracing properties of NeRF. This is achieved by merging rays depending on a variable shading rate, which reduces the overall number of queries to the neural network. We demonstrate the generalizability of our approach by implementing three alternative functions for the determination of the shading rate. The first method uses the gaze of users to effectively implement a foveated rendering technique in NeRF. For the other two techniques, we utilize shading rates based on edges and saliency. Based on a psychophysical experiment and multiple image-based metrics, we suggest a set of parameters for each technique, yielding an optimal tradeoff between rendering performance gain and perceived visual quality.

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.

Initial motivation when starting exergaming is a key factor towards enabling long-term engagement and adherence, especially among older adults. To increase, in particular, the initial motivation of older adults, we introduce the concept of diminishing gaze assistance (GA), assess its feasibility for virtual reality (VR) exergames, and investigate the effects on motor learning, performance, and motivation in older adult users. First, we conducted a focus group followed by a pre-study on the development of VR exergames for older adults and VR gaze assistance. The results informed the design and implementation of our gaze-assisted throwing exergame, which was then evaluated in a follow-up main study. Participants of the main study were randomly assigned to the GA and Motor (control) group, and had to complete a VR throwing task, in which participants had to aim and throw at three targets at varying angles. The GA group received declining gaze assistance, in which the ball trajectory was initially guided by their gaze (rather than their physical (motor) throwing) before guidance was gradually reduced until their physical (motor) throwing ability was solely responsible for hitting the target. Motivation and user experience were assessed using the Questionnaire on Current Motivation before and during, and the short scale of intrinsic motivation questionnaire after the task. The results show that the GA was generally perceived positively. In particular, the initial confidence of the GA group was rated higher, and we observed evidence suggesting increased confidence throughout the trial.

Virtual reality (VR) games intensify storytelling experiences by letting players take the role of a character. However, in contrast to films, novels, or games, VR experiences often remain centered around one single character without using the potential of complex multiprotagonist plots. Our work engages in this critical topic by investigating the design of immersive and natural transitions between different characters. First, we conducted a scoping review to identify existing multiprotagonist VR games (N=18) and grouped their used transition techniques into four categories. Based on these findings and prior research, we designed two transition techniques (Static Map vs. Rebodying) and conducted a between-participants (N=36) study to explore their effect on user experience. Our results show that Rebodying outperforms Static Map regarding the perceived realism, acceptance, and spatial understanding of the character transitions. Both conditions do not differ significantly in terms of cybersickness. Finally, we provide future directions for developing, improving, and exploring of multiprotagonist transition techniques in VR games.

Tile-based locomotion (TBL) is a popular locomotion technique for computer, console, and board games. However, despite its simplicity and unconventional movement, the transfer of TBL to virtual reality (VR) as a game platform remains unexplored. To fill this gap, we introduce TBL for VR on the example of two techniques: a controller and a feet-based one. In a first user study, we evaluated the usability and acceptance of the techniques compared to teleportation and touchpad locomotion. In a second exploratory user study, we evaluated the user experience of both TBL techniques in a maze and a museum scenario. The findings show that both techniques provide enjoyment and acceptable usability by creating either a relaxing (controller-based) or a physically active (feet-based) solution. Finally, our results highlight that TBL techniques work particularly well for small, constrained spaces that allow users to focus on exploring details in the nearby environment (important for games) in contrast to large open spaces that require faster locomotion, like teleportation.

Research on intelligent virtual agents (IVAs) often concerns the implementation of human-like behavior by integrating artificial intelligence algorithms. Thus far, few studies focused on mimicry of cognitive imperfections inherent to humans in IVAs. Neglecting to implement such imperfect behavior in IVAs might result in less believable or engaging human-agent interactions. In this paper, we simulate human imprecision in conversational IVAs’ temporal statements. We conducted a survey to identify temporal statement patterns, transferred them to a conversational IVA, and conducted a user study evaluating the effects of time precision on perceived anthropomorphism and usefulness. Statistical analyses reveal significant interaction between time precision and agents’ use of memory aids, indicating that (i) imprecise agents are perceived as more human-like than precise agents when responding immediately, and (ii) unnaturally high levels of temporal precision can be compensated for by memory aid use. Further findings underscore the value of continued inquiry into cultural variations.

We present a novel view on gaze event classification by redefining it as a time-to-event problem. In contrast to previous models, which consider the classification as discrete events, our redefinition allows for estimating the remaining time until the next saccade event. Therefore, we provide a feature analysis and an initial solution for compensating the latency of wearable eye-trackers build in today’s head-mounted displays. Similar to previous classifiers, we utilize oculomotor features such as velocity, acceleration, and event durations. In total, we analyze 104 extracted features of three datasets and apply different regression methods. We identify optimal window sizes for each feature and extract the importance of all extracted windows using recursive feature elimination. Afterwards, we evaluate the performance of all regressors using earlier selected features. We show that our selected regressors can predict the time-to-event better than the baseline, indicating the potential usage of time-to-event prediction of saccades.

We present mixed reality (MR) tunneling, a novel method to balance the trade-off between limited render performance and high visual quality of video see-through head-mounted displays (VST-HMDs) through fusing images of two types of camera sensors with different resolutions and frame rates. By merging a color video stream from an external stereoscopic camera with the grayscale VST commonly integrated into today’s standalone virtual reality (VR) headsets, we create a perceptually high-resolution and wide field of view VSTHMD prototype. The external high-resolution VST displayed at the central foveal to the para-peripheral region of the human visual field complements the low-resolution, low-latency grayscale VST at the far peripheral region, producing a tunneling effect, which simulates the human foveal and peripheral vision, with the potential to reduce cybersickness as in the tunneling effect in immersive VR. We propose two extensions to the MR tunneling method. The first one accommodates the user’s head movement speed by fading out the external VST when fast head movements are detected, thus potentially compensating for video streaming latency. The second one is a foveated MR tunneling effect, which displays the center of the external VST based on the tracked user eye movements. We evaluated the three MR tunneling methods in a within-subject study with 24 participants. The user study demonstrates the potential of our prototype and techniques based on the example of an assembly task that requires hand-eye coordination, untethered locomotion, and fine motor skills. The results demonstrate that, although not significant, the MR tunneling effects lead to higher overall usability, less perceived motion sickness, and a better sense of presence.1

Nowadays, high-power and multi-spectral lasers are used in many scientific experiments and industrial processes. Those laser sources can rapidly cause permanent damage to human eyes. Research and development work with those laser sources requires typically wearing personal protective equipment (PPE), such as laser safety goggles as eye protectors. Currently, laser safety goggles are based on optical spectral filters, which block spectral bands where hazardous laser radiation is emitted. Such laser safety goggles can filter up to 99% of the visible spectrum, rendering researchers working in hazardous and complex laboratory environments visually impaired. Video see-through head-mounted displays (VST-HMD) could be used as eye protectors without reducing users’ visibility of the environment since they can be constructed such that all laser and ambient light is blocked from the human eye. To date, this application domain is still largely unexplored in the MR community. To our best knowledge, there has been no comprehensive work that investigates the human factors of such an eye protection method at an advanced optics laboratory. In this work, we present the results of an empirical study where we evaluate the usability, perceived safety, advantages, and limitations of using VST-HMDs as laser safety goggles. We use a stereoscopic VST-HMD developed through a human-centered design approach at one of the most advanced optics laboratories in the world. 18 participants including 14 laser experts evaluated the current prototype. Our user evaluation and field studies confirm that the complex and hazardous working conditions at high-energy laser laboratories could be significantly improved with MR technology.

Natural interaction between multiple users within a shared virtual environment (VE) relies on each other's awareness of the current position of the interaction partners. This, however, cannot be warranted when users employ noncontinuous locomotion techniques, such as teleportation, which may cause confusion among bystanders. In this paper, we pursue two approaches to create a pleasant experience for both the moving user and the bystanders observing that movement. First, we will introduce a Smart Avatar system that delivers continuous full-body human representations for noncontinuous locomotion in shared virtual reality (VR) spaces. Smart Avatars imitate their assigned user's real-world movements when close-by and autonomously navigate to their user when the distance between them exceeds a certain threshold, i.e., after the user teleports. As part of the Smart Avatar system, we implemented four avatar transition techniques and compared them to conventional avatar locomotion in a user study, revealing significant positive effects on the observers' spatial awareness, as well as pragmatic and hedonic quality scores. Second, we introduce the concept of Stuttered Locomotion , which can be applied to any continuous locomotion method. By converting a continuous movement into short-interval teleport steps, we provide the merits of non-continuous locomotion for the moving user while observers can easily keep track of their path. Thus, while the experience for observers is similarly positive as with continuous motion, a user study confirmed that Stuttered Locomotion can significantly reduce the occurrence of cybersickness symptoms for the moving user, making it an attractive choice for shared VEs. We will discuss the potential of Smart Avatars and Stuttered Locomotion for shared VR experiences, both when applied individually and in combination.

Virtual reality (VR) multiplayer games increasingly use asymmetry (e.g., differences in a person’s capability or the user interface) and resulting interdependence between players to create engagement even when one player has no access to a head-mounted display (HMD). Previous work shows this enhances player experience (PX). Until now, it remains unclear whether and how an asymmetric game design with interdependences creates comparably enjoyable PX for both an HMD and a non-HMD player. In this work, we designed and implemented an asymmetric VR game (different in its user interface) with two types of interdependence: strategic (difference in game information/player capability) and biometric (difference in player’s biometric influence). Our mixed-methods user study (N=30) shows that asymmetries positively impact PX for both player roles, that interdependence strongly affects players’ perception of agency, and that biometric feedback—while subjective—is a valuable game mechanic.

Various redirected walking (RDW) techniques have been proposed, which unwittingly manipulate the mapping from the user’s physical locomotion to motions of the virtual camera. Thereby, RDW techniques guide users on physical paths with the goal to keep them inside a limited tracking area, whereas users perceive the illusion of being able to walk infinitely in the virtual environment. However, the inconsistency between the user’s virtual and physical location hinders passive haptic feedback when the user interacts with virtual objects, which are represented by physical props in the real environment.In this paper, we present a novel reinforcement learning approach towards RDW with passive haptics. With a novel dense reward function, our method learns to jointly consider physical boundary avoidance and consistency of user-object positioning between virtual and physical spaces. The weights of reward and penalty terms in the reward function are dynamically adjusted to adaptively balance term impacts during the walking process. Experimental results demonstrate the advantages of our technique in comparison to previous approaches. Finally, the code of our technique is provided as an open-source solution.

Developers of interactive systems have a variety of interaction techniques to choose from, each with individual strengths and limitations in terms of the considered task, context, and users. While there are taxonomies for desktop, mobile, and virtual reality applications, augmented reality (AR) taxonomies have not been established yet. However, recent advances in immersive AR technology (i.e., head-worn or projection-based AR), such as the emergence of untethered headsets with integrated gesture and speech sensors, have enabled the inclusion of additional input modalities and, therefore, novel multimodal interaction methods have been introduced. To provide an overview of interaction techniques for current immersive AR systems, we conducted a literature review of publications between 2016 and 2021. Based on 44 relevant papers, we developed a comprehensive taxonomy focusing on two identified dimensions – task and modality. We further present an adaptation of an iterative taxonomy development method to the field of human-computer interaction. Finally, we discuss observed trends and implications for future work.

Redirected walking (RDW) is a locomotion technique that guides users on virtual paths, which might vary from the paths they physically walk in the real world. Thereby, RDW enables users to explore a virtual space that is larger than the physical counterpart with near-natural walking experiences. Several approaches have been proposed and developed; each using individual platforms and evaluated on a custom dataset, making it challenging to compare between methods. However, there are seldom public toolkits and recognized benchmarks in this field. In this paper, we introduce OpenRDW, an open-source library and benchmark for developing, deploying and evaluating a variety of methods for walking path redirection. The OpenRDW library provides application program interfaces to access the attributes of scenes, to customize the RDW controllers, to simulate and visualize the navigation process, to export multiple formats of the results, and to evaluate RDW techniques. It also supports the deployment of multi-user real walking, as well as reinforcement learning-based models exported from TensorFlow or PyTorch. The OpenRDW benchmark includes multiple testing conditions, such as walking in size varied tracking spaces or shape varied tracking spaces with obstacles, multiple user walking, etc. On the other hand, procedurally generated paths and walking paths collected from user experiments are provided for a comprehensive evaluation. It also contains several classic and state-of-the-art RDW techniques, which include the above mentioned functionalities.

Augmented reality (AR) provides enormous potential to improve navigation assistance interfaces by displaying information directly into the user's field of view. In maritime contexts, such AR interfaces could supplement conventional solutions that require users to interpret spatial positions visualized on two-dimensional maps. In order to design useful navigation assistance, it is crucial to understand how egocentric distances of displayed objects are perceived and how different design attributes influence depth estimation. While previous research mainly focused on depth perception in indoor environments and rather short distances, this paper presents an investigation of the perceived egocentric distance of virtual objects in distances up to 75 meters in an open outdoor environment. In a perceptual matching task experiment using the Microsoft HoloLens 2, participants had to move objects with different (i) shape, (ii) coloration, and (iii) relation to floor to various target distances. Our results suggest that participants overestimated the distance to virtual objects across all tested distances since they significantly underproduced target distances for all investigated design factors. Based on these results, we explored potential design implications for a maritime AR navigation assistance on a ship in the local port area.

Redirected jumping (RDJ) is a locomotion technique that allows users to explore a virtual space that is larger than the available physical space by imperceptibly manipulating users' virtual viewpoints according to different gains. In previous redirected jumping work, different types of gains were imposed separately, without considering the possible interaction effects of horizontal and vertical gains on the jumping distance perception. To figure out how humans perceive distance manipulation when more than one gain is used, in this paper, we explored joint horizontal and vertical gains that manipulate horizontal and vertical distances at the same time during two-legged takeoff jumping in the virtual space. We estimated and analyzed horizontal and vertical detection thresholds by conducting a user study, fitting the data to two-dimensional psychometric functions, and visualizing the fitted 3D plots. We provided quantitative insights into the effects of joint gains on detection thresholds, where the imperceptible range for one gain can be affected by the variation of the other gain. Finally, we designed redirected jumping-based games as applications with joint horizontal and vertical gains and demonstrated the effectiveness of the redirected jumping technique.

Avatars in virtual reality (VR) with fully articulated hands enable users to naturally interact with the virtual environment (VE). Interactions are often performed in a one-to-one mapping between the movements of the user’s real body, for instance, the hands, and the displayed body of the avatar. However, VR also allows manipulating this mapping to introduce non-isomorphic techniques. In this context, research on manipulations of virtual hand movements typically focuses on increasing the user’s interaction space to improve the overall efficiency of hand-based interactions.

Cognitive-physical exercises can reduce the progression of dementia. However, traditional methods often induce problems (e.g., lack of motivation), whereas the success of recent virtual reality (VR) exergames such as Beat Saber may provide a playful, motivational, and immersive alternative. Yet, until now, it remains unclear which game mechanics, concepts, and designs work best for people with dementia, and how to implement exergames for and with this user group. In this paper, we adapted a human-centered design approach to address the specifics of developing VR exergames for people with dementia. This includes semi-structured interviews with stakeholders and contextual inquiries to better analyze the user requirements. Based on our analysis, we present Memory Journalist VR - a novel VR exergame specifically designed for people with dementia in a participatory design process. We report the qualitative evaluation based on the feedback gathered in five focus group sessions. Finally, we discuss the lessons learned, which provide important insights for the design of future VR exergames for people with dementia: (i) creating social gaming activities with a focus on shared aspects, (ii) support of an inverse game flow channel addressing decline and variance in cognitive-physical abilities, and (iii) ensuring a safe VR exergame experience.

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.

Redirected jumping (RDJ) allows users to explore virtual environments (VEs) naturally by scaling a small real-world jump to a larger virtual jump with virtual camera motion manipulation, thereby addressing the problem of limited physical space in VR applications. Previous RDJ studies have mainly focused on detection threshold estimation. However, the effect VE or selfrepresentation (SR) has on the perception or performance of RDJs remains unclear. In this paper, we report experiments to measure the perception (detection thresholds for gains, presence, embodiment, intrinsic motivation, and cybersickness) and physical performance (heart rate intensity, preparation time, and actual jumping distance) of redirected forward jumping under six different combinations of VE (low and high visual richness) and SRs (invisible, shoes, and human-like). Our results indicated that the detection threshold ranges for horizontal translation gains were significantly smaller in the VE with high rather than low visual richness. When different SRs were applied, our results did not suggest significant differences in detection thresholds, but it did report longer actual jumping distances in the invisible body case compared with the other two SRs. In the high visual richness VE, the preparation time for jumping with a human-like avatar was significantly longer than that with other SRs. Finally, some correlations were found between perception and physical performance measures. All these findings suggest that both VE and SRs influence users' perception and performance in RDJ and must be considered when designing locomotion techniques.

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.

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.

Prior studies have explored the possibility of inducing social anxiety (SA) in virtual reality (VR). Among various existing protocols for this purpose, the Trier Social Stress Test (TSST) has been proven to be robust in evoking SA in the majority of participants in both in vivo as well as VR conditions. The TSST consists of giving a speech and performing mental arithmetic calculations each for five minutes in front of three persons. In this paper, we present an adaptation of TSST to investigate the effects of different numbers of virtual humans (VHs) (i.e., three, six, or fifteen) on perceived SA. In addition, we compare the results with an in vivo TSST with three real persons in the audience. Twenty four participants took part in this experiment. As a result, physiological arousal could be observed with VR inducing SA yet less than in vivo TSST. Furthermore, some of the subjective measures showed a high state of anxiety experienced during the experiment. An effect of the virtual audience size could be observed only in heart rate (HR) as a virtual audience size of three VHs induced the highest HR responses which was significantly different from an audience of size six and fifteen.

Bipedal walking is generally considered to be the most natural and common locomotion technique in the physical world, for humans, and the most presence-enhancing form of locomotion in virtual reality (VR). However, there are significant differences in the way people walk in VR compared to their walking behaviour in the real world. For instance, previous studies have shown a significant decrease of gait parameters, in particular, velocity and step length in the virtual environment (VE). However, those studies have only considered short periods of walking. In contrast, many VR applications involve extended exposures to the VE and often include additional cognitive tasks such as way-finding. Hence, it remains an open question whether velocity during VR walking will further slowdown over time or if users of VR will eventually speed-up and adapt their velocity to the VE and move with the same speed as in the real world.

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.

We report an experiment in which participants compared the size of a visual sphere to a haptic sphere in VR. The sizes from two modalities were either congruent or conflicting (with different disparities). Importantly, three standard references (small, medium and large) for haptic sizes were used with the method of constant stimuli. Results show a dominant functional priority of the visual size perception. Moreover, observers demonstrated a central tendency effect: over-estimation for smaller haptic sizes but under-estimation for larger haptic sizes. The results are discussed in the framework of adaptation level theory for haptic size reference, and provide important implications for the design of 3D visuo-haptic human-computer interaction.

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.

The combination of virtual reality (VR) and gamification opens up new vistas for innovative forms of therapy for alcohol use disorder (AUD) and have enormous potential to improve traditional therapy methods. In this paper, three gamified and one non-gamified AUD therapy applications for VR are introduced and evaluated. The games are based on two behavioral therapy methods, which are Cue Exposure Therapy (CET) and Approach Avoidance Training (AAT). The games are realized in the context of a virtual supermarket, which is considered as a relapse-risky environment. The aim is to help AUD patients practice avoiding alcohol first in a VR-based simulation and later in a real supermarket. In preparation for a long-term clinical study, a usability study was conducted with 13 healthy participants. The results show that the VR game was enjoyed, increased the motivation, and fewer errors were made than in the comparable non-gamified application.

We evaluate the ability of locally present participants to localize an avatar head's gaze direction in 360° hosted telepresence. We performed a controlled user study to test two potential solutions to indicate a remote user's gaze. We analyze the influence of the user's distance to the avatar and display technique on localization accuracy. Our experimental results suggest that all these factors have a significant effect on the localization accuracy with varying effect sizes.

Real walking is the most natural way to locomote in virtual reality (VR), but a confined physical walking space limits its applicability. Redirected walking (RDW) is a collection of techniques to solve this problem. One of these techniques aims to imperceptibly rotate the user's view of the virtual scene in order to steer her along a confined path whilst giving the impression of walking in a straight line in a large virtual space. Measurement of perceptual thresholds for the detection of such a modified curvature gain have indicated a radius that is still larger than most room sizes. Since the brain is an adaptive system and thresholds usually depend on previous stimulations, we tested if prolonged exposure to an immersive virtual environment (IVE) with increased curvature gain produces adaptation to that gain and modifies thresholds such that, over time, larger curvature gains can be applied for RDW. Therefore, participants first completed a measurement of their perceptual threshold for curvature gain. In a second session, the same participants were exposed to an IVE with a constant curvature gain in which they walked between two targets for about 20 minutes. Afterwards, their perceptual thresholds were measured again. The results show that the psychometric curves shifted after the exposure session and perceptual thresholds for increased curvature gain further increased. The increase of the detection threshold suggests that participants adapt to the manipulation and stronger curvature gains can be applied in RDW, and therefore improves its applicability in such situations.

Mixed reality (MR)opens up new vistas for human-robot interaction (HRI)scenarios in which a human operator can control and collaborate with co-located robots. For instance, when using a see-through head-mounted-display (HMD)such as the Microsoft HoloLens, the operator can see the real robots and additional virtual information can be superimposed over the real-world view to improve security, acceptability and predictability in HRI situations. In particular, previewing potential robot actions in-situ before they are executed has enormous potential to reduce the risks of damaging the system or injuring the human operator. In this paper, we introduce the concept and implementation of such an MR human-robot collaboration system in which a human can intuitively and naturally control a co-located industrial robot arm for pick-and-place tasks. In addition, we compared two different, multimodal HRI techniques to select the pick location on a target object using (i)head orientation (aka heading)or (ii)pointing, both in combination with speech. The results show that heading-based interaction techniques are more precise, require less time and are perceived as less physically, temporally and mentally demanding for MR-based pick-and-place scenarios. We confirmed these results in an additional usability study in a delivery-service task with a multi-robot system. The developed MR interface shows a preview of the current robot programming to the operator, e. g., pick selection or trajectory. The findings provide important implications for the design of future MR setups.

In this paper we present a floor-based user interface (UI) that allows multiple users to explore a spatial augmented reality (SAR) environment with both monoscopic and stereoscopic projections. Such environments are characterized by a low level of user instrumentation and the capability of providing a shared interaction space for multiple users. However, projector-based systems using stereoscopic display are usually single-user setups, since they can provide the correct perspective for only one tracked person. To address this problem, we developed a set of guidance cues, which are projected onto the floor in order to assist multiple users regarding (i) the interaction with the SAR system, (ii) the identification of regions of interest and ideal viewpoints, and (iii) the collaboration with each other. In a user study with 40 participants all cues were evaluated and a set of feedback elements, which are essential to guarantee an intuitive self-explaining interaction, was identified. The results of the study also indicate that the developed UI guides users to more favorable viewpoints and therefore is able to improve the experience in a multi-user SAR environment.

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.

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.

We present a hybrid system combining immersive and non-immersive technology for traffic engineering experts in the cooperative process of construction site planning and decision-making. We exploit a four-sided CAVE setup, which allows a 360° view of the actual real-world location, while an interactive tabletop positioned in the center of the CAVE provides a map-based 2D planning view. By selecting different locations on the digital map, the 360° environment changes with respect to the selected spot. The tabletop can display more detailed data, e. g., traffic flow and traffic light programs. In the described setup group decisions can be made more effectively compared to current workplace situations. In preliminary focus group discussions, we received positive feedback and plan to expand the system's features in the future.

Animating with keyframes gives animators a lot of control but they can be tedious and complicated to work with. Currently, different solutions try to simplify animation creation by recording the natural hand movements of the user. However, most of the solutions are bound to 2D animations [1] or suffer from a low workflow speed [4]. The proposed Unity plugin AnimationVR uses the HTC Vive system to enable the puppeteering animation technique in VR while still allowing for a fast workflow speed by utilizing the 6DOF controllers. During storyboarding or rapid prototyping, the user can immediately see the results of their actions. Also, Animation Vr is written for easy integration in already existing Unity projects. The plug in was evaluated by four animation experts who agreed that Animation Vr accelerates the workflow while decreasing the animation precision. This trade-off makes it useful for storyboarding in professional environments. The experts also noted the ease of use of the puppeteering technique which could enable beginners to create complex animations without any experience with animating.

Animating with keyframes gives animators a lot of control but they can be tedious and complicated to work with. Currently, different solutions try to simplify animation creation by recording the natural hand movements of the user. However, most of the solutions are bound to 2D animations [1] or suffer from a low workflow speed [2]. The proposed Unity plugin Animation Vr uses the HTC Vive system to enable the puppeteering animation technique in VR while still allowing for a fast workflow speed by utilizing the controllers of the VR system. Also, Animation Vr is written for easy integration in already existing Unity projects. The plugin was evaluated with four animation experts. The consensus was that Animation Vr increases the workflow speed while decreasing the animation precision. This tradeoff makes it useful for storyboarding in professional environments. Additionally, the plugin could improve the understanding of VR storytelling as the animators would create and instantly review the animations in the correct medium. The experts also noted the ease of use of the puppeteering technique which could enable beginners to create complex animations with little to no experience with Animation Vr. Additionally, the accessibility for animation beginners could improve the communication in animation teams between animators and directors.

We introduce Camera Time Warp (CamWarp), a novel reprojection technique for video-see-through augmented reality, which reduces the registration error between captured real-world videos and rendered virtual images. Instead of rendering the image plane locked to the virtual camera, CamWarp renders the image plane at the real-world position it was captured at, and compensates for potential artifacts. We conducted two experiments to evaluate the effectiveness of CamWarp. In the first experiment participants were asked to report subjective discomfort while moving their head in a pattern inspired by the ISO 9241-9 Fitts' Law task at different speeds while the video feed was rendered at varying frame rates. The results show that the technique can significantly reduce subjective levels of discomfort and cybersickness symptoms for all tested configurations. In the second experiment participants were asked to move physical objects on a projected path as quickly and precisely as possible. Results show a positive effect of CamWarp on speed and accuracy.

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.

Understanding real walking in virtual environments (VEs) is important for immersive experiences, allowing users to move through VEs in the most natural way. Previous studies have shown that basic implementations of real walking in virtual spaces, 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 user's physical locomotion. However, these findings have been reported in most cases only for young persons, e.g., students, whereas older adults are clearly underrepresented in such studies. Recently, virtual reality (VR) has received significant public and media attention. Therefore, it appears reasonable to assume that people at different ages will have access to VR, and might use this technology more and more in application scenarios such as rehabilitation or training. To better understand how people at different ages walk and perceive locomotion in VR, we have performed a study to investigate the effects of (non-)isometric mappings between physical movements and virtual motions in the VE on the walking biomechanics across generations, i.e., younger and older adults. Three primary domains (pace, base of support and phase) of spatio-temporal parameters were identified to evaluate gait performance. The results show that the older adults walked very similar in the real and VE in the pace and phasic domains, which differs from results found in younger adults. In contrast, the results indicate differences in terms of base of support domain parameters for both groups while walking within a VE and the real world. For non-isometric mappings, we found in both younger and older adults an increased divergence of gait parameters in all domains correlating with the up- or down-scaled velocity of visual self-motion feedback. The results provide important insights into the design of future VR applications for older adults in domains ranging from medicine and psychology to rehabilitation.

We are pleased to present the technical papers for IEEE VR 2018: the 25th IEEE Conference on Virtual Reality and 3D User Interfaces, held March 18-22, 2018 in Reutlingen, Germany. IEEE VR 2018 features two categories of submissions: (i) VR Journal Papers, and (ii) VR Conference Papers. Both categories have their own program committees, submission processes, and review processes. This year, 178 submissions were submitted to the Journal track from which 29 were accepted as articles to IEEE TVCG (16.3%). All of these will be presented at the IEEE VR 2018 conference, along with 6 additional papers in the VR area that were published in IEEE TVCG during the past year. Furthermore, 6 submission (3.4%) were recommended for a regular issue of TVCG with major revisions with reviewer continuity. Each of the papers in this special issue went through a rigorous two-round review process. All accepted journal papers are published in a special issue of IEEE Transactions on Visualization and Computer Graphics (TVCG). The Proceedings of the IEEE Conference on Virtual Reality and 3D User Interfaces contains all of the accepted conference papers and the poster abstracts.

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.

This work is observing the impacts/influence of different mapping functions between the user's flick gesture and the animation of the flicked object. The flick gesture, in which the user quickly swipes a finger across the screen and lifts the finger without slowing down, is a popular interaction technique on multitouch displays, e. g. for navigating on digital maps. While flick operations are well established on small mobile touch screens, the exact implementation of this technique on large multitouch tabletops needs to be adjusted to several parameters, especially flick velocity and inertia duration.

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.

This video presents the experimental setup of an immersive flight simulation system, which combines body tracking with a head-mounted display. Users are hanging freely in a climbing harness in order to improve the impression to fly. The base system was created by a group of students during one semester as a bachelor project. A study revealed that a high degree of presence is achievable by the combination of body-posture based control and 3D visualization via a head-mounted display while hanging freely in a climbing gear. Furthermore the results of a study that compares two different steering methods are presented. Both control methods seem to be quite interesting and intuitively controllable but show individual preferences among the participants of the study. In our experiments very frequently strong vaction effects were reported when flying turns to one side. The setup very likely causes simulator sickness, especially if a participant was bad in controlling his flight.

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).

Current virtual reality (VR) technologies have enormous potential to allow humans to experience computer-generated immersive virtual environments (IVEs). Many of these IVEs support near-natural audiovisual stimuli similar to the stimuli generated in our physical world. However, decades of VR research have been devoted to exploring and understand differences between perception and action in such IVEs compared to real-world perception and action. Although, significant differences have been revealed for spatiotemporal perception between IVEs and the physical world such as distance underestimation, there is still a scarcity of knowledge about the reasons for such perceptual discrepancies, in particular regarding the perception of temporal durations in IVEs. In this article, we explore the effects of manipulated zeitgebers, cognitive load and immersion on time estimation as yet unexplored factors of spatiotemporal perception in IVEs. We present an experiment in which we analyze human sensitivity to temporal durations while experiencing an immersive head-mounted display (HMO) environment. We found that manipulations of external zeitgebers caused by a natural or unnatural movement of the virtual sun had a significant effect on time judgments. Moreover, using the dual-task paradigm the results show that increased spatial and verbal cognitive load resulted in a significant shortening of judged time as well as an interaction with the external zeitgebers. Finally, we discuss the implications for the design of near-natural computer-generated virtual worlds.

Redirected walking allows users to walk through a large-scale immersive virtual environment (IVE) while physically remaining in a reasonably small workspace. Therefore, manipulations are applied to virtual camera motions so that the user's self-motion in the virtual world differs from movements in the real world. Previous work found that the human perceptual system tolerates a certain amount of inconsistency between proprioceptive, vestibular and visual sensation in IVEs, and even compensates for slight discrepancies with recalibrated motor commands. Experiments showed that users are not able to detect an inconsistency if their physical path is bent with a radius of at least 22 meters during virtual straightforward movements. If redirected walking is applied in a smaller workspace, manipulations become noticeable, but users are still able to move through a potentially infinitely large virtual world by walking. For this semi-natural form of locomotion, the question arises if such manipulations impose cognitive demands on the user, which may compete with other tasks in IVEs for finite cognitive resources. In this article we present an experiment in which we analyze the mutual influence between redirected walking and verbal as well as spatial working memory tasks using a dual-tasking method. The results show an influence of redirected walking on verbal as well as spatial working memory tasks, and we also found an effect of cognitive tasks on walking behavior. We discuss the implications and provide guidelines for using redirected walking in virtual reality laboratories.

A large body of literature has analyzed differences between perception in the real world and virtual environments (VE) in terms of space, distance and speed perception. So far, no empirical data has been collected for time misperception in immersive VEs to our knowledge. However, there is evidence that time perception can deviate from veridical judgments, for instance, due to visual or auditive stimulation related to motion misperception. In this work we evaluate time perception during walking motions with a pilot study in an immersive head-mounted display (HMD) environment. Significant differences between time judgments in the real and virtual environment could not be observed.

Locomotion is one of the most fundamental processes in the real world, and its consideration in immersive virtual environments (IVEs) is of major importance for many application domains requiring immersive walkthroughs. From a simple physics perspective, such self-motion can be defined by the three components speed, distance, and time. Determining motions in the frame of reference of a human observer imposes a significant challenge to the perceptual processes in the human brain, and the resulting speed, distance, and time percepts are not always veridical. In previous work in the area of IVEs, these components were evaluated in separate experiments, i. e., using largely different hardware, software and protocols.

One major benefit of wearable computers is that users can naturally move and explore computer-mediated realities. However, researchers often observe that users' space and motion perception severely differ in such environments compared to the real world, an effect that is often attributed to slight discrepancies in sensory cues, for instance, caused by tracking inaccuracy or system latency. This is particularly true for virtual reality (VR), but such conflicts are also inherent to augmented reality (AR) technologies. Although, head-worn displays will become more and more available soon, the effects on motion perception have rarely been studied, and techniques to modify self-motion in AR environments have not been leveraged so far. In this paper we introduce the concept of computer-mediated optic flow, and analyze its effects on self-motion perception in AR environments. First, we introduce different techniques to modify optic flow patterns and velocity. We present a psychophysical experiment which reveals differences in self-motion perception with a video see-through head-worn display compared to the real-world viewing condition. We show that computer-mediated optic flow has the potential to make a user perceive self-motion as faster or slower than it actually is, and we discuss its potential for future AR setups.

Recent developments in the fields of display technology provide new possibilities for engaging users in interactive exploration of three-dimensional (3D) virtual environments (VEs). Tracking technologies such as the Microsoft Kinect and emerging multi-touch interfaces enable inexpensive and low-maintenance interactive setups while providing portable solutions for engaging presentations and exhibitions. In this poster we describe an extension of the smARTbox, which is a responsive touch-enabled stereoscopic out-of-the-box technology for interactive setups. We extended the smARTbox by making the entire setup portable, which provides a new interaction experience, when exploring 3D data sets. The portable tracked multi-touch interface supports two different interaction paradigms: exploration by multi-touch gestures as well a s exploration by lateral movements of the entire setup. Hence, typical gestures supporting rotation and panning can be implemented via multi-touch gestures, but also via actual movements of the setup.

Accurate perception of size and distance in a three-dimensional virtual environment is important for many applications. However, several experiments have revealed that spatial perception of virtual environments often deviates from the real world, even when the virtual scene is modeled as an accurate replica of a familiar physical environment. While previous research has elucidated various factors that can facilitate perceptual shifts, the effects of geometric rendering parameters on spatial cues are still not well understood.

This article presents an analysis of using multiple Microsoft Kinects to track users in a VR system. More specifically, we analyse the capability of Kinects to track infrared points for use in VR applications. Multiple Kinect sensors may serve as a low cost and affordable means to track position information across a large lab space in applications where precise location tracking is not necessary. We present our findings and analysis of the tracking range of a Kinect sensor in situations in which multiple Kinects are present. Overall, the Kinect sensor works well for this application and in lieu of more expensive options, the Kinect sensors may be a viable option for very low-cost tracking in VR applications.

Natural walking can provide a compelling experience in immersive virtual environments, but it remains an implementation challenge due to the physical space constraints imposed on the size of the virtual world. The use of redirection techniques is a promising approach that relaxes the space requirements of natural walking by manipulating the user's route in the virtual environment, causing the real world path to remain within the boundaries of the physical workspace. In this paper, we present and apply a novel taxonomy that separates redirection techniques according to their geometric flexibility versus the likelihood that they will be noticed by users. Additionally, we conducted a user study of three reorientation techniques, which confirmed that participants were less likely to experience a break in presence when reoriented using the techniques classified as subtle in our taxonomy. Our results also suggest that reorientation with change blindness illusions may give the impression of exploring a more expansive environment than continuous rotation techniques, but at the cost of negatively impacting spatial knowledge acquisition.

Walking is the most natural form of locomotion for humans, and real walking interfaces have demonstrated their benefits for several navigation tasks. With recently proposed redirection techniques it becomes possible to overcome space limitations as imposed by tracking sensors or laboratory setups, and, theoretically, it is now possible to walk through arbitrarily large virtual environments. However, walking as sole locomotion technique has drawbacks, in particular, for long distances, such that even in the real world we tend to support walking with passive or active transportation for longer-distance travel. In this article we show that concepts from the field of redirected walking can be applied to movements with transportation devices. We conducted psychophysical experiments to determine perceptual detection thresholds for redirected driving, and set these in relation to results from redirected walking. We show that redirected walking-and-driving approaches can easily be realized in immersive virtual reality laboratories, e. g., with electric wheelchairs, and show that such systems can combine advantages of real walking in confined spaces with benefits of using vehicle-based self-motion for longer-distance travel.

Motion perception in immersive virtual environments significantly differs from the real world. For example, previous work has shown that users tend to underestimate travel distances in virtual environments (VEs). As a solution to this problem, researchers proposed to scale the mapped virtual camera motion relative to the tracked real-world movement of a user until real and virtual motion are perceived as equal, i.e., real-world movements could be mapped with a larger gain to the VE in order to compensate for the underestimation. However, introducing discrepancies between real and virtual motion can become a problem, in particular, due to misalignments of both worlds and distorted space cognition. In this paper, we describe a different approach that introduces apparent self-motion illusions by manipulating optic flow fields during movements in VEs. These manipulations can affect self-motion perception in VEs, but omit a quantitative discrepancy between real and virtual motions. In particular, we consider to which regions of the virtual view these apparent self-motion illusions can be applied, i.e., the ground plane or peripheral vision. Therefore, we introduce four illusions and show in experiments that optic flow manipulation can significantly affect users' self-motion judgments. Furthermore, we show that with such manipulations of optic flow fields the underestimation of travel distances can be compensated.

Head-mounted displays (HMDs) allow users to observe virtual environments (VEs) from an egocentric perspective. However, several experiments have provided evidence that egocentric distances are perceived as compressed in VEs relative to the real world. Recent experiments suggest that the virtual view frustum set for rendering the VE has an essential impact on the user's estimation of distances. In this article we analyze if distance estimation can be improved by calibrating the view frustum for a given HMD and user. Unfortunately, in an immersive virtual reality (VR) environment, a full per user calibration is not trivial and manual per user adjustment often leads to mini- or magnification of the scene. Therefore, we propose a novel per user calibration approach with optical see-through displays commonly used in augmented reality (AR). This calibration takes advantage of a geometric scheme based on 2D point - 3D line correspondences, which can be used intuitively by inexperienced users and requires less than a minute to complete. The required user interaction is based on taking aim at a distant target marker with a close marker, which ensures non-planar measurements covering a large area of the interaction space while also reducing the number of required measurements to five. We found the tendency that a calibrated view frustum reduced the average distance underestimation of users in an immersive VR environment, but even the correctly calibrated view frustum could not entirely compensate for the distance underestimation effects.

Recent developments in the area of touch and display technologies have suggested to combine multi-touch systems and stereoscopic visualization. Stereoscopic perception requires each eye to see a slightly different perspective of the same scene, which results in two distinct projections on the display. Thus, if the user wants to select a 3D stereoscopic object in such a setup, the question arises where she would touch the 2D surface to indicate the selection. A user may apply different strategies, for instance touching the midpoint between the two projections, or touching one of them.

In recent years many advances have enabled users to naturally navigate large-scale graphical worlds. The entertainment industry is increasingly providing visual and body-based cues to users to increase the natural feel of their navigational experience. So far, however, none of the existing solutions fully support the most natural locomotion through virtual worlds. Techniques and technologies which have the advantage of insights into human perceptual sensitivity thus have to be considered. In this context, by far the most natural way to move through the real world is via a full body experience where we receive sensory stimulation to all of our senses, i.e. when walking, running, biking or driving. With some exciting technological advances, people are now beginning to get this same full body sensory experience when navigating computer-generated, three-dimensional environments. Enabling an active and dynamic ability to navigate large-scale virtual scenes is of great interest for many 3D applications demanding locomotion, such as video games, edutainment, simulation, rehabilitation, military, tourism or architecture. Today it is still mostly impossible to freely move through computer generated environments in exactly the same way as the real world. Unnatural and artificial approaches are instead applied, providing only the visual sensation of self-motion. Computer graphics environments were initially restricted to visual displays combined with interaction devices - for example the joystick or mouse - providing often unnatural inputs to generate self-motion. Today, more and more interaction devices like Nintendo Wii, Microsoft Kinect or Sony EyeToy enable intuitive and natural interaction. In this context many research groups are investigating natural, multimodal methods of generating self-motion in virtual worlds based on such consumer hardware.

Motion perception in immersive virtual reality environments significantly differs from the real world. For example, previous work has shown that users tend to underestimate travel distances in immersive virtual environments (VEs). As a solution to this problem, some researchers propose to scale the mapped virtual camera motion relative to the tracked real-world movement of a user until real and virtual motion appear to match, i. e., real-world movements could be mapped with a larger gain to the VE in order to compensate for the underestimation. Although this approach usually results in more accurate self-motion judgments by users, introducing discrepancies between real and virtual motion can become a problem, in particular, due to misalignments of both worlds and distorted space cognition. In this paper we describe a different approach that introduces apparent self-motion illusions by manipulating optic flow fields during movements in VEs. These manipulations can affect self-motion perception in VEs, but omit a quantitative discrepancy between real and virtual motions. We introduce four illusions and show in experiments that optic flow manipulation can significantly affect users' self-motion judgments. Furthermore, we show that with such manipulation of optic flow fields the underestimation of travel distances can be compensated.

Computer graphics systems provide sophisticated means to render virtual 3D space to 2D display surfaces by applying planar geometric projections. In a realistic viewing condition the perspective applied for rendering should appropriately account for the viewer's location relative to the image. As a result, an observer would not be able to distinguish between a rendering of a virtual environment on a computer screen and a view “through” the screen at an identical real-world scene. Until now, little effort has been made to identify perspective projections which cause human observers to judge them to be realistic. In this article we analyze observers' awareness of perspective distortions of virtual scenes displayed on a computer screen. These distortions warp the virtual scene and make it differ significantly from how the scene would look in reality. We describe psychophysical experiments that explore the subject's ability to discriminate between different perspective projections and identify projections that most closely match an equivalent real scene. We found that the field of view used for perspective rendering should match the actual visual angle of the display to provide users with a realistic view. However, we found that slight changes of the field of view in the range of 10-20% for two classes of test environments did not cause a distorted mental image of the observed models.

In visual perception, change blindness describes the phenomenon that persons viewing a visual scene may apparently fail to detect significant changes in that scene. These phenomena have been observed in both computer-generated imagery and real-world scenes. Several studies have demonstrated that change blindness effects occur primarily during visual disruptions such as blinks or saccadic eye movements. However, until now the influence of stereoscopic vision on change blindness has not been studied thoroughly in the context of visual perception research. In this paper, we introduce change blindness techniques for stereoscopic virtual reality (VR) systems, providing the ability to substantially modify a virtual scene in a manner that is difficult for observers to perceive. We evaluate techniques for semiimmersive VR systems, i.e., a passive and active stereoscopic projection system as well as an immersive VR system, i.e., a head-mounted display, and compare the results to those of monoscopic viewing conditions. For stereoscopic viewing conditions, we found that change blindness phenomena occur with the same magnitude as in monoscopic viewing conditions. Furthermore, we have evaluated the potential of the presented techniques for allowing abrupt, and yet significant, changes of a stereoscopically displayed virtual reality environment.

The display units integrated in today's head-mounted displays (HMDs) provide only a limited field of view (FOV) to the virtual world. In order to present an undistorted view to the virtual environment (VE), the perspective projection used to render the VE has to be adjusted to the limitations caused by the HMD characteristics. In particular, the geometric field of view (GFOV), which defines the virtual aperture angle used for rendering of the 3D scene, is set up according to the display field of view (DFOV). A discrepancy between these two fields of view distorts the geometry of the VE in a way that either minifies or magnifies the imagery displayed to the user. It has been shown that this distortion has the potential to affect a user's perception of the virtual space, sense of presence, and performance on visual search tasks. In this paper, we analyze the user's perception of a VE displayed in a HMD, which is rendered with different GFOVs. We introduce a psychophysical calibration method to determine the HMD's actual field of view, which may vary from the nominal values specified by the manufacturer. Furthermore, we conducted two experiments to identify perspective projections for HMDs, which are identified as natural by subjects--even if these perspectives deviate from the perspectives that are inherently defined by the DFOV. In the first experiment, subjects had to adjust the GFOV for a rendered virtual laboratory such that their perception of the virtual replica matched the perception of the real laboratory, which they saw before the virtual one. In the second experiment, we displayed the same virtual laboratory, but restricted the viewing condition in the real world to simulate the limited viewing condition in a HMD environment. We found that subjects evaluate a GFOV as natural when it is larger than the actual DFOV of the HMD--in some cases up to 50 percent--even when subjects viewed the real space with a limited field of view.

Miniaturized unmanned flying robots, also referred to as MUAVs (Micro Unmanned Aerial Vehicles) open up completely new fields of innovative applications in the areas of civil security, cellular networks, surveying, entertainment and media. The AVIGLE project is based on the vision of a novel, widely applicable avionic service platform which supports multiple high-tech services by using open interfaces. Recent developments in the area of lithium polymer batteries and carbon fiber-reinforced plastic materials let MUAVs become an aerial platform, that can be equipped with a variety of sensors such as image or time of flight (ToF) cameras. Furthermore, it is also possible to mount communication technologies on the platform in order to let the MUAVs work as communication hot spots or relais at places where no cellular networks are available. In this paper we present a system of systems concept of an Unmanned Aerial System working as a service platform for different Concepts of Operations (ConOps).

In visual perception, change blindness describes the phenomenon that persons viewing a visual scene may apparently fail to detect significant changes in that scene. These phenomena have been observed in both computer generated imagery and real-world scenes. Several studies have demonstrated that change blindness effects occur primarily during visual disruptions such as blinks or saccadic eye movements. However, until now the influence of stereoscopic vision on change blindness has not been studied thoroughly in the context of visual perception research. In this paper we introduce change blindness techniques for stereoscopic projection systems, providing the ability to substantially modify a virtual scene in a manner that is difficult for observers to perceive. We evaluate techniques for passive and active stereoscopic viewing and compare the results to those of monoscopic viewing conditions. For stereoscopic viewing conditions, we found that change blindness phenomena occur with the same magnitude as in monoscopic viewing conditions. Furthermore, we have evaluated the potential of the presented techniques for allowing abrupt, and yet significant, changes of a stereoscopically displayed virtual reality environment.

Physical characteristics and constraints of today's head-mounted displays (HMDs) often impair interaction in immersive virtual environments (VEs). For instance, due to the limited field of view (FOV) subtended by the display units in front of the user's eyes more effort is required to explore a VE by head rotations than for exploration in the real world.

In immersive virtual environments (IVEs), users can control their virtual viewpoint by moving their tracked head and walking through the real world. Usually, movements in the real world are mapped one-to-one to virtual camera motions. With redirection techniques, the virtual camera is manipulated by applying gains to user motion so that the virtual world moves differently than the real world. Thus, users can walk through large-scale IVEs while physically remaining in a reasonably small workspace. In psychophysical experiments with a two-alternative forced-choice task, we have quantified how much humans can unknowingly be redirected on physical paths that are different from the visually perceived paths. We tested 12 subjects in three different experiments: (E1) discrimination between virtual and physical rotations, (E2) discrimination between virtual and physical straightforward movements, and (E3) discrimination of path curvature. In experiment E1, subjects performed rotations with different gains, and then had to choose whether the visually perceived rotation was smaller or greater than the physical rotation. In experiment E2, subjects chose whether the physical walk was shorter or longer than the visually perceived scaled travel distance. In experiment E3, subjects estimate the path curvature when walking a curved path in the real world while the visual display shows a straight path in the virtual world. Our results show that users can be turned physically about 49 percent more or 20 percent less than the perceived virtual rotation, distances can be downscaled by 14 percent and upscaled by 26 percent, and users can be redirected on a circular arc with a radius greater than 22 m while they believe that they are walking straight.

To better understand motion perception in immersive virtual environments, we conducted a user study to quantify perception of scene motion as subjects yawed their heads. We measured psychometric functions of scene-velocity thresholds for different head motions and then extracted 75% thresholds, creating scene-velocity thresholds as functions of three measures of head motion: 1) Angular Range, 2) Peak Angular Velocity, 3) and Peak Angular Acceleration. We also measured scene-velocity thresholds for four phases of head motion: 1) the Start of the head turn, 2) the Center of the head turn, 3) the End of the head turn, 4) and All of the head turn. Scene-velocity thresholds increased as head motion increased for all tested conditions.

In order to increase a user's sense of presence in an artificial environment some researchers propose a gradual transition from reality to the virtual world instead of immersing users into the virtual world directly. One approach is to start the VR experience in a virtual replica of the physical space to accustom users to the characteristics of VR, e.g., latency, reduced field of view or tracking errors, in a known environment. Although this procedure is already applied in VR demonstrations, until now it has not been verified whether the usage of such a transitional environment - as transition between real and virtual environment - increases someone's sense of presence. We have observed subjective, physiological and behavioral reactions of subjects during a fully-immersive flight phobia experiment under two different conditions: the virtual flight environment was displayed immediately, or subjects visited a transitional environment before entering the virtual flight environment. We have quantified to what extent a gradual transition to the VE via a transitional environment increases the level of presence. We have found that subjective responses show significantly higher scores for the user's sense of presence, and that subjects' behavioral reactions change when a transitional environment is shown first. Considering physiological reactions, no significant difference could be found.

The display units integrated in todays head-mounted displays (HMDs) provide only a limited field of view (FOV) to the virtual world. In order to present an undistorted view to the virtual environment (VE), the perspective projection used to render the VE has to be adjusted to the limitations caused by the HMD characteristics. In particular, the geometric field of view (GFOV), which defines the virtual aperture angle used for rendering of the 3D scene, is set up according to the display's field of view. A discrepancy between these two fields of view distorts the geometry of the VE in a way that either minifies or magnifies the imagery displayed to the user. Discrepancies between the geometric and physical FOV causes the imagery to be minified or magnified. This distortion has the potential to negatively or positively affect a user's perception of the virtual space, sense of presence, and performance on visual search tasks.

Traveling through immersive virtual environments (IVEs) by means of real walking is an important activity to increase naturalness of VR-based interaction. However, the size of the virtual world often exceeds the size of the tracked space so that a straightforward implementation of omni-directional and unlimited walking is not possible. Redirected walking is one concept to solve this problem of walking in IVEs by inconspicuously guiding the user on a physical path that may differ from the path the user visually perceives. When the user approaches a virtual object she can be redirected to a real proxy object that is registered to the virtual counterpart and provides passive haptic feedback. In such passive haptic environments, any number of virtual objects can be mapped to proxy objects having similar haptic properties, e.g., size, shape and texture. The user can sense a virtual object by touching its real world counterpart. Redirecting a user to a registered proxy object makes it necessary to predict the user's intended position in the IVE. Based on this target position we determine a path through the physical space such that the user is guided to the registered proxy object. We present a taxonomy of possible redirection techniques that enable user guidance such that inconsistencies between visual and proprioceptive stimuli are imperceptible. We describe how a user's target in the virtual world can be predicted reliably and how a corresponding real-world path to the registered proxy object can be derived.

In this paper we introduce a virtual locomotion system that allows navigation within any large-scale virtual environment (VE) by real walking. In contrast to the work of Razzaque et al. (2001) we have developed generic redirected walking concepts by combining motion compression, i. e., scaling the real distance users walk, rotation gains, which make the real turns smaller or larger, and curvature gains, which bend the user's walking direction such that s/he walks on a curve. Furthermore, we introduce the new concept of dynamic passive haptics which extends passive haptics (Insko et al., 2001; Kohli et al., 2005) in such a way that any number of virtual objects can be sensed by means of real proxy objects having similar haptic capabilities, i. e., size, shape and surface structure. We have evaluated these concepts and explain technical details regarding their integration into legacy 3D graphics applications.

Redirected walking allows users to walk through large-scale immersive virtual environments (IVEs) while physically remaining in a reasonably small workspace by intentionally injecting scene motion into the IVE. In a constant stimuli experiment with a twoalternative-forced-choice task we have quantified how much humans can unknowingly be redirected on virtual paths which are different from the paths they actually walk. 18 subjects have been tested in four different experiments: (E1a) discrimination between virtual and physical rotation, (E1b) discrimination between two successive rotations, (E2) discrimination between virtual and physical translation, and discrimination of walking direction (E3a) without and (E3b) with start-up. In experiment E1a subjects performed rotations to which different gains have been applied, and then had to choose whether or not the visually perceived rotation was greater than the physical rotation. In experiment E1b subjects discriminated between two successive rotations where different gains have been applied to the physical rotation. In experiment E2 subjects chose if they thought that the physical walk was longer than the visually perceived scaled travel distance. In experiment E3a subjects walked a straight path in the IVE which was physically bent to the left or to the right, and they estimate the direction of the curvature. In experiment E3a the gain was applied immediately, whereas the gain was applied after a start-up of two meters in experiment E3b. Our results show that users can be turned physically about 68% more or 10 % less than the perceived virtual rotation, distances can be up- or down-scaled by 22%, and users can be redirected on an circular arc with a radius greater than 24 meters while they believe they are walking straight.

In this paper we introduce new user interface concepts for fish tank virtual reality (VR) systems based on autostereoscopic (AS) display technologies. Such AS displays allow to view stereoscopic content without requiring special glasses. Unfortunately, until now simultaneous monoscopic and stereoscopic display was not possible. Hence prior work on fish tank VR systems focussed either on 2D or 3D interactions. In this paper we introduce so called interscopic interaction concepts providing an improved working experience, which enable great potentials in terms of the interaction between 2D elements, which may be displayed either in monoscopic or stereoscopic, e.g., GUI items, and the 3D virtual environment usually displayed stereoscopically. We present a framework which is based on a software layer between the operating system and its graphical user interface supporting the display of both mono- as well as stereoscopic content in arbitrary regions of an autostereoscopic display. The proposed concepts open up new vistas for the interaction in environments where essential parts of the GUI are displayed monoscopically and other parts are rendered stereoscopically. We address some essential issues of such fish tank VR systems and introduce intuitive interaction concepts which we have realized

Figure 1: Using hybrid travel approaches (left) in outdoor pedestrian mode using scaled user movements in a 3D building evaluation system, (middle) in indoor pedestrian mode displayed in Google Earth, and (right) in outdoor mode in Microsoft Virtual Earth. In this paper we present hybrid traveling concepts that enable users to navigate immersively through 3D geospatial environments displayed by arbitrary applications such as Google Earth or Microsoft Virtual Earth. We propose a framework which allows to integrate virtual reality (VR) based interaction devices and concepts into such applications that do not support VR technologies natively. In our proposed setup the content displayed by a geospatial application is visualized stereoscopically on a head-mounted display (HMD) for immersive exploration. The user’s body is tracked in order to support natural traveling through the VE via a walking metaphor. Since the VE usually exceeds the dimension of the area in which the user can be tracked, we propose different strategies to map the user’s movement into the virtual world intuitively. Moreover, commonly available devices and interaction techniques are presented for both-handed interaction to enrich the navigation process.