This paper presents the first systematic investigation of how congruence in visual self-representation influences self-perception and behavior. We span a continuum from the physical self through avatars with graded self-similarity to clearly dissimilar avatars in virtual reality (VR). In a 1 ×4 within-user study, participants completed movement and quiz tasks in either physical reality or a digital twin environment in VR, where they embodied one of three avatars: a photorealistic self-similar avatar, a dissimilar same-gender avatar, or a dissimilar opposite-gender avatar. Subjective measures included presence, sense of embodiment, self-identification, and perceived change, and were complemented by an objective movement metric of behavioral change. Compared to physical reality, VR, even with a self-similar avatar, produced lower presence, a weaker sense of embodiment, and reduced self-identification, revealing a persistent gap in visual congruence. Within VR, self-similar avatars enhanced body ownership, self-location, and self-identification relative to dissimilar avatars. Conversely, dissimilar avatars produced measurable behavioral changes compared with self-similar ones. Gender cues, however, had little impact in gender-neutral tasks. Overall, the findings show that photorealistic self-similar avatars reinforce embodiment and self-identification. However, VR still falls short of achieving congruence with physical reality, underscoring key challenges for avatar realism and ecological validity.

The global prevalence of mental health disorders has created a substantial treatment gap. To support clinicians and increase access to care, researchers in the field of Artificial Intelligence (AI) and Virtual Reality (VR) have investigated technology-mediated psychotherapy for years. However, research about stakeholders' concerns and their readiness to use AI in psychotherapy remains scarce. This study focuses on a user-centered approach to accommodate patients' concerns and, based on the results, implement measures to foster self-disclosure and trust towards an embodied AI therapist in VR. First, we conducted an online study with mental health patients $(N=152)$, which identified data autonomy and transparency as their primary ethical concerns. In a subsequent in-person VR study $(N=90)$ we compared effects of increased data autonomy and transparency on self-disclosure and trust towards an embodied AI therapist. Results indicated that higher data autonomy led to greater self-disclosure, while transparency had no significant effect. Manipulating data autonomy and transparency did not affect perceived trust, though exploratory calculations revealed that women reported significantly higher trust levels than men. These findings illuminate patients' priorities and provide implications for technical designs for AI-driven mental health care.

Integrated Virtual Reality (IVR) systems are central to avatar-mediated use cases in Virtual Reality (VR), reconstructing users' movements on avatars. They differ primarily in their tracking architectures, which determine how completely and accurately users' movements are captured and reconstructed on avatars. Many current IVR systems reduce user-worn hardware, trading reconstruction accuracy against cost and setup complexity, yet their impact on user experience and task performance across use cases remains underexplored. We compared three reduced user-worn IVR systems. Each system has distinct technical approaches: (1) Captury (markerless outside-in optical tracking), (2) Meta Movement SDK (markerless inside-out optical tracking), and (3) Vive Trackers (marker-based outside-in optical tracking with IMUs). In a 3x5 mixed-design, participants performed five tasks, simulating different use cases, to probe distinct aspects of these systems. No system consistently outperformed the others. Meta excelled in hand-based, fast-paced interactions, while Captury and Vive performed better in lower-body tasks and during full-body pose observation. These findings underscore the need to evaluate reduced user-worn IVR systems within the specific use case. We offer practical guidance for system selection based on use-case demands and released our tasks as an open-source, extensible framework to support future evaluations for selecting IVR systems.

Social Virtual Reality (SVR) allows users to meet and build relationships through embodied avatars and real-time interaction in virtual spaces. While embodiment can strengthen social connections and presence, it can also intensify negative encounters, making SVR particularly vulnerable to harassment. Despite frequent reports of verbal, visual, and "physical" violations in SVR, little is known about how harassment reshapes users' self-perception, including their sense of embodiment, self-identification, closeness, and avatar customization preferences. We conducted a controlled experiment with 52 participants who experienced either a neutral or a harassment condition in a scenario modeled after real SVR incidents. Participants perceived the harassing peer as significantly more negative, annoying, and disturbing than the neutral peer. Contrary to prior reports, harassment did not significantly affect well-being measures, including emotional state, self-esteem, and physiological arousal, within this controlled scenario. However, participants reported stronger bodily change, attributed more of their own attitudes and emotions to their avatars, and increased interpersonal distance when personal space was invaded. Self-reported coping strategies included ignoring, stepping back, using humor, and retaliating. Notably, avatar customization preferences shifted across conditions. Participants in the neutral condition favored personalized avatars, whereas those in the harassment condition more frequently preferred anonymity in public spaces. Together, these findings demonstrate that harassment in SVR not only exploits embodiment but also reshapes self-perception. We further contribute methodological insights into how harassment can be ethically and reproducibly studied in controlled SVR-like experiments.

Virtual Reality Exposure Therapy (VRET) has become an effective, customizable, and affordable treatment for various psychological and physiological disorders. Specifically, it is used to treat specific anxiety disorders, such as acrophobia or arachnophobia, for decades. However, to ensure a positive outcome for patients, we must understand and control the effects potentially caused by the technology and medium of Virtual Reality (VR) itself. This article specifically investigates the impact of the Plausibility illusion (Psi), as one of the two theorized presence components, on the fear of heights. In two experiments, 30 participants each experienced two different heights with congruent and incongruent object behaviors in a 2 x 2 within-subject design. Results show that the strength of the congruence manipulation plays a significant role. Only when incongruencies are strong enough will they be recognized by users, specifically in high fear conditions, as triggered by exposure to increased heights. If incongruencies are too subtle, they seem to be overshadowed by the stronger fear reactions. Our evidence contributes to recent theories of VR effects and emphasizes the importance of understanding and controlling factors potentially assumed to be incidental, specifically during VRET designs. Incongruencies should be controlled so that they do not have an unwanted influence on the patient’s fear response.

Interpupillary distance (IPD) is the most important parameter for creating a user-specific stereo parallax, which in turn is crucial for correct depth perception. This is why contemporary Head-Mounted Displays (HMDs) offer adjustable lenses to adapt to users’ individual IPDs. However, today’s Video See-Through Augmented Reality (VST AR) HMDs use fixed camera placements to reconstruct the stereoscopic view of a user’s environment. This leads to a potential mismatch between individual IPD settings and the fixed Inter-Camera Distances (ICD), which can lead to perceptual incongruencies, limiting the usability and, potentially, the applicability of VST AR in depth-sensitive use cases. To investigate this incongruency between IPD and ICD, we conducted a 2 × 3 mixed-factor design user study using a near-field, open-loop reaching task comparing distance judgments of Virtual Reality (VR) and VST AR. We also investigated changes in reaching performance via perceptual calibration by incorporating a feedback phase between pre- and post-phase conditions, with a particular focus on the influence of IPD-ICD differences. Our Linear Mixed Model (LMM) analysis showed a significant difference between VR and VST AR, an effect of IPD-ICD mismatch, and a combined effect of both factors. However, subjective measures showed no effect underlining the subconscious nature of the perception of VST AR. This novel insight and its consequences are discussed specifically for depth perception tasks in AR, eXtended Reality (XR), and potential use cases.

Autonomous vehicles allow people to focus on parallel tasks while the vehicle handles the driving task itself. This enables new opportunities like mobile workspaces. This paper explores the conceptualization and prototyping of a collaborative workspace in autonomous vehicles. Through a user-centered design approach, we developed a concept that utilizes the space of the vehicle interior, particularly windows, as interactive display surfaces. A prototype was simulated in virtual reality to empirically investigate its influence on collaborative work. Our work focused on two research questions: 1) How should a collaborative workspace in an autonomous vehicle be designed to utilize the unique spatial properties of an autonomous vehicle and 2) to what extend the proposed design supports Workspace Awareness, Social and Spatial Presence - factors of successful remote collaboration. The results of the empirical study indicate that including the utilization of the vehicle interior significantly improves Workspace Awareness and Social Presence compared to a layout centered only on the windshield as interaction surface. However, no significant differences were observed in Spatial Presence between the two layouts. This research highlights the potential of spatial interactions to transform autonomous vehicles into effective collaborative workspaces by leveraging the spatial affordances of the vehicle interior. It underscores the importance of user-centered design and utilizing simulation in virtual reality for the development of applications for non-driving related tasks. This work contributes to the understanding of how autonomous vehicles can be adapted for collaborative work, opening new possibilities for mobile workspaces.

This paper investigates if and how self-similarity and having motor control impact sense of embodiment, self-identification, and body weight perception in Augmented Reality (AR). We conducted a 2x2 mixed design experiment involving 60 participants who interacted with either synchronously moving virtual humans or independently moving ones, each with self-similar or generic appearances, across two consecutive AR sessions. Participants evaluated their sense of embodiment, self-identification, and body weight perception of the virtual human. Our results show that self-similarity significantly enhanced sense of embodiment, self-identification, and the accuracy of body weight estimates with the virtual human. However, the effects of having motor control over the virtual human movements were notably weaker in these measures than in similar VR studies. Further analysis indicated that not only the virtual human itself but also the participants' body weight, self-esteem, and body shape concerns predict body weight estimates across all conditions. Our work advances the understanding of virtual human body weight perception in AR systems, emphasizing the importance of factors such as coherence with the real-world environment.

This study explores how people interact in dyadic social eXtended Reality (XR), focusing on two main factors: the animation type of a conversation partner's avatar and how immersed the user feels in the virtual environment. Specifically, we investigate how 1) idle behavior, 2) AI-generated gestures, and 3) motion-captured movements from a confederate (a controlled partner in the study) influence the quality of conversation and how that partner is perceived. We examined these effects in both symmetric interactions (where both participants use VR headsets and controllers) and asymmetric interactions (where one participant uses a desktop setup). We developed a social XR platform that supports asymmetric device configurations to provide varying levels of immersion. The platform also supports a modular avatar animation system providing idle behavior, real-time AI-generated co-speech gestures, and full-body motion capture. Using a 2×3 mixed design with 39 participants, we measured users' sense of spatial presence, their perception of the confederate, and the overall conversation quality. Our results show that users who were more immersed felt a stronger sense of presence and viewed their partner as more human-like and believable. Surprisingly, however, the type of avatar animation did not significantly affect conversation quality or how the partner was perceived. Participants often reported focusing more on what was said rather than how the avatar moved.

Spatial computing is set to change the way we work. It will enable both focused work through a higher degree of immersion and collaborative work through enhanced integration of shared interaction spaces or interaction partners. With the Apple Vision Pro, the level of immersion can be adjusted seamlessly. So far, there have been no systematic studies on how this adjustability affects work performance when working alone or together. The present empirical study fills this research gap by varying the level of immersion across three stages (high, medium, low) while solving various tasks with the Apple Vision Pro. The results show that selective attention improves significantly with increasing immersion levels. In contrast, social presence decreases with increasing immersion. In general, participants performed better in the individual task than in the collaborative task. However, the degree of immersion did not influence the collaborative performance. In addition, we could not determine any adverse effects on depth perception or user experience after use. The present study provides initial contributions to the future of spatial computing in professional settings and highlights the importance of balancing immersion and social interaction in a world where digital and physical spaces seamlessly coexist.

Virtual reality (VR) offers various opportunities for innovative therapeutic approaches, especially regarding self-related mind-body interventions. We introduce a VR body swap system enabling multiple users to swap their perspectives and appearances and evaluate its effects on virtual sense of embodiment (SoE) and perception- and cognition-based self-related processes. In a self-compassion-framed scenario, twenty participants embodied their personalized, photorealistic avatar, swapped bodies with an unfamiliar peer, and reported their SoE, interoceptive awareness (perception), and self-compassion (cognition). Participants’ experiences differed between bottom-up and top-down processes. Regarding SoE, their agency and self-location shifted to the swap avatar, while their top-down self-identification remained with their personalized avatar. Further, the experience positively affected interoceptive awareness but not self-compassion. Our outcomes offer novel insights into the SoE in a multiple-embodiment scenario and highlight the need to differentiate between the different processes in intervention design. They raise concerns and requirements for future research on avatar-based mind-body interventions.

Climate change is one of the most pressing global challenges in the 21st century. Urgent actions favoring the environment’s well-being are essential to mitigate its potentially irreversible consequences. However, the delayed and often distant nature of the effects of sustainable behavior makes it challenging for individuals to connect with the issue personally. Immersive media are an opportunity to introduce innovative feedback mechanisms to highlight the urgency of behavior effects. We introduce a VR carbon calculator that visualizes users’ annual carbon footprint as CO2-filled balloons over multiple periods. In a 2 × 2 design, participants calculated and visualized their carbon footprint numerically or as balloons over one or three years. We found no effect of our visualization but a significant impact of the visualized period on participants’ environmental self-efficacy. These findings emphasize the importance of target-oriented design in VR behavior interventions.

This work presents a study where we used incongruencies on the cognitive and the perceptual layer to investigate their effects on perceived plausibility and, thereby, presence and spatial presence. We used a $2 \times 3$ within-subject design with the factors familiar size (cognitive manipulation) and immersion (perceptual manipulation). For the different levels of immersion, we implemented three different tracking qualities: rotation-and-translation tracking, rotation-only tracking, and stereoscopic-view-only tracking. Participants scanned products in a virtual supermarket where the familiar size of these objects was manipulated. Simultaneously, they could either move their head normally or need to use the thumbsticks to navigate their view of the environment. Results show that both manipulations had a negative effect on perceived plausibility and, thereby, presence. In addition, the tracking manipulation also had a negative effect on spatial presence. These results are especially interesting in light of the ongoing discussion about the role of plausibility and congruence in evaluating XR environments. The results can hardly be explained by traditional presence models, where immersion should not be an influencing factor for perceived plausibility. However, they are in agreement with the recently introduced Congruence and Plausibility (CaP) model and provide empirical evidence for the model’s predicted pathways.

In social virtual reality (social VR), users are threatened by potential cybercrimes, such as identity theft, sensitive data breaches, and embodied harassment. These concerns are heightened by the increasing interest in the metaverse, the advancements in photorealistic 3D user reconstructions, and the rising incidents of online privacy violations. Designing secure social VR applications that protect users while enhancing their experience, acceptance and trust remains a challenge. This article investigates potential identity management solutions in social VR, and their impacts on usability and user acceptance. We developed a social VR prototype with novel and established countermeasures, including motion biometric verification, and conducted a study with 52 participants. Our findings reveal diverse preferences for identity management and underscore the importance of authenticity, autonomy, and reciprocity. Key findings include: passive verification is favored for pragmatic user experience, while active verification is preferred for its hedonic quality; continuous or periodic verification strengthens users’ confidence in their privacy; and while user awareness promotes authentic engagement, it may also diminish the willingness to disclose personal information. This research not only offers foundational insights into the evaluated scenarios and countermeasures, but also sheds light on the designs of more trustworthy and inclusive social VR applications.

This work evaluates how the asymmetry of device configurations and verbal communication influence the user experience of social eXtended Reality (XR) for self-perception, other-perception, and task perception. We developed an application that enables social collaboration between two users with varying device configurations.We compare the conditions of one symmetric interaction, where both device configurations are Head-Mounted Displays (HMDs) with tracked controllers, with the conditions of one asymmetric interaction, where one device configuration is an HMD with tracked controllers and the other device configuration is a desktop screen with a mouse. In our study, 52 participants collaborated in a dyadic interaction on a sorting task while talking to each other. We compare our results to previous work that evaluated the same scenario without verbal communication. In line with prior research, self-perception is influenced by the immersion of the used device configuration and verbal communication. While co-presence was not affected by the device configuration or the inclusion of verbal communication, social presence was only higher for HMD configurations that allowed verbal communication. Task perception was hardly affected by the device configuration or verbal communication. We conclude that the device in social XR is important for self-perception with or without verbal communication. However, the results indicate that the device configuration only affects the qualities of social interaction in collaborative scenarios when verbal communication is enabled. To sum up, asymmetric collaboration maintains the high quality of self-perception and interaction for highly immersed users while still enabling the participation of less immersed users.

This article investigates the influence of input/output device characteristics and degrees of immersion on the User Experience (UX) of specific eXtended Reality (XR) effects, i.e., presence, self-perception, other-perception, and task perception. It targets universal access to social XR, where dedicated XR hardware is unavailable or can not be used, but participation is desirable or even necessary. We compare three different device configurations: (i) desktop screen with mouse, (ii) desktop screen with tracked controllers, and (iii) Head-Mounted Display (HMD) with tracked controllers. 87 participants took part in collaborative dyadic interaction (a sorting task) with asymmetric device configurations in a specifically developed social XR. In line with prior research, the sense of presence and embodiment were significantly lower for the desktop setups. However, we only found minor differences in task load and no differences in usability and enjoyment of the task between the conditions. Additionally, the perceived humanness and virtual human plausibility of the other were not affected, no matter the device used. Finally, there was no impact regarding co-presence and social presence independent of the level of immersion of oneself or the other. We conclude that the device in social XR is important for self-perception and presence. However, our results indicate that the devices do not affect important UX and usability aspects, specifically, the qualities of social interaction in collaborative scenarios, paving the way for universal access to social XR encounters and significantly promoting participation.

The Field of View (FoV) is a central technical display characteristic of Head-Mounted Displays (HMDs), which has been shown to have a notable impact on important aspects of the user experience. For example, an increased FoV has been shown to foster a sense of presence and improve peripheral information processing, but it also increases the risk of VR sickness. This article investigates the impact of a wider but inhomogeneous FoV on the perceived plausibility, measuring its effects on presence, spatial presence, and VR sickness as a comparison to and replication of effects from prior work. We developed a low-resolution peripheral display extension to pragmatically increase the FoV, taking into account the lower peripheral acuity of the human eye. While this design results in inhomogeneous resolutions of HMDs at the display edges, it also is a low complexity and low-cost extension. However, its effects on important VR qualities have to be identified. We conducted two experiments with 30 and 27 participants, respectively. In a randomized 2x3 within-subject design, participants played three rounds of bowling in VR, both with and without the display extension. Two rounds contained incongruencies to induce breaks in plausibility. In experiment 2, we enhanced one incongruency to make it more noticeable and improved the shortcomings of the display extension that had previously been identified. However, neither study measured the low-resolution FoV extension’s effect in terms of perceived plausibility, presence, spatial presence, or VR sickness. We found that one of the incongruencies could cause a break in plausibility without the extension, confirming the results of a previous study.

This paper presents an openly available implementation of a modular pipeline architecture for character animation. It effectively decomposes frequently necessary processing steps into dedicated character processors, such as copying data from various motion sources, applying inverse kinematics, or scaling the character. Processors can easily be parameterized, extended (e.g., with AI), and freely arranged or even duplicated in any order necessary, greatly reducing side effects and fostering fine-tuning, maintenance, and reusability of the complex interplay of real-time animation steps.

Our work investigates the influence of self-related cues in the design of virtual humans on body perception in virtual reality. In a $2\times 2$ mixed design, 64 participants faced photorealistic virtual humans either as a motion-synchronized embodied avatar or as an autonomous moving agent, appearing subsequently with a personalized and generic texture. Our results unveil that self-related cues through embodiment and personalization yield an individual and complemented increase in participants' sense of embodiment and self-identification towards the virtual human. Different body weight modification and estimation tasks further showed an impact of both factors on participants' body weight perception. Additional analyses revealed that the participant's body mass index predicted body weight estimations in all conditions and that participants' self-esteem and body shape concerns correlated with different body weight perception results. Hence, we have demonstrated the occurrence of double standards through induced self-related cues in virtual human perception, especially through embodiment.

Spatial User Interfaces along the Reality-Virtuality continuum heavily depend on accurate depth perception. However, current display technologies still exhibit shortcomings in the simulation of accurate depth cues, and these shortcomings also vary between Virtual or Augmented Reality (VR, AR: eXtended Reality (XR) for short). This article compares depth perception between VR and Video See-Through (VST) AR. We developed a digital twin of an existing office room where users had top erform five depth-dependent tasks in VR and VST AR. Thirty-two participants took part in a user study using a 1 × 4 within-subjects design. Our results reveal higher misjudgment rates in VST AR due to conflicting depth cues between virtual and physical content. Increased head movements observed in participants were interpreted as a compensatory response to these conflicting cues. Furthermore, a longer task completion time in the VST AR condition indicates a lower task performance in VST AR. Interestingly, while participants rated the VR condition as easier and contrary to the increased misjudgments and lower performance with the VST AR display, a majority still expressed a preference for the VST AR experience. We discuss and explain these findings with the high visual dominance and referential power of the physical content in the VST AR condition, leading to a higher spatial presence and plausibility.

Virtual Reality (VR) allows us to replace our visible body with a virtual self-representation (avatar) and to explore its effects on our body perception. While the feeling of owning and controlling a virtual body is widely researched, how VR affects the awareness of internal body signals (body awareness) remains open. Forty participants performed moving meditation tasks in reality and VR, either facing their mirror image or not. Both the virtual environment and avatars photorealistically matched their real counterparts. We found a negative effect of VR on body awareness, mediated by feeling embodied in and changed by the avatar. Further, we revealed a negative effect of a mirror on body awareness. Our results indicate that assessing body awareness should be essential in evaluating VR designs and avatar embodiment aiming at mental health, as even a scenario as close to reality as possible can distract users from their internal body signals.

Currently, there is an ongoing debate about the influencing factors of one’s extended reality (XR) experience. Plausibility, congruence, and their role have recently gained more and more attention. One of the latest models to describe XR experiences, the Congruence and Plausibility model (CaP), puts plausibility and congruence right in the center. However, it is unclear what influence they have on the overall XR experience and what influences our perceived plausibility rating. In this paper, we implemented four different incongruencies within a virtual reality scene using breaks in plausibility as an analogy to breaks in presence. These manipulations were either located on the cognitive or perceptual layer of the CaP model. They were also either connected to the task at hand or not. We tested these manipulations in a virtual bowling environment to see which influence they had. Our results show that manipulations connected to the task caused a lower perceived plausibility. Additionally, cognitive manipulations seem to have a larger influence than perceptual manipulations. We were able to cause a break in plausibility with one of our incongruencies. These results show a first direction on how the influence of plausibility in XR can be systematically investigated in the future.

Body awareness is relevant for the efficacy of psychotherapy. However, previous work on virtual reality (VR) and avatar-assisted therapy has often overlooked it. We investigated the effect of avatar individualization on body awareness in the context of VR-specific user experience, including sense of embodiment (SoE), plausibility, and sense of presence (SoP). In a between-subject design, 86 participants embodied three avatar types and engaged in VR movement exercises. The avatars were (1) generic and gender-matched, (2) customized from a set of pre-existing options, or (3) personalized photorealistic scans. Compared to the other conditions, participants with personalized avatars reported increased SoE, yet higher eeriness and reduced body awareness. Further, SoE and SoP positively correlated with body awareness across conditions. Our results indicate that VR user experience and body awareness do not always dovetail and do not necessarily predict each other. Future research should work towards a balance between body awareness and SoE.

When blending virtual and physical content, certain incongruencies emerge from hardware limitations, inaccurate tracking, or different appearances of virtual and physical content. They restrain us from perceiving virtual and physical content as one experience. Hence, it is crucial to investigate these issues to determine how they influence our experience. We present a virtualized augmented reality simulation that can systematically examine single incongruencies or different configurations.

Photorealistic avatars show great potential in social VR and VR collaboration. However, identity and privacy issues are threatening avatars' authenticity in social VR. In addition to the necessary authentication and protection, effective solutions are needed to convey avatars' authenticity status to users and thereby enhance the overall trustworthiness. We designed several visual indicators (VIs) using static or dynamic visual effects on photorealistic avatars and evaluated their effectiveness in visualizing avatars' authenticity status. In this study we explored suitable attributes and designs for conveying the authenticity of photorealistic avatars and influencing their perceived trustworthiness. Furthermore, we investigated how different interactivity levels influence their effectiveness (the avatar was either presented in a static image, an animated video clip, or an immersive virtual environment). Our findings showed that using a full name can increase trust, while most other VIs could decrease users' trust. We also found that interactivity levels significantly impacted users' trust and the effectiveness of VIs. Based on our results, we developed design guidelines for visual indicators as effective tools to convey authenticity, as a first step towards the improvement of trustworthiness in social VR with identity management.

Many studies show the significance of the Proteus effect for serious virtual reality applications. The present study extends the existing knowledge by considering the relationship (congruence) between the self-embodiment (avatar) and the virtual environment. We investigated the impact of avatar and environment types and their congruence on avatar plausibility, sense of embodiment, spatial presence, and the Proteus effect. In a $2\times 2$ between-subjects design, participants embodied either an avatar in sports- or business wear in a semantic congruent or incongruent environment while performing lightweight exercises in virtual reality. The avatar-environment congruence significantly affected the avatar's plausibility but not the sense of embodiment or spatial presence. However, a significant Proteus effect emerged only for participants who reported a high feeling of (virtual) body ownership, indicating that a strong sense of having and owning a virtual body is key to facilitating the Proteus effect. We discuss the results assuming current theories of bottom-up and top-down determinants of the Proteus effect and thus contribute to understanding its underlying mechanisms and determinants.

Mixed Reality (MR) applications along Milgram's Reality-Virtuality (RV) continuum motivated a number of recent theories on potential constructs and factors describing MR experiences. This paper investigates the impact of incongruencies that are processed on different information processing layers (i.e., sensation/perception and cognition layer) to provoke breaks in plausibility. It examines the effects on spatial and overall presence as prominent constructs of Virtual Reality (VR). We developed a simulated maintenance application to test virtual electrical devices. Participants performed test operations on these devices in a counterbalanced, randomized 2×2 between-subject design in either VR as congruent or Augmented Reality (AR) as incongruent on the sensation/perception layer. Cognitive incongruence was induced by the absence of traceable power outages, decoupling perceived cause and effect after activating potentially defective devices. Our results indicate that the effects of the power outages differ significantly in the perceived plausibility and spatial presence ratings between VR and AR. Both ratings decreased for the AR condition (incongruent sensation/perception) compared to VR (congruent sensation/perception) for the congruent cognitive case but increased for the incongruent cognitive case. The results are discussed and put into perspective in the scope of recent theories of MR experiences.

Applying image schema theory to the design of user interfaces has been shown to lead to more intuitive, inclusive, and innovative interaction. We propose that this success can be transferred to the design of data physicalisations (dataphys). But currently designers didn't use image schemas purposefully because the documentation of image schemas is too bulky to apply in practice. Here we propose an image schema toolkit as a more concise instrument to support dataphys design processes. In this work we report on a research-through-design approach aimed at finding appropriate instantiations of image schemas to include in the toolkit. In an iterative process including analysis, synthesis, and evaluation, we created image schema icons, tokens, and interactive objects. Through the design and evaluation of these artefacts we generated knowledge about image schemas, how to instantiate them in visual and physical ways and how to organize them in a toolkit.

This article investigates the effects of different XR displays on the perception and plausibility of personalized virtual humans. We compared immersive virtual reality (VR), video see-through augmented reality (VST AR), and optical see-through AR (OST AR). The personalized virtual alter egos were generated by state-of-the-art photogrammetry methods. 42 participants were repeatedly exposed to animated versions of their 3D-reconstructed virtual alter egos in each of the three XR display conditions. The reconstructed virtual alter egos were additionally modified in body weight for each repetition. We show that the display types lead to different degrees of incongruence between the renderings of the virtual humans and the presentation of the respective environmental backgrounds, leading to significant effects of perceived mismatches as part of a plausibility measurement. The device-related effects were further partly confirmed by subjective misestimations of the modified body weight and the measured spatial presence. Here, the exceedingly incongruent OST AR condition leads to the significantly highest weight misestimations as well as to the lowest perceived spatial presence. However, similar effects could not be confirmed for the affective appraisal (i.e., humanness, eeriness, or attractiveness) of the virtual humans, giving rise to the assumption that these factors might be unrelated to each other.

The embodiment of avatars in virtual reality (VR) is a promising tool for enhancing the user’s mental health. A great example is the treatment of body image disturbances, where eliciting a full-body illusion can help identify, visualize, and modulate persisting misperceptions. Augmented reality (AR) could complement recent advances in the field by incorporating real elements, such as the therapist or the user’s real body, into therapeutic scenarios. However, research on the use of AR in this context is very sparse. Therefore, we present a holographic AR mirror system based on an optical see-through (OST) device and markerless body tracking, collect valuable qualitative feedback regarding its user experience, and compare quantitative results regarding presence, embodiment, and body weight perception to similar systems using video see-through (VST) AR and VR. For our OST AR system, a total of 27 normal-weight female participants provided predominantly positive feedback on display properties (field of view, luminosity, and transparency of virtual objects), body tracking, and the perception of the avatar’s appearance and movements. In the quantitative comparison to the VST AR and VR systems, participants reported significantly lower feelings of presence, while they estimated the body weight of the generic avatar significantly higher when using our OST AR system. For virtual body ownership and agency, we found only partially significant differences. In summary, our study shows the general applicability of OST AR in the given context offering huge potential in future therapeutic scenarios. However, the comparative evaluation between OST AR, VST AR, and VR also revealed significant differences in relevant measures. Future work is mandatory to corroborate our findings and to classify the significance in a therapeutic context.

A novel theoretical model recently introduced coherence and plausibility as the essential conditions of XR experiences, challenging contemporary presence-oriented concepts. This article reports on two experiments validating this model, which assumes coherence activation on three layers (cognition, perception, and sensation) as the potential sources leading to a condition of plausibility and from there to other XR qualia such as presence or body ownership. The experiments introduce and utilize breaks in plausibility (in analogy to breaks in presence): We induce incoherence on the perceptual and the cognitive layer simultaneously by a simulation of object behaviors that do not conform to the laws of physics, i.e., gravity. We show that this manipulation breaks plausibility and hence confirm that it results in the desired effects in the theorized condition space but that the breaks in plausibility did not affect presence. In addition, we show that a cognitive manipulation by a storyline framing is too weak to successfully counteract the strong bottom-up inconsistencies. Both results are in line with the predictions of the recently introduced three-layer model of coherence and plausibility, which incorporates well-known top-down and bottom-up rivalries and its theorized increased independence between plausibility and presence.

Embodiment and body perception have become important research topics in the field of virtual reality (VR). VR is considered a particularly promising tool to support research and therapy in regard to distorted body weight perception. However, the influence of embodiment on body weight perception has yet to be clarified. To address this gap, we compared body weight perception of 56 female participants of normal weight using a VR application. They either (a) self-embodied a photorealistic, non-personalized virtual human and performed body movements in front of a virtual mirror or (b) only observed the virtual human as other's avatar (or agent) performing the same movements in front of them. Afterward, participants had to estimate the virtual human's body weight. Additionally, we considered the influence of the participants' body mass index (BMI) on the estimations and captured the participants' feelings of presence and embodiment. Participants estimated the body weight of the virtual human as their embodied self-avatars significantly lower compared to participants rating the virtual human as other's avatar. Furthermore, the estimations of body weight were significantly predicted by the participant's BMI with embodiment, but not without. Our results clearly highlight embodiment as an important factor influencing the perception of virtual humans' body weights in VR.

The appearance of avatars can potentially alter changes in their users’ perception and behavior. Based on this finding, approaches to support the therapy of body perception disturbances in eating or body weight disorders by mixed reality (MR) systems gain in importance. However, the methodological heterogeneity of previous research has made it difficult to assess the suitability of different MR systems for therapeutic use in these areas. The effects of MR system properties and related psychometric factors on body-related perceptions have so far remained unclear. We developed an interactive virtual mirror embodiment application to investigate the differences between an augmented reality see-through head-mounted-display (HMD) and a virtual reality HMD on the before-mentioned factors. Additionally, we considered the influence of the participant’s body-mass-index (BMI) and the BMI difference between participants and their avatars on the estimations. The 54 normal-weight female participants significantly underestimated the weight of their photorealistic, generic avatar in both conditions. Body weight estimations were significantly predicted by the participants’ BMI and the BMI difference. We also observed partially significant differences in presence and tendencies for differences in virtual body ownership between the systems. Our results offer new insights into the relationships of body weight perception in different MR environments and provide new perspectives for the development of therapeutic applications.

Virtual Reality can impose cognitive demands on users and influence their task performance. These cognitive demands, however, have been difficult to measure precisely without inducing breaks of presence. Based on findings in psychological science on how motion trajectories reflect underlying cognitive processes, we investigated entropy (i.e. the degree of movement irregularity) as an unobtrusive measure of mental workload. Entropy values were obtained from a time-series history of controller movement data. Mental workload is considered high over a given time interval, when the measured entropy is high as well. By manipulating the difficulty of a simple rhythm game we could show that the results are comparable to the results of the NASA-TLX questionnaire, which is currently used as the gold standard in VR for measuring mental workload. Thus, our results pave the way for further investigating the entropy of controller movements as a precise measurement of mental workload in VR.

When human operators locomote actively in virtual environments (VE), the movement range often has to be adapted to the limited dimensions of the physical space. This however might lead to a conflict between sensory information originating from user movements and sensory feedback provided through the virtual locomotion. To investigate whether different locomotion strategies that adapt virtual movement to the limited physical space impact cognitive processes, two experiments were conducted. The first experiment used walking in place, the second study scale of locomotion to investigate the impact of locomotion adaptation on the acquisition of spatial knowledge and user experience. We systematically analyzed body-based sensorial conflicts for the different adaptation strategies and reveal that neither walking in place nor scale of locomotion impacts spatial knowledge acquisition or user experience. We can conclude that visual cues indicating locomotion combined with body-based rotational cues seem to be sufficient for the acquisition of spatial knowledge and that locomotion with controllers seems efficient and preferable for users. The results link system-driven typologies with human-centered factors to guide systematic tests of locomotion techniques in virtual environments for future studies.

Which features and characteristics must virtual agents have to elicit social presence in humans? In order to investigate this objectively, experimental paradigms relying on implicit cognitive phenomena can be employed. In the present study, two aims were reached: First, we built a mixed reality apparatus using affordable consumer VR hardware and other off-the-shelf components to detect implicit cognitive phenomena on the basis of small reaction times with a precision of several milliseconds. Secondly, using this apparatus, we showed that a virtual agent can indeed elicit an implicit phenomenon which was hitherto assumed to be restricted to human participants: social Inhibition of Return (sIOR). sIOR is indicated by an increase in reaction time of about 20 ms that occurs when one subject reaches to the same target to which a co-actor had just responded to [19]. Skarratt, Cole and Kingstone [17] found that only a real co-actor, but not an animated one could induce this inhibitory effect. However, their virtual agent was displayed as a video on a 2D-TV-screen, which was only weakly immersive. In contrast, we found in two experiments that an animated agent presented via a more immersive VR headset could elicit the sIOR phenomenon. Further research has to be done to identify the reasons why this agent - or why VR per se - evokes an sIOR phenomenon. Moreover, the underlying mechanism of why sIOR occurs are not fully understood yet. The current findings open the way to further investigate these questions in experimental settings relying on VR.

Introduction. An increasing number of location-based entertainment centers offers the possibility of entering multi-user virtual reality (VR) scenarios. Until now, neither cognition and emotions of users nor team experience have been scientifically evaluated in such an application. The present study investigated the gain of positive social interdependence while experiencing an adventure on the Immersive Deck of Illusion Walk (Berlin, Germany). Method. The preliminary version of a VR group adventure of the company was enriched by a task establishing social interdependence (IDP condition). The impact of IDP on social presence and cooperation (i.e., mutual importance) was evaluated relative to a control task without interdependence (nIDP condition). Results. Social IDP increased social presence and cooperation among participants. Additionally, behavioral involvement (part of presence), certain aspects of the adventure experience, and the affective evaluation during the experience were positively influenced by IDP. Discussion. The present study showed that interdependence can substantially enhance social presence and cooperation (i.e., mutual importance) in a VR setting already characterized by social co-experience. Thus, it revealed one design option (social IDP) to improve the experience, particularly the social experience, of location-based entertainment. Conclusion. The present research addressed one goal of location-based VR hosts to scientifically established design principles for social and collective adventures by supporting the impact of “collectively mastering an adventurous challenge”. In addition, our evaluation demonstrated that the multi-modal tracking, the free movement, as well as the multi-user features enabled natural interaction with other users and the environment, and thereby engendered a comfortable social experience.