Christian Merz, M.Sc.

Abstract: 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 1x4 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.

Abstract: 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.

Abstract: 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.

Abstract: Background High emotional arousal (EA) is a core feature of borderline personality disorder (BPD). While virtual reality (VR) has shown promise in treating emotion-based disorders, research on VR applications for BPD remains limited, especially in adolescence. This study aimed to validate a novel VR-based aVeRsive tension paradigm for assessing EA in adolescents and young adults with BPD symptoms. Methods In a multimodal study, we investigated the validity of aVeRsive tension: We surveyed 62 patients with BPD symptoms and 62 healthy controls (HC) aged 13–25 years who completed two VR sessions (stress/control condition). Each session included an adapted Trier Social Stress Test (TSST) followed by a cyberball paradigm. Subjective EA ratings and physiological measurements were taken during the sessions. Results The BPD group showed significantly higher EA levels compared to HC across both conditions. While both groups exhibited peak EA after TSST, HC demonstrated EA reduction during Cyberball in both conditions. The BPD group maintained elevated EA levels in the stress condition. Physiological data partially supported these findings, with the BPD group showing higher heart rates, particularly during Cyberball in the stress condition. Discussion The aVeRsive tension paradigm successfully discriminated between BPD and HC groups, capturing both subjective and physiological responses. The sustained EA in the BPD group during stress conditions aligns with characteristic emotion dysregulation patterns. While task-specific effects were observed, with TSST eliciting stronger responses than Cyberball, the paradigm effectively simulated real-life stressors in a controlled VR environment. Conclusion This study validates the aVeRsive tension protocol as a promising tool for assessing EA in adolescents and young adults with BPD symptoms. The VR-based approach offers advantages in experimental control and ecological validity, showing potential for both diagnostic assessment and therapeutic intervention in clinical settings.

Abstract: As demand grows for cross-device collaboration in virtual environments, users increasingly join shared spaces on varying hardware ranging from head-mounted displays (HMDs) to everyday lower-immersion smartphones. This paper investigates smartphone-based participation compared with fully immersive VR in dyadic asymmetric interaction. One participant joins via an HMD, while the other uses a smartphone. Through a collaborative sorting task, we evaluate self-perception (presence, embodiment), other-perception (co-presence, social presence, avatar plausibility), and task-perception (task load, enjoyment). We compare our results with previous work that examined VR-VR and desktop-VR pairings. The results show that smartphone users report lower self-perception than VR users. However, other-perception remains comparable to immersive setups. Interestingly, smartphone participants experience lower mental demand. It appears that device familiarity and intuitive interfaces can compensate for reduced immersion. Overall, our work highlights the viability of smartphones for asymmetric interaction, offering high accessibility without impairing social interaction.

Abstract: In this work, we explored asymmetric collaboration under two distinct tasks: collaborative sorting and conversational talking tasks. We answer the research question of how different tasks impact the user experience in asymmetric interaction. Our mixed design compared one symmetric and one asymmetric interaction and two tasks, assessing self-perception (presence, embodiment), other-perception (co-presence, social presence, plausibility), and task perception (task load, enjoyment). 52 participants collaborated in dyads on the two tasks, either using head-mounted displays (HMDs) or one participant using an HMD and the other a desktop setup. Results indicate that differences in social presence diminished or disappeared during the purely conversational talking task in comparison to the sorting task. This indicates that differences in how we perceive a social interaction, which is caused by asymmetric interaction, only occur during specific use cases. These findings underscore the critical role of task characteristics in shaping users’ social XR experiences and highlight that asymmetric collaboration can be effective across different use cases and is even on par with symmetric interaction during conversations.

Abstract: 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.

Abstract: In social virtual reality (VR), harassment persists as a pervasive and critical issue. Prior work emphasizes its perceived realness and emotional impact. However, the influence of avatar design, particularly the role of self-similarity, remains underexplored. Self-similar avatars can enhance user identification and engagement, yet potentially intensify the psychological and physiological effects of harassment. Existing studies often rely on interviews or user-generated content, lacking systematic analysis and controlled comparisons. To address these gaps, we present a process for creating realistic VR harassment scenarios. We built a scenario based on existing literature and validated it with expert reviews and user feedback. We propose a 2 x 2 between-subjects design to systematically examine users' emotional and physiological states, their identification with avatars, and the effects of avatar self-similarity. The study design will deepen the understanding of harassment dynamics in VR. Additionally, it can provide actionable insights for designing safer, more inclusive virtual environments that promote user well-being and foster equitable communities.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: ABSTRACT The development of embodied Virtual Reality (VR) systems involves multiple central design choices. These design choices affect the user perception and therefore require thorough consideration. This article reports on two user studies investigating the influence of common design choices on relevant intermediate factors (sense of embodiment, presence, motivation, activation, and task load) in a VR application for physical exercises. The first study manipulated the avatar fidelity (abstract, partial body vs. anthropomorphic, full-body) and the environment (with vs. without mirror). The second study manipulated the avatar type (healthy vs. injured) and the environment type (beach vs. hospital) and, hence, the avatar-environment congruence. The full-body avatar significantly increased the sense of embodiment and decreased mental demand. Interestingly, the mirror did not influence the dependent variables. The injured avatar significantly increased the temporal demand. The beach environment significantly reduced the tense activation. On the beach, participants felt more present in the incongruent condition embodying the injured avatar.

Abstract: In this paper, we present a serious game with the goal to provide an engaging and immersive experience to foster the players' understanding of dynamic networked systems. Confronted with attacking swarm networks, the player has to analyse their underlying network topologies and to systematically dismantle the swarms using a set of different weapons. We detail the game design, including the artificial intelligence of the swarm, the play mechanics and the level designs. Finally, we conducted an analysis of the play performances of a test group over the course of the game which revealed a positive learning outcome.

Abstract: In this demo paper, we present the design of a virtual reality (VR) first-person shooter (FPS) in which the player fends off waves of hostile flying swarm robots that took over the Earth. The purpose of this serious game is to train the player in understanding networks by learning how to dismantle them. We explain the play and game mechanics and the level designs tailored to provide an engaging experience and to re-enforce the network perspective of the swarm dynamics.