Virtual Reality (VR) technology offers promising opportunities to improve traditional treadmill-based rehabilitation programs. We present an immersive VR rehabilitation system that includes a head-mounted display and motion sensors. The application is designed to promote the experience of relatedness, autonomy, and competence. The application uses procedural content generation to generate diverse landscapes. We evaluated the effect of the immersive rehabilitation system on motivation and affect. We conducted a repeated measures study with 36 healthy participants to compare the immersive program to a traditional rehabilitation program. Participants reported significant greater enjoyment, felt more competent and experienced higher decision freedom and meaningfulness in the immersive VR gait training compared to the traditional training. They experienced significantly lower physical demand, simulator sickness, and state anxiety, and felt less pressured while still perceiving a higher personal performance. We derive three design implications for future applications in gait rehabilitation: Immersive VR provides a promising augmentation for gait rehabilitation. Gamification features provide a design guideline for content creation in gait rehabilitation. Relatedness and autonomy provide critical content features in gait rehabilitation.

This paper reports on the effect of visually-anchored prediction accuracy of haptic information on the perceived presence of virtual environments. We designed an experiment which explicitly prevented confounding factors potentially introduced by virtual body ownership and/or agency. The experimental design consisted of two main conditions defining congruent vs incongruent visual and haptic cues. Presence was measured during as well as after exposure. A distance estimation task solely based on motor action and the visually-anchored spatial model of the environment was executed to control for perceptual binding. 56 healthy volunteers were randomly assigned to one of two groups in a single-blind mixed-group design study. The study revealed increased presence for high prediction accuracy and decreased presence for low prediction accuracy, while perceptual binding still occurred. The observed effect sizes were in the medium range. The results indicate a significant correlation between prediction accuracy of haptic information and the perceived realness and presence of a virtual environment which gives rise to a discussion about models for dissociative symptom derealisation.

This paper presents an immersive Virtual Reality (VR) therapy system for gait rehabilitation after neurological impairments, e.g., caused by accidents or strokes: The system targets increase of patients' motivation to perform the repeated exercise by providing stimulating virtual exercise environments with the final goal to increase therapy efficiency and effectiveness. Instead of simply working out on immobile stationary devices, the system allows them to walk through and explore a stimulating virtual world. Patients are immersed in the virtual environments using a Head-Mounted Display (HMD). Walking patterns are captured by motion sensors attached to the patients' feet to synchronize locomotion speed between the real and the virtual world. A user-centered design process evaluated usability, user experience, and feasibility to confirm the overall goals of the system before any sensitive clinical trials with impaired patients can start. Overall, the results demonstrated an encouraging user experience and acceptance while it did not induce any unwanted side-effects, e.g., nausea or cyber-sickness.

This article reports the impact of the degree of personalization and individualization of users' avatars as well as the impact of the degree of immersion on typical psychophysical factors in embodied Virtual Environments. We investigated if and how virtual body ownership (including agency), presence, and emotional response are influenced depending on the specific look of users' avatars, which varied between (1) a generic hand-modeled version, (2) a generic scanned version, and (3) an individualized scanned version. The latter two were created using a state-of-the-art photogrammetry method providing a fast 3D-scan and post-process workflow. Users encountered their avatars in a virtual mirror metaphor using two VR setups that provided a varying degree of immersion, (a) a large screen surround projection (L-shape part of a CAVE) and (b) a head-mounted display (HMD). We found several significant as well as a number of notable effects. First, personalized avatars significantly increase body ownership, presence, and dominance compared to their generic counterparts, even if the latter were generated by the same photogrammetry process and hence could be valued as equal in terms of the degree of realism and graphical quality. Second, the degree of immersion significantly increases the body ownership, agency, as well as the feeling of presence. These results substantiate the value of personalized avatars resembling users' real-world appearances as well as the value of the deployed scanning process to generate avatars for VR-setups where the effect strength might be substantial, e.g., in social Virtual Reality (VR) or in medical VR-based therapies relying on embodied interfaces. Additionally, our results also strengthen the value of fully immersive setups which, today, are accessible for a variety of applications due to the widely available consumer HMDs.

This paper investigates the effect of avatar realism on embodiment and social interactions in Virtual Reality (VR). We compared abstract avatar representations based on a wooden mannequin with high fidelity avatars generated from photogrammetry 3D scan methods. Both avatar representations were alternately applied to participating users and to the virtual counterpart in dyadic social encounters to examine the impact of avatar realism on self-embodiment and social interaction quality. Users were immersed in a virtual room via a head mounted display (HMD). Their full-body movements were tracked and mapped to respective movements of their avatars. Embodiment was induced by presenting the users' avatars to themselves in a virtual mirror. Afterwards they had to react to a non-verbal behavior of a virtual interaction partner they encountered in the virtual space. Several measures were taken to analyze the effect of the appearance of the users' avatars as well as the effect of the appearance of the others' avatars on the users. The realistic avatars were rated significantly more human-like when used as avatars for the others and evoked a stronger acceptance in terms of virtual body ownership (VBO). There also was some indication of a potential uncanny valley. Additionally, there was an indication that the appearance of the others' avatars impacts the self-perception of the users.

Classical reminiscence therapy has been shown to effectively enhance the stability of memory and identity in people with dementia. Typically, reminiscence therapy uses biography artifacts like photos and personal items and objects. Today, many of these artifacts are from the digital realm providing new options to adapt or even improve the purely analog therapy. In this work we propose a method to enhance reminiscence therapy by computer simulated biographic associations. Our approach provides assistance for associative reasoning on affective stimuli and thus enables access to biographic content so that no deliberate search is required. We develop a recommender model for mapping mental states to biographic content based on similarity. The system dynamically adapts its state and the depicted digital artifacts to the responses of the user. It is a first step towards an immersive reminiscence therapy which will incorporate associated stimuli on multiple channels to increase effectiveness. A preliminary study showed encouraging results concerning the usability of the system.