In virtual reality (VR), portals serve as a common metaphor for relocation, allowing users to navigate large virtual environments. However, portal design is often ad hoc, leaving developers without clear principles for their intentional design and placement to support specific experiential or performance goals. We present a taxonomy for VR portals, deconstructing them into three main dimensions: World-related, Portal-related, and User-related. Based on the suggested taxonomy, we implemented eight unique portals varying across three categories: World Integration (Integrated vs. Non-Integrated), Nature Definition (Obvious vs. Subtle/Hidden), and Destination Visibility (Preview vs. Occluded). We assess the impact of these factors, focusing on spatial memory, presence, and experience in a user study with 32 participants. Our results show that World-Integrated portals improve spatial memory and realism, while the exposure of portal’s unusual Nature mainly affects perceived realism. Visibility of the portal’s Destination positively affected user comfort, acceptance, and presence. We discuss the insights for the intentional design of a portal-based relocation techniques that support comfortable and intuitive navigation. Such techniques are particularly suitable for small physical spaces, where portals enable space-efficient, self-overlapping virtual architectures.

We present a novel shape-shifting haptic device, Shiftly, which renders plausible haptic feedback when touching virtual objects in Virtual Reality (VR). By changing its shape, different geometries of virtual objects can be approximated to provide haptic feedback for the user's hand. The device employs only three actuators and three curved origamis that can be programmatically folded and unfolded to create a variety of touch surfaces ranging from flat to curved. In this paper, we present the design of Shiftly, including its kinematic model and integration into VR setups for haptics. We also assessed Shiftly using two user studies. The first study evaluated how well Shiftly can approximate different shapes without visual representation. The second study investigated the realism of the haptic feedback with Shiftly for a user when touching a rendered virtual object. The results showed that our device can provide realistic haptic feedback for flat surfaces, convex shapes of different curvatures, and edge-shaped geometries. Shiftly can less realistically render concave surfaces and objects with small details.

We present CoboDeck - our proof-of-concept immersive virtual reality haptic system with free walking support. It provides prop-based encountered-type haptic feedback with a mobile robotic platform. Intended for use as a design tool for architects, it enables the user to directly and intuitively interact with virtual objects like walls, doors, or furniture. A collaborative robotic arm mounted on an omnidirectional mobile platform can present a physical prop that matches the position and orientation of a virtual counterpart anywhere in large virtual and real environments. We describe the concept, hardware, and software architecture of our system. Furthermore, we present the first behavioral algorithm tailored for the unique challenges of safe human-robot haptic interaction in VR, explicitly targeting availability and safety while the user is unaware of the robot and can change trajectory at any time. We explain our high-level state machine that controls the robot to follow a user closely and rapidly escape from him as required by the situation. We present our technical evaluation. The results suggest that our chasing approach saves time, decreases the travel distance and thus battery usage, compared to more traditional approaches for mobile platforms assuming a fixed parking position between interactions. We also show that the robot can escape from the user and prevent a possible collision within a mean time of 1.62 s. Finally, we confirm the validity of our approach in a practical validation and discuss the potential of the proposed system.

Virtual reality (VR) is limited in many ways and often is incomparable to real-world experience. Walkable smooth uneven surfaces are inherent to reality but extremely lacking in VR. At the same time, VR offers a lot of possibilities for manipulations. In this paper, we focus on human height and slant perception of the uneven surfaces with multi-sensory stimulation in VR. By employing viewport manipulations, haptic, and vibrotactile stimuli, we explore the possibility to simulate uneven surfaces different from the physical props used.Our results suggest that the use of a rounded prop helps to create a more convincing illusion of an uneven surface that is significantly higher than the physical one. The multi-sensory stimulation brings both height and slant estimations closer to the values suggested by the visual cues if there is no conflict with the haptic sensations. The use of a flat prop is less realistic and leads to massive height and slant underestimations as opposed to those suggested by visual cues. However, if the curved prop cannot be used, a flat surface might still be used to simulate small dents and bumps.

Visual information plays an important part in the perception of the world around us. Recently, head-mounted displays (HMD) came to the consumer market and became a part of everyday life of thousands of people. Like with the desktop screens or hand-held devices before, the public is concerned with the possible health consequences of the prolonged usage and question the adequacy of the default settings. It has been shown that the brightness and contrast of a display should be adjusted to match the external light to decrease eye strain and other symptoms. Currently, there is a noticeable mismatch in brightness between the screen and dark background of an HMD that might cause eye strain, insomnia, and other unpleasant symptoms. In this paper, we explore the possibility to significantly lower the screen brightness in the HMD and successfully compensate for the loss of the visual information on a dimmed screen. We designed a user study to explore the connection between the screen brightness in HMD and task performance, cybersickness, users' comfort, and preferences. We have tested three levels of brightness: the default Full Brightness, the optional Night Mode and a significantly lower brightness with original content and compensated content. Our results suggest that although users still prefer the brighter setting, the HMDs can be successfully used with significantly lower screen brightness, especially if the low screen brightness is compensated.

In this paper we introduce the concept of flexible spaces - a novel redirection technique that generalizes the use of overlapping (impossible) spaces and change blindness in an algorithm for dynamic layout generation. Flexible spaces is an impossible environment that violates the real world constancy in favor of providing the experience of seamless, unrestricted natural walking over a large-scale virtual environment (VE).