This paper presents an approach to alleviating the server-client communication bottleneck in collocated multi-user virtual reality (VR). Instead of transmitting unique packets to each client, the system multicasts the same packets to all users, combining packetization, visibility-aware prioritization, and lightweight acknowledgments to ensure efficiency and fairness. To enable rapid scene completion, the environment is partitioned into independent fixed-size packets that can be decoded immediately upon arrival, and transmission order is guided by precomputed visibility footprints. Scalability is achieved through repeated multicast until compact bitmap acknowledgments confirm reception, keeping communication cost mostly independent of the number of clients. A controlled study with 23 participants in groups of 7 and 16 showed that this method reconstructs environments several times faster and with fewer missing parts than a conventional unicast TCP-based approach. These findings demonstrate that multicast transmission over commodity Wi-Fi can support large collocated VR groups.

Redirection in virtual reality (VR) enhances haptic feedback versatility by relaxing the need for precise alignment between virtual and physical objects. In mixed reality (MR), where users see the real world and their own hands, haptic redirection enables a physical interaction with virtual objects but poses greater challenges due to altering real-world perception. This paper investigates the effect of the realism of the user's surroundings and of the user's hand on haptic redirection. The user's familiarity with their actual physical surroundings and their actual hand could make the redirection manipulations easier-or harder-to detect. In a user study (N = 30) participants saw either a virtual environment or their actual physical surroundings, and saw their hand rendered either with a generic 3D model or with a live 2D video sprite of their actual hand. The study used a two-alternative forced choice (2AFC) design asking participants to detect hand redirections that bridged physical to virtual offsets of varying magnitudes. The results show that participants were not more sensitive to 2D video sprite hand redirection than to VR hand redirection, which supports the use of haptic redirection in MR.

The paper introduces PreVR, a method for allowing the user of a VR application to preview a virtual environment (VE) around any number of corners. This way the user can gain line of sight to any part of the VE, no matter how distant or how heavily occluded it is. PreVR relies on a multiperspective visualization that implements a higher-order disocclusion effect with piecewise linear rays that bend multiple times as needed to reach the visualization target. PreVR was evaluated in a user study ($\mathrm{N}=88$) that investigates four points on the VR interface design continuum defined by the maximum disocclusion order $\delta$. In a first control condition (CC0), $\delta=0$, corresponds to conventional VR exploration with no preview capability. In a second control condition (CC1), $\delta=1$, corresponds to the prior art approach of giving the user a preview around the first corner. In a first experimental condition (EC3), $\delta=3$, so PreVR provided up to third-order disocclusion. In a second experimental condition (ECN), $\delta$ was not capped, so PreVR could provide a disocclusion effect of any order, as needed to reach any location in the VE. Participants searched for a stationary target, for a dynamic target moving on a random continuous trajectory, and for a transient dynamic target that appeared at random locations in the maze and disappeared 5s later. The study quantified VE exploration efficiency with four metrics: viewpoint translation, view direction rotation, number of teleportations, and task completion time. Results show that the previews afforded by PreVR bring a significant VE exploration efficiency advantage. ECN outperforms EC3, CC1, and CC0 for all metrics and all tasks, and EC3 frequently outperforms CC1 and CC0.

An important application of augmented reality (AR) is the design of interfaces that reveal parts of the real world to which the user does not have line of sight. The design space for such interfaces is vast, with many options for integrating the visualization of the occluded parts of the scene into the user's main view. This paper compares four AR interfaces for disocclusion: X-ray, Cutaway, Picture-in-picture, and Multiperspective. The interfaces are compared in a within-subjects study (N = 33) over four tasks: counting dynamic spheres, pointing to the direction of an occluded person, finding the closest object to a given object, and finding pairs of matching numbers. The results show that Cutaway leads to poor performance in tasks where the user needs to see both the occluder and the occludee; that Picture-in-picture and Multiperspective have a visualization comprehensiveness advantage over Cutaway and X-ray, but a disadvantage in terms of directional guidance; that X-ray has a task completion time disadvantage due to the visualization complexity; and that participants gave Cutaway and Picture-in-picture high, and Multiperspective and X-ray low usability scores.