Spherical fish tank virtual reality (FTVR) displays attempt to create a virtual "crystal ball" experience using head-tracked rendering. Almost all of these systems have omitted stereo cues, making them easy to build, but it is not clear how much this omission degrades the 3D experience. In this study, we evaluate performance and subjective effects of stereo on 3D perception and interaction tasks with a spherical FTVR display. To control for calibration error and tracking latency, we perform the evaluation on a simulated spherical display in VR. The results of our study provide a clear recommendation for the design and use of spherical FTVR displays: while omitting stereo may not be readily apparent for users, their performance will be significantly degraded (20% - 91% increase in median task time). Therefore, including stereo viewing in spherical displays is critical for use in FTVR.

Fish Tank Virtual Reality (FTVR) displays create a compelling 3D spatial effect by rendering to the perspective of the viewer with head-tracking. Combining FTVR with a spherical display enhances the 3D experience with unique properties of the spherical screen such as the enclosing shape, consistent curved surface, and borderless views from all angles around the display. The ability to generate a strong 3D effect on a spherical display with head-tracked rendering is promising for increasing user's performance in 3D tasks. An unanswered question is whether these natural affordances of spherical FTVR displays can improve spatial perception in comparison to traditional flat FTVR displays. To investigate this question, we conducted an experiment to see whether users can perceive the depth and size of virtual objects better on a spherical FTVR display compared to a flat FTVR display on two tasks. Using the spherical display, we found significantly that users had 1cm depth accuracy compared to 6.5cm accuracy using the flat display on a depth-ranking task. Likewise, their performance on a size-matching task was also significantly better with the size error of 2.3mm on the spherical display compared to 3.1mm on the flat display. Furthermore, the perception of size-constancy is stronger on the spherical display than the flat display. This study indicates that the natural affordances provided by the spherical form factor improve depth and size perception in 3D compared to a flat display. We believe that spherical FTVR displays have potential as a 3D virtual environment to provide better task performance for various 3D applications such as 3D designs, scientific visualizations, and virtual surgery.

A mixed reality experience with a physical display, that situates 3D virtual content within the real world, has the potential to help people work and play with 3D information. However, almost all of such "fish tank virtual reality" (FTVR) systems have been isolated to a single-person experience, making them unsuitable for collaborative tasks. In this paper, we present a display system that allows two people to have unobstructed 3D perspective views into a spherical display while still being able to see and talk to one another. We evaluated the system through qualitative observation at a four-day exhibition and found it was effective for providing a convincing, shared 3D experience.

Head-tracked 3D displays can provide a compelling 3D effect, but even small inaccuracies in the calibration of the participant's viewpoint to the display can disrupt the 3D illusion. We propose a novel interactive procedure for a participant to easily and accurately calibrate a head-tracked display by visually aligning patterns across a multi-screen display. Head-tracker measurements are then calibrated to these known viewpoints. We conducted a user study to evaluate the effectiveness of different visual patterns and different display shapes. We found that the easiest to align shape was the spherical display and the best calibration pattern was the combination of circles and lines. We performed a quantitative camera-based calibration of a cubic display and found visual calibration outperformed manual tuning and generated viewpoint calibrations accurate to within a degree. Our work removes the usual, burdensome step of manual calibration when using head-tracked displays and paves the way for wider adoption of this inexpensive and effective 3D display technology.