Overview
Our research on distance estimation and perceptual adaptation in real and virtual environments is designed to better understand how people perceive virtual environments. We are especially interested in examining why people underestimate distance in different kinds of virtual environments and how experience in a virtual environment affects perception of the size and distance of objects.
Virtual Environment Facilities
Our large-screen immersive display (LSID) system consists of three 10 ft wide x 8 ft high screens placed at right angles to one another, forming a three-walled room. Computer-generated images are rear projected onto the wall screens by three Projection Design F1+ projectors with a resolution of 1280x1024, providing participants with 270 degrees of nonstereoscopic, immersive visual imagery. A ceiling projector also provides front projected ground imagery on the floor. The primary interfaces for our large-screen immersive display system are an instrumented bicycle and a Woodway treadmill.
Our head-mounted display (HMD) system is an NVIS nVisor ST with optical see through functionality. The HMD contains two small LCOS displays each with resolution of 1280 x 1024 pixels. An Intersense Vistracker IS-1200 6 degrees-of-freedom optical tracker is mounted on the HMD to measure participants’ position and orientation.
Participant wearing the head-mounted display system.
Participant walking in the large-screen immersive display system.
Projects
Below we describe our individual projects on distance estimation and perceptual adaptation. Click on the titles of projects to download pdfs of the published research.
Roll over image to see real and virtual outdoor environment.
|
Order Effects in Distance Estimation Does experience in a virtual environment change distance perception in the corresponding real environment and vice versa? This question is important not only for practical reasons, but for theoretical reasons as well. On a practical level, documenting possible carryover effects is important for evaluating whether training in a virtual environment can be accurately transferred to the real environment. On a theoretical level, inducing changes in distance perception through experience can provide information about the processes involved in making distance estimates. We examined how experience in a specific virtual environment changes distance perception in the corresponding real environment and vice versa by having people make two sets of distance estimates in one of the following conditions: 1) real environment first, virtual environment second; 2) virtual environment first, real environment second; 3) real environment first, real environment second; or 4) virtual environment first, virtual environment second. In the first experiment, participants imagined how long it would take to walk to targets in real and virtual environments. Participants’ first estimates were significantly more accurate in the real than in the virtual environment. When the second environment was the same as the first environment (real-real and virtual-virtual), participants’ second estimates were also more accurate in the real than in the virtual environment. When the second environment differed from the first environment (real-virtual and virtual-real), however, participants’ second estimates did not differ significantly across the two environments. A second experiment in which participants walked blindfolded to targets in the real environment and imagined how long it would take to walk to targets in the virtual environment replicated these results. These subtle, yet persistent order effects suggest that memory can play an important role in distance perception. |
Roll over image to see the effects of scaling the pole sizes and separation angle.
|
Adapting to Scale Changes in Virtual Environments A large body of work examining distance estimation in virtual environments has shown that distances are underestimated in virtual environments, especially when the environment is viewed through a head mounted display (HMD) system, A related question that has received far less attention is how does calibrating space perception in one virtual environment affect space perception in another virtual environment? We addressed this question by examining whether experience with making distance estimates in a virtual environment of one scale affects people’s perception of the same distances in an identical virtual environment of a different scale. In each of four experiments, participants first gained experience making distance estimates in a tunnel-like virtual environment with feedback (adaptation) and then made additional distance estimates in an identical, but differently scaled virtual environment without feedback (test). The same distances were used in adaptation and test. We examined three types of scale changes: 1) changing the size of the tunnel, 2) changing the size of the targets, and 3) changing the separation of the targets. In the first two experiments, we compared the effect of scaling only the tunnel with the effect of simultaneously scaling everything (i.e., the tunnel, targets, and target separation). We used joystick movement in the first experiment and blindfolded walking in the second experiment to determine whether the same effects on distance estimation were observed with different types of locomotion. In addition, we examined whether the direction of the scale change affected distance estimates by carrying out adaption in a small tunnel and test in a large tunnel, and vice versa. In the third experiment, we examined how changing both the size of the targets and the separation between the targets affected distance estimates via blindfolded walking. In the final experiment, we examined how changing either the size of the targets or the separation between the targets affected distance estimates via blindfolded walking. We found that changes in target size always affected distance estimates at test. When the targets became smaller, participants overshot distance and when the targets became larger, participants undershot distance. Changes in the size of the tunnel or the separation between the targets (without a change in the size of the targets) had a minimal effect on distance estimates. These results indicate that distance estimates at test were strongly influenced by familiar size cues for distance. However, participants' adjustments of their distance estimates were only a small proportion of the 3.3 factor by which object size was increased or decreased from adaptation to test. Further work is needed to better understand how people integrate information from multiple distance cues in the face of scale changes. |
 Image of target poles in virtual hallway.
|
Estimating Distance in Real and Virtual Environments Virtual environments are commonly displayed using one of two technologies: a head-mounted display (HMD) or a large-screen immersive display (LSID) system. Users can also view targets using augmented reality (AR), in which virtual targets are superimposed on a view of the real environment seen through an HMD. Distance perception is commonly measured using one of two tasks: direct blindfolded walking or timed imagined walking. Here, we compared different visual presentation methods using two measurement protocols, while keeping the setting, targets, distances, visual model, and the methods constant. We asked participants to estimate the distance to a pair of poles located 6 to 18 meters in front of them in a hallway setting. Each participant viewed the same hallway environment in one of the following six presentation methods: 1. Real: unrestricted real-world view of hallway 2. Real+HMD: real-world view of hallway seen through an HMD 3. Virtual+HMD: virtual model of hallway viewed in an HMD 4. Virtual+LSID: virtual model of hallway viewed on multiple large screens 5. Photorealistic+LSID: photograph-based presentation of hallway viewed on multiple large screens 6. AR: augmented reality presentation of virtual target objects superimposed on a real hallway seen through HMD. Our first experiment compared the first five presentation methods using the timed imagined walking protocol suitable for assessing distance estimation in both LSID and HMD systems. The second experiment compared non-LSID presentation methods (conditions 1 through 3) along with the AR condition using a blindfolded walking protocol. Somewhat surprisingly, we found a similar level of accuracy when the virtual environment was displayed on the HMD and on the LSID. This result suggests that the ample differences between the two display technologies do not lead to differences in distance perception, at least as measured by the timed imagined walking protocol. We also found that the use of photorealistic visual model did not substantially remedy distance compression experienced by the participants in the virtual environment displayed using a LSID system. The most glaring difference between the results obtained using timed imagined walking and direct blindfolded walking was the performance of participants in Real+HMD condition. While both measurement methods indicated significant underestimation of distances in Virtual+HMD condition relative to the real world estimates, the difference between Real+HMD and Real conditions was evident only using the blindfolded walking protocol. When participants viewed the targets in the real world through the HMD but imagined moving to the targets while standing in place, there was no difference between the Real and the Real+HMD conditions. When participants viewed the targets through the HMD and then actually walked to the targets, they underestimated distance in the Real+HMD condition relative to the real condition. Thus, the effect of the HMD encumbrance only impacted distance estimates when the participants were required to physically walk to the target. This may be related to a greater effect of the tipping point or pull from the cables when walking than when standing still. This investigation represents an important step in making direct comparisons of distance estimation across display systems and measurement protocols. Such comparisons have been difficult to make across the many prior studies of distance perception due to the wide variation in critical factors such as the visual targets and settings, the fidelity of the visual virtual model, and the range of distances examined. Our results both confirm conclusions from other studies of distance estimation and raise new questions about distance estimation in real and virtual environments. Further work is needed to determine how multiple factors work together to produce underestimation of distance in virtual environments. |