this article we focus on the seemingly contradictory results of two quite different approaches to the problem, one dealing with the properties of visually perceived space and the other with visually directed action

Abstract not found

this article should be addressed to either Sergio S. Fukusima, Department of Psychology, FFCLRP, University of Sat Paulo, Ribeiro Preto, Sat Paulo, Brazil, CEP 14050-901, or Jack M. Loomis, Department of Psychology, University of California, Santa Barbara, California 93106-9660. Electronic mail may be sent via Intemet to fukusima@usp.br or loomis @ psych.ucsb.edu. distance is not linked tightly to that of exocentric distance (see also Gogel, 1977), our focus here is on the former. It generally is accepted that when visual cues to distance are reduced greatly, egocentric distance is misperceived (e.g., Baird, 1970; Da Silva, 1985: Foley, 1977, 1980; Foley & Held, 1972; Gogel, 1974; Holway & Boring, 1941; Kiinnapas, 1968; Philbeck & Loomis, 1997; Sedgwick, 1986). Under "full-cue" conditions, in which a stimulus-rich envi- ronment is viewed under good illumination, however, there is little agreement about whether perception is accurate, mainly because of the diversity of findings stemming from different experimental methods. With respect to egocentric distance, much of the research conducted under full-cue conditions suggests that perceived distance is nearly linear in physical distance and appropriately scaled, at least for targets within 20 m (e.g., verbal reports, Da Silva, 1985; Sedgwick, t986; Teghtsoonian & Teghtsoonian, 1969, t970; blind walking to previewed targets, Corlett, Patla, & Williams, 1985; Elliott, 1986, 1987: Elliott, Jones, & Gray, 1990; Loomis, Da Silva, Fujita, & Fukusima, 1992; Rieser, Ashmead, Talor, & Youngquist, 1990; Steenhuis & Goodale, 1988; Thomson, 1983); in those studies, power functions with exponents close to 1.0 were obtained. The results of other research under the same viewing conditions and over the' same physical distances suggest a c...

We conducted three experiments to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large-screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40 to 60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments, particularly when people made real environment estimates first. In Experiment 2, 10- and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults underestimated time to walk in both environments for distances of 60 to 80 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Twelve-yearolds’ time-to-walk estimates were also very similar across the two environments under both viewing conditions, but 10-year-olds exhibited greater underestimation in the virtual than in the real environment. A third experiment showed that adults ’ time-towalk estimates were virtually identical to walking without vision. We conclude that distance perception may be better in virtual environments involving large-screen immersive displays than in those involving head-mounted displays (HMDS).

Can distance perception be studied using virtual reality (VR) if distances are systematically underestimated in VR head-mounted displays (HMDs)? In an experiment in which a real environment was observed through an HMD, via live video, distances, as measured by visually directed walking, were underestimated even when the perceived environment was known to be real and present. However, the underestimation was linear, which means that higher-order space perception effects might be preserved in VR. This is illustrated in a second experiment, in which the visual horizon was artificially manipulated in a simulated outdoor field presented in immersive VR. As predicted by the claim that angle of declination from the horizon may serve as a strong cue to distance, lowering the horizon line produced “expansive ” judgments of distance (power function exponents greater than one) both in verbal and in motor estimates.

The determinants of visual scale (size and distance) under monocular viewing are still largely unknown. The problem of visual scale under monocular viewing becomes readily apparent when one moves about within a virtual environment. It might be thought that the absolute motion parallax of stationary objects (both in real and virtual environments), under the assumption of their stationarity, would immediately determine their apparent size and distance for an observer who is walking about. We sought to assess the effectiveness of observer-produced motion parallax in scaling apparent size and distance within near space. We had subjects judge the apparent size and distance of real and virtual objects under closely matched conditions. Real and virtual targets were 4 spheres seen in darkness at eye level. The targets ranged in diameter from 3.7 cm to 14.8 cm and were viewed monocularly from different distances, with a subset of the size/distance combinations resulting in projectively equivalent stimuli at the viewing origin. Subjects moved laterally plus and minus 1 m to produce large amounts of motion parallax. When angular size was held constant and motion parallax acted as a differential cue to target size and distance, judged size varied by a factor of 1.67 and 1.18 for the real and virtual environments, respectively, well short of the four-fold change in distal size. Similarly, distance judgments varied by factors of only 1.74 and 1.07, respectively. We conclude that absolute motion parallax only weakly determines the visual scale of nearby objects varying over a four-fold range in size.

The accuracy of depth judgments that are based on binocular disparity or structure from motion (motion parallax and object rotation) was studied in 3 experiments. In Experiment 1, depth judgments were recorded for computer simulations of cones specified by binocular disparity, motion parallax, or stereokinesis. In Experiment 2, judgments were recorded for real cones in a structured environment, with depth information from binocular disparity, motion parallax, or object rotation about the y-axis. In both of these experiments, judgments from binocular disparity information were quite accurate, but judgments on the basis of geometrically equivalent or more robust motion information reflected poor recovery of quantitative depth information. A 3rd experiment demonstrated stereoscopic depth constancy for distances of 1 to 3 m using real objects in a well-illuminated, structured viewing environment in which monocular depth cues (e.g., shading) were minimized. It has been pointed out that the geometric information supporting the perception of depth from binocular disparity is actually less determinate than that supporting the recovery of structure from object rotation or motion parallax

When an object’s motion is influenced by gravity, as in the rise and fall of a thrown ball, the vertical component of acceleration is roughly constant at 9.8 m/sec 2. In principle, an observer could use this information to estimate the absolute size and distance of the object (Saxberg, 1987a; Watson, Banks, von Hofsten, & Royden, 1992). In five experiments, we examined people’s ability to utilize the size and distance information provided by gravitational acceleration. Observers viewed computer simulations of an object rising and falling on a trajectory aligned with the gravitational vector. The simulated objects were balls of different diameters presented across a wide range of simulated distances. Observers were asked to identify the ball that was presented and to estimate its distance. The results showed that observers were much more sensitive to average velocity than to the gravitational acceleration pattern. Likewise, verticality of the motion and visibility of the trajectory’s apex had negligible effects on the accuracy of size and distance judgments. People need to process the absolute distance and size of objects in order to act in the environment. For example, in order to catch and grasp a thrown ball successfully, a person must place his/her hands in the appropriate

When people have visual access to the same space, judgments of this shared visual space (shared vista) can facilitate communication and collaboration. This study establishes baseline performance on a shared vista task in real environments and draws comparisons with performance in visually immersive virtual environments. Participants indicated which parts of the scene were visible to an assistant or avatar (simulated person used in virtual environments) and which parts were occluded by a nearby building. Errors increased with increasing distance between the participant and the assistant out to 15 m, and error patterns were similar between real and virtual environments. This similarity is especially interesting given recent reports that environmental geometry is perceived differently in virtual environments than in real environments.

The static form of the size-distance invariance hypothesisasserts that a given proximal stimulus size (visual angle) determines a unique and constant ratio of perceived-object size to perceived object distance. A proposed kinetic invariance hypothesis asserts that a changing proximal stimulus size (an expanding or contracting solid visual angle) produces a constant perceived size and a changing perceived distance such that the instantaneous ratio of perceived size to perceived distance is determined by the instantaneous value of visual angle. The kinetic invariance hypothesis requires a new concept, an operating constraint, to mediate between the proximal expansion or contraction pattern and the perception of rigid object motion in depth. As a consequence of the operating constraint, expansion and contraction patterns are automatically represented in consciousness as rigid objects. In certain static situations, the operation of this constraint produces the anomalous perceived-size-perceived-distance relations called the sizedistance paradox. The size-distance invariance hypothesis (SDIH) asserts that a given proximal stimulus size (visual angle) determines a unique constant ratio of perceived object size to