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Zhi Li, Frank Durgin; Slant perception differs for planar and uneven surfaces. Journal of Vision 2010;10(7):78. doi: 10.1167/10.7.78.
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© ARVO (1962-2015); The Authors (2016-present)
Simulated environments often seem too small. Attempts to improve the perception of scale often involve applying realistic but planar textures to environmental surfaces. We have adopted a different approach in which three-dimensional objects (“rocks”) that provide binocular, motion, and surface-occlusion cues for surface unevenness are embedded in simulated planar surfaces. Here we provide direct evidence that perceived surface orientation is more veridical when such uneven textures are used, especially in near space. The simulated surfaces used in this study were presented in an immersive virtual environment through a head mounted display using pincushion-corrected and calibrated optics with full head-motion compensation. Participants made verbal estimates of the geographical (relative to horizontal) orientations of large surfaces presented at different simulated distances, but scaled in 3 dimensions so that the projected textures were equivalent across distances. At the nearest viewing distance (1 m), estimates of surface orientation for slopes below 30 deg were fairly accurate when the textures were rendered with rocks. (They protruded about 5 cm at this distance.) When the rocks were instead flattened against the surface, so that surface unevenness was compressed to less than 0.01 cm (“flagstones”), slanted surfaces in the same range appeared much more frontal than they were. At a much farther viewing distance (16 m) perceived surface orientation was steeper for both types of displays, but the surfaces embedded with rocks (now boulders), still appeared less frontal than the surfaces embedded with (equally large) flagstones. The near and far-space effects of uneven surfaces may be moderated somewhat differently. The far-space effect, in particular, may reflect the presence of gradients of surface self-occlusion for uneven surfaces. Factors affecting perceived surface orientation may also play an important role in scaling perceived distance.
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