Abstract
When we move through rigid environments, surface orientations of static objects do not appear to change. Most studies have investigated the perception of optical slant which is defined in an egocentric frame of reference and thus, is entirely dependent on the perspective of the observer. We investigated the perception of geographical slant, which is invariant across different viewing perspectives, and compared it to optical slant. In Experiment 1, participants viewed a 3D triangular target surface covered with triangular phosphorescent texture elements presented at eye level at one of 5 slants from 0° to 90°, each at 0° or 40° tilt. Participants turned 180° to adjust a 2D line or a 3D surface to match the slant of the target surface. In Experiment 2, the difference between optical and geographical slant was increased by changing the height of the surface to be judged. In Experiment 3, target surfaces were continuously rotated +/- 25° and viewed in the dark as well as in a lighted room. In Experiment 1, the overall pattern of judgments exhibited only slight differences between response measures. In Experiment 2, slant judgments were slightly overestimated when the surface was at a low height and at 0° tilt. We compared optical slants of the surfaces to geographical slants. While sometimes inaccurate, participants' slant judgments remained invariant across changes in viewing perspective. Optical slants failed to predict mean judgments. In Experiment 3, judgments were the same in the dark and lighted conditions. There was also no effect of motion on mean slant judgments, although motion decreased variability. We conclude that participants' judgments were invariant as predicted by geographical slant although with an overall mean error of about 5°. Judgments did not vary as predicted by optical slant.
Meeting abstract presented at VSS 2018