Detecting orientation of a surface: the rectangularity postulate and primary depth cues.

Computational metaphors for determining the orientation of planar surfaces represented in line drawings have exploited a postulate that often surfaces are rectangular. Previous research implies that people follow such logic with real surfaces in ecological viewing. However, this research is problematic methodologically and some research does not directly address the issue. The stimuli used in this study were rectangular and trapezoidal; the latter shape was used to mislead with regard to orientation under the rectangularity postulate. Viewing conditions were monocular and binocular, with and without observer movement. The results suggest that the rectangularity postulate was important under stationary monocular viewing but diminished with movement and was not apparent during binocular viewing. General arguments about the importance of secondary depth cues in ecological viewing are developed.