THE DISCRIMINABILITY OF LOCAL SURFACE-STRUCTURE

The ability of observers to discriminate depth and orientation differe nces between separated local regions on object surfaces was examined. The objects were defined by many optical sources of information simult aneously, including shading, texture, motion, and binocular disparity. Despite the full-cue nature of the displays, the observers' performan ce was relatively poor, with Weber fractions ranging from 10% to 40%. The Weber fractions were considerably lower for discriminations of sur face-orientation differences than for similar discriminations of depth differences. The ability of observers to discriminate surface-orienta tion differences was approximately invariant over the separation of th e regions in the projected image. In contrast, the ability to discrimi nate depth differences was highly influenced by the amount of image se paration. This qualitative difference between the perception of depth intervals and surface-orientation differences suggests that knowledge of depths and orientations may be represented separately within the hu man visual system.