Depth Perception and Its Special Case,Slant in Depth,as Independent of Apparent Orientation (Perspective) in Depth

Abstract

The relationships of the perception of depth, slant in depth, and of apparent orientation in depth were examined. Trained Os judged the presence or absence of slant (45° in the sagittal plane) and of its direction concomitantly with judgments of relative depth between luminous standard and comparison rods. It was shown that perception of slant in depth is a special case of depth perception. Failure to perceive slant or the attribution of slant to vertical rods was accompanied by inaccurate judgments of depth, suggesting that the determinants in such non-veridical judgments were non-attendance to cues, guessing, fatigue, etc. The concomitance of veridical judgments of slant and accurate judgments of depth suggested that Os were attending depth cues assiduously. However, accurate judgments of depth were also made when Os detected slant but reported its inclination in the non-veridical direction, i.e., where apparent reversals of orientation in depth (perspective reversals of three-dimensional objects) were possible. This suggests that vis-a-vis depth perception the percept was veridical, but that in interpreting their two-dimensional retinal image, Os reversed the spatial ordering along the depth dimension of the near and far parts of an object. Apparent reversal of orientation in depth seems to be a process distinct from that involved in depth perception.