The Relationship between Texture Gradient and Perceived Slant-in-Depth: Direct or Mediated?

Judgments were obtained of the surface texture and rotation in depth of a briefly-exposed monocularly-viewed rectangular grid rotated in depth and a set of projective equivalents of the grid presented in the frontalparallel plane. The judgments were secured when the grids were presented alone and when they were followed by a masking textured surface after interstimulus intervals (ISIs) ranging from 0 to 120 ms. In the absence of the mask judged texture varied corresponding to the variations of optical texture both for the rotated rectangular grids and the frontalparallel projections. Judgements of orientation in the absence of the mask varied corresponding to the variations in objective orientation for the rectangular grid and corresponding to the projective equivalent rotations for the frontalparallel projections. Introduction of the mask at ISI = 0 led to disruption of discriminative gradient and orientation judgments. The degree of disruption decreased as ISI increased. These findings were interpreted as supporting a mediational hypothesis of the relationship between optical texture and perceived slant-in-depth. In contrast to the direct perception hypothesis advanced by Gibson, the mediational hypothesis assigns an important role to the perceptual representation of the optical gradient. When the formation of this representation is arrested by processing of the mask, the relationship between optical texture and perceived slant-in-depth is disrupted.