Perceiving the orientation in depth of real surfaces: background pattern affects motion and pictorial information.

Motion information contributes weakly to veridical depth perception of real stimuli. To test whether background pattern might enhance veridicality, observers judged the orientations in depth of pictorially matched trapezoidal and rectangular surfaces, with and without a rectangular grid of vertical stripes in a frontal plane behind surfaces; viewing was monocular with lateral head motions of 15 cm extent. The grid did not enhance veridicality; instead, surfaces actually or pictorially slanted to the frontal plane were judged more slanted with the grid present. In a second experiment, observers were static or moved through 30 cm; the grid had little effect during stasis, but again elicited judgments of greater slant during motion, despite broadly veridical responses without the grid. Results from actual slant are interpreted in terms of motion contrast and suggest that motion information may be important in conveying differences in orientation. Results from pictorial slant suggest that the influence of pictorial information increases as its complexity increases.