Detecting slant-in-depth of real trapezoidal and rectangular surfaces: moving-monocular viewing equivalent to...

Cues from binocularity and observer motion are often believed to be more important in perceiving depth than pictorial cues such as relative visual size and linear perspective. Both binocularity and motion are effective in simulated displays. However, for real stimuli evincing nonveridical pictorial cues, binocularity has been more effective than motion; sometimes motion has had an insignificant effect. This may reflect inadequate extent of motion, an assertion investigated in the present study. Two groups of observers determined whether rectangular and trapezoidal surfaces were slanted-in-depth under stationary-monocular (SM), stationary-binocular (SB), and moving-monocular conditions with 15-cm (15MM) and 25-cm (25MM) lateral head-motion extents according to group. The trapezoidal surfaces appeared as rectangular during SM viewing to mislead regarding slant. The effect of pictorial cues was substantially diminished during SB viewing whereas 15MM viewing was weak, 25MM was as effective as SB viewing. Comparison of the overall numbers of correct responses for the two groups indicated no contextual biasing.