PICTORIAL DEPTH CUES - A NEW SLANT

Pictorial depth cues such as perspective projection, aspect ratio, and texture gradients can specify mathematically the slant of a planar su rface. We performed experiments to measure the accuracy of human perce ption of surface slant from these cues. We calculated the perceived sl ant from judgments of the relative lengths of a pair of orthogonal lin es embedded in the surface. Our results indicate that slant judgments are accurate to within 3 deg. This level of accuracy was achieved whet her the cues were luminance differences or equiluminous color differen ces. We found no evidence of the recession to the frontal plane that h as been reported by Gibson [J. J. Gibson, The Perception of the Visual World (Houghton Mifflin, Boston, Mass., 1950)] and others. We did fin d evidence suggesting that subjects do not make accurate depth estimat es of disconnected surfaces. This may be the source of the discrepancy between our measures and those of Gibson and others. This research, c ombined with previous findings, supports a model of perception that in volves at least two and possibly more representations of space: one lo cal veridical representation of surface orientation derived primarily from pictorial cues and another global representation of observer-cent ered distance derived primarily from binocular disparity and motion pa rallax.