Ecological optics and visual slant.

Flock's "A Possible Optical Basis for Monocular Slant Perception" is criticized as being a theory of stimuli rather than a theory of perception. To account for accurate monocular slant perception, the theory requires 9 assumptions, including the unproved ability of the eye to register random texture density. The alternative hypothesis is proposed that monocular visual slant is a function primarily of contour perspective which varies with the size, shape, and viewing distance, as well as slant, of plane surfaces.