Is there an interaction between perceived direction and perceived aspect ratio in stereoscopic vision?

Abstract

In monocular vision, the horizontal/vertical aspect ratio (shape) of a fronto-parallel rectangle can be based upon the comparison of the perceived directions of the rectangle's edges. In binocular vision of a typical three-dimensional scene (when occlusions are present) this is not the case: fronto-parallel rectangles would be perceived in a distorted fashion if an observer were to base perceived aspect ratio on the perceived directions of the rectangle's edges. We psychophysically investigated stereoscopically perceived aspect ratios of fronto-parallel occluding and occluded rectangles for various distances and fixation depths. We found that observers did not perceive the distortions as predicted on the basis of the above-mentioned comparison of the perceived visual direction of the edges of the rectangle. Our results strongly suggest that the mechanism that determines perceived aspect ratio is dissociated from the mechanism that determines perceived direction. The consequences of the findings for the Kanizsa, Poggendorff, and horizontal/vertical illusions are discussed.