Anisotropies in depth thresholds of spatial patterns?

Stereopsis can provide essential depth information for recognizing objects and determining their spatial layout. Although some processing components are unique to stereopsis, lower monocular visual components can also affect stereopsis. For instance, we found an oblique effect for depth threshold, analogous to some monocular oblique effects. Are explanations of the stereo-oblique effect different from, or similar to, those of oblique effects for monocular vision? We used several experimental conditions to examine possible explanations as to why depth thresholds are larger for oblique patterns than for vertical ones. Possible explanations include (1) sparseness of horizontal disparities resulting from (a) shrinkage of vertical extent or (b) stretching of horizontal extent in oblique patterns; (2) introduction of vertical disparities in oblique patterns; and (3) the "stereo aperture problem" (viz. only disparities perpendicular to the pattern's orientation are encoded). While sparseness of horizontal disparity information may explain a small part of the oblique effect, the stereo aperture problem can account for most of it. We will discuss the implications of our results in terms of models of human stereopsis and the design of stereoscopic displays.