The absence of depth constancy in contour stereograms

Stereoscopic surfaces constructed from Kanizsa-type illusory contours or ex plicit luminance contours were tested for three-dimensional (3-D) shape con stancy. The curvature of the contours and the apparent viewing distance bet ween the surface and the observer were manipulated. Observers judged which of two surfaces appeared more curved. Experiment 1 allowed eye movements an d revealed a bias in 3-D shape judgment with changes in apparent viewing di stance, such that surfaces presented far from the observer appeared less cu rved than surfaces presented close to the observer. The lack of depth const ancy was approximately the same for illusory-contour surfaces and for expli cit-contour surfaces. Experiment 2 showed that depth constancy for explicit -contour surfaces improved slightly when fixation was required and eye move ments were restricted. These experiments suggest that curvature in depth is misperceived, and that illusory-contour surfaces are particularly sensitiv e to this distortion.