The Poggendorf illusion in stereoscopic space.

The stereoscopic depth separation between the bisecting rectangle and the oblique line of a Poggendorf configuration was manipulated by varying the direction and magnitude of disparity carried by the rectangle. Based upon data of 6 subjects, the magnitude of the illusion decreased with increasing depth separation regardless of the direction of disparity. Depth separation varied directly with disparity. These findings make plain that depth adjacency can operate symmetrically in stereoscopic space.