Beghi, Xausa, & Zanforlin (1991a) and Beghi, Xausa, De Biasio, & Zanforlin (1991b) have presented visual stereokinetic phenomena. When a bar is rotated in the image plane, it appears to be slanted in depth. Likewise, when a circle with an off-centered dot is rotated, a three-dimensional (3-D) cone is perceived. Finally, when an ellipse is rotated in the image plane, an ellipsoid is perceived th...