p321fig08.40 Visible occluders capture the boundaries that they share with moving edges.  Invisible occluders do not.  Consequently, the two types of motions are influenced by different combinations of feature tracking signals.<BR>||  Motion grouping across occluders (J. Lorenceau, D. Alais 2001). Rotating contours observed through apertures. Determine direction of a circular motion. [, in]visible occluders  http://persci.mit.edu/demos/square/square.html