Occluding edges or convexities . This is what separates occluding from occluded surfaces. The projections of projected surfaces . Corresponding to edges and convexities there are only margins between adjacent areas in the ambient optic array. Reversible occlusion-disocclusion .
Optical occlusion occurs in time, and is perfectly reversible.
Points of observation usually move, and so do objects. Hence concealed and revealed surfaces are continually interchanging . Reversible changes in the optic array . Corresponding to any changing occlusion of surfaces is a unique change at the margins between areas in the optic array. This change of optical structure or texture is also reversible.