From: The World In Your Head by Steven Lehar
Fig. 6.6 The basic function of perception can be described as a simultaneous abstraction of perceived forms to their axis of central symmetry, together with a reification of that pattern of symmetry to construct an amodal completion of the percept based on the perceived regularity. A spherical surface (A) is completed as a whole sphere; a cylindrical surface (B) is completed to a full cylinder; and that cylinder is extrapolated (C) along its axis in both directions. (D) A planar surface is extrapolated outward in the plane. (E) Perceptual reification of a simple scene, showing amodal completion of hidden rear surfaces. Notice the amodal “shadows” cast by foreground objects, which require background surfaces to be completed through the occlusion from their visible portions.