From: The World In Your Head by Steven Lehar
Fig. 6.1 (A) A local portion of a surface viewed through an aperture creates an amodal percept of a continuous surface extending outward from the visible portion. (B) If the visible portion contains a visual edge, that edge is perceived amodally to extend outward in both directions, dividing the two regions of different color, by the principle of good continuation. (C) If the edge has no defined contrast polarity, then the amodally completed edge also has no defined contrast polarity, unless, as in this case, the contrast reversals are periodic, in which case the pattern is perceived to complete with the same periodicity. (D) Amodal completion also respects the Gestalt principle of closure and (E) the Gestalt principle of symmetry in the completion of the amodal percept.