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. 2015 Apr 28;9:218. doi: 10.3389/fnhum.2015.00218

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Copyright © 2015 Redies.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Examples of visual effects (illusions). (A) Kanizsa’s (1955) triangle. Note the bright and sharply demarcated illusory triangle that is induced by spatially separate black circles (pac-mans) and the segmented outlines of a triangle. (B) Impossible staircase (Penrose and Penrose, 1958). This object is impossible in three-dimensional space because the steps continuously descend or ascend. (C) A similar visual effect was used by M. C. Escher in his artwork Klimmen en Dalen (1960). Note that the image showing the isolated effect is not a beautiful artwork while Escher’s lithograph is (C). M. C. Escher’s “Klimmen en Dalen” © 2015 The M.C. Escher Company – The Netherlands (www.mcescher.com). All rights reserved. Used by permission.