Illusory Contours, Optical Illusions Wiki
Visual Illusion In The Natural World Best Sale
Illusory contours - Wikipedia
Gestalt psychology - Wikipedia
How to explain the Opponent-Process Theory using pictures for
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Lilac chaser - Wikipedia
Visual Illusion In The Natural World Best Sale
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Checker shadow illusion
Cartoon of the Boeing X-51A Waverider (source: Wikipedia)