Hollow-Face illusion
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The Hollow-Face illusion is an optical illusion in which the perception of a concave mask of a face appears as a normal convex face.
While a convex face will appear to look in a single direction, and a flat face such as the Lord Kitchener Wants You poster can appear to follow the moving viewer, a hollow face can appear to move its eyes faster than the viewer: looking forward when the viewer is directly ahead, but looking at an extreme angle when the viewer is only at a moderate angle.
Says Richard Gregory, "The strong visual bias of favouring seeing a hollow mask as a normal convex face (figure 1), is evidence for the power of top-down knowledge for vision (Gregory 1970). This bias of seeing faces as convex is so strong it counters competing monocular depth cues, such as shading and shadows, and also very considerable unambiguous information from the two eyes signalling stereoscopically that the object is hollow.
Another example of the Hollow Face illusion is "gathering For Gardner" dragon. This dragon's head seems to follow the viewer's eyes everywhere (even up or down). This cut out dragon can be printed from: http://www.grand-illusions.com/images/articles/opticalillusions/dragon_illusion/dragon.pdf
[edit] References
- "Knowledge in perception and illusion" by Richard Gregory, Phil. Trans. R. Soc. Lond. B (1997) 352, 1121–1128 - authoritative introduction to optical illusions.
