Best illusions of 2012: The Exorcist illusion

MacGregor Campbell, consultant

Here's a freaky twist on a classic illusion.

Thomas Papathomas, a vision researcher at Rutgers University in New Brunswick, New Jersey, has created a new variation on the hollow-mask illusion - where viewers find it difficult to distinguish whether they are seeing a mask's interior or its exterior.

Papathomas's version uses both a hollow mask and a hollow torso, each inverted from the other so that when the head is concave, the torso is convex, and vice-versa. As the torso and head rotate, in the same direction, they appear to rotate oppositely to one another, resulting in the head appearing to twist unnaturally.

Papathomas calls this the "Exorcist Illusion," referring to a famous scene in the 1973 horror movie, The Exorcist, in which a girl possessed by the devil twists her head around a full 360 degrees.

This illusion requires no satanic involvement however. A constantly rotating hollow mask - or torso - appears to rotate in one direction when the exterior is facing the viewer, and the opposite direction when the interior faces the viewer. Since the brain and the torso are inverted from one another, when one appears to rotate clockwise, the other seems to rotate anticlockwise.

Papathomas created this illusion for the Neural Correlate Society's 2012 Illusion of the Year contest.

For more illusions, check out last year's winners, or visit our archive of Friday Illusions.

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