For most viewers, the "silhouette illusion"— which involves viewing the spinning animated silhouette of a dancer — appears to be rotating clockwise.  However, for a few, the image is turning counterclockwise. Online quizzes interpret the rotational direction seen by the viewer as an indication of his or her status as a right-brained, creative type, or a logical and left-brain-leaning individual.

However, the preference for seeing the figure spinning clockwise rather than counterclockwise is dependent upon the angle at which the viewer sees the image, according to a Nikolaus Troje, a psychologist at Queen's University in Ontario. [Best Visual Illusion of 2010 Defies Gravity]

"Our visual system, if it has a choice, seems to prefer the view from above," Troje said. "It's a perceptual bias. It makes sense to assume that we are looking down onto objects that are located on the ground below us rather than floating in the air above us."

Troje and his collaborator Matthew McAdam, also a psychologist at Queen's University, transformed the silhouette into two three-dimensional images that rotated simultaneously clockwise or counterclockwise. The idea was to demonstrate that the silhouette's ambiguous depth allows its motion to be interpreted in two different ways. [See it here]

The psychologists showed these images to 24 individuals. Participants most often reported the dancer was spinning counterclockwise if they had a perspective of looking down on the image. If they were looking up at the image, it was more likely to appear to rotate clockwise. So, the viewing angle caused the difference in perception, not the viewer's personality, according to the researchers.

The illusion was created by the Japanese animator Nobuyuki Kayahara, and he embedded conflicting cues about the depth of the image. The dancer's outstretched hand and foot, and the shadow of her feet, offer conflicting clues as to which direction she is actually moving, Troje and McAdam wrote in a study published online Nov. 14 in the journal i-Perception.

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