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The "silhouette illusion" used in many online quizzes to indicate things about a user's personality, whether he or she is left- or right-brained etc, is actually of no use for finding such things out.

The illusion, in which a silhouetted woman is seen turning on the spot, arises from the fact that - from the information given - she could actually be turning either clockwise or anticlockwise. Despite the fact that there isn't enough information to tell, though, the viewer's brain will insist that it can in fact see which way the lady is rotating. A majority of viewers see her as turning clockwise, but many go for anti-clockwise.

The silhouette illusion was designed in 2003 by Nobuyuki Kayahara, a Flash designer in Japan, but has been extensively ripped off. People have theorised that the direction of rotation perceived says something about the viewer - that their perception of the spin direction is influenced by which hemisphere of their brain is dominant, and going on to infer things about their personality.

All that's utter hogwash, according to Dr Niko Troje of Queen's University in Canada.

“Our visual system, if it has a choice, seems to prefer the view from above,” says Troje. “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.”

According to a study performed by Dr Troje and his colleagues, viewing angle is all-important in the answer offered up by people's brains to the silhouette. As people are naturally predisposed to assume they are looking at things from above, they tend to assume they are and so decide that the lady is spinning clockwise.

Troje and his fellow Queen's trick-cyclist Matthew McAdam document their findings in a paper published by the journal i-Perception. ®

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