The Spinning Dancer
The Silhouette Illusion



The Spinning Dancer
The Silhouette Illusion

  Spinning Dancer Depending on the perception of the observer, the apparent direction of spin may change any number of times, although some observers may have difficulty perceiving a change in motion at all.

One way of changing the direction perceived is to use averted vision and mentally look for an arm going behind instead of in front, then carefully move the eyes back.

Some may perceive a change in direction more easily by narrowing visual focus to a specific region of the image, such as the spinning foot or the shadow below the dancer and gradually looking upwards.

One can also try to tilt one's head to perceive a change in direction.

The Spinning Dancer, also known as the silhouette illusion, is a kinetic, bistable optical illusion resembling a pirouetting female dancer. The illusion, created by web designer Nobuyuki Kayahara, involves the apparent direction of motion of the figure.

Some observers initially see the figure as spinning clockwise and some counterclockwise. The illusion derives from the lack of visual cues for depth.

For instance, her arms could be swinging either closer to the viewer and to the left or farther from the viewer and to the left, and hence with her circling clockwise or counter-clockwise on either her left or right foot.

She changes leg because she is facing either towards or away from the observer, there being no surface features on the silhouette to indicate at any point which side of her is presented: the least ambiguous positions are her profiles when she is on either side of her circle, though it's still not known whether the foreground or background leg is on the floor, and from where she moves indeterminately either on the near or far arc across to the other profile.

There are other optical illusions that originate from the same or similar kind of visual ambiguity. One example is the Necker Cube.

The illusion has been incorrectly identified as a scientific personality test that supposedly reveals which hemisphere of the brain is dominant in the observer.

Under this unproven interpretation, it has been popularly called the Right Brain–Left Brain test, and was widely circulated on the Internet during late 2008 to early 2009.

During this time it was established that the silhouette is more often seen rotating clockwise than counter-clockwise. According to an online survey of over 1600 participants, approximately two thirds of observers initially perceived the silhouette to be rotating clockwise.

In addition, observers who initially perceived a clockwise rotation had more difficulty experiencing the alternative. These results can be explained by a psychological study providing evidence for a viewing-from-above bias that influences observers' perceptions of the silhouette. Kayahara's dancer is presented with a camera elevation slightly above the horizontal plane.

Consequently, the dancer may also be seen from above or below in addition to spinning clockwise or counter-clockwise, and facing toward or away from the observer.

Upon inspection, one may notice that in Kayahara's original illusion, seeing the dancer spin clockwise is paired with constantly holding an elevated viewpoint and seeing the dancer from above.

The opposite is also true, an observer maintaining a counter-clockwise percept has assumed a viewpoint below the dancer. If observers report perceiving Kayahara's original silhouette as spinning clockwise more often than counter-clockwise, there are two chief possibilities.

They may have a bias to see it spinning clockwise, or they may have a bias to assume a viewpoint from above. To tease these two apart, the researchers created their own versions of Kayahara's silhouette illusion by recreating the dancer and varying the camera elevations.

This allowed for clockwise/from-above (like Kayahara's original) and clockwise/from-below pairings. The results indicated that there was no clockwise bias, but rather viewing-from-above bias. Furthermore, this bias was dependent upon camera elevation. In other words, the greater the camera elevation, the more often an observer saw the dancer from above.

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