The link above is a video of three dancers, all rotating in one direction. As the video progresses, the outside dancers will take on more human characteristics, while the middle dancer remains a black shadow.
When this video was first produced, media spread that the video revealed whether the watcher was right-brained dominate or left-brained dominate. However, there is no scientific evidence to support this hypothesis.
The idea of the video is to represent
how people's depth perception is inaccurate when there are a lack of visual cues for depth. When the dancers are all black shadows, one person's perception of the dancer is that she is circling clockwise while another person views her spinning counter-clockwise. At the beginning of the video, there are no surface features or human characteristics to reveal which way the dancer is facing, so viewers will see opposing legs on the ground and arms spinning in the air. Thus, the dancer motion is dependent on how the viewer perceives the shadow. It is when the outside dancers take on human characteristics and visual cues for depth that the viewer understands the illusion. The outside dancers will spin in opposing directions, and the middle dancers will remain spinning dependently on how the viewer perceives the image. The image may also be influenced by the outside dancers.