Behold the spinning dancer, a dark female silhouette on a white background. Watch as she gracefully spins with computer animated wonder.
This post has nothing to do with search engine optimization, it is just a cool image. Most people (myself included) will see the dancer spinning from left to right, clockwise. You have excess spleen qi in your left frontal crockus. This means that you’re a vibrant personality whose passions are apparent to everyone around you, but sometimes you are indecisive.
If you see her spinning counter-clockwise, the right ascension of your natal chart lies in your sagittal broab – don’t panic it’s ok. Just watch this awesome 1970’s educational video explaining brain chemistry and everything will fall into place.
The spinning dancer is an example of something called bistable perception. As an object that can be seen in either of two ways, it’s in the same class of illusion as the Necker cube and the face-vase.
Your visual system has evolved to construct a reasonable mental image of the world with a limited amount of information, and it uses a dizzying array of assumptions to do so. In the natural world these assumptions are mostly valid, and there’s only one right way to interpret any given set of signals. Artists and sundry neuroscientists, however, can consciously exploit the assumptions your brain makes about the objects it’s looking at to produce images with two or more equally valid interpretations.
When presented with stimuli that have two valid, mutually contradictory interpretations, your brain just picks one. Then, sometimes, it picks the other. We still don’t understand why this happens, or what role conscious efforts might play in this shift in perception. Many people are able to make the dancer shift directions at will, but the strategies I’ve seen almost always invoke a change of focus – I shift my attention to her feet, or scroll up and down, others look at her hands or to her side.
See more of the explanation from Gabbro.