he Notorious Frankfurter Illusions... The Floating Sausage...
As funny as all this sounds... this technique can actually be used to help focus your mind into a creative learning state. Some people stare at candles while others imagine floating away on a cloud, but these mindfulness exercises offer a great reward while paradoxically asking for very little.
Basically, the ‘sausage’ is caused by two mechanisms, (1) physiological double images and (2) interocular rivalry and suppression" - Michael Bach, The Frankfurter Illusion