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What: The Ouchi illusion is an illusion named after its creator, Japanese graphics artist Hajime Ouchi. In 1977, you'll observe that the disc in the middle seems to float above the background. And when you move your head, it may seem to be moving slightly, but in fact, we know it's a stationary and fixed 2D circle.

How To: You can enhance the intensity of this illusion by increasing the contrasting colors (the original artist designed it with black and white). Also, you can change the length and height of the rectangles. For me, when they are short and long (or long and short), the illusion is the most powerful. Also, if I scroll up and down a bit (adding a little movement), it makes the effect much stronger.

Explain it: Looking around and reading several papers made me more confused than when I started. However, I finally found a great explanation: The illusion is caused by random eye movements, which are independent in the horizontal and vertical directions. Nevertheless, the two types of patterns in the figure almost cancel out the effect of the eye movements parallel to each type of pattern. As a result, the neurons stimulated by the disk send the signal that the disk shakes because of the horizontal part of the eye movements, while the neurons stimulated by the background send the signal that the movements are due to the independent vertical part. Since the two areas shake independently, the brain interprets the areas as corresponding to separate and independent objects.