OPTICAL ILLUSIONS AND BRAIN - TWISTING TOYS
Here it gives the impression that you're gazing at spirals, yet you aren't; they're merely circles... quite deceptive!
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What: The actual name of this illusion is the intertwining illusion. It was documented by Dr. Baingio Pinna in 2002. It's the first of Pinna’s illusions that I've re - coded in optical toys, and it's my personal favorite. If you haven't already realized, the illusion consists of a series of concentric circles, yes, truly concentric, and it's not a spiral at all.
How To: There are some interesting things to experiment with here. Mainly, you can adjust the angles to figure out when the illusion appears strongest to you and when it completely disappears. The same principle applies to the colors of the squares and the background. You'll notice that the contrasts are crucial for enhancing the illusion!
Explain it: If you played around with the colors using the customization tools, you'd find that contrast is one of the key factors. Although I couldn't access the cited paper, some research [2] indicates that your peripheral vision (where the illusion has the greatest effect) tracks the angles of the squares and assumes the shapes are spirals. This causes you to perceive them that way, even when you know they're not.