Fraser spiral illusion

The Fraser Spiral is an optical illusion that was first described in 1908 by British psychologist James Fraser.

The illusion is known as the false spiral, or by its original name, the twisted cord illusion. The overlapping arc segments appear black and appear to form a spiral, however, the sheets are a series of concentric circles.

The visual distortion is ( the differently colored strands ) is prepared by combining a periodic line pattern (circles) with the misaligned parts. The Zöllner illusion and the Café Wall illusion based on a similar principle as many other visual effects that give a succession of inclined elements that the eye phantom twists and deviations supposedly seen.

The illusion is enhanced by the helical components in the checkered background.