Fraser spiral
The Fraser spiral is an optical illusion first described by the British psychologist James Fraser in 1908.
The illusion is also known in English by names that can be translated as false spiral and twisted cord illusion . The overlapping arc segments appear black and appear to be spiraling, but the arcs are a series of concentric circles.
The visual distortion is created by combining a regular pattern of lines (circles) with misaligned parts (the differently colored strands). The Zöllner illusion and the Café Wall Illusion are based on a similar principle to many other visual effects, in which a sequence of inclined elements causes the eye to believe that it can detect phantom turns and deviations.
The illusion is enhanced by the spiral components in the checkered background.