Fraser Spiral

The Fraser spiral, also called false spiral and twisted cord illusion is a shape distortion visual illusion first discovered in 1908 by the British psychologist James Fraser. The image appears to be a spiral, while in reality it is a series of concentric circles. The illusion is triggered by mixing regular figures (the concentric circles) with the staggered, alternating black and white stripes (the checkered background magnifies the effect).

The same principle is used by the Café Wall illusion and by the Zollner illusion, with slight modifications.

Fraser's Spiral: even though it seems a regular spiral, it consists of concentric circles