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Fraser spiral illusion

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Fraser spiral illusion

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

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

The visual distortion is produced by combining a regular line pattern (the circles) with misaligned parts (the differently colored strands). Zollner illusion and the cafe wall illusion are based on a similar principle, like many other visual effects, in which a sequence of tilted elements causes the eye to perceive phantom twists and deviations.

The illusion is augmented by the spiral components in the checkered background.

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