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The Fraser spiral illusion is an optical illusion that was first described by the British psychologist Sir James Fraser (1863 – 1936) 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 a series of concentric circles. The visual distortion is produced by combining a regular line pattern (the circles) with misaligned parts (the differently colored strands). Zöllner's illusion and the café 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. ==See also== * Op-art * Mathematics and art 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fraser spiral illusion」の詳細全文を読む スポンサード リンク
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