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The Spiral That Isn’t

A twisted cord winding in towards the centre. Or four circles.

Celle-ci n’est pas encore traduite : ses textes sont en anglais.

Illusion

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A twisted cord winding in towards the centre. Or four circles.

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A spiral assembled from tilts

There is no spiral: the cords make four separate circles around the same centre. Every short stroke is tilted a little inwards, and the visual system joins those local tilts into one path that keeps turning in — a spiral nobody drew.

The British psychologist James Fraser described it in 1908. Follow a ring with your finger and it comes back to where it started; let your eye run along it and it slides inwards again.

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