Fraser optical illusion - Fraser spiral illusion

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). Zollner's 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.

Fraser spiral illusion

Sir James Fraser (1863–1936), British psychologist
The Fraser spiral illusion is an optical illusion that was first described by the British psychologist Sir James Fraser in 1908.

Fraser spiral
Fraser spiral
Fraser’s Spirals
Fraser spiral
Fraser spiral
Construction of the circular figures
From "A new visual illusion of direction" by James Fraser
British Journal of Psychology 2: 307-337, 1908

In the construction of the circular figures a circular area is divided by radial lines into a certain number of equal sectors (e.g. 48 in Fig. 5). A series of concentric circles are then described at such intervals that the quadrangular divisions obtained have each three equal sides, the outer circumferential side and the two radial sides, and one side (the inner circumferential) which is slightly shorter. These quadrangular areas are thus approximate squares and on being bisected diagonally in both directions give a new group of approximate squares which is used as the basis of the background of the illusory figure to be produced. The two sets of diagonals of the second group of approximate squares are the original radial and circular lines, and on these lines rest the 'units of direction.' The 'units of direction' all bear the same relation in size to the approximate squares on which they lie, so that in the completed figure the members of each radial series of similar geometrical parts diminish in size centripetally by geometrical progression, and the members of any circular series are of equal size.

The chequer-work background is composed of a double series of dark and light broad spiral bands running in counter directions, and formed by the visual union of the black and white squares with the grey squares. The units of any one circular series all correspond to the same circle in one of two ways-either the centre of area of a Unit corresponds to the centre of a black or white square; or, the marginal dividing line of two 'units' corresponds at its central part to the diagonal line of a black or white square, that is, to part of the actual circular curve.
Read more here: "A new visual illusion of direction" by James Fraser

the circular figures the circular figures
The use of the effect Fraser
effect Fraser
effect Fraser
Parallel lines of the twisted braids
Parallel lines of the twisted braids
You're looking at the vertical lines
You're looking at the horizontal lines

Some parts appear to expand while others appear to contract.
Copyright Takahiro Chishima 2008 (January 12)
from Takahiro Chishima, Takushoku University,
Tokyo, Japan, January 12, 2008
"Fractal spiral illusion"
Concentric rings made up of fractal islands appear to form spirals.
Fractal spiral illusion

Copyright Hitoshi & Shinobu Arai 2007
from Professor Hitoshi Arai, Graduate School of Mathematical Sciences,
University of Tokyo, October 4, 2007

From: Ritsumeikan University

False spirals by Akiyoshi Kitaoka
Fraser spiral
© Akiyoshi Kitaoka
Fraser spiral
With the effect of the apparent rotation
© Akiyoshi Kitaoka Visual Phenomena
Fraser spiral With the effect of the apparent rotation
  Visual Phenomena & Optical Illusions REFERENCES:
• James Fraser. "A new visual illusion of direction" // British Journal of Psychology 2: 307-337, 1908.
• Morgan, M. J. and Moulden, B. "The Munsterberg Figure and Twisted Cords." Vision Research 26, 1793-1800, 1986.
• Pappas, T. "The False Spiral Optical Illusion." The Joy of Mathematics. San Carlos, CA: Wide World Publ./Tetra, p. 114, 1989.
"A new visual illusion of direction" by James Fraser. British Journal of Psychology 2: 307-337, 1908.
• Cucker, Felix (2013). Manifold Mirrors: The Crossing Paths of the Arts and Mathematics. Cambridge University Press. pp. 163–166.
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