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. It is a unique illusion, where the observer can verify the concentric strands manually. When the strands are highlighted in a different colour, it becomes obvious to the observer that no spiral is present.
See also
References
- Fraser, James (January 1908). "A New Visual Illusion of Direction". British Journal of Psychology. 2 (3): 307–320. doi:10.1111/j.2044-8295.1908.tb00182.x. ISSN 0950-5652.
- Cucker, Felipe (2013). Manifold Mirrors: The Crossing Paths of the Arts and Mathematics. Cambridge University Press. pp. 163–166. ISBN 978-0-521-72876-8.
- Stern, Tom (October 1, 2013). Philosophy and Theatre: An Introduction. Routledge. p. 57. ISBN 9781134575985.
- See Bach, Michael. "Fraser Illusion". Visual Phenomena & Optical Illusions. Archived from the original on 2011-11-02. Retrieved 2005-06-11.
External links
- Fraser's Spiral from MathWorld
- Bach, Michael. "Fraser Illusion". Visual Phenomena & Optical Illusions. Archived from the original on 2011-11-02. Retrieved 2005-06-11. An interactive Fraser Spiral
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