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. In this illusion, overlapping black arc segments appear to form a spiral; in reality, the arcs are a series of concentric circles.
Discovery
The Fraser spiral illusion is named for British psychologist James Fraser. Fraser published his findings in a 1908 edition of the 'British Journal of Psychology', in an article entitled "A New Visual Illusion of Direction".
Description
When looking at a Fraser spiral, one sees what appears to be a spiral of twisted rope against a checkerboard pattern. In reality, the spiral is actually a series of concentric circles.
Explanation
The visual distortion is produced by combining a regular line pattern (the circles) with misaligned parts (the differently colored strands or "twists"), an effect that is augmented by the spiral components of the background. 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 an image incorrectly. Like similar illusions, the Fraser spiral illusion is created by the way the retina and brain process images.
Applications
The Fraser spiral, like other perceptual illusions, is useful in the study of perception and vision. The way optical illusions are perceived in the brain gives researchers clues as to how images are processed and interpreted.
ReferencesISBN links support NWE through referral fees
- Bruce, Vicki. "Unsolved Mysteries Of The Mind: Tutorial Essays In Cognition" January, 1996. Psychology Press. ISBN 0863773931
- Fraser, J. "A New Visual Illusion of Direction" 1908. Brit J Psych 2:307–320
- Morgan, MJ and B. Moulden. "The Münsterberg figure and twisted cords" 1986. Vision Res 26:1793–1800
External links
- Fraser's Spiral from MathWorld
- An interactive Fraser Spiral
- Fraser Spiral
- Excerpts from Fraser's "A new visual illusion of direction", published in 1908.
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