Poggendorff illusion

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The Poggendorff illusion is an optical illusion that involves the brain's perception of the interaction between diagonal lines and horizontal and vertical edges.

Discovery

The Poggendorff illusion is named for Johann Poggendorff (1796-1877), a German physicist who first described it in 1860. Poggendorff had received a letter from astronomer Johann Karl Friedrich Zöllner, describing an illusion created by a fabric design. While pondering this illusion (which became known as Zöllner's illusion, Poggendorff noted that the diagonal lines in the pattern appeared to be misaligned. Poggendorff described this illusion, which later became known as the Poggendorff illusion.[1]

Description

The Poggendorff illusion is an image where thin diagonal lines are positioned at an angle behind wider stripes. When observing these thin lines, they appear to be misaligned; in the example, the blue line on the left appears to line up with the black line on the right. In actuality, the blue and red lines match up.

Explanation

While the true cause of the Poggendorff illusion is not yet understood, scientists have advanced a number of theories, two of which are the most popular.

The angular displacement theory proposes that, in processing, the brain exaggerates all acute angles and minimizes all obtuse angles. When detecting contour orientation, lateral inhibition causes cells in the retina to respond differently to different angles. This would then cause the orientation of the two lines to appear to be on differing trajectories. Critics of this theory point out that when the middle bar is removed, the illusion is still present. With no contour present, the illusion does not appear to depend on lateral inhibition of the contour-orientation cells.

A second theory, the depth-processing or consistency theory proposes that the figures is processed as a three dimensional object, not a two dimensional figure. The theory suggests that the brain processes the central rectangle as a three dimensional figure that exists in a plane directly in front of the viewer, while the diagonal lines are perceived as horizontal planes that recede away from the viewer. As in the angular displacement theory, acute angles are overestimated and obtuse angles are underestimated, but for different reasons. Instead of two dimensional distortion, the effect is theoretically caused by a misperception of perspective representation. Unfortunately, the depth processing theory fails to explain certain variants of the Poggendorff illusion, as well as the fact that the illusory effect of the illusion drastically weakens or disappears when the Poggendorff figure is rotated so that the diagonal intersecting lines are oriented vertically.[2]

Applications

Like other perceptual illusions, the Poggendorff illusion provides a way for scientists to study the way that information is received and processed by the human visual system and brain.

Notes

  1. Michael Bach, "Poggendorff Illusion" "Optical Illusions and Visual Phenomena" June 2003. Retrieved October 25, 2007.
  2. "Poggendorff" IllusionWorks. 1997. Retrieved October 25, 2007.

References
ISBN links support NWE through referral fees

  • Coren, Stanley and J. S. Gigus. Seeing is Deceiving: The Psychology of Visual Illusion 1978. Lawrence Erlbaum.
  • Noe, Alva. Is the Visual World a Grand Illusion? (Journal of Consciousness Studies Controversies in Science & the Humanities) June 2002. Imprint Academic. ISBN 0907845231
  • Schiffman, Harvey. Sensation and Perception 1995. John Wiley & Sons.

External links

All links Retrieved November 16, 2007.

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