Poggendorff Illusion. Pictures and description. Explanation optical illusion

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Poggendorff optical illusion

Johann Christian Poggendorff
(29 December 1796 – 24 January 1877), German physicist

Johann Christian Poggendorff was a German physicist, born in Hamburg. By far the greater and more important part of his work related to electricity and magnetism. Poggendorff is known for his electrostatic motor which is analogous to Wilhelm Holtz's electrostatic machine. In 1841 he described the use of the potentiometer for measurement of electrical potentials without current draw.

Description of the Poggendorff illusion
In the figure the diagonal line segments do not appear to be segments of a discontinuous straight line (collinear) when in fact they are. This illusion is known as the Poggendorff illusion after its founder (Coren & Girgus, 1978). Several factors affect the degree of misperception experienced in this illusion. One such variable is the separation of the verticals: The greater the separation, the greater the illusion. In this experiment, separation of the verticals and the length of the diagonal segments are both manipulated. This experiment thus allows students to evaluate whether each variable affects the illusion and, more interestingly, whether the effect of vertical separation is strengthened or diminished depending on the length of the diagonal lines. This experiment also allows students to evaluate whether varying the separation of the verticals affects the illusion more or less than does varying the length of the diagonals.

In 1860, Zöllner sent his discovery in a letter to physicist and scholar Johann Christian Poggendorff, editor of Annalen der Physik und Chemie, who subsequently discovered the related Poggendorff illusion, in the original drawing of Zöllner.

The Poggendorff illusion is a geometrical-optical illusion that involves the misperception of the position of one segment of a transverse line that has been interrupted by the contour of an intervening structure (here a rectangle). It is named after Poggendorff, the editor of the journal, who discovered it in the figures Johann Karl Friedrich Zöllner submitted when first reporting on what is now known as the Zöllner illusion, in 1860.

In the adjacent picture, a straight black and red line is obscured by a grey rectangle. The blue line, rather than the red line, appears to be a continuation of the black one, which is clearly shown not to be the case on the second picture. Instead there is an apparent position shift of the lower portion of the line. The magnitude of the illusion depends on the properties of the obscuring pattern and the nature of its borders.

Many detailed studies of the illusion, including "amputating" various components point to its principal cause: acute angles in the figure are seen by viewers as expanded though the illusion diminishes or disappears when the transverse line is horizontal or vertical. Other factors are involved.
Wikipedia

Visual Phenomena & Optical Illusions REFERENCES:
• Coren, Stanley and J. S. Gigus, 1978. Seeing is Deceiving: The Psychology of Visual Illusion, New Jersey, Lawrence Erlbaum.
• Coren, Stanley and J.S. Girgus, 1978. "Visual illusions," in R. Held, H. W. Leibowitz, and H. L. Teuber, eds., Handbook of Sensory Physiology, vol. III: Perception, New York, Springer-Verlag.
• Gilliam, Barbara, 1971. "A depth processing theory of the Poggendorff illusion," Perception & Psychophysics, 10, 211-216.
• Gillam, Barbara, 1980, "Geometrical illusions," Scientific American, 242, 102-111.
• Greene, E., and M. Verloop., 1994. "Anomalous and luminance contours produce similar angular induction effects," Perception, 23, 147-156.
• Greene, E., and J. Fisher, 1993. "Classical illusion effects with nonclassic stimuli: Angular induction from decomposing lines into point arrays, Perception & Psychophysics, 56, 575-589.
• Greene, E., 1988. "The corner Poggendorff," Perception, 17, 65-70.
• Lucas, A., and G. H. Fisher, 1969. "Illusions in concrete situations: II Experimental studies of the Poggendorff illusion," Ergonomics, 12, 395-402.
• Masini, R., R. Sciaky, et. al., 1992. "The orientation of a parallel-line texture between the verticals can modify the strength of the Poggendorff illusion," Perception & Psychophysics, 33, 235-242.
• Poulton, E. C., 1985. "Geometric illusions in reading graphs," Perception & Psychophysics, 37, 543-548.
• Robinson, J. O., 1972. The Psychology of Visual Illusion, London, Hutchinson.
• Rock, Irvin, 1984. Perception, New York, W.H. Freeman.
• Schiffman, Harvey, 1995. Sensation and Perception, New York, John Wiley & Sons.
• Spivey-Knowlton, M. J. and B. Bridgeman, 1993. ""Spatial context affects the Poggendorff illusion," Perception & Psychophysics, 53, 467-474.

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