Ehrenstein illusion

The Ehrenstein illusion is an optical illusion studied by the German psychologist de (1899 – 1961) in which the sides of a square placed inside a pattern of concentric circles take an apparent curved shape (Figure 1).

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  Ehrenstein illusion (1)

• Ehrenstein2.gif

  Illusion (2)

• Ehrenstein figure.svg

  Illusion (3); adding a circle (bottom) destroys the illusion of a bright central disk.

Sometimes the name "Ehrenstein" is associated with one of the illusory contour figures (Figure 2). The ends of the dark segments produce the illusion of circles. The apparent figures have the same color as the background, but appear brighter. A similar effect is obtained in the Kanizsa triangle.