Ehrenstein illusion

The Ehrenstein illusion is an optical illusion studied by the German psychologist Walter Ehrenstein (1899 – 1961) in which the sides of a square placed inside a pattern of concentric circles take an apparent curved shape.[1][2]

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  Original Ehrenstein illusion, where a square appears curved when placed inside of concentric circles
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  Alternative Ehrenstein illusion, where the ends of the dark segments produce the illusion of circles
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  The illusion of a bright central disk (above) is destroyed by adding a circle (bottom).

Sometimes the name "Ehrenstein" is associated with one of the illusory contour figures where the ends of the dark segments produce the illusion of circles.[3][4][5] The apparent figures have the same color as the background, but appear brighter. A similar effect is obtained in the Kanizsa triangle.

References

1. A catalogue of illusions at Ritsumeikan University
2. W. Ehrenstein (1925). "Versuche über die Beziehungen zwischen Bewegungs- und Gestaltwahrnehmung" [Experiments on the Relationships Between the Perception of Motion and of Gestalt]. Zeitschrift für Psychologie. 96: 305–352.
3. Ehrenstein illusion at Scholarpedia
4. W. Ehrenstein (1941). "Über Abwandlungen der L. Hermannschen Helligkeitserscheinung". Zeitschrift für Psychologie. 150: 83–91.
5. W. Ehrenstein (1954). Probleme der ganzheitspsychologischen Wahrnehmungslehre. Leipzig: Barth.