Lipps illusion

Last updated January 20, 2026

The Lipps illusion is a geometric-optical directional illusion discovered by the German philosopher and psychologist Theodor Lipps. It consists of the fact that parallel lines are no longer perceived as parallel due to inserted kinks.^[1]

The human perception compensates for kinked lines by perceiving them as approximately straight. The middle sections of the five polygons, each consisting of three segments, are perceived as tilted relative to each other, even though they are parallel. This is caused by the alternating downward and upward orientation of the outer segments. This phenomenon is illustrated in the left part of the diagram. The right side of the illustration clarifies the parallelism of the middle sections.^[2]

References

↑ Lippsche Täuschung Lexikon der Psychologie on: spektrum.de
↑ Thomas Ditzinger: Illusionen des Sehens - Eine Reise in die Welt der visuellen Wahrnehmung. (engl.: Illusions of Vision - A Journey into the World of Visual Perception.) Second completely revised and expanded edition. Springer Science+Business Media, Springer-Verlag Berlin Heidelberg 2013, ISBN 978-3-642-37711-2, pp. 15 and 16.

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[1] Lippsche Täuschung Lexikon der Psychologie on: spektrum.de

[2] Thomas Ditzinger: Illusionen des Sehens - Eine Reise in die Welt der visuellen Wahrnehmung. (engl.: Illusions of Vision - A Journey into the World of Visual Perception.) Second completely revised and expanded edition. Springer Science+Business Media, Springer-Verlag Berlin Heidelberg 2013, ISBN 978-3-642-37711-2, pp. 15 and 16.

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