TypeSize and shape
InteractiveYes: sliders and a check
First described1860
The long lines are parallel, but they seem to lean toward and away from each other.
Try this
- Change Angle of the short lines: the tilt is strongest at fairly sharp angles.
- Tick Hide the short lines to see them run straight.
Why it happens
The short lines bias how your visual system reads the angle of the long ones. Neurons that respond to edges at particular angles interact with their neighbors, and sharp angles tend to be "expanded" in perception, which pushes the long lines' apparent direction away from the short lines. Johann Karl Friedrich Zöllner published it in 1860 after noticing the effect on a fabric pattern.
Did you know?
Zöllner was an astrophysicist; the paper reporting the illusion was in a physics journal.
References
- Zöllner F. (1860). Ueber eine neue Art von Pseudoskopie und ihre Beziehungen zu den von Plateau und Oppel beschriebenen Bewegungsphänomenen. Annalen der Physik, 186, 500-523. doi:10.1002/andp.18601860712
- Background on Wikipedia
The illusion on this page is drawn by code written for this site. Last checked 1 November 2026.
Frequently asked questions
Are the lines in the Zöllner illusion parallel?
Yes. Hide the short lines to check.
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