The red lines are perfectly straight, but they look bent outward in the middle.
Try this
- Change Number of rays: more rays make a stronger bow.
- Tick Hide the rays and the lines straighten.
Why it happens
One idea is that the rays look like motion toward a vanishing point, as if you were moving forward. Mark Changizi and colleagues proposed that the brain predicts how the scene will look a split second in the future to make up for the delay in processing, and in that predicted scene the lines would bend. Other accounts focus on how the angles where the rays cross the lines are misjudged, as in the Zöllner illusion.
Did you know?
Ewald Hering described it in 1861. The reverse version, with lines in front of rays coming from two sides, makes lines look pinched instead.
References
- Changizi M., Hsieh A., Nijhawan R., Kanai R. (2008). Perceiving the Present and a Systematization of Illusions. Cognitive Science, 32, 459-503. doi:10.1080/03640210802035191
- 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 Hering illusion curved?
No, they are straight. Hide the rays to see.
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