You see a white triangle, brighter than the background, sitting on top. There are no lines drawing it.
Try this
- Tick Turn the circles away: the triangle disappears instantly.
- Change Mouth of the circles to see how wide the gaps need to be.
Why it happens
Your brain prefers the simplest explanation for what it sees. Three circles that each happen to have a wedge missing in exactly the right place is unlikely; a white triangle lying on top of three circles is likely. So the brain builds the triangle, complete with edges ("illusory contours") and extra brightness. Brain imaging and recordings in monkeys show that early visual areas respond to these imaginary edges as if they were real. Gaetano Kanizsa wrote about these subjective contours in Scientific American in 1976.
Did you know?
Kanizsa first published the effect in 1955, in Italian. The triangle often looks whiter than the white page around it.
References
- Kanizsa G. (1976). Subjective Contours. Scientific American, 234, 48-52. doi:10.1038/scientificamerican0476-48
- Background on Wikipedia
The illusion on this page is drawn by code written for this site. Last checked 1 November 2026.
Frequently asked questions
Is there a triangle in the Kanizsa triangle?
No. Your brain creates its edges and even makes it look brighter than the background.
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