At the center of each set of lines you see a small circle that looks brighter than the white page around it. There is no circle and no change in brightness.
Try this
- Change Size of the gaps: the bright disk grows and fades.
- Tick Close the gaps and the discs vanish.
Why it happens
The ends of the lines line up into the edge of a shape that is not there, and your visual system fills in that shape and makes it look brighter than the background, the same way it builds the triangle in the Kanizsa figure. These are called illusory or subjective contours. Lothar Spillmann and Birgitta Dresp's review describes how cells in the visual cortex respond to such contours as if they were real edges, and why the brightening is still not fully explained.
Did you know?
Walter Ehrenstein reported it in 1941 while studying a version of the Hermann grid.
References
- Spillmann L., Dresp B. (1995). Phenomena of Illusory Form: Can We Bridge the Gap between Levels of Explanation?. Perception, 24, 1333-1364. doi:10.1068/p241333
- 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 circle in the middle?
No. Close the gaps and it disappears.
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