Faint gray spots appear where the white streets cross. Look straight at one and it vanishes.
Try this
- Make the streets wider with Width of the white streets: the spots fade.
- Tick Swap black and white for light spots on dark streets.
Why it happens
The classic textbook explanation is lateral inhibition in the retina: a crossing is surrounded by more white than the middle of a street, so cells looking at it are suppressed more and report it as darker. The spots disappear where you look directly because the central part of the retina has smaller receptive fields. Newer work questions whether this tells the whole story, since bending the streets slightly can kill the effect. Ludimar Hermann reported it in 1870.
Did you know?
The spots are strongest in your side vision, which is why the one you look at directly always seems to disappear.
References
- Hermann L. (1870). Eine Erscheinung simultanen Contrastes. Pflüger, Archiv für die Gesammte Physiologie des Menschen und der Thiere, 3, 13-15. doi:10.1007/bf01855743
- SCHRAUF M., LINGELBACH B., WIST E. (1997). The Scintillating Grid Illusion. Vision Research, 37, 1033-1038. doi:10.1016/s0042-6989(96)00255-6
- Background on Wikipedia
The illusion on this page is drawn by code written for this site. Last checked 1 November 2026.
Frequently asked questions
Why do gray dots appear in the Hermann grid?
The textbook answer is lateral inhibition in the retina; researchers have found it is not the complete story.
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