Hermann Grid Illusion
One of the most famous optical illusions in history. Why do spots appear where there are none?
🧐 What do you see?▼
Stare at the grid of black squares or move your eyes across it. You will likely see ghostly gray smudges at the white intersections in your peripheral vision.
If you look directly at one intersection, the spot usually disappears, only to reappear at the other intersections you aren't currently focusing on.
🧠 Why this works▼
Classically, this is explained by **Lateral Inhibition** in the retinal ganglion cells. Each cell has a "center-surround" receptive field.
Cells located at an *intersection* receive more light in their "surround" (from the four white paths) compared to cells located on a *straight* white path (only two white paths). Because "surround" light inhibits the central signal, the intersection cell actually fires *less* than the path cell, making the intersection appear darker.
🧪 Try variations▼
- Vary Intensity: Use the Intensity slider to change the width of the white paths. Notice how thinner paths can sometimes make the effect even more aggressive.
- Distance: Moving further from the screen makes the receptive fields in your periphery overlap more, often enhancing the spots.
❓ FAQ▼
Is the lateral inhibition theory correct?
While standard for decades, recent research suggests it's more complex, involving cortical processing, as the spots persist even when the grid is slightly wavy or distorted.