Mach Bands Illusion

Look at the vertical bars of gray. At the boundary where a lighter bar meets a darker bar, you likely see a glowing thin line on the light side and a dark thin shadow on the dark side.

These glowing/dark bands aren't physically there—each bar is a perfectly solid, flat color.

This is Lateral Inhibition at work in your retina. When a photoreceptor is triggered by light, it actually *inhibits* (turns down) the signal of its neighbors.

At the edge of a light band, the cells on the "light" side are being inhibited by darker neighbors on one side and lighter neighbors on the other. Because the dark neighbors inhibit *less*, those specific "border" cells fire more strongly, creating the illusion of an extra-bright band. This is the brain's way ofautomatic edge enhancement.

• Pause to Verify: Hit the Pause button to reveal red helper lines. Use them to block your view of the boundaries and see the colors snap back to being flat and solid.
• Ambient Light: This effect is often stronger when your screen is at a high brightness level in a dark room.