Optical Illusions - Cone Fatigue

Cone fatigue

Cone fatigue

Stare at the image above for 20 seconds and then look at the blank white area right beside it. The after image you see has the opposite colors of the picture you just stared at due to “cone fatigue.”

The eye contains special cells called photoreceptors that detect light. We have two types of photoreceptors - rods and cones.  Rods can detect light and dark while cones are good at detecting colors such as red,green and blue.  ConeFatigueWhen you stare at a specific color for too long, the cells that detect that color will get tired, or fatigued. The after image is a result of all your photoreceptors not being in balance. As the photoreceptors become less tired, which takes between 10 and 30 seconds, the balance is recovered and the after image disappears.

When red, green and blue are added together we see white (see picture to the right). If you stare at something red, your red cones will get tired. If you then look at something white, you will see an afterimage that is cyan, the complementary color of red. If you stare at something green, the after image will be magenta. Once the cones recover from fatigue and become active again, the after image disappears. 

Vision scientists study why photoreceptors get fatigued and how they recover.

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