Why Do Afterimages Occur?

Afterimages occur when the color receptors in the eye get fatigued. As the eye is exposed to a white or bright background, the fatigued color receptors do not function as efficiently, causing them to report an imbalance of colors to the brain which is translated into afterimages.

Afterimages are optical illusions that appear as though an image is lingering even when the visual exposure has ended. They can be split into two categories, positive and negative.

Positive afterimages retain the original colors of the image while negative afterimages reverse the colors. Positive afterimages look identical or similar to the original image, most often seen when suddenly closing the eyes. For a few seconds, the scene remains visible despite the eyes being shut. The phenomenon is not well understood but thought to come from retinal inertia, in which the cells take time to respond to the sudden absence of stimuli. They are extremely quick, lasting only a few hundred milliseconds.

Negative afterimages are more distinct and thought to be caused by the opponent process theory of color vision. Located in the retina of the eye, rods and cones are responsible for capturing and reporting images and colors to the brain and are a key component in the creation of afterimages.