Afterimage

An afterimage is a visual impression that persists after the stimulus producing it has disappeared. It may retain the stimulus's colors or appear in complementary colors.

Photoreceptor adaptation: A change in photoreceptor sensitivity after sustained exposure to light. Uneven adaptation across cone types helps produce color afterimages when the stimulus disappears.
Color vision: The visual capacity to distinguish wavelengths of light through neural processing. Afterimage colors reveal how color perception depends on adapted visual pathways.
Stare-inversion illusion: A visual illusion in which sustained fixation on an image is followed by a perceptual reversal or transformation. Its demonstrations commonly use afterimages to reveal effects of prolonged fixation.
Color constancy: The ability to perceive an object's color as relatively stable under changes in illumination. Comparing afterimages with color constancy separates adaptation effects from stable object-color judgments.
Entoptic phenomenon: A visual effect whose source lies within the eye rather than in external objects. Entoptic effects arise from structures or processes within the eye, not necessarily from a vanished external stimulus.
Opponent-process theory: A theory of color vision in which neural channels encode opposing pairs such as red–green and blue–yellow. Opponent channels help explain why some afterimages appear in colors opposite to the original stimulus.
Retina: The light-sensitive tissue lining the back of the eye, containing photoreceptors and neural circuits. The retinal signals that initiate an afterimage begin with light-sensitive cells.
Flag afterimage illusion: A demonstration in which viewing a colored flag produces a complementary-colored afterimage resembling its reversed colors. The familiar example makes complementary afterimage colors easy to observe.
Visual fatigue: A temporary decline in visual comfort or performance after sustained visual effort or exposure. Prolonged exposure that produces afterimages can also contribute to temporary visual discomfort.
Phosphene: A perception of light without light entering the eye, caused by mechanical, electrical, or neural stimulation. Phosphenes produce visual impressions without the preceding visual stimulus characteristic of an afterimage.

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