Afterimage

An afterimage is a visual phenomenon in which an image continues to be perceived even after the exposure to the original visual stimulus has ended. The effect occurs because photochemical activity in the retina continues for a period after the eyes are no longer exposed to the stimulus that produced it, a familiar everyday example being the dim, persistent patch that seems to float in a person's vision after briefly looking directly at a bright light source such as a camera flash. Afterimages are classified as physiological, meaning a normal function of a healthy visual system, or pathological, as in the condition palinopsia, in which afterimage-like persistence of vision occurs abnormally. The phenomenon reflects processing at both the level of the retina and the level of the brain's visual cortex, where mechanisms of neural adaptation in the occipital lobe modify how ongoing visual signals are represented, in a manner researchers have compared to an automatic color balance adjustment in photography. Afterimages demonstrate that the visual system continues actively processing and adjusting to visual information for some time after external stimulation has actually stopped.