värijälkikuvat

Värijälkikuvat, a Finnish term, translates to color afterimages. This optical phenomenon occurs when one stares at a bright color for a sustained period and then shifts their gaze to a neutral surface, such as white. The viewer then perceives a faint image of the complementary color. For example, after staring at a red square, one might see a cyan square when looking away.

The physiological basis for värijälkikuvat lies in the photoreceptor cells in the retina, specifically the cone cells responsible for color vision. Prolonged stimulation of one type of cone cell (e.g., those sensitive to red light) leads to a temporary "fatigue" or desensitization. When the eye is then exposed to a neutral stimulus, the less fatigued cone cells become relatively more active. This differential activity is interpreted by the brain as the complementary color.

The intensity and duration of the initial stimulus influence the strength and persistence of the afterimage. Brighter and longer exposures generally produce more vivid and longer-lasting värijälkikuvat. This phenomenon is a common demonstration in visual perception studies and is often used to illustrate the principles of color opponency in the visual system. While typically brief, under certain conditions, afterimages can be noticeable for several seconds.