efterbilder

Efterbilder, or afterimages, are perceptual images that persist after the presentation of a stimulus has ended. They commonly arise from sustained exposure to bright light, contrasts, or color fields and can be seen by most observers. In many languages, including Swedish, the term efterbilder describes this phenomenon.

Mechanisms involve the retina and visual cortex. Prolonged stimulation bleaches photopigments in the cones or rods, reducing responsiveness. When the stimulus is removed, the fatigued photoreceptors recover more slowly, producing a residual image. In color afterimages, opponent-process mechanisms bias perception toward complementary colors (for example, after staring at red, a greenish afterimage is often seen). Some afterimages are positive, retaining the same color as the stimulus for a brief period due to retinal persistence; others are negative, showing color complements.

Types and characteristics: afterimages vary with brightness, duration, and the area stimulated. They are often stable for a few seconds but can last longer under certain conditions. Eye movements can shift the spatial location of the perceived afterimage even though the image is formed on the retina.

Applications and relevance: afterimages are used in psychophysics to study color vision and adaptation. They can also appear in art and design as optical tricks or perceptual effects. Everyday experiences, such as looking at a bright sunset or a strong colored object and then glancing away, illustrate the phenomenon.

Historical notes: descriptions of afterimages date back to early optical and physiological studies, and they remain a common demonstration of sensory adaptation. Modern research investigates neural correlates using electrophysiology and imaging methods.