Jälkikuvitus

Jälkikuvitus, a Finnish term, translates to "after-image" or "aftereffect" and refers to a visual phenomenon where an image persists in one's vision after the stimulus has been removed. This is a common experience, often noticed after looking at a bright light or a strongly contrasting image for a period. The effect is temporary and can be positive, negative, or neutral depending on the original stimulus.

Positive after-images occur when the perceived image is similar in color and brightness to the original stimulus. This can happen when the photoreceptor cells in the retina are fatigued but not completely overwhelmed. Negative after-images are more common and involve a reversal of colors and brightness. For example, staring at a red object and then looking at a white surface often results in seeing a green after-image. This is due to a process called lateral inhibition, where surrounding cells inhibit the response of the fatigued cells, leading to a perception of the complementary color.

The duration and intensity of an after-image depend on several factors, including the brightness and duration of the original stimulus, the color of the stimulus, and individual differences in visual perception. While usually harmless, prolonged or unusually intense after-images can sometimes be indicative of underlying eye conditions and may warrant a consultation with an eye care professional. Jälkikuvitus is a fascinating demonstration of the complex workings of the human visual system and the adaptive mechanisms of the eye.