Jälkikuva

Jälkikuva is a Finnish term that translates to "afterimage" in English. It refers to a visual perception that occurs after the stimulus causing it is removed. This phenomenon is a common experience and is related to how the human eye and brain process visual information.

There are two main types of afterimages: positive and negative. A positive afterimage is similar in color and brightness to the original stimulus and fades relatively quickly. A negative afterimage, on the other hand, appears as the complementary color of the original stimulus. For example, staring at a bright red object for a period and then looking at a white surface might produce a green afterimage. This occurs due to the fatigue of photoreceptor cells in the retina. When you stare at a color, the cones in your eyes that are sensitive to that color become fatigued. When you then look away at a neutral surface, the less-fatigued cones become more active, and your brain interprets this imbalance as the complementary color.

Afterimages can be influenced by factors such as the duration of exposure to the original stimulus, the intensity of the stimulus, and individual differences in visual perception. While often a fleeting and harmless optical illusion, understanding afterimages can provide insights into the mechanics of vision and neural processing. They are a natural consequence of the way our eyes adapt to light and color.