persistence of vision

Persistence of vision is a commonly-accepted although somewhat controversial theory which states that the human eye always retains images for a fraction of a second (around 0.04 second). This means that everything we see is a subtle blend of what is happening now and what happened a fraction of a second  ago. In film and video, this phenomena is often claimed to account for ability to perceive a sequence of frames as a continuous moving picture.




Persistence of vision. Your eyes have memory! The human eye forms an image on the retina - the light sensitive part - and transfers information about the image to the brain. Just like film in a camera, this process involves reactions. The light falling on the retina stimulates nerves. It takes time for the stimulation to clear. Normally we dont look at one thing for a long period, so further stimulation to clear. Normally we dont look at one thing for a long period, so further stimulation happens, over - riding the last image about 20 times a second. If we stare at things, however, things are different - especially when we stare at the dark and light areas ( as in the example below) Dark regions have little (or no) light coming from them so no stimulation occurs. The eye grows used to the image it sees , and the nerves go on relaying the same information over and over.

In the initially strange, example below the brain is confused by what it sees, and tries to add detail to it. Only when you close you eyes (zero stimulation) does the fading image of Jesus of Nazareth "appear". Unexpected is the fact that his hair is dark - whereas in the image, its bright! This is the result of over-stimulation. Some people imagine they see a colour image- in this case the result of their brain - over actively filling in missing detail.