An afterimage is also called a ghost image and it represents an optical illusion that appears and stays in a perceptual filed of a person after the original image stopped from being in the perceptual field. So far we’ve presented you some illusions that can change their form, now we’re going to show you an illusion involving color conversion.
What to see and what to do?
You can see just a little below two images: a picture of a white rose on a grey background and in the other image you can see a green spot on a blue background. The first picture is the important one, because it can help us see the illusion. You have to concentrate your attention on the green spot for about a minute, the longest you look at it the stronger the effect will be. Right after you ceased watching the green spot rapidly move your look at the white rose… there you should see that the rose is not longer white but pink. Some of you may see a powerful color, others a pale color.
How does it work?
One of the most known afterimages is the bright glow that remains on the retina after you looked at a strong light source for a few seconds.
In general afterimages come in two forms: positive when we retain the original color (for example when the dimension or the movement is changed) and negative when the colors are inverted. In this case we have a negative afterimage.
A negative after image can appear because the overstimulation of the cone cells or the photoreceptors of the eye. In this case the overstimulation can create lose of sensitivity; even if in general the photoreceptors can deal with the light conversion or with the color conversion by rapidly filtering what is normal for the eye, in this case they have to adjust. To be more precise the retina gets tired from the overstimulation so it stops from responding.
When we change the image with a white space the adapted photoreceptors have a weak signal so the colors are “blind”. But there are also the photoreceptors that weren’t affected by the strong image. In this case the colors are still pure and fresh and they send a strong signal… although the color is the opposite of the one we’ve seen because that is how the brain interprets it.