Optical illusion : Negative afterimage

Look at the red point in the end of the nose for 30 seconds, then look up to the roof of your house and keep blinking your eyes. You will see the original image

Want to know how this thing works:

Well in reality, it is no more than an optical illusion that involves the brain's after sight. This illusion is called as "negative afterimage". It is caused by cells located in the eyes, called ganglions, which sends messages to the brain by coding or identifying the colors in pairs of primary colors.

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