By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) - If you stare at a dim light bulb without moving your eyes for about ten seconds, and then look at a blank wall or ceiling, you will likely see an afterimage of the light. The size of this afterimage will depend on how far away the wall or ceiling is: the further away the wall, the larger the afterimage. This happens even though the size of the light bulb itself does not change.

Using MRI technology, researchers tracked observer’s brain activity as they saw afterimages of varying sizes on a screen positioned at varying distances. They found that the retina and the brain actually played tricks to achieve this goal and make the size look the same.