Try this... it's just weird! http://www.michaelbach.de/ot/col_rapidAfterimage/index.html I remember vision tricks like this when I was a kid in the video arcade playing "spy hunter". When playing this game you'll often find your eyes fixated on a region of the screen near the top of the display. As a result, after a while the car you're driving at the bottom of the screen would just disappear!