Gabby sent me an email with this cunning optical illusion. Click on the picture to see it animated in a window of its own. Then, without blinking or moving your eye, stare intently at the cross-hairs for as long as you can. If you are like most of us after a few seconds you will start to see a ghostly green-dot moving around the circle. After much longer you should start to see the pink-dots begin to fade away - eventually melting into the grey background. If you let your eyes drift away from the cross-hairs for even an instant then that illusion will be lost!
If you don't stare at the dot but instead follow it around with your eyes it stays pink all the time.
There are no green dots at all in the animation - all the green is an illusion.
Don't be cruel and send the picture to your friends with a covering note such as "Beware! someone has modified your computer so it can tell where you are looking. The dots change colour when they see you are not paying attention!" OK? You don't have any friends that would fall for that? Right.
An explanation, and a few more cunning illusions will follow in a week or so...
And did you follow the dot around with your eyes? Ha! Caught you. There is no moving dot. The animation just blanks out the pink ones in turn. You can see that if you make it stop. With Internet Explorer you just press the Esc key while you are watching the dots and it will freeze. Start it again by pressing F5.
And... did you notice, as I just did, if you stop the animation with the Esc key and just stare at the cross hairs the pink dots fade away. The fading has nothing to do with the movement.
