1- Fix your gaze on the central black point on the bird, as well as while the sky flashes. When the bird starts to fly, follow it, and keep staring at the black fixation point.
2- You’ll start to notice, that the “empty bird” is filled-in with a color similar to the previous background’s color. The colored image produces illusory colors, an afterimage on “empty” shape, which induces an effect opposite to the well known “afterimage” effect.
3- The common “afterimage” effect yields perceived complementary color, whereas the current effect shows an appearance of a color similar to that of the background, where originally, no physical color was present in the empty shape.
I could not help sharing it. It was 2nd prize at 2009 Best Illusion of the Year Contest. Change the colors. It is really amazing!
There are many works based on the fact that when our eyes stares at a color with a white background we see the complementary colors.
At this site you can do an interesting experiment with your children.
© 2009 Yuval Barkan & Hedva Spitzer
Source: Illusion Contest.
It's copyrighted and I didn't ask permission to the authors because I didn't find their address. I hope they understand that I'm publishing it here instead of sharing the link to assure people watch it.
Few people click at links. I think I'm promoting this work and it has to do with science that must be known by everybody.
If the authors ask I can remove it. I hope they don't.