What do you see? Inspired by the description of some simple experiments in the book "Mind and Nature" by Gregory Bateson I decided to try to program them.
Please click on start on all 4 and think about what you see.
In the first canvas you should see two balls. One is moving towards you and one is moving away from you. Of course the screen is only 2 and not 3 dimensional so nothing can really move towards or away from you if you sit or stand in front of the screen. So it is really just 2 circles getting bigger and smaller and getting a bit of a darker color while getting smaller and a lighter color when they get bigger.
In the second canvas not much has changed even though it is not as good as the first one. So what is different? The color stays the same all the time now and only the size of the balls is changing.
In the third canvas the balls appear to only move slightly, if at all. But something seems to get in front of them. Here the circles stay the same size but their color changes.
What about the fouth one, did it confuse you? Some people I showed this said they felt confused while others just stated it would look cool or whatever. But obviously it doesn't feel right like the first one. Why? Because now the ball that is moving away is getting brighter and the one coming closer is getting darker. That's not how we know it from the real world. That's why it causes some confusion for some people. But in our age of digital media everywhere it is not really so unexpected, that's why not everyone feels confused. What I did was just letting the color get brighter when the circle gets smaller and darker when the circle gets bigger.
There are some more interesting optical illusions / demonstrations you can find in the book (even though they are by far not the main purpose of the book). What describing these experiments demonstrates is that we usually don't think about how we perceive what we see. Our eyes take in some information and then it is processed in our brain and only after that we see what we see. We don't see the raw information but only what the brain makes out of it. But our brain can easily be fooled, even if we principally know how the process works and so we should always keep in mind that the world might not be as our brain makes it out to be.