Boing Boing has this post showing some cool illusions that rely on brightness differences. There are a few of them, but this is the a good one. The two squares A and B are actually exactly the same color. Seriously.
I have copy-pasted the areas next each other as proof below.
I love optical illusions because they show just how fallible our brains really are. It feels like we are getting a reliable picture of the world when in fact our consciousness is actually getting something far more complex from the subconscious.
We don’t see an image like a camera – at any one time we are only really seeing a surprisingly small area and our subconscious is doing gymnastics to give what we think we see.
Generally this works very well, but these “tricks” can sometimes mistakes – enter the optical illusion. You can be sure that this kind of thing happens in lots of areas other than vision – for example our sense of morality.