Yeah it is. That one with the green circle though. If you focus on it, you just see one of the purple circles blank out.
Is this anything to do with the fact that green is the opposite of pink in the colour cycle? Plus when looking in the middle you see them, maybe because of the way phospherous in the monitors are firing, or maybe even the shortcuts the brain makes to make you see what you do?
I'm a bit confused by that one, but it must be something like that. Many optical illusions are because of the shortcuts it takes, because of how complex the world actually is, it wouldn't be able to process everything in great detail.
Theres an example with a piano thats just made out of wood and is really flat, but from an angle, its just a load of flat boards. If i can find it, i'll post it.
That stairs one is very interesting and has been around a long time. Though its impossible to build... theres the same sort of thing with a box too which is kewl.