"it's awesome just what the eye sees isn't it? makes you wonder whether what goes on in the brain seeing images like that =)"

Actually (AFIK), it not what the eye sees, it's what the brain makes of it. And that includes the "Pavement Artist's" effects...

The Eye just sees (OK, a little simplistic, but ...)
The Brain tries to make sense of what the eye sees. It tries to put what is seen into a context that it knows. Most of what it knows is drawn from every-day world experience ('cos humankind would have died out milennia ago if it couldn't do that. - mostly by stumbling over the edges of cliffs with one single step ...ooooooppppss.......). Which is why clever tricks can trick the brain. The brain interprets what is seen into the context/"world view" it has set up.

Which is also (co-incidentally) why the whole 2D artistic genre exists. After all - all you're looking at is a flat (2D) image - which the brain translates into the "most likely" 3D representation of that 2D image...

Sorry - getting too philosophical here. I'll shut up...

Cheers,
Diolma