I see abstract art everywhere. In the patterns of worn and cracked tile. In the texture of leather. The grain of wood. I think it has something to do with certain levels of contrast, and certain measures of fractal complexity. The brain just responds to it, even though there's no easy formulation.
I read a story in Scientific American once where they looked at the fractal complexity of Jackson Pollack's work and compared it to photographs of a forest, and there was a mathematical match. So it might have something to do with what we're most comfortable with in our primate brains.
Wow that's interesting, who would think that we could be so in tune with nature without doing any calculations. I wonder if it had to do with the golden rule?