>>10
I suppose those are distinct layers of abstraction, but you must look at it by converging the two eyes at a point behind the pattern making it possible to trick the brain into matching one element of the pattern, as seen by the left eye, with another (similar looking) element, beside the first, as seen by the right eye. This gives the illusion of a plane bearing the same pattern but located behind the real wall. The distance at which this plane lies behind the wall depends only on the spacing between identical elements.