I guess that's the same reason solutions pop into your head after a day or so without even thinking about the problem. Your unconscious keeps working on it. I've read somewhere that this part of the brain is much faster than the part that actually does analytical thinking, since it deals with primitive functions and signal processing.
Yeah, your unconcious brain is performing FFTs like mad on your visual and auditory inputs with out effort but try to do an FFT with the thinking part of your brain and you're hooped with out extensive training in maths, and an uncanny ability to compute.
