So what makes people separated in time and geography create the same strange patterns? The answer lies not in the art, but in the brains of the artists. Dr. Dominic Ffytch of the Institute of Psychiatry in London treats people with a rare type of visual disorder. His patients have reported seeing peculiar shapes and patterns appearing before their eyes. But according to Dr. Ffytch, they don't have a problem with their eyes, but rather the part of their brain that deals with vision.

To investigate this condition, he designed a special apparatus that stimulates the visual part of the brain. With eyes closed, the patient wears a pair of goggles equipped with light emitting diodes. The goggles are hooked to a computer that regulates the number of flashes experienced per second. The flashes induce patterns that the patient "sees" even with their eyes closed. Paradoxically, Ffytch explains, you can duplicate the same phenomena when too little information gets into the visual system. So if an artist goes into a cave with no source of light, they just might start seeing these patterns too.