A neurologist friend of mine recently told me the following tale. A retired professor came to his office and said, "I think I have had a stroke." My friend asked what his grounds were for saying so, and the professor replied, "I have begun to see phantom figures repeatedly rising out of the floor to my left. Something must have happened in the occipital lobe of my brain on the right side." Sure enough, a scan revealed a small blood clot in the very region of the brain that processes left visual field information.

The professor’s phantoms vanished after a couple of weeks as the clot dissipated. It is interesting to speculate what, in an earlier age, such visions might have prompted: what cathedrals, what wars, what reports from beyond. But to a mind prepared and informed, the upwardly floating spirits immediately implied something much more sensible, not to say more interesting.