In Oliver Sacks' classic The Man Who Mistook His Wife For A Hat the title is comic and almost absurd but his book provides fascinating explanation of a neurological condition in which a man does mistake his wife for a hat without realizing it. Sacks introduces the lay reader to another phenomenon--how a stroke leaves a person unable to see things on one side of the visual field and how the stroke victim also has no inkling that anything is wrong or missing with his perception. In fact, in both cases, nothing is wrong with the eyes, only with the way the brain processes visual information.
There is a name for this condition, prosopagnosia, and it describes a small fraction of people who cannot recognize faces--even the faces of loved ones The condition puzzles researchers but they are beginning to understand how facial recognition works, which may help those with prosopagnosia. With her colleagues, Marlene Behrmann at Carnegie Mellon University has gathered some pieces of the puzzle by comparing the brains of individuals who are face-blind to those who are face-sighted. Their results hint at how we recognize faces not in a flash of insight, not as a kind of photographic image, but by building up recognition on a neurological assembly line. Recognition is encoded in the brain as face space.
