In 1988, a 27-year-old man identified as CK sustained head injuries in an auto accident that left him with a strange impairment: He has normal eyesight and cognition, but he can't recognize objects. He can laboriously identify them by their component parts, but often they just look like "blobs." Yet he easily recognizes faces.
A team of researchers, headed by psychologist Morris Moscovitch of the University of Toronto in Mississauga, Ontario, realized the man could help resolve a "long-standing debate" over whether facial recognition is a special system or whether it relies on neural mechanisms that are also involved in object recognition. In a series of experiments with the man, reported in the September Journal of Cognitive Neuroscience, Moscovitch and his colleagues provide the strongest evidence yet that facial recognition is indeed a highly specific brain function.
The researchers put their subject through 19 types of experiments which included showing him upside-down faces, cartoon faces, partial faces, animal faces, and faces made out of vegetables. The man performed as well as or better than controls did in recognizing most types of faces, but his performance plummeted with an upside-down face or a photograph that had been "fractured." The authors conclude that the facial recognition system depends on the face being upright, and on preservation of the spatial relationship between two of three key features: eyes, nose, and mouth.
The study is a "gorgeous" case, says Dartmouth University neuroscientist Michael Gazzaniga. "It shows how incredibly selective this face selector must be."