Nicholas Wade in The New York Times:
The brain has an amazing capacity for recognizing faces. It can identify a face in a few thousandths of a second, form a first impression of its owner and retain the memory for decades. Central to these abilities is a longstanding puzzle: how the image of a face is encoded by the brain. Two Caltech biologists, Le Chang and Doris Y. Tsao, reported in Thursday’s issue of Cell that they have deciphered the code of how faces are recognized. Their experiments were based on electrical recordings from face cells, the name given to neurons that respond with a burst of electric signals when an image of a face is presented to the retina. By noting how face cells in macaque monkeys responded to manipulated photos of some 2,000 human faces, the Caltech team figured out exactly what aspects of the faces triggered the cells and how the features of the face were being encoded. The monkey face recognition system seems to be very similar to that of humans.
Just 200 face cells are required to identify a face, the biologists say. After discovering how its features are encoded, the biologists were able to reconstruct the faces a monkey was looking at just by monitoring the pattern in which its face cells were firing. The finding needs to be confirmed in other laboratories. But, if correct, it could help understand how the brain encodes all seen objects, as well as suggesting new approaches to artificial vision. “Cracking the code for faces would definitely be a big deal,” said Brad Duchaine, an expert on face recognition at Dartmouth. It is a remarkable advance to have identified the dimensions used by the primate brain to decode faces, he added — and impressive that the researchers were able to reconstruct from neural signals the face a monkey is looking at. Human and monkey brains have evolved dedicated systems for recognizing faces, presumably because, as social animals, survival depends on identifying members of one’s own social group and distinguishing them from strangers.