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A Dedicated System For Processing Faces

If you're planning to rob a bank, there's one thing you must not forget: to cover your face. Otherwise, just a brief glance will allow all the other social animals around you to identify you. What is the neural basis of the extraordinary ability of humans to recognize faces? Localized strokes can selectively destroy face recognition abilities while preserving the ability to recognize other objects ("prosopagnosia") (1). Furthermore, functional magnetic resonance imaging (fMRI), a technique that measures blood flow changes induced by brain activation, consistently reveals several discrete brain regions that respond more to faces than to other objects (2). One of these regions, the fusiform face area, shows increased blood flow even when subjects merely imagine faces (3). These findings suggest that face processing is mediated by specialized modules inside the human brain. Such specialization is surprising since, from introspection, it seems that our recognition of faces flows seamlessly into that of all the other objects in the world.

Are face-selective regions unique to humans? Charles Gross and co-workers studied a large region in the macaque brain known as the temporal lobe and reported in 1981 that this region contains some cells that respond exclusively to faces and not to other visual forms (4). This was a remarkable finding: How can a single cell be wired to detect something so complex as a face? The discovery immediately turned fuzzy questions about holistic integration and gnostic units into a concrete research goal: What are face cells detecting, and how are they wired?

One problem, however, stood in the way of understanding these cells: It was difficult to find them. In single-unit recording experiments, one can see only as far as the tip of one's electrode (100 µm wide). Several groups that studied face cells reported that they were scattered throughout the temporal lobe, with at most 10 to 20% of the cells in any one region being face-selective...