Faces of Perception

Article excerpt

It's tough to explain how people so easily tell one face from another

Newborn babies are wrinkled, wide-eyed strangers in a strange land of light, shadow, and color. Nonetheless, these little bundles of visual innocence take an immediate shine to faces.

Just a few hours after birth, infants begin to imitate adults' smiles, frowns, and other expressions. Given a choice, the same babies gaze longer at a picture of their mother's face than at an image of the face of a female stranger. They also boast a budding aptitude for telling strangers' faces apart and give particular notice to faces rated as attractive by adults.

The magnetic pull that faces exert on babies' attention has stimulated much research by psychologists over the past 30 years. In related work, neuroscientists are pursuing the brain areas that enable most adults to say with confidence, "I never forget a face." Debate over the meaning of all this research has now come to a head.

Some scientists suspect that newborns possess an innate ability to spot basic facial features, such as two eyes situated above a mouth. As a result of humanity's extended evolution in small groups, where it's critical to discern friends from foes, genes now give human brains a head start in decoding faces, according to these researchers.

Consequently, they add, a few brain areas--in particular, a small patch of right-brain tissue just behind the ear--specialize in perceiving and recognizing faces. People who incur damage to these regions neither recognize the faces of those they know nor remember new faces.

An alternate explanation of face recognition, however, is gaining momentum. Its adherents argue that infants come equipped not with a special face-recognition capability but only with preferences for general perceptual features, such as curved contours. Babies use these visual inclinations as a launching pad for learning to recognize faces, say researchers in this camp.

A propensity for looking at faces may coexist with preferences for several other visual categories in newborns, none of which is predetermined by genes, these researchers argue. By 3 to 4 months of age, infants usually prefer pictures of cats over horses, tigers over cats, chairs over tables, and mammals over birds. Such curious predilections probably exist even in newborns, these scientists propose.

Moreover, they point out, the behind-the-ear brain area most directly implicated in face recognition actually coordinates all sorts of expert visual judgments. It's just as crucial for making deft distinctions among classic cars, bird species, and imaginary creatures with no faces as it is for recognizing pictures of one's high school classmates. Damage to this part of the brain hinders object recognition to a lesser extent than it does face recognition, but the effect is still noticeable, add supporters of this view.

The theoretical division runs deep among face researchers. "Debate about the nature of face recognition is unbelievably heated right now," says neuroscientist Charles A. Nelson of the University of Minnesota in Minneapolis. "It has polarized groups of researchers."

In the long run, this dispute will yield major scientific insights, holds neuroscientist Nancy Kanwisher of the Massachusetts Institute of Technology. "It will take a while to figure out how the brain carves up visual perception," she says. "This is how science works."

It's hard to know precisely what a baby sees when he or she looks at a face looming overhead. Studies indicate that newborns perceive a fuzzy world, devoid of sharp delineations among objects and the nuances of noses, cheeks, and other parts of the facial landscape.

Despite their vague take on the world, infants have an innate preference for gazing at facelike sights, such as a pair of round blobs over a horizontal line, contends psychologist Mark H. Johnson of Birkbeck College in London. …