May 17, 2002 -- Spotting a friend in a crowd can be difficult, but imagine trying to find one monkey in a stadium full of them.

A 6-month-old baby would do well at the task, say scientists.

New research suggests that infants are better at remembering and recognizing the faces of monkeys than older babies and adults are.

In a similar way that people zoom in on sounds of certain languages at young ages, we also fine-tune our brains to recognize certain kinds of faces as we age — namely, human. In doing so, this study suggests, we eventually tune out the ability to recognize other kinds of faces.

The work carries implications in an ongoing debate over whether face recognition is an innate skill of genetic origin or one that is learned.

"This proves that it's a learned ability," argues Charles Nelson, a professor of child development, neuroscience and pediatrics at the University of Minnesota and co-author of the study appearing in this week's Science. "We know newborns have some genetic potential for face recognition, but this shows they develop it by experience."

Tuning In

To test face recognition, Olivier Pascalis of the University of Sheffield in England and Michelle de Haan of University College London showed adults and 6- and 9-month-old infants a series of two headshots of white men or women and two headshots of macaque monkeys. Included in each set of pictures was one face that the subject had seen before.

They discovered that the 6-month-olds easily distinguished between individual human faces and individual monkeys. This was evident in the way the babies gazed longer at the human and monkey faces that they had seen before. Babies only 3 months older and adults could also distinguish human faces, but found it nearly impossible to tell apart one monkey face from another.

"This is probably a reflection of the brain's 'tuning in' to the perceptual differences that are most important for telling human faces apart, and losing the ability to detect those differences that are not so useful," said de Haan in a release.

This kind of narrowing of perception is also evident in the way babies older than 6 months lose their abilities to differentiate between sounds that are not heard in their native languages.

"This is a fascinating result," says Martha Farah, director of the Center for Cognitive Neuroscience at the University of Pennsylvania. "We naturally think of development as a process of acquiring new abilities. So any time you see an ability being lost in development, it's a flag."

Farah, however, says she suspects that genetic programming, more than learning, is at play.

Is That You, Mom?

Farah points to her recent studies of a young man who, as a newborn, sustained damage to an area of his brain called the fusiform gyrus. This zone is believed to host a person's genetically programmed ability to process faces. Farah says that while the boy's general vision is fine, his ability to recognize faces is so poor that he can't even recognize his parents.

She argues that if recognizing faces is a learned ability, then this boy should be able to recognize faces — but he can't.

"According to my reading," she says, "we come into the world with a genetically programmed mechanism for recognizing faces and spend out first year stocking it with enough experience of faces that it becomes narrowly tuned to the types of faces we see."

Nelson agrees that some genetic pre-programming exists, but, he believes it's experience that makes that programming work. He says this is demonstrated by studies that show how children raised by abusive parents are unusually adept at recognizing anger in faces and children neglected by depressed parents are better tuned to recognizing sad expressions.

Other work has shown that infants raised by one race are slightly less adept at recognizing faces of other races. And Paul Quinn of Washington and Jefferson College in Pennsylvania, has shown that babies reared by two mothers are more attuned to female faces and babies raised by two fathers prefer to look at male faces.

The difference between an innate ability and one that's based on an innate ability but develops through experience may be subtle, but when it comes to treatment, it's key.

People with a condition known as prosopagnosia lose their ability to recognize faces. Those with autism are notoriously poor at recognizing faces and facial expressions. Nelson says his studies imply that encouraging people with these conditions to focus on human faces and facial expression when they're 6 months old or younger might help remedy the problems.

Fake Heads in Cribs

To further test the theory, Pascalis, who is a former student of Nelson, plans to expose infants to pictures of monkey faces on a regular basis for the first nine months of their lives. He wants to learn if this can effectively train the infants' brains to recognize individual monkey faces even as they grow older. The team has also tested adults who work with monkeys on a regular basis to see if they develop a keen sense for primate faces.

It seems learning faces, like learning new languages, is more difficult for adults.

"The adults don't seem to recognize faces," said Pascalis. "Instead they seem to focus on other features like body type and fur."

The next step is to zero in on exactly what age infants begin to "tune" their abilities to recognize certain faces. To do this Nelson's team is preparing a somewhat bizarre experiment. They have recruited an artist to craft very realistic human heads with faces and they plan to place the heads in cribs with babies of different ages.

They will then test the babies to see how well they recognize the heads later on. This way, they hope to learn at which age babies learn to never forget a face.