Apparently, keeping an open mind is a lot harder than not passing judgment on your neighbor's overgrown lawn. Research appearing in the 17 May issue of Science shows that babies rapidly learn to tell human faces apart but lose their ability at distinguishing those of other species. The same kind of honing of perception happens as infants learn a language, suggesting that the brain learns about speech and sight in the same way.
Perception researchers have long thought that a baby's ability to recognize human faces improved gradually into adolescence. Language, on the other hand, improves in a flash. Although newborns can distinguish phonetic sounds of all the world's languages, by 8 months infants can only distinguish the vowels of their native language.
To determine whether the visual system undergoes a similar "perceptual narrowing," a team led by neuroscientist Olivier Pascalis at the University of Sheffield, U.K., presented pictures of human or monkey faces to babies. The babies stared at each image for about half a minute, then the researchers presented them with the pictures again, throwing unfamiliar images into the mix. The team videotaped the experiments and measured how much time the babies spent watching each face, expecting them to look at a face longer if they didn't recognize it. At 6 months, babies were just as good at telling which human and monkey faces they had seen before. But by 9 months, the babies could only recognize individual human faces--they spent just as much time perusing a monkey face whether or not they had seen it before. These results suggest that between 6 and 9 months of age, babies customize their visual perception, just as they do with the sounds of cooing parents.
The findings suggest that the brain devotes most of its resources to stimuli we encounter most frequently--strengthening relevant connections between neurons and letting others fall by the wayside, says research psychologist Paul Quinn at Washington and Jefferson College in Washington, Pennsylvania. "It's a bit of a 'use it or lose it' type of story." In addition, he says, the study suggests that our abilities to learn language and learn to recognize each other may have evolved from the same mechanism.
Pascalis's Web page