Study Illuminates How Babies Learn to Speak
MICHELE NORRIS, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.
ROBERT SIEGEL, host:
And I'm Robert Siegel.
The story now about babies and what happens in their brains as they learn language.
Michelle Trudeau reports on a new study in the scientific journal Neuro Report.
MICHELLE TRUDEAU reporting:
From birth, baby's brains are bathed in the sounds of language, but how do they get from hearing those sounds to speaking them? That's what neuroscientist Patricia Kuhl from the University of Washington is studying. What happens in the brain that prepares a baby to move from speech perception to speech production?
Dr. PATRICIA KUHL (University of Washington): We want to know how it is that we train our muscles, our tongues and lips to do that very precise mother tongue kind of thing.
TRUDEAU: Now the part of the brain responsible for speech perception is called Wernicke's Area, named after a 19th Century German neurologist, and the part in charge of speech production is Broca's Area, after a French 19th Century neurologist.
Both are in the left hemisphere of the brain, about three inches apart, and both are essential for language development.
Dr. KUHL: So one wants to know how does the understanding area of the brain talk to the part of the brain that actually has to do the work in producing language?
TRUDEAU: To find out how and when these two language centers start communicating with each other, Kuhl went right to the source, babies. Newborns, six month olds and 12 month olds. She used a new technology called MEG that tracks millisecond by millisecond the activity of brain cells. So each baby was placed in this device, which looks like an enormous hair dryer, you can see a picture of it on NPR's web site, and then the researchers played different sounds to the babies.
There were speech-like sounds, single syllables.
Dr. KUHL: This what the babies heard.
(Soundbite of computer-based syllables)
TRUDEAU: And non speech sounds, tones and harmonics.
(Soundbite of computer-based tones)
Dr. KUHL: In one respect we're asking does the brain know the difference between things that can be produced by a mouth and things that can't.
TRUDEAU: While the babies listened to these various sounds, the scientists watched brain activity. First in the newborns, their speech recognition areas lit up indicating their brains differentiated speech sounds and non speech sounds right from birth. But -
Dr. KUHL: As a newborn the areas of the brain that do the work of speech production do not light up to any of these signals.
TRUDEAU: But as babies got older, Broca's speech production area became increasingly involved.
Dr. KUHL: And as you move toward six months and 12 months, Broca's Area is definitely activated by these speech signals. The more speech like it is, the more activated that area becomes.
TRUDEAU: And, Kuhl reports, by 12 months brain activity is synchronized between the two language centers, but only when the babies hear the syllables.
Dr. KUHL: It's as though they're both talking to each other by 12 months, as though Broca's Area is now saying I know what that is. I know that this is a signal that my mouth and tongue and lips produce.
TRUDEAU: As most parents will tell you, babies are beginning to speak their first words around one year of age. Patricia Kuhl has now shown us why. By this age millions of nerve cells in the baby's two language centers are successfully connected and communicating. First hearing the sound, then producing it, hearing it, producing it. Practicing over and over, closer and closer to the correct pronunciation.
Neuroscientist Bill Greenough, from the University of Illinois at Urbana-Champaign, says this study is a technical tour de force. Watching the action inside a baby's brain at the speed of thought. Seeing nerves turned on only by the sounds of language.
Dr. BILL GREENOUGH (University of Illinois, Urbana-Champaign): The brain is going into its environment and selectively grabbing out sounds that have to do with speech and processing them in a completely different way from the way that other sounds are being processed.
TRUDEAU: So hearing lots of language, Greenough adds, from parents and others supplies the two language centers of a baby's brain with lots of material to work with and to eventually perfect into spoken words.
For NPR News, I'm Michelle Trudeau.
SIEGEL: You can also find out what robots and chimpanzees are teaching researchers about the origins of language at NPR.org.
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