Once, experts feared that young children exposed to more than one language would suffer "language confusion," which might delay their speech development. Today, parents often are urged to capitalise on that early knack for acquiring language.As the relatively new science of bilingualism pushes back to the origins of speech and language, scientists are teasing out the earliest differences between brains exposed to one language and brains exposed to two.Researchers have found ways to analyse infant behaviour, where babies turn their gazes, how long they pay attention, to help figure out infant perceptions of sounds and words and languages, of what is familiar and what is unfamiliar to them.
Now, analysing the neurologic activity of babies' brains as they hear language, and then comparing those early responses with the words that those children learn as they get older, is helping explain not just how the early brain listens to language, but how listening shapes the early brain.Recently, researchers at the University of Washington used measures of electrical brain responses to compare so-called monolingual infants, from homes in which one language was spoken, to bilingual infants exposed to two languages.Of course, since the subjects of the study, adorable in their infant-size EEG caps, ranged from six months to 12 months of age, they weren't producing many words in any language.Still, the researchers found that at six months, the monolingual infants could discriminate between phonetic sounds, whether they were uttered in the language they were used to hearing or in another language not spoken in their homes. By ten to 12 months, however, monolingual babies were no longer detecting sounds in the second language, only in the language they usually heard.
The researchers suggested that this represents a process of "neural commitment," in which the infant brain wires itself to understand one language and its sounds.In contrast, the bilingual infants followed a different developmental trajectory. At six to nine months, they did not detect differences in phonetic sounds in either language, but when they were older, ten to 12 months, they were able to discriminate sounds in both."What the study demonstrates is that the variability in bilingual babies' experience keeps them open," said Dr Patricia Kuhl, co-director of the Institute for Learning and Brain Sciences at the University of Washington and one of the authors of the study.The learning of language, and the effects on the brain of the language we hear, may begin even earlier than six months of age.Janet Werker, a professor of psychology at the University of British Columbia, studies how babies perceive language and how that shapes their learning. Even in the womb, she said, babies are exposed to the rhythms and sounds of language, and newborns have been shown to prefer languages rhythmically similar to the one they've heard during fetal development.In one recent study, Dr Werker and her collaborators showed that babies born to bilingual mothers not only prefer both of those languages over others, but are also able to register that the two languages are different.In addition to this ability to use rhythmic sound to discriminate between languages, Dr Werker has studied other strategies that infants use as they grow, showing how their brains use different kinds of perception to learn languages, and also to keep them separate.
In a study of older infants shown silent videotapes of adults speaking, four-month-olds could distinguish different languages visually by watching mouth and facial motions and responded with interest when the language changed.By eight months, though, the monolingual infants were no longer responding to the difference in languages in these silent movies, while the bilingual infants continued to be engaged.Dr Kuhl calls bilingual babies "more cognitively flexible" than monolingual infants. Her research group is examining infant brains with an even newer imaging device, magnetoencephalography, or MEG, which combines an MRI scan with a recording of magnetic field changes as the brain transmits information.Previous research by her group showed that exposing English-language infants in Seattle to someone speaking to them in Mandarin helped those babies preserve the ability to discriminate Chinese language sounds, but when the same "dose" of Mandarin was delivered by a television programme or an audiotape, the babies learned nothing. (New York Times)
