Perri Klass, M.D. / New York Times News Service

Once, experts feared that young children exposed to more than one language would suffer “language confusion,” which might delay their speech development. Today, parents are urged to capitalize 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 analyze infant behavior — 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.

Analyzing the neurologic activity of babies’ brains as they hear language, and comparing those responses with the words the 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.

Differing trajectories

Recently, researchers at the University of Washington used measures of electrical brain responses to compare infants from homes in which one language was spoken to bilingual infants. Of course, since the subjects of the study ranged from 6 months to 12 months of age, they weren’t producing many words in any language.

Still, the researchers found that at 6 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 10 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 brain wires itself to understand one language and its sounds.

The bilingual infants followed a different developmental trajectory. At 6 to 9 months, they did not detect differences in phonetic sounds in either language, but at 10 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. “They do not show the perceptual narrowing as soon as monolingual babies do. It’s another piece of evidence that what you experience shapes the brain.”

Learning new skills

The learning of language — and its effects on the brain — may begin even earlier than 6 months of age.

Janet Werker, a professor of psychology at the University of British Columbia, said that even in the womb, 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 study, 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.

And over the past decade, Ellen Bialystok, a professor at York University in Toronto, has shown that bilingual children develop crucial skills such as learning different ways to solve logic problems or handle multitasking. These skills are often considered part of the brain’s “executive function,” higher-level cognitive abilities that are localized in the frontal and prefrontal cortex.

Bilingualism in America

An estimated 9 percent of American adults are bilingual — that is, fluent in more than one language. In Europe, that figure is closer to 50 percent.

Research indicates that the ability to learn a second language decreases with age. Younger Americans, aged 18-29, are more likely to be bilingual, with 43 percent able to speak a second language, compared with 25 percent of those aged 30 to 49 and 22 percent of those aged 50 to 64.

Only 15 percent of Americans 65 and older are bilingual.

Sources: Scientific American,