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Bilingual Effects in the Brain

A new study found certain brain functions that are enhanced in teens who are fluent in more than one language. The finding gives new insight into how our senses help shape our brains.

About 1 in 5 children nationwide speak a language other than English at home. Children who grow up learning to speak 2 languages tend to learn English words and grammar more slowly than those who speak only English. But studies have found that bilingual children tend to be better than monolingual children at multitasking. They are also better at focusing their attention—for example, homing in on a voice in a noisy school cafeteria.

Dr. Nina Kraus and her colleagues at Northwestern University have been using scalp electrodes to analyze activity in the brain circuits that process complex sounds (called the auditory brainstem response). They noted that musicians show attention and memory advantages similar to those seen in bilinguals. In past work, the researchers found that musicians have enhanced auditory brainstem responses to the timing and harmonics in sound. The scientists decided to test whether bilingual teens, whose brains are still developing, would also show an enhanced response to complex sounds.

The researchers studied 48 incoming first year high school students, 23 of whom were proficient in both Spanish and English. The rest were proficient only in English. The study was funded by NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). Results appeared in the April 30, 2012, advance online edition of the Proceedings of the National Academy of Sciences.

The researchers played the speech syllable “da” to the teens, using electrodes to record the intensity of their auditory brainstem response. Bilinguals showed a larger response than monolinguals. When the sound was played with a background of babble, monolingual teens had a less intense response than when it was played alone. In contrast, bilinguals showed virtually identical responses with and without the background babble.

In another experiment, the teens were given a selective attention test in which they were asked to click a mouse when a 1, but not a 2, was seen or heard. The test involved 500 trials of 1or 2 seconds each over a period of 20 minutes. The bilingual teens outperformed the monolingual teens on this test.

The researchers then compared the results of the 2 sets of experiments. Among bilingual teens, the intensity of the auditory brainstem response during the babble test correlated with attention test scores. In contrast, there was no correlation among the monolingual teens. These findings suggest that the bilingual experience may help improve selective attention by enhancing the auditory brainstem response.

“Bilingualism serves as enrichment for the brain and has real consequences when it comes to executive function, specifically attention and working memory,” Kraus says. The team next plans to explore whether learning a language later in life can bring similar benefits.

“The bilingual juggles linguistic input and, it appears, automatically pays greater attention to relevant versus irrelevant sounds,” says team member Dr. Viorica Marian. “Rather than promoting linguistic confusion, bilingualism promotes improved 'inhibitory control,' or the ability to pick out relevant speech sounds and ignore others.”

—by Harrison Wein, Ph.D.