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The Evidence Speaks Well of Bilingualism's Effect on Kids

October 07, 2002|JUDY FOREMAN | SPECIAL TO THE TIMES

Kids who grow up in bilingual homes may be slower to speak than other kids, but once they've learned both languages they appear to have a number of intellectual advantages.

People who speak two languages early in life quickly learn that names of objects are arbitrary, said Suzanne Flynn, a professor of linguistics and second-language acquisition at the Massachusetts Institute of Technology. "So they deal with a level of abstraction very early."

Also, bilingual kids become exceptionally good at learning to ignore "misleading information," said Ellen Bialystok, professor of psychology at York University in Toronto.

Bialystok tests bilingual and monolingual 4-year-olds with what she calls the "tower game," which involves building towers with either Lego or Duplo blocks. Duplo blocks are similar to the familiar Lego ones, but they're roughly twice as big. Every block, regardless of its size, holds one "family," Bialystok tells kids. The child's task then becomes to look at a tower and say how many families it can hold. The trick is that a tower made of seven Lego blocks is the same height as a tower made of four Duplos. To answer correctly the question of which tower holds more families (the Lego tower), the child has to ignore this obvious visual fact.

"By age 5, monolingual children can do this," said Bialystok, but bilingual kids can do it at 4. "This is the advantage of bilingualism"--in other words, a child can focus attention and ignore distractions.

Bilingual kids also learn another useful skill--how to switch back and forth between tasks when the rules (such as the rules of a language) change, said Adele Diamond, director of the Center for Developmental Cognitive Neuroscience at the University of Massachusetts Medical School in Waltham.

Learning to adapt to a new set of rules means learning how to inhibit--or not pay attention to--a previously learned set, a skill that depends on development of a particular part of the brain, the prefrontal cortex, which functions in concert with other areas.

In bilingualism, said Diamond, "you are constantly having to exercise inhibition because otherwise one language would intrude. We think this puts such a heavy demand on the system that it pushes the brain to mature earlier."

This ability to filter out distractions and switch back and forth between tasks may give bilingual kids a leg up in school, she said.

In many studies, researchers use the Stroop test. The child is presented with a list of colors, but each color's name is written in ink of a different color. For instance, the word "red" would be written in green ink. Sometimes, the rule is that the child must say the name of the color and sometimes the child must say the color of the ink instead. For kids who can't yet read, Diamond uses pictures of circles on a computer screen.

Diamond then uses functional MRI scans to see which areas of the child's brain are needed when the rules keep switching. Constant rule switching, she said, causes the brain to recruit extra neural circuits, whereas tasks that don't involve rule switching do not.

Large Area of Brain Used

Even in monolingual people, language processing is so central to being human that the brain devotes a huge amount of "real estate" to it, said Patricia K. Kuhl, director of the Center for Mind, Brain and Learning at the University of Washington.

For 99% of right-handed people, the brain processes language mostly in the left hemisphere. In left-handers, it's often, though not always, reversed.

Specifically, speech production is governed by Broca's area, a small region in the left inferior frontal cortex of the brain--beneath the temple. Language comprehension, on the other hand, occurs in Wernicke's area, which lies farther back. (Sign language, by the way, uses the same areas, as well as visual processing areas. If a person who communicates by sign language has a stroke in Broca's area, he may become aphasic--unable to speak--just like a person who uses oral speech.)

Getting the brain up to speed for language processing takes years. A recent imaging study by Steven Petersen, a cognitive neuroscientist at Washington University in St. Louis, showed that even in kids ages 7 to 10, the brain was working harder at language tasks than brains of adults. That's because "kids are still learning," he said. And kids who learn two languages, not surprisingly, have an even tougher challenge.

When babies are born, they are "citizens of the world," said Kuhl, who studies language development in babies in the U.S., Sweden, Japan and Russia. Newborns don't classify sounds; they simply hear and respond (by turning their heads) to all sounds. But over the first six months, as they become "bathed" in their native language, a baby's brain does a kind of statistical analysis that said, in essence, "This sound is important. I'd better file it away for future use." Or, "This other sound is not important. I can forget it."

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