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The Evidence Speaks Well of Bilingualism's Effect on Kids
October 7, 2002
Judy Foreman, Los Angeles 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."
Using computer-generated vowel sounds and sophisticated statistical analyses of
babies' responses, Kuhl has shown that by 6 months of age, Swedish babies and
American babies "have totally different perceptions of the exact same sound"
from the computer. Other researchers, including those from the University of
British Columbia, have shown similar results.
These distinctions become ingrained for life. While Japanese babies learn that
there's no meaningful difference between the sound for "L" and the sound for
"R," American babies learn there is. The result, for Japanese adults, is that it
is very difficult to distinguish between "L" and "R" because the two sounds,
said Kuhl, are in the same storage "bin."
But mapping exactly where language "bins" reside is a tricky, and fascinating,
business. Neuroscientist Joy Hirsch of Columbia University uses functional MRI
scanning to study bilingual adults, half of whom became bilingual as toddlers
and half of whom learned a second language as an adult. The question was simple:
"When one learns a second language, is
that represented in the same area of the brain as the native language?"
Hirsch's subjects, who spoke a variety of languages--English, Chinese, German,
French, etc.--were shown a picture and were asked to describe it first in one
language, then in the second language. In adults who had learned a second
language early, as toddlers, electrical activity in Broca' s area looked
virtually identical, regardless of which language was being
used. But when people had acquired a second language later, the scans showed two
separate parts of Broca's area lighting up.
This suggests that when the learning is early, "the brain treats multiple
languages as one language. But when one learns later in life, the sorting out
seems to be done more spatially," says Hirsch, whose research has been used by
both sides in the bilingual education debate.
At the Montreal Neurological Institute, Denise Klein also finds brain
differences depending on when people learn a second language. Using PET scans,
she has found that people who are fully bilingual in French and English use the
same area of the brain as an "internal dictionary," regardless of which language
they're speaking. By contrast, people who are
not truly bilingual, that is, who learn a second language after childhood, need
to recruit additional brain areas to find words in their nonnative language,
suggesting the brain has to work harder to do this.
Neurosurgeons, too, have documented that multiple languages can be stored in
discrete parts of the brain. Dr. George Ojemann, a professor of neurology at the
University of Washington School of Medicine in Seattle, operates on people who
suffer severe epileptic seizures, some of whom are bilingual, and maps the
precise location of each language.
With the patient awake and able to speak, Ojemann shows a picture of, say, a
banana, and asks the patient to name it. By using very precise electrical
stimulation of specific regions in the brain, Ojemann can get the patient to
talk, say, in French but not English, then stimulate a nearby area and get the
opposite result.
Separate Circuits
Though there is some overlap, this suggests that there are "somewhat separate
neuronal circuits for different languages," said Ojemann, who has recently been
able to map different languages to single neurons.
"If you have two languages, all lines of evidence show there is separate real
estate for different languages" in the brain, agrees Patricia Kuhl of the
University of Washington.
So what, if anything, does all this imply for bilingual education? "We are
nowhere near knowing what it implies," she said, though researchers are trying
to find out. Even though the answers are not all in, she added, there seems to
be a "great advantage" to being multilingual.
Judy Foreman is a lecturer on medicine at Harvard Medical School. She can be
reached at judyforeman@attbi.com. Her column appears occasionally in Health.
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