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Bilingualism
is Great for the Brain The most
striking thing about today’s emotional debate about bilingual
education is how little of it is informed by science. To be sure,
the study of bilingualism and the brain is a work in progress.
Neuroscientists still don’t understand why some bilingual adults who
have strokes can speak in one language afterwards, but not the other.
And they’re not positive how important it is to learn a second
language as a toddler. (Very important, in all probability.) They’re
still sorting out under what circumstances a second language is stored
in a different part of the brain from the first. But in recent
years, especially with the advent of brain imaging tools such as PET and
fMRI scans, there’s a growing consensus that growing up truly
bilingual is terrific for kids’ brain development. People who
speak two languages have a “distinct advantage,” says Suzanne Flynn,
a professor of linguistics and second language acquisition at the
Massachusetts Institute of Technology. From an early age, bilingual
people are “better able to abstract information…they learn early
that names of objects are arbitrary, so they deal with a level of
abstraction very early.” Granted, kids who grow up in bilingual homes may be slower than monolingual kids to acquire either language, but once they’ve learned both, they appear to have a number of intellectual advantages. Bilingual
kids, for instance, become exceptionally good at learning to “ignore
misleading information,” says 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. The Duplo
blocks are just like the familiar Lego ones except that 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 7 Lego blocks is the same height as a tower made of 4
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,” says 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,
says Adele Diamond, director of the Center for Developmental Cognitive
Neuroscience at the Eunice Kennedy Shriver Center Campus of 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, says 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 it 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 says. In many
studies, researchers use the Stroop test.
The child is presented with a list of colors such as red, blue,
green, but the names of the colors are 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. (Try it. I
guarantee you’ll feel very dumb.) For kids who can’t yet read,
Diamond use 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 says,
causes the brain to recruit extra neural circuits, whereas tasks that
don’t involve rule witching do not. Even in
monolingual people, language processing is so central to being human
that the brain devotes a huge amount of “real estate” to it, says
Patricia K. Kuhl, director of the Center for Mind, Brain and Learning at
the University of Washington. For 99
percent of right-handed people, the brain processes language mostly in
the left hemisphere. In left-handers, it’s often, though not always
reversed. Among other things, this means that if a left-handed person
needs brain surgery, it’s crucial to map where language areas are to
avoid damaging them, notes neurophysiologist Susan Bookheimer at the
David Geffen School of Medicine at UCLA. 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 aged 7 to 10, the brain was working harder at language tasks than brains of adults. That’s because “kids are still learning,” he says. And kids who
learn two languages, not surprisingly, have an even tougher challenge. When babies
are born, they are “citizens of the world,” says Kuhl, who studies language
development in babies in the US, 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 says, 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 six 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, says 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 a
young or older 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,” say 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
non-native 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. Though there is some overlap,
this suggests that there are “somewhat separate neuronal circuits for
different languages,” says 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
Washington. So what, if anything, does all this imply for bilingual education? “We are nowhere near knowing what it implies,” she says, though researchers are trying to find out. Even though the answers are not all in, she adds, there seems to be a “great advantage” to being multilingual. And in that case, why is there such a fuss over bilingual education? Loraine Obler, a professor of speech and hearing sciences at the City University of New York, puts it this way: “People’s emotions are heavily invested in the language they speak. They want everyone around them to be the same. It just makes people uncomfortable to hear languages they don’t understand.” Judy
Foreman is Lecturer on Medicine at Harvard Medical School and an
affiliated scholar
at the Women’s Studies Research Center
at Brandeis University.. Her column appears every other week.
Past columns are available on www.myhealthsense.com.
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