DENVER - Researchers have found a way to reverse what
appears to be a universal decline in foreign language speech
perception that begins toward the end of the first year of
life.
University of Washington neuroscientist Patricia
Kuhl reported today that 9-month-old American infants who
were exposed to Mandarin Chinese for less than five hours in
a laboratory setting were able to distinguish phonetic
elements of that language. It is the first experimental
demonstration of phonetic learning from natural exposure to
language under controlled
laboratory conditions, she
said.
In a companion study headed by Kuhl, another group
of American infants was exposed to the same Mandarin material
using a professionally produced DVD or audiotape but showed
no ability to distinguish phonetic units of that
language.
"The findings indicate that infants can extract
phonetic information from first-time foreign-language
exposure in a relatively short period of time at 9 months of
age, but only if the language is produced by a human,
suggesting that social interaction is an important component
of language learning," said Kuhl.
She presented the
findings at the annual meeting of the American Association
for the Advancement of Science as part of a symposium on
"Learning to Communicate What Children Can't Afford to
Miss."
Kuhl, who is co-director of the UW's Center for
Mind, Brain & Learning and a professor of speech and hearing
sciences, has shown in earlier work that children are born
"citizens of the world" with the ability to distinguish among
the sounds used in all languages. But sometime in the second
six months of life infants begin to concentrate on learning
the sounds of their native language and lose their ability to
distinguish the sounds important to foreign languages. This
same inability is why many adults have difficulty learning a
foreign language and tend only to discriminate the sounds of
their native language.
In the two studies, infants were
tested to see if they could distinguish between two Mandarin
sounds that do not occur in English. Americans often hear
both sounds as “chee” or “she.” These sounds are difficult
for adult Americans to distinguish between but present no
problem for native Mandarin speakers.
In the first study,
normally developing 9-month-olds were exposed to Mandarin
during a dozen 25-minutes sessions spaced out over four
weeks. During these sessions, native Mandarin speakers read
from children's books and played with toys while speaking
Mandarin. Four different speakers, two men and two women,
conducted the sessions, so the babies were exposed to a
variety of speaking styles. A control group of infants was
exposed to the same procedure in English.
Both groups then
were tested for their ability to distinguish between the two
Mandarin sounds using a head-turn conditioning procedure that
is frequently used in tests of infant speech perception. The
infants exposed to Mandarin were significantly better at
distinguishing the two target sounds than were infants who
only heard English. In fact, the performance of the American
infants exposed to Mandarin for the first time between 9 and
10 months was statistically equivalent to infants in Taiwan
who had listened to Mandarin for 10 months, according to
Kuhl. The results show that the decline in foreign-language
speech perception can be reversed with short-term exposure,
she said.
In addition, the phonetic learning of Mandarin
appears to be long lasting. The American infants were tested
from two to 12 days after their last exposure to Mandarin and
the researchers found there were no significant differences
in their ability to discriminate between the sounds.
"In
previous learning studies babies were exposed to artificial
languages for a few minutes and no one expected that kind of
exposure to produce long-lasting effects," said Kuhl "We
predicted that learning in this natural situation would
produce a longer lasting effect. We were surprised to see
some of our babies hang on to the information for 12 days.
This indicates the learning was potent and we are curious to
know how long they will retain the ability to distinguish
between the sounds."
To do that, Kuhl and her colleagues
have retested the infants at 14 and will again at 30 months
of age. Thoset data are now being analyzed.
The second
study explored the role of social interaction in learning a
foreign language. The procedure was similar to the initial
study except that half the infants were exposed to Mandarin
by a DVD showing the same Mandarin speakers and materials on
a 17-inch television. The other infants received their
Mandarin exposure from an audio-only presentation of the
DVD.
At the end of the Mandarin exposure all of the
infants were tested using the same head-turn procedure.
Results clearly showed that DVD or audiotape exposure did not
lead to phonetic learning, Kuhl said. The infants in this
experiment scored at the same level as the English-only
babies in the first study who were not exposed to any
Mandarin. The researchers also noted that the infants who
watched the DVD or listened to the audiotape paid
significantly less attention than the babies who were in the
live Mandarin and English conditions.
"Video plus audio or
audio-only presentation did not work for infants 9 and 10
months of age," Kuhl said. "That’s not how infants learn
language. Our results show the importance of testing audio
and video language learning products aimed at children and
already on the market for their effectiveness."
She added,
"Babies are very sophisticated language learners who use
every clue provided to learn – the sounds they hear, their
statistical distribution and even the social clues provided
by speakers – to crack code. The babies were mesmerized by
the sight and sound of the foreign language speakers. You
could see their little brains absorbing the
information.
"These new studies show the importance of
timing – at 9 months infants are in a sensitive period for
language learning. They also show the importance of social
interaction in learning language. In addition, the studies
suggest how language learning draws on all aspects of
infants' cognitive abilities, including their attraction to
'motherese' (a form of exaggerated speech) spoken by adults
to babies; the statistical learning that infants engage in by
analyzing language; and the ability to follow the gaze of
another person to an object to understand what they are
talking about."
Co-investigators on the two studies are
Feng-Ming Tsao and Huei-Mei Liu, post-doctoral researchers at
the UW who earned their doctorates at the university. The
research was funded by the National Institutes of Health, the
Human Frontiers Science Program, the William P. and Ruth
Gerberding Professorship and the Talaris Research Institute
and Apex Foundation created by Bruce and Jolene
McCaw.
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For more information, contact Kuhl at (206)
685-1921 or pkkuhl@u.washington.edu. Kuhl will be in Denver
Feb. 15-17 and can be reached at the Hotel Teatro, (303)
228-1100.
