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.
UW neuroscientist Patricia Kuhl reported this week 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. Those 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.