For weeks before birth, babies absorb the nuances of their mothers' words. And within hours after they are born, they can already tell the difference between their native language and foreign tongues.

The new finding suggests that language learning begins prenatally, perhaps as soon as fetuses are able to hear — after about 30 weeks of gestation — with their initial focus on vowel sounds, which are louder, longer and more rhythmic than consonants.

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"The mother has first dibs on influencing the child's brain," said Patricia Kuhl, of the Institute for Learning & Brain Sciences at the University of Washington, in a press release. "The vowel sounds in her speech are the loudest units and the fetus locks onto them."

Previous studies have shown that the perception of speech sounds develops in infants long before they are able to speak themselves.

Between the ages of 6 months and a year, for example, babies quickly get better at telling the difference between sounds often used in their native languages. At the same time, they rapidly lose the ability to distinguish between the typical sounds of other languages.

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To see just how early those abilities develop, Kuhl and colleagues tested 40 American newborns and 40 Swedish newborns, all between seven hours and three days old. While still in the hospital, each infant listened through headphones to 17 computer-generated examples of the English vowel sound used in syllables like "fee" and 17 examples of the Swedish vowel sound used in syllables like "fy." During the experiment, babies sucked on sensor-equipped pacifiers.

When exposed to vowel sounds from their non-native language, babies sucked longer than they did if they heard vowel sounds that their mothers frequently spoke, the researchers will report in the journal Acta Paediatrica. Sucking longer is an established response in infants to something that is unfamiliar or novel to them.

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"The results of our study support the hypothesis that language experienced in utero affects vowel perception," the researchers wrote. "These results suggest that birth is not a benchmark that reflects a complete separation between the effects of nature versus those of nurture on infants' perception of the phonetic units of speech."

Long before parents start watching their words, it seems, their kids are taking in everything they say.

Photo: A fetus in the third trimester. Credit: iStockPhoto