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A new study suggests that babies learn bits of their native languages even before they are born.

A baby develops the ability to hear by about 30 weeks’ gestation, so he can make out his mother’s voice for the last two months of pregnancy. Researchers tested 40 American and 40 Swedish newborns to see if they could distinguish between English and Swedish vowel sounds. The study is scheduled for future publication in the journal Acta Paediatrica.

The scientists gave the babies, ranging in age from 7 hours to 75 hours, pacifiers that counted the number of sucks they made. As the babies sucked, they listened to Swedish and English vowel sounds; the more they sucked, the more the sounds were played. The researchers inferred the babies’ interest in the sound by the amount of sucking.

American babies consistently sucked more often when hearing Swedish vowel sounds, suggesting that the infants had not heard them before, and Swedish babies sucked more when hearing English vowels.

Learning so quickly after birth was unlikely, the researchers concluded, so the babies’ understanding the difference between native and nonnative sounds could be attributed only to prenatal learning.

“Even in late gestation, babies are doing what they’ll be doing throughout infancy and childhood — learning about language,” said the lead author, Christine Moon, a professor of psychology at Pacific Lutheran University.



The researchers set up a system to test how well an infant recognizes vowel sounds. They measured the number of times a baby sucked on a pacifier that triggered various vowel sounds. The babies tended to suck faster on their pacifiers when they heard the vowel sounds of a foreign language as opposed to the one their mothers spoke.