A new study from researchers at Kansas University has found that unborn babies are able to distinguish between different languages as early a month before they are born.

The study found that unborn children, at an average of 8 months in the womb, are able to distinguish the difference between someone speaking in English and someone speaking Japanese, even if the languages were being spoken by the same person. Two dozen pregnant American women and their in-utero babies took part in the study conducted by a team from KU’s Department of Linguistics, and published in the journal NeuroReport.  

The study used a non-invasive magnetocardiogram (MCG) - sensing technology that can detect fetal heartbeats, breathing and other body movements. According to study leaders, previous research had shown that language development began as early as a few days after birth, with babies just a few days old showing sensitivities to different languages, such as sucking pacifiers at different rates when different languages were spoken.

“This early discrimination led us to wonder when children’s sensitivity to the rhythmic properties of language emerges, including whether it may, in fact, emerge before birth,” said Utako Minai, associate professor of linguistics and team leader for the study, according to a press release from Kansas University. “Fetuses can hear things, including speech, in the womb. It’s muffled, like the adults talking in a ‘Peanuts’ cartoon, but the rhythm of the language should be preserved and available for the fetus to hear, even though the speech is muffled.”

A previous study had also suggested that babies in the womb were sensitive to different languages, but it hadn’t determined whether the babies were reacting to different languages, or just to different speakers. For this study, Minai had a bilingual speaker make two recordings, one in English and one in Japanese, to play for the babies in utero. English and Japanese are considered to be rhythmically distinct languages.

When the babies heard the familiar English language, their heart rates did not change, even when played a second English recording. However, their heart rates did change when they were first played an English recording, and then a second recording of the unfamiliar language of Japanese.

“These results suggest that language development may indeed start in utero, Minai said.  “Fetuses are tuning their ears to the language they are going to acquire even before they are born, based on the speech signals available to them in utero. Prenatal sensitivity to the rhythmic properties of language may provide children with one of the very first building blocks in acquiring language.” Minai said the finding was “extremely exciting” for language development research, and could potentially apply to other fields.