Babies Process Sound Differently After Hearing Two Languages in the Womb

Babies who hear more than one language while they’re growing in the womb may be more able to hear a wider range of speech after they’re born.

While babies with mothers that only spoke one language were found to be tuned into a specific pitch—corresponding with their mother’s language—babies of bilingual mothers were more sensitive to a wider range of pitches, and less tuned into a specific one, according to a new paper in the journal Frontiers in Human Neuroscience.

This implies that bilingual babies start to learn about languages differently before they’re even born.

baby in womb
Stock image of parents talking to a baby bump (main) and a fetus in the womb (inset). Babies differ in how they process speech depending on if their mother is bilingual or monolingual.


Previous research over the past few decades has found that babies learn about speech in the womb, especially in the third trimester, with newborns preferring their mother’s voice to others and even recognizing stories told to them while they were in the womb.

However, not much research has yet been done into how fetuses process speech if their mother is bilingual and speaks multiple languages while pregnant.

“Languages vary in the timing aspects of speech, such as rhythm and accentuation, but also pitch and phonetic information. This means that fetuses from bilingual mothers are expected to be immersed in a more complex acoustic environment that those from monolingual mothers,” study co-author Carles Escera, a professor at the University of Barcelona’s Institute of Neurosciences, said in a statement.

In the paper, the researchers—from the University of Barcelona in Spain—describe how they studied 131 sets of mothers and babies aged between 1 and 3 days old in Catalonia, where 42 percent of the population regularly speak both Catalan and Spanish.

The mothers completed a questionnaire, where it was found that 41 percent of them spoke only one language during their pregnancy (9 percent of which was in Catalan and 91 percent in Spanish), while the remaining 59 percent spoke both, or one and another language.

The researchers then measured the babies’ brain responses using electrodes on their foreheads, which they used to determine an electrophysiological brain response known as the “frequency-following response” (FFR). They then tested the babies’ reactions to varying speech sounds that represented sounds common to the different languages: the vowel /a/ at a steady pitch (like in the word “wash”), /a/ rising in pitch, the vowel /o/, and a transition.

“The contrasting vowels /o/ and /a/ belong to the phonetic repertoire of both Spanish and Catalan, which is partly why we chose them,” co-author Sonia Arenillas-Alcón, also a researcher at the University of Barcelona, said in the statement.

“Low frequency sounds like these vowels are also transmitted through the womb reasonably well, unlike mid- and high- frequency sounds that reach the fetus in a degraded and attenuated manner.”

The results showed that the monolingual babies’ brains showed a higher response to the the /o a/ sound, meaning that they were more sensitive to this specific pitch found in their mother’s language.

The bilingual babies, on the other hand, were more sensitive to all the sounds in general, with no specific uptick in response for any given sound.

“Here we show that exposure to monolingual or a bilingual speech has different effects at birth on ‘neural encoding’ of voice pitch and vowel sounds: that is, how information about these aspects of speech has been initially learned by the fetus,” study co-author Natàlia Gorina-Careta, a researcher at the University of Barcelona, said in the statement.

“At birth, newborns from bilingual mothers appear more sensitive to a wider range of acoustic variation of speech, whereas newborns from monolingual mothers seem to be more selectively tuned to the single language they have been immersed in.”

talking to baby
Stock image of a father talking to a baby.


This may represent a trade-off between selectivity and efficiency in how newborns and fetuses learn about pitch and speech.

“Our data show that prenatal language exposure modulates the neural encoding of speech sounds as measured at birth. These results emphasize the importance of prenatal language exposure for the encoding of speech sounds at birth, and provide novel insights into its effects,” said Escera.

The researchers stress that the languages spoken while pregnant likely have very little impact on how the baby learns about speech after birth, so monolingual and bilingual parents need not worry about the impact their speech has on their children.

“Based on our results, we cannot make any recommendation to multilingual parents. The sensitive period for language acquisition lasts long after birth, and thus postnatal experience may well overshadow the initial changes undertaken in the womb,” said Jordi Costa Faidella, an associate professor at the University of Barcelona.

“Future investigation into how a bilingual language environment modulates sound encoding during the first years of life will shed more light into this issue.”

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