Researchers suggest that babies may be able to hear differences in language a month before they are born.
Published in the journal NeuroReport, scientists from the University of Kansas used a magnetocardiogram (MCG) to study two dozen mothers who were eight months pregnant. This technology can measure magnetic fields produced by electrical activity in the heart.
A bilingual speaker was asked to make two recordings, one in English and one in Japanese, to be played in succession to the fetus. These two languages are quite rhythmically distinctive.
Using the MCG, the team found that the heart rate of the fetus increased when they heard the language they were unfamiliar with, Japanese. When they heard English, their heart rates did not change.
"These results suggest that language development may indeed start in utero,” Utako Minai, the lead author on the study, said in a statement. “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. Pre-natal sensitivity to the rhythmic properties of language may provide children with one of the very first building blocks in acquiring language.”
Previous research has found that human language development can start just a few days after birth. Babies have been shown to be sensitive to rhythmic differences between languages, by monitoring how they react to different languages – like sucking more intently on a pacifier.
Another previous study looked at fetal language recognition, but it used ultrasound and had two different people speaking the different languages. In that study, it was not clear if the fetuses were responding to the changed person or the different language. By using an MCG, this study was also more sensitive to beat-by-beat changes of the heart when compared to ultrasound.
The sound heard in the womb is unlikely to be clear and concise, according to Minai, but more like a “Peanuts cartoon”. However, the rhythm can still be observed and picked out.
"We think it is an extremely exciting finding for basic science research on language,” said Minai. “We can also see the potential for this finding to apply to other fields."