The controversial idea that there are universals in the ways we use music received a boost in 2018, with the finding that people from 60 different countries were pretty good at judging whether a totally unfamiliar piece of music from another culture was intended to soothe a baby or to be danced to. Now, new research involving some of the same team has revealed that foreign lullabies that babies have never heard before work to relax them.
Constance M. Bainbridge and Mila Bertolo from Harvard University led the new study, published in Nature Human Behaviour, on 144 babies with an average age of 7 months. After being fitted with sensors to monitor their heart rate and level of sweating, each baby sat in a high chair or recliner or on its parent’s lap while watching animated characters lip-synching to 14-second bursts of songs.
These songs came from the Natural History of Song Discography, a collection of songs from around the world, and eight were used as lullabies in the societies in which they were selected. The rest were intended to express love, heal the sick or be danced to. All of the songs were sung by solo vocalists, without background music.
As well as looking at the heart rate and skin sweating data, the team used video of the babies’ faces to monitor their pupil size. If these measures decreased, this would indicate that the baby was relaxing.
Based on some of these measures, at least, the team found that babies did indeed seem more relaxed during the lullabies than the other songs. “While heart rates dropped almost immediately following the onset of singing, regardless of song type, this drop was more pronounced during the lullabies,” the team writes. Whether the baby was 2 or 14 months old, the effect was the same, suggesting that it couldn’t simply be the result of exposure to music with age. The team also found that the babies’ pupils were smaller during the lullabies than the other songs.
The sweating results were less clear cut, however. These levels increased over the course of the experiment, perhaps because the babies were becoming more bored and fussy, the researchers suggest. But while a baby listened to a lullaby, this increase was temporarily slowed.
What might explain these effects? The lullabies and the other songs certainly differed acoustically. The lullabies tended to be slower, and to have smaller pitch ranges and a less steady beat. As the researchers note, the earlier work on adults listening to unfamiliar songs found that the more a song was characterised by these specific features, the more confident a listener was that it was intended to be a lullaby.
The team then compared these earlier adult ratings with their new results. And they found that the more that the adults had judged a song to be directed towards infants, the bigger the reduction in heart rate while the baby listened to it. “This result confirms that the acoustic effects of the songs drove the relaxation effects on them,” the team writes.