Singing to babies has long been a way of soothing a cranky child. A study involving Te Herenga Waka—Victoria University of Wellington researchers has revealed new information about why lullabies are so soothing to children around the world.

The study, led by researchers from Harvard, showed that infants relax to lullabies even when they are from unfamiliar cultures and in unfamiliar languages. Dr Sam Mehr, who works at both the University in the School of Psychology and at Harvard, supervised and designed the study.

Dr Mehr, along with the University’s Dr Alia Martin and Mila Bertolo and Connie Bainbridge from Harvard University, recruited infants from the Boston area to watch animated characters sing lullabies and other songs from around the world. They recorded the babies’ response to the different songs.

“What we found was that infants’ heart rate and electrodermal activity was lower during the lullabies compared to the non-lullabies. From the video we gathered, we could also measure the infants’ pupil size as they listened to the songs and found that their pupils were less dilated during the lullabies—another indicator of their relaxation,” Ms Bertolo says.

The babies were relaxed by the lullabies regardless of where the lullabies were from or what language they were in.

“This suggests that the soothing effects of lullabies in infants are not just a result of them being familiar with mum or dad’s voice, but that features of the songs themselves that are inherently soothing,” Dr Mehr says. “We see similar effects across the whole first year of a baby’s life, which suggests that this effect occurs in all babies, not just really young ones.”

The research team now have lots of interesting avenues to pursue for future research.

“This study shows that lullabies vary from non-lullabies systematically, and other studies have shown that adult listeners are also able to identify lullabies from other cultures as well, Ms Bertolo says.

“In follow up work we’re starting to figure out what the musical features really are that make lullabies work so well across ages and cultures,” Dr Mehr says.

They will also be investigating what infants might understand about the social context of lullabies—for example, whether they assume someone singing lullabies may signal they are likely to provide care for the infant, Ms Bertolo says.

The study was recently published in the journal Nature Human Behaviour.