From time immemorial, parents – especially mothers have sung lullabies – soothing, repetitive cradle songs – to their babies, even when they didn’t have to go to sleep.
The term comes from the Middle English word “lullen” (to lull) and “by” (near).
There was even a theory, apparently false, that “lullaby” is derived from “Lilith-Abi” (Hebrew for “Lilith, begone”) because according to Jewish tradition, Lilith was a demon who was believed to steal children’s souls in the night. To guard against Lilith, Jewish mothers would hang four amulets on nursery walls and sing to their babies.
In some societies, lullabies have been sung to capture the infant’s attention and pass down tradition – and, of course, to get them to fall asleep.
Now a new study by researchers at Vanderbilt University Medical Center in Tennessee and Emory University School of Medicine in Georgia have studied lullabies scientifically and found that infants’ sensitivity to their musical rhythm supports their social development and synchronizes caregiver-infant social engagement.
How can lullabies help infants with their social development?
Engaging infants with a song provides a readymade means for supporting social development and interaction, according to a study just published by the Proceedings of the National Academy of Sciences under the title “Music of Infant-Directed Singing Entrains Infants' Social Visual Behavior.”
The team got permission from the parents of 112 infants who were either two months or six months old to study them. They tracked the babies’ moment-by-moment eye-looking to reveal that the rhythm of caregivers’ singing caused infant eye-looking to become synchronized with the caregivers’ social cues at sub-second time scales. As early as two months of age, when infants are first engaging with others in an interactive manner, they were two times more likely to look to the singers’ eyes time-locked to the musical beat than would be expected by chance.
When they were half-a-year old, infants are highly experienced in face-to-face musical games and developing increasingly sophisticated rhythmic and communicative behaviors like babbling. At this milestone, they were more than four times as likely to look to the singers’ eyes synchronized to the musical beats.
“Singing to infants seems like such a simple act, but it is full of rich and meaningful social information,” said Miriam Lense, the study’s lead author, assistant professor of otolaryngology (ear-nose-and-throat) and co-director of the music cognition lab at Vanderbilt. “Here we show that when caregivers sing to their infants, they are intuitively structuring their behavior to support the caregiver-infant social bond and infant social learning.”
During testing, the researchers used eye-tracking technology to measure every movement of each infant’s eyes while they watched videos of people engaging them with song.
“For this study, we used videos of singing rather than live singing to ensure that any change in infant looking behavior was due to the infant and not the singer adjusting to the infant,” Lense noted. “Infants could look anywhere while watching the videos but we found that their looking behavior was not random.
“Critically, the predictable rhythm of singing is essential for this entrained social interaction. When we experimentally manipulated the singing so that it no longer has a predictable rhythm, entrainment was disrupted and infants no longer successfully synchronized their eye-looking to the caregivers’ social cues,” she said.
“Critically, the predictable rhythm of singing is essential for this entrained social interaction. When we experimentally manipulated the singing so that it no longer has a predictable rhythm, entrainment was disrupted and infants no longer successfully synchronized their eye-looking to the caregivers’ social cues.”
Miriam Lense
The researchers confirmed their findings in a different group of six-month-old infants who watched both the original videos of singing and videos that had been manipulated to be jittered so that their rhythms were no longer predictable.
While the infants again displayed eye-looking to the original videos when the singing was rhythmically predictable, this time-locked eye-looking effect was no longer present when the predictable rhythm had been disrupted.
“This is important because it reveals a remarkable physical coupling between caregiver behavior and infant experience,” said Dr. Warren Jones, the study’s senior author and an autism expert at Emory. “Without conscious awareness, something as simple and intuitive as caregiver singing sets in motion a whole cascade of behaviors that alters infants’ experiences.”
“Although what a caregiver expresses is important, when and how they express social cues is particularly critical for infant-caregiver communication,” Lense added. “Rhythmic predictability – a universal feature of song – is an integral mechanism for structuring social interactions and supporting infant social development.”
Reyna Gordon, an associate professor of otolaryngology and co-director of Vanderbilt’s music cognition lab, said the study underscores that making music is not only about entertainment; it is a core aspect of early socio-emotional development.
“It is remarkable that these infants are basically tracking the beat of music with their eyes by modulating their eye contact with the singer’s eyes around the beat (or pulse) of singing,” said Gordon, who was not involved in the study.
“These findings represent a major step forward in our understanding of the extent that very young children are sensitive to musical rhythm, suggesting that innateness for music is intertwined with early social engagement,” she said.
Lense said her team has now extended the research to study synchronization in autism as part of the Sound Health Initiative, a partnership between the US National Institutes of Health and the John F. Kennedy Center for the Performing Arts.