Babies group together their squeals and growls to prepare for speech

The growls and squeals babies make before they start babbling may not be random noises, but the basic building blocks of speech development. Starting in the first month of life, babies create these noises in clusters, not sporadically, which suggests they are “practising” before learning to talk.

“Our findings reveal that infants engage in practice with various vocal types from the earliest months of life… laying a foundation for further language development,” says HyunJoo Yoo at the University of Alabama in Tuscaloosa.

Previous studies have examined the babbling babies make from around 5 to 7 months old, says Yoo. However, the three most common kinds of more basic infant vocalisations – squeals, growls and medium-pitch vowel-like noises called vocants – have rarely been investigated.

To learn more, Yoo and her colleagues asked the parents of 130 babies – 71 boys and 59 girls, who all appeared to be developing as normal and lived in or around Atlanta, Georgia – to place small voice recorders in the pockets of the infants’ clothing for 16 hours per day, once a month for the first two years after birth.

The researchers randomly selected 21 segments of 5 minutes in duration from each day of the recordings of each baby. They then categorised each of the sounds the babies made as either squeals, growls, vocants or other noises, such as blowing raspberries.

The team found that all the babies showed a clustering together of squeals, growls or both. This means they happened more often than by mere chance over the 5-minute periods and therefore weren’t just random noises, but perhaps preparations for speech, says Yoo.

Overall, 40 per cent of the squeals and growls occurred in clusters. In 61 per cent of the recordings, the clusters were made up of either squeals or growls, not both.

For 87 per cent of the babies, the preference for either squeal or growl clustering was related to their age, with squeals in particular being more common in those who were at least 5 months old. That might be because high-pitched squeals require more advanced control over the vocal cords, but this finding requires further investigation, says Yoo.

The researchers also found that the babies clustered vocants, but the analysis didn’t focus on these.

Surprisingly, even the youngest babies created sound clusters, says Yoo. This contrasts with previous research suggesting infants start “playing” with language at around 3 to 4 months old, but more research is needed to confirm these findings, she says. “We are not inclined to view this pattern of age results as offering the final word about vocal category clustering.”