Baby sounds aren’t random, new research into speech finds

The sounds babies make in their first year of life may be less random than previously believed, a researcher from the University of Texas at Dallas has found.

Assistant Professor Dr Pumpki Lei Su is the co-lead author on two recent articles in which researchers examined the sounds babies make, finding that children in their first year of life are more active than previously thought in their acquisition of speech.

“We observed in these studies that infant vocalisations are not produced randomly; they form a pattern, producing three categories of sounds in clusters,” Dr Su said.

“The home recordings we analysed included times when adults were interacting with their child and when children were on their own, showing that children explore their vocal capabilities with or without language input from an adult.”

In two seperate studies, one published May 29 in PLOS ONE (focused on typically developing infants), and the other, published Feb. 25 in the Journal of Autism and Developmental Disorders, (focused on infants who later received a confirmed diagnosis of autism) the researchers documented how children “play” vocally, learning what actions produce certain sounds and then repeating that process.

Dr Su’s team studied a dataset of all-day home recordings from more than 300 children amassed by the Marcus Autism Center, a subsidiary of Children’s Healthcare of Atlanta, and coded by senior author Dr. D. Kimbrough Oller’s team at The University of Memphis.

“Parents tell us that sometimes a baby will just scream or make low-frequency sounds for a really long period. But it’s never been studied empirically,” Dr Su said. “With access to a huge dataset from hundreds of children during the first 12 months of their lives, we set out to quantitatively document how babies explore and cluster patterns as they practice different sound categories.”

Sound types are characterised by pitch and wave frequency as squeals, growls or vowellike sounds. The PLOS ONE study used more than 15,000 recordings from 130 typically developing children in the dataset. Infants showed significant clustering patterns: 40 per cent of recordings showed significantly more squeals than expected by chance, and 39 per cent showed clustered growls. Clustering was common at every age, with the highest rates occurring after five months of age.

“Of the 130 infants, 87 per cent showed at least one age at which their recordings showed significant squeal clustering and at least one age with significant growl clustering,” Dr Su said. “There was not a single infant who, on evaluation of all the available recordings, showed neither significant squeal nor growl clustering.”

The study, she continued, represents the first large-scale empirical study investigating the nonrandom occurrence of the three main sound types in infancy.

In the Journal of Autism and Developmental Disorders article, Dr Su and her colleagues demonstrated that this exploration behaviour also occurs during the first year in children who are later diagnosed with autism spectrum disorder.

“Whether or not a child is eventually diagnosed with autism, they are clustering sounds within one vocal category at a time,” she explained. “While one cannot rule out the possibility that some patterns may be mimicry, these are not just imitations; they are doing this with and without the presence of a parent, even in the first month of life. This process of learning to produce sounds is more endogenous, more spontaneous than previously understood.”

“We tend to think babies are passive recipients of input. And certainly, parents are their best teachers. But at the same time, they’re doing a lot of things on their own.”

Other researchers who contributed to both articles include co-lead author Dr. Hyunjoo Yoo of The University of Alabama; Dr. Edina Bene from The University of Memphis; Dr. Helen Long of Case Western Reserve University; and Dr. Gordon Ramsay from the Emory University School of Medicine. Additional researchers from the Marcus Autism Center contributed to the Journal of Autism and Developmental Disorders study.