Researcher finds sound progress in babies' speech development

Dr. Pumpki Lei Su, an assistant professor of speech, language, and hearing in the School of Behavioral and Brain Sciences, is co-lead author on two recent articles in which researchers examined the sounds babies make. The results suggest that children in their first year are more active than previously thought in their acquisition of speech.

"We observed in these studies that infant vocalizations are not produced randomly; they form a pattern, producing three categories of sounds in clusters," said Su, who also directs the Language Interaction and Language Acquisition in Children Lab (LILAC Lab) at the Callier Center for Communication Disorders. "The home recordings we analyzed 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."

One study, 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.

Within the past 40 to 50 years, scientists have realized that vocalizations before a child's first word are meaningful precursors for speech and can be broken into sequential stages of cooing, vocal play and babbling. 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," 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 characterized 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% of recordings showed significantly more squeals than expected by chance, and 39% showed clustered growls. Clustering was common at every age, with the highest rates occurring after 5 months of age.

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

Su said the study 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, Su and her colleagues demonstrated that this exploration behavior 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," Su said. "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."

Su has received a three-year grant from the National Institute on Deafness and Other Communication Disorders (NIDCD) to study parents' use of "parentese" -- or baby talk -- with autistic children. Parentese is an exaggerated style of speech often containing high-pitched elongated words and singsong diction.

Parentese is portrayed in the literature as a type of optimal input for typically developing children, who tend to pay better attention and respond to it more than they do to normal speech. It also helps children learn to segment words. But is it also ideal for autistic children?

"One hypothesis of why parentese works is that it encourages social interaction by being very animated," Su said. "Autistic children have differences in social communication and responses to sensory stimuli. Would they also find parentese engaging? Could it be too loud or extreme? This new grant will allow me to examine whether parentese facilitates word learning for autistic children compared to a more standard adult-directed register."

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.

The research was funded by grants from the NIDCD (R01DC015108) and the National Institute of Mental Health (P50MH100029), both components of the National Institutes of Health.