Babies Don't Talk Out of Both Sides of Their Mouths

Study finds babbling is more than gibberish

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HealthDay Reporter

THURSDAY, Aug. 29, 2002 (HealthDayNews) -- When your baby repeats sounds and smiles at you, you might think he's just whistling Dixie.

But, says a Dartmouth College professor, he's hard at work at the business of learning language and expressing emotions.

By looking at videotapes of babies' mouths as they made sounds, researchers found that when babies made repeated phonetic sounds such as "goo-goo," "da-da," or "ba-ba," the right side of their mouths were always opened more than the left side, a condition called right asymmetry. In adults, it is known that right asymmetry of the mouth indicates brain activity in the left side, and that is where most language skills originate.

Further, every time the babies smiled, the left side of their mouths were more open than the right, called left asymmetry, which is an indication of right brain activity. The right side of the brain controls emotions.

The results were the same for all 10 babies in the study.

"This is the earliest demonstration of asymmetry in young babies in the production of languages, and also the earliest demonstration of right hemisphere emotional function," says Dartmouth professor Laura Ann Petitto, author of the study.

This shows, she says, that babies' earliest sounds and smiles are not just the way they practice motor skills such as moving their lips or their jaws, but are related to speech development and emotions.

"When a baby's babbling, he's not just doing something silly and trivial, but is hard at work actively producing the sounds of language and testing out combinations," she says.

The results of her study appear in tomorrow's issue of Science.

In the study, Petitto and her colleague, Siobhan Holowka, studied videotapes of the 10 babies between the ages of 5 months and 12 months. To prevent language-specific bias, five babies were learning English and five were learning French. Using a scoring technique called a "laterality index," which measures asymmetry in adults' mouths as a diagnostic tool for brain damage after a stroke, the researchers recorded the asymmetry of the babies' mouths for three different kinds of mouth activity.

The first was babbling, which Petitto describes as sounds found in language with consonant-vowel repetition, like "da-da," "goo-goo," or "ba-ba." The second were non-babbling, generalized sounds with no phonetic content and including bodily function sounds like burping or belching. The third were smiles, generally indicating enjoyment.

When scored on the laterality index, all the babies had right-mouth asymmetry while babbling, equal-mouth openings when making other sounds, and left-mouth asymmetry when smiling.

"This is the first time this index has ever been applied to babies and we found that language lateralization is up and running at a very young age," she says. "It addresses the big question of the origin of human language capacity and how it happens."

Swarthmore linguistics professor Donna Jo Napoli says the study is interesting, but is skeptical that the results were so dramatic.

"It is one more piece of evidence that language is inherent and a basic human need," she says, "but I am very surprised by the fact that all the babies had the same response."

While using the laterality index is an attempt to be objective about the results, she says, the researchers still had to make decisions as to what sounds would be considered babble and what sounds were not babbling, and she doesn't see that information in the study.

"When results come out so clean, we want to know some objective way of making the distinction of how the noises and smiles were categorized," she says. "Further, 10 babies is a pilot study, and I would like to see a larger study since they're pinning so much on the asymmetry they find."

However, Petitto says, "There is no controversy as to how babbling is defined. These are universally accepted definitions."

She is continuing her work on asymmetry in babies.

"We're working on using it as a means of detecting language deficits before a child learns to speak," she says.

What To Do

Some interesting information on a baby's first way of communicating can be found at Great Ormond Street Hospital. For another take on tot talk, visit University of Wisconsin-Madison.

SOURCES: Laura Ann Petitto, Ph.D., professor, Psychological and Brain Sciences and Department of Education, Dartmouth College, Hanover, N.H.; Donna Jo Napoli, Ph.D., professor, linguistics, Swarthmore College, Swarthmore, Pa.; Aug. 30, 2002 Science

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