Washington, Aug. 29 (Reuters): Baby babble is not a random exercise in mouth control, but a solid step toward speech, involving the left side of the brain where language originates, researchers said today.
Babies as young as five months old are engaging the left hemisphere of the brain, the researchers said.
They can tell because the right side of the mouth deforms slightly when the babies babble — a phenomenon well known in adult speech, said Laura Ann Petitto of Dartmouth College in Hanover, New Hampshire, who helped lead the study.
“When babies babble, they babble out of the right side of the mouth,” Petitto, a cognitive neurologist, said.
“When making vocalisations that are not babbling, it came out of the middle of the mouth. Smiles skewed to the left.”
The study, published in Friday’s issue of the journal Science, suggests that babies are trying to learn to talk when they babble. Petitto hopes it will help settle a heated debate over when language skills kick in.
“We pretty much agree that babbling has something to do with language. The question is, what drives it,” she said.
“For example there is a very real and prevailing group of people who argued for decades that babbling is absolutely not language in the beginning, that it is really the brain’s struggle to get more and more control over the mouth and the tongue and the lips.” This is a “hot potato,” she said, because the argument is used in theories about how language developed in early humans.
“The most prevailing view is that first we stood up and then the jaw dropped down and then the brain got more and more control of the jaw and then later, magically, these creatures decided to invent language,” Petitto said.
“First this creature stood up and went ‘uh’ and then suddenly realised that it could say ‘uh’ and mean ‘club.’”
She and Siobhan Holowka of McGill University in Montreal wanted to disprove this idea, but it is hard to find a non-invasive way to test small babies. Then they settled on the idea of watching their mouths.
“It is known in adults that when you are talking, the right side of the mouth is pulled down a little more,” she said, although this is hard to see “live” because “the human visual system seeks symmetry and fixes it”.
It is believed that this occurs because the left side of the brain, which controls the right side of the body, has the language centres.
Petitto and Holowka videotaped 10 babies aged 5 months to a year who were exposed to two different languages — French and English. “We were able to show it had nothing to do with the language they were being exposed to,” Petitto said.
If babbling is not involved in language, she says, then it should randomly use the right, left and centre of the mouth. But while cooing and other vocalisations did this, babbling clearly used the right.
To their surprise, the babies smiled more on the left. “The whole left side of the face gets scrunched up,” Petitto said. “It is because the emotional centres of the brain are on the right side.”
This suggests that babies smile because they feel genuine pleasure, not because they have somehow been socialised or conditioned to do so, Petitto said.