The New York Times
Saturday, October 5, 2002
By MARY DUENWALD
An 11-month-old baby, her face spattered with food and her lips wet with drool, pushes her chin toward the camera and says, "Da da da da da" in a soft singsong voice
A few seconds later, though, the picture freezes and a small grid appears, superimposed over the baby's mouth. Look carefully and the lines enable you to see that as the baby babbles, her mouth opens wider on the right side than on the left. Suddenly, what was merely cute becomes scientifically interesting.
If the baby babbles mainly on the right, the researchers say, it means that babbling is a form of language.
This assertion is radical and disputed because of its implications. Scientists believe that if they can figure out how babies learn to talk, they can better understand how language came to exist and thereby gain insight into the way people have been able to distinguish themselves from apes. The underlying question is, Are people are born with an innate ability to use language? Or do they gain that ability as they mature?
"What permits humans to have this remarkable communication system?" asked Dr. Elissa L. Newport, a psycholinguist at Rochester University. "Is it that we evolved some specialized brain tissue that serves language in particular? Or is it just that we got really smart with a lot of fancy cognitive abilities?"
The baby in the video was one of 10, all 5 months to a year old, who were taped in the act of babbling and found to demonstrate a bigger opening on the right. Given the way the brain operates " the left hemisphere controls the right side of the body and the right hemisphere, the left " this shows that babbling engages the brain's left hemisphere more than its right, the researchers say.
Because the left side of the brain is thought to control language, this means that babbling is a "fundamentally linguistic activity," according to Dr. Laura-Ann Petitto of Dartmouth, one of the researchers.
"We've known for years that when adults talk, their mouths move asymmetrically," Dr. Petitto said. "Some researchers have said that this lateralization is completed by age 7, and some have said by age 5. This is the earliest demonstration of left-side lateralization to date."
Dr. Petitto and Siobhan Holowka, a graduate student at McGill University in Montreal, observed the babies, five from English-speaking families and five from French, as they entered the babbling stage. The subjects were videotaped not only as they said ba ba ba and da da da but also as they made nonbabbling noises like "ahhhh" and as they smiled quietly. Although all 10 babies opened their mouths wider on the right when babbling, they opened equally on each side when making random sounds.
"If in babbling, the child were just working through mastering the motor output of the mouth, then all sounds should come out equally," Dr. Petitto said. "But babbling was different. The findings support the idea that the brain has tissue dedicated specifically to learning language."
Dr. Petitto was also surprised to see that when the babies smiled, their mouths opened wider on the left side. "That was a stunning finding," she said, "the earliest demonstration that the brain's right hemisphere mediates emotion."
Dr. Paul Bloom, a professor of psychology and linguistics at Yale, agreed that Dr. Petitto's research suggested that "humans have a dedicated language ability from the start." Language capacity may be built into the human brain, he said, just as the capacity for song is built into the bird's brain or the capacity to dance in meaningful patterns into the bee's.
"It is entirely consistent with natural selection that humans would possess a language ability," Dr. Bloom said. "If I told you that there is something special about color vision, that color vision uses special parts of the brain, you'd yawn. Visual perception is obviously built in. Why wouldn't language be also? It's central to being human."
This view accords with the theory proposed 45 years ago by the linguist Noam Chomsky that humans are born with the ability to use language.
But many experts argue that language is not hard-wired into the brain. Babies are not born with language, these scientists say, but rather learn language as they grow, making use of the brain's capacity for complex tasks, the tongue's ability to articulate and the instinct for socialization. Through imitation and practice, they learn to speak and understand the language they hear.
"We love to look at each other, share information with each other, imitate each other. That's what's innate," said Dr. Elizabeth Bates, the director of the Center for Research in Language at the University of California at San Diego. "The human brain has been tuned for social learning. We have a general purpose device for acquiring culture, technology and language. Yes, we're the only species on the planet with full-blown language, but we're also the only species with ice hockey and international finance and funeral parlors."
A baby babbles out of the right side of the mouth, Dr. Bates said, not because the left brain contains a language organ but because the left brain is in charge of fine-motor activity. "The left hemisphere is also more responsive to complex auditory stimuli, not just speech but rapid tone sequences," she said.
Dr. Philip Lieberman, a professor of cognitive and linguistic science at Brown, points to studies showing that adults whose brains have been damaged on the left side by strokes have difficulty with speech, but also with making any other kinds of sounds with their mouth. "The left hemisphere may be involved in babbling," Dr. Lieberman said, "but it's involved in all kinds of other things, too." Complex conversation of the kind adults engage in, he added, involves both sides of the brain.
Certain species of monkeys also babble, said Dr. John L. Locke, a specialist in the biology of human communication at New York University, and this suggests that babbling evolved well before language did. When baby monkeys babble, Dr. Locke said, their family members tend to pick them up and care for them. He suggests that babbling evolved as a way for babies to call their mothers. "Babbling begins when weaning is going on, at a time when the mother isn't always in the same room with the baby," he said. "Nature may have built in this system for the baby to get the mother's attention."
In developing language, he said, humans built upon this native babbling ability.
Dr. Peter F. MacNeilage, a professor of psychology at the University of Texas, suggests that the first human words may have grown out of babbling. He notes that the word for mother in most languages uses a nasal sound like "mmmm," the kind a baby can make while nursing. "Early hominid mothers heard these noises and decided these noises stand for `me,' " he said.
Dr. Petitto argues that vocalization is not fundamental to language. Her earlier research indicates that profoundly deaf babies and hearing babies of deaf parents, babble with their hands, and they produce rhythmic syllables in one-and-a-half-second bursts, roughly the same amount of time it takes a hearing baby to say "da da da da da." The signing babies, Dr. Petitto said, hit the same milestones in language development as hearing babies " babbling, stringing together unlike sounds and first words " on the same timetable. "If learning language were a process of gaining control over the human speech mechanism, then a child learning sign language should show a completely different timetable," she said. "But the human brain shows no preference for speech. It takes the tongue if you give it the tongue. It takes the hand if you give it the hand."
But Dr. Locke and others say that the brain's left hemisphere also governs the kind of activity involved in signing. Studies have shown that when babies begin babbling, they also begin moving their right hands rhythmically. "Those are linked systems," Dr. Locke said, "but it doesn't mean that the child knows much of anything about language."
As a child moves beyond babbling and first words and learns grammar and syntax, Dr. Bates said, the brain tissue involved is altered, so that by adulthood, parts of the brain are dedicated to language. "You do end up with a highly specialized brain," she said. "Learning sculpts the brain."
Dr. Locke suggests that transition happens between the ages of 2 and 3, when children learn to apply the rules of their own languages .
"You'll hear a child refer to `two mouses,' " Dr. Locke said. "This is not an imitation of the word mouses. It's the first time they're being truly creative in the sense of structure. It's proof that they know how to play the game. I take that to be the onset of hard-core language."