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Babies learn to speak the same way that some birds learn how to sing.
Infants don't learn to speak just by imitating the sounds of older humans in their midst, according to new research. Mom's gentle touch, or her loving smile, helps the baby learn that some sounds are more pleasing than others, thus moving it along the avenue of language development.
"The parents responses serve as cues to the infant that that was a successful sound," says psychologist Michael Goldstein of Franklin and Marshall College in Lancaster, Pa. Goldstein began a research project while working on his doctorate at Indiana University that flies in the face of much conventional wisdom.
His findings, published in a recent issue of the Proceedings of the National Academy of Sciences , show that humans learn to speak through a variety of mechanisms, including both imitation and social interaction with others. Most experts have contended that we learn to talk purely by imitation, but Goldstein's work suggests it is far more complicated than that.
A Lesson From the Birds
So while he's barely out of graduate school, he's already on a course that establishes him as a high-profile target in the ongoing debates about the development of verbal skills. And he owes it all to cowbirds.
The brown-headed cowbird is one of the stranger critters in the avian world, in that the females lay their eggs in the nest of another species and let another bird hatch and nurture their young. Within about a month, the young cowbirds desert their foster home and join whatever flock of cowbirds they can find in the vicinity.
Goldstein began studying cowbirds because he was intrigued by one aspect of their maturing process. Only male cowbirds learn to sing. But they are taught to sing by females.
And here's the odd part.
"The females don't sing," says Meredith West, Goldstein's faculty adviser at Indiana University, a specialist in behavior development in animals and humans. "In fact, they can't sing."
The males in the flock don't teach them because, West says, "they hang off on their own. They don't interact with the younger males."
So the adult females are tasked with teaching the young males how to do something they can't do themselves. They do it by paying attention to the youngsters and letting them know when they are getting closer to the right song.
"If you and I were trying to talk, and I started looking away, and looking down, and not giving you any feedback or not paying any attention to what you were saying, you would change how you tried to talk," she says. "And that's just what happens with the birds."
Goldstein wanted to take that a step further and see if human infants follow a similar course. So he set up a terrific playroom at Indiana University and elicited the support of 30 moms with 8-month-old babies, about the age that infants begin pronouncing vowels and forming marginal syllables.
The moms were divided into two groups of 15, one to test the effect of social interaction, and the other to serve as a control group for the experiment. Each mom and her baby spent two half-hour sessions in the playroom. The first was just a getting acquainted session to allow the baby and the mom to be comfortable with the setting, Goldstein says.
The next day the moms returned to the playpen, which was wired for sound and video. As Goldstein watched through a one-way mirror, and looked at monitors from three digital cameras, the babies spent the first 10 minutes of the half-hour session just playing, as they would if they were at home.
During the second 10-minute session, Goldstein had 15 of the mothers respond physically, by moving closer and touching the child, and smiling, whenever the infant uttered a sound that was more "speech-like," he says. But the mothers were instructed not to talk.
The final 10-minute session was a repeat of the first, when baby and mom were free to play.
The second group of 15 moms followed the same procedure, with one significant difference. Moms were allowed to respond to the infants during the second 10-minute segment, but the response was not linked to any verbalization by the baby. They did so on cue from Goldstein, ensuring that babies in each group had equal stimulus to yak it up.
Significant Step Up in Speech
The difference, Goldstein says, was dramatic. The babies in the first group reacted to their mothers' approval by becoming more vocal, both in quantity and quality. The second group, where the mother's response was not linked to verbal activity, remained unchanged during all three of the 10-minute segments.
What that shows, he says, is that learning to speak involves social interaction, not just imitation, because the mothers weren't talking, they were just reacting. Incidentally, the mothers did not know the purpose of the experiment until it was all over.
Of course, the babies didn't start reciting the Gettysburg Address. But electronic monitoring and analysis of their vocalizations show clearly that there was a significant difference in the "quality of the sounds," Goldstein says.
"It's not a question of did they say words," he says. "It's a question of did the infrastructure of speech improve."
The vowels the babies uttered were the vowels used to pronounce words, and their simple syllables met "all the acoustic requirements for mature speech" during the segment when the mothers were expressing approval by smiling or touching, Goldstein adds.
Of course, an experiment based on the performance of just 15 babies isn't likely to convince other researchers who think imitation is the name of the game, but Goldstein says it's a start. He has lots of other experiments lined up, ready to go.
He's past the stage of studying the cowbird, and looking forward to the time when he and his wife, also a psychologist, have children of their own. Rest assured they won't leave them in someone else's nest.
Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times , he now lives in Juneau, Alaska.
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