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.