New research shows baby babbling changes the way parents speak to their infants, suggesting that infants are shaping their own learning environments.

Researchers from Cornell University's Behavioral Analysis of Beginning Years (B.A.B.Y) Laboratory found that adults unconsciously modify their speech to include fewer unique words, shorter sentences, and more one-word replies when they are responding to a baby's babbling, but not when they are simply speaking to a baby.

"Infants are actually shaping their own learning environments in ways that make learning easier to do," said Steven Elmlinger, lead author of "The Ecology of Prelinguistic Vocal Learning: Parents Simplify the Structure of Their Speech in Response to Babbling." "We know that parents' speech influences how infants learn -- that makes sense -- and that infants' own motivations also change how they learn. But what hasn't been studied is the link between how infants can change the parents, or just change the learning environment as a whole. That's what we're trying to do."

In the study, 30 mother-infant pairs went to the lab's play space for 30-minute sessions on two consecutive days. The 9- and 10-month-old babies could roam freely around the environment, which was filled with toys, a toy box and animal posters. The babies wore overalls with hidden wireless microphones to record their speech, and were also videotaped by three remote-controlled digital video cameras.

Researchers measured parents' vocabulary and syntax, and calculated the change in babies' vocal maturity from the first to the second day. They found that babies whose mothers provided more learning opportunities -- by using simplified speech with fewer unique words and shorter utterances -- were faster learners of new speech sounds on the second day.

The research contributes to a growing body of work that demonstrates the important role infants play in shaping their own language learning environment. Interventions to improve at-risk children's learning should encourage people to be responsive to their baby's babbling, said senior author Michael Goldstein, associate professor of psychology.

"It's not meaningless," he said. "Babbling is a social catalyst for babies to get information from the adults around them."

The study was supported by the National Science Foundation.