A baby's first words may seem spur of the moment, but really, the little ones have practiced their "Mamas" and "Dadas" for months in their minds.
Using what looks like a hair dryer from Mars, researchers from the University of Washington have taken the most precise peeks yet into the fireworks display of neural activity that occurs when infants listen to people speak.
They found that the motor area of the brain, which we use to produce speech, is very active in babies 7 to 12 months old when they listen to speech components.
"What we're seeing is that the babies are practicing because they want to talk back," says Patricia Kuhl, a speech psychologist at the University of Washington and the lead author on the paper, published Monday in the Proceedings of the National Academies of Sciences.
Kuhl used a machine called a magnetoencephalograph, or MEG, that measures the brain's magnetic field from outside the head. Unlike MRIs or CTs, which require that patients be completely still, the MEG can scan images in moving patients, which works out perfectly for fidgety babies.
Babies undergo a huge transition from 7 months to 12 months that is very important for language acquisition, Kuhl says. At the age of 7 months, a baby can distinguish sounds from different languages, such as English or Spanish. But by 12 months the baby focuses in on her or his native language and begins to tune out foreign speech.
Kuhl placed 57 babies aged either 7 months or 12 months under the machine and played repeated human sounds for them. The speakers played repeated "da" and "ta" syllables in English and then "da" in Spanish.
They found that the motor part of the brain lit up when the baby listened to the sounds, indicating that they were trying to mimic or respond to the speech. By 12 months, the babies, who had English-speaking parents, had a harder time responding to the Spanish-language sounds.
Susan Goldin-Meadow, a developmental psychologist from the University of Chicago who was not involved in the study, says it furthers understanding of how babies process language. "We've had the behavioral data for a while," she says. "But this provides evidence on the neural level."
Kuhl says that her research supports parent's use of "parentese," or baby speak, a form of talking to babies with a higher pitch, slower pace and exaggerated facial expressions. "This is a good way to promote their itty-bitty social skills to develop," she says.
Not everyone sees this as an endorsement of parentese, though. Barbara Lust, a cognitive scientist from Cornell University who was not involved in the study, says the results "show more generally how important surrounding your child with language is, but it doesn't make a strong enough argument for needing to talk to a baby in a motherese way."
Kuhl says her next steps are to have researchers speak to the baby using parentese and analyze the baby's reactions, to see if the children respond more strongly to it.
The take-home message for new moms and dads, she says: "Talk to your baby; you're prompting it to act on the world."