From "goo-goo" and "gaa-gaa" to "please" and "thank you," learning to talk is a complex and mysterious process.

Now, scientists report that a mother's body language can turn her baby's babbles into more speech-like sounds. The mother's smiles and touches might be as important as words in getting her infant to prattle with style.

The researchers studied 30 mothers and their infants, whose ages averaged 8 months. Each mother-baby pair played in a room of toys for 10 minutes.

For the next 10 minutes, half of the mothers reacted immediately to their babies' vocal sounds by smiling, moving closer, and touching the infants. The mothers didn't talk at all.

The other half of the mothers acted the same way, but usually not right after their babies made sounds.

In the first group, baby-talk became almost instantly more clear, with distinct sounds, such as "gu" and "da." Those babies also breathed more deeply, which improved sound quality further. And babies in the first group kept their edge over the others for at least another 10 minutes.

The study, by researchers in Pennsylvania and Indiana, was the first evidence that an adult's gestures and actions can help babies learn to make vocal sounds.

If the babies agree with this finding, they're not telling.—E. Sohn