The new finding suggests that language learning begins prenatally, perhaps as soon as fetuses are able to hear -- after about 30 weeks of gestation -- with their initial focus on vowel sounds, which are louder, longer and more rhythmic than consonants.

"The mother has first dibs on influencing the child's brain," said Patricia Kuhl, of the Institute for Learning & Brain Sciences at the University of Washington, in a press release. "The vowel sounds in her speech are the loudest units and the fetus locks onto them."

Previous studies have shown that the perception of speech sounds develops in infants long before they are able to speak themselves.

Between the ages of 6 months and a year, for example, babies quickly get better at telling the difference between sounds often used in their native languages. At the same time, they rapidly lose the ability to distinguish between the typical sounds of other languages.