WEDNESDAY, Feb. 15 (HealthDay News) -- Babies can understand many words sooner than they can actually say them, a new study indicates.

Researchers from the University of Pennsylvania say 6- to 9-month old babies learn the meaning of the words for certain foods and body parts through their daily exposure to language. They said most psychologists don't think this type of word comprehension is possible until a child is closer to 1 year.

"I think it's surprising in the sense that the kids at this age aren't saying anything, they're not pointing, they're not walking," said the study's co-author, Elika Bergelson, a doctoral student in Penn's department of psychology, in a university news release. "But actually, under the surface, they're trying to put together the things in the world with the words that go with them."

In conducting the study, researchers had 33 babies between 6 and 9 months old view a screen with a picture of a food and a body part while sitting with their parents. The parents were given phrases to say to the child, asking them to find the apple, for instance. An eye-tracking device revealed the babies' responses to the phrases.

In a second test, the children went through the same process but saw pictures of typical food scenes and a whole person, not just body parts.

After taking into account possible reasons for errors or distraction among the babies, the researchers compared the responses of the 6- to 9-month-old infants with those of 50 other babies ranging from 10 to 20 months of age.

In both tests, the researchers found the 6- to 9-month-olds looked more often at the picture that was named than any other images. The researchers argued this was a sign that they knew what the word meant.

"There had been a few demonstrations of understanding before, involving words like 'mommy' and 'daddy,'" study co-author, Daniel Swingley, an associate professor in the psychology department, said in the news release. "Our study is different in looking at more generic words, words that refer to categories."

Bergelson added, "We're testing things that look different every time you see them. There's some variety in apples and noses, and 'nose' doesn't just mean your nose; it could mean anybody's nose. This is one of the things that makes word learning complicated: Words often refer to categories, not just individuals."

The study's authors said babies at 8 and 9 months performed no better than 6- and 7-month-old infants. They said no significant improvement was seen until the children reached about 14 months of age. They could not explain exactly why performance did not improve for so long.

"I think this study presents a great message to parents: You can talk to your babies and they're going to understand a bit of what you're saying," Swingley concluded. "They're not going to give us back witty repartee, but they understand some of it. And the more they know, the more they can build on what they know."

Their study was published online this week in the Proceedings of the National Academy of Sciences.

More information

The U.S. National Institutes of Health provides more information on infant development.