Feb. 19, 2001 (San Francisco) -- Learning our first language is the toughest homework assignment we'll ever have, and we do it before we can walk or crawl. So how do we do it? New studies show that babies grasp language by using a variety of skills that are hardwired into their brains before birth.
The skills include the ability to detect patterns of sounds and tones, the ability to detect and remember isolated words, and the ability to remember the frequency that words occur together in spoken sentences.
"We think all these things are working at the same time," says researcher Michael Brent, PhD, an associate professor of computer science at Washington University in St. Louis.
The results were presented here Monday at the annual meeting of the American Association for the Advancement of Science.
Researchers have debated for years whether most of our ability to pick up language is hardwired, or whether our brains are sculpted mostly by our experiences in life, Brent says. They've also debated which specific cues the babies pick up on as they learn.
As anyone who has listened to a conversation in a foreign language knows, it's hard to tell where one word ends and another begins. But amazingly, babies learn how to do that within a year or two.
In the 1980s, many researchers thought that babies learned words in isolation, particularly when the mother spoke to their babies in the lilting and simplified tones that researchers call "motherese." For example, if a mother held up a red ball and said "red," the child would learn the word "red," Brent says.
In the 1990s, many researchers concluded that not all mothers speak this way to their babies. Instead, they hypothesized that babies focus more on the frequency of particular words in sentences they hear, he explains.
Now, Brent and his colleagues have shown that babies do in fact learn from isolated words. The researchers analyzed hours of recorded speech from eight mothers to their babies. They put a tape recorder in a fanny pack that the women wore in around their home, then they listened to the tape and analyzed speech patterns on a computer.
The studies started when the babies were 9 months old and stopped when the babies were 15 months old.
It turned out that 9% of the time mothers spoke to their babies, they uttered isolated words. What's more, the more frequently the mother spoke a particular word, the more likely a baby was to know that word at the end of the study.
"This does not mean that parents should use monosyllabic speech," Brent emphasizes. "Don't worry about how you speak to your baby: Without trying, you'll naturally speak to them in the way they learn."
Other research has shown that babies may learn words by acting as "little statisticians," says Jenny Saffran of the University of Wisconsin, Madison. That means that they automatically keep track of how often a pair of sounds occur together in a sentence.
For example, a mother might coo the words "pretty baby" to her infant. By hearing these and other words repeatedly, the baby learns "pretty" is one word and "baby" is another word. Specifically, the babies learn that the sounds represented by "pr" and "t" often occur together in English, while the "t" sound is not often followed by the "b" sound.
"Eight-month-old babies can do this," Saffran says.
They also have another skill that could help them learn language -- a skill that's lost in adults. In new work published last month in the journal Developmental Psychology, Saffran showed that most babies have perfect pitch, while adults don't.
That means that babies can tell the pitch of a tone without hearing any other sound. With the exception of a few musicians, most adults have lost that ability, instead relying on the relative pitch of two sounds that occur together.
Perfect pitch allows babies to extract meaning from the pitch of different sounds they hear. Such skills are particularly important for babies who learn tonal languages as their first language.
In tonal languages, which constitute one-third of the world's languages, including Cantonese, Thai, and Vietnamese, a word has a different meaning depending on the pitch with which it is spoken, Saffran says.
In fact, babies use a variety of strategies, focusing on the most meaningful cues they receive, says Rebecca Gomez, PhD, an assistant professor of psychology at Johns Hopkins University in Baltimore.
Besides just learning associations between words that occur adjacent to each other in a spoken sentence, they also learn words that are more widely separated. Gomez used an artificial language to test this ability.
It turned out that 18-month-old toddlers, but not 12-month olds, can discern more widely separated words, suggesting that babies pick up a new strategy as they continue to learn.
"That shows a lot of flexibility in their minds," she says.