Baby Talk
Learning language, researchers are finding, is an astonishing act of brain computation--and it's performed by people too young to tie their shoes
An infant's next step is learning to fish out individual words from the nonstop stream of sound that makes up ordinary speech. Finding the boundaries between words is a daunting task, because people don't pause . . . between . . . words . . . when . . . they speak. Yet children begin to note word boundaries by the time they are 8 months old, even though they have no concept of what most words mean. Last year, Jusczyk and his colleagues reported results of an experiment in which they let 8-month-old babies listen at home to recorded stories filled with unusual words, like hornbill and python. Two weeks later, the researchers tested the babies with two lists of words, one composed of words they had already heard in the stories, the other of new unusual words that weren't in the stories. The infants listened, on average, to the familiar list for a second longer than to the list of novel words.
The cadence of language is a baby's first clue to word boundaries. In most English words, the first syllable is accented. This is especially noticeable in words known in poetry as trochees--two-syllable words stressed on the first syllable--which parents repeat to young children (BA-by, DOG-gie, MOM-my). At 6 months, American babies pay equal amounts of attention to words with different stress patterns, like gi-RAFFE or TI-ger. By 9 months, however, they have heard enough of the typical first-syllable-stress pattern of English to prefer listening to trochees, a predilection that will show up later, when they start uttering their first words and mispronouncing giraffe as raff and banana as nana. At 30 months, children can easily repeat the phrase "TOM-my KISS-ed the MON-key," because it preserves the typical English pattern, but they will leave out the the when asked to repeat "Tommy patted the monkey." Researchers are now testing whether French babies prefer words with a second-syllable stress--words like be-RET or ma-MAN.
Decoding patterns. Most adults could not imagine making speedy progress toward memorizing words in a foreign language just by listening to somebody talk on the telephone. That is basically what 8-month-old babies can do, according to a provocative study published in 1996 by the University of Rochester's Newport and her colleagues, Jenny Saffran and Richard Aslin. They reported that babies can remember words by listening for patterns of syllables that occur together with statistical regularity.
The researchers created a miniature artificial language, which consisted of a handful of three-syllable nonsense words constructed from 11 different syllables. The babies heard a computer-generated voice repeating these words in random order in a monotone for two minutes. What they heard went something like "bidakupadotigolabubidaku." Bidaku, in this case, is a word. With no cadence or pauses, the only way the babies could learn individual words was by remembering how often certain syllables were uttered together. When the researchers tested the babies a few minutes later, they found that the infants recognized pairs of syllables that had occurred together consistently on the recording, such as bida. They did not recognize a pair like kupa, which was a rarer combination that crossed the boundaries of two words. In the past, psychologists never imagined that young infants had the mental capacity to make these sorts of inferences. "We were pretty surprised we could get this result with babies, and with only brief exposure," says Newport. "Real language, of course, is much more complicated, but the exposure is vast."
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