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Be careful what you say: Little ears might be listening and remembering.
Infants appear to remember relatively complex words even when they occur without other stimuli, suggesting that babies hear and memorize the words being used by adults and others around them, according to research by Peter Jusczyk, Ph.D., and colleagues in the department of psychology at Johns Hopkins University.
The study appeared in the September 26 edition of Science.
The investigators recorded women reading three different children’s stories, each lasting about 10 minutes. The recordings were then played for infants at their homes daily for 10 days until the infants had heard each story 10 times. Next, the investigators identified 36 content words that occurred most frequently in the stories and arranged those in lists of 12 words each.
Two weeks after the last visit to the infants’ homes, the babies were placed in a testing booth in a laboratory at Johns Hopkins where they listened to the recorded list of content words from the stories. This was followed by a recorded list of other, similar sounding words that did not occur in the stories.
A light flashed above the speaker through which the tape recording was played. When the infants looked at the light, the word lists began and continued to play as long as the infants looked toward the light. Babies who stopped listening to the words looked away from the light, telling the researchers how long the infants had listened to specific lists of words.
"What we found was that the babies listened significantly longer to the list of words from the stories," Jusczyk said.
The findings corroborated what had been observed in previous tests using the same method, yet Jusczyk and colleagues wanted to make sure the infants were not listening longer to the story words simply because they found them more interesting.
To control for this possibility, the investigators brought a new group of infants to the lab who had never heard the stories on tape. When those infants heard the lists of the story words and the nonstory words, they showed no preference and actually listened slightly longer to the nonstory words.
"That showed us that the experience the babies had at home listening to the stories had an impact on what they really remembered," Jusczyk said.
He noted, as well, that the infants learned the words even though they never had any personal contact with the women who narrated the stories.
"Imagine what happens when you actually have the baby in your arms and you are reading the story and you are turning the pages of the book," he said. "You’d expect that they would be even more inclined to store some of that information."
The babies who had never heard the stories listened an average of about six seconds to the story words and slightly more than that for the nonstory words. The infants who had heard the stories listened an average of less than six seconds to the nonstory words, but nearly seven seconds to the story words.
"A second doesn’t sound like a lot of time, but it’s consistent," Jusczyk said. "The whole object of this was to see whether, when infants are listening to people talk or listening to people read stories to them, they are storing any information away about sound patterns that occur frequently."
The most remarkable finding of all was that the babies recognized the words even though they sounded slightly different in list form than they had in the stories.
"When we just read a list, we actually pronounce the words a little bit differently," he said. "They have a different acoustic form than in the stories."
The findings may help piece together how children acquire language, which requires storing both sounds and meanings. It may be that babies are storing sounds in infancy and begin to link those sounds with meaning at around 18 months, when they begin to talk.