Infants are able to distinguish one voice amid a clutter of
distracting background noise, psychologists have discovered, and
the skill may be critical in a baby's mysterious ability to learn
Scientists do not understand how the brain is able to focus on one particular voice or sound amid the cacophony of background noise, an auditory phenomenon known as the "cocktail party effect." Adults are able to overcome the effect, paying selective attention to one voice during a conversation with that person, while ignoring other voices. But, until now, there had been no strong evidence that infants shared the same talent.
Peter Jusczyk, a professor in the Department of Psychology, has discovered just that. He and Rochelle Newman, a psychology graduate student at the State University of New York at Buffalo, have found that infants an average of 7 and a half months old can accomplish the feat. The findings are detailed in a scientific paper published in the November issue of Perception & Psychophysics, a journal for experimental psychologists. The paper was co-authored by Newman and Jusczyk.
They suggest in their paper that the ability may play an important role in learning language by increasing the amount of information available to infants, who are striving to understand the sounds of words and the melody of sentence structure.
"Put simply, in order to learn a language, infants must be able to hear it, and this requires the ability to separate it from background noise," Newman and Jusczyk said in the paper. " They may have to 'tune out' all sorts of competing noises around the home to gain any information from their caregivers' speech. If they were unable to do this, they would have to draw on a much smaller set of utterances in order to discover the structure and organization of their native language."
The psychologists noted that there has been "a surprising dearth of research" to explore the cocktail party effect in infants.
"Like adults, infants often are engaged in noisy situations. ... Infants also have to deal with competition from other speech, such as that from the television down the hall, and from their siblings in the next room. Yet there has been almost no research on infants demonstrating the extent to which they can succeed at this difficult task."
Jusczyk has written a book about the history of infant speech perception, a field that began only about 25 years ago, he said. His book, The Discovery of Spoken Language, to be published by the MIT Press, is scheduled for release in early 1997.
Because infants cannot be questioned directly, researchers must design elaborate testing methods. "With an infant, you have to ask the questions indirectly," said Jusczyk, who joined the Hopkins faculty this summer, coming here from SUNY-Buffalo.
"Do they listen longer to this one, or how are they responding to something?"
To test how babies deal with the cocktail party effect, Jusczyk and Newman studied the responses of 24 infants; a woman repeated a specific word, such as "cup" or "dog," over and over, while a man in the background read the mundane narrative of the scientific method used in the experiment. Later, taped passages were played to the infants. Some of the passages revolved around the theme of cup or dog.
Most of the infants paid more attention to the passages containing the familiar words than they did to passages that did not contain "cup" or "dog." For example, during two experiments in which the woman's voice was slightly louder than the background voice, up to 87 percent of the infants paid more attention to the passages containing the familiar words. The results demonstrated that the babies had learned the words, despite the background noise.
Studying the effect in babies could provide insights into how they learn language. But such insights might also be helpful to scientists trying to design computers that understand speech.
"What is interesting about this is how quickly babies are able to progress" in learning language, whereas the most powerful computers are unable to efficiently decipher spoken language, Jusczyk said.
"It is mysterious. If we had a better understanding of how infants are able to do this, we probably would get a lot farther in terms of how we could get machines to do this," he said.
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