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Deaf infants suggest basic template of language
STANFORD -- Like any baby, Mary learned her native language in stages - stringing syllables together into words by 12 months, beginning sentences by 18 months. Because Mary is deaf, though, that language was expressed with her hands in signs.
Deaf infants pick up language on the same schedule as hearing babies, psychologist Laura Petitto told members of the American Association for the Advancement of Science in Chicago on Feb. 8. And from the beginning, they use word signs in a different way than they use other gestures. Those findings are evidence for an entirely new theory of language acquisition, Petitto said.
The prevailing theory has been that infants acquire language as they develop the ability to make sounds into speech. Petitto said that the evidence from deaf children shows that the key is not the mode - speech or signs - but an innate human capacity to recognize language patterns.
A child is born with a basic structure-seeking mechanism that combs through adults' language looking for repeated patterns, she theorizes. Starting with syllables and the rhythms that bind them, babies analyze more and more information about the rules for building words, phrases and sentences.
First, they learn the form - babbling in meaningless sequences that look or sound like sentences. "Later, the child hangs meaning on the form," Petitto said.
"This is how human language gets started in the first place," she said. "A child needs this structure in order to get started in using language. It does not matter whether the patterns are spoken or signed. Providing he sees or hears the rhythm and structure that he seeks, the child will take that information and use it."
Petitto, an associate professor of psychology at McGill University in Montreal, is a 1991-92 fellow at the Center for Advanced Study in the Behavioral Sciences at Stanford University. In the March 22, 1991, issue of Science, she published the results of a study showing that deaf babies babble with sign language. This was one of several discoveries, over more than a decade of studying how deaf and hearing infants acquire language, that form the basis of her new theory.
Her research has shown that children learn language in the same stages, and on the same timetable, whether they learn with signs, speech or both. Contrary to expectations that humans have an innate instinct to prefer speech, Petitto's studies show that hearing children with one deaf parent simultaneously reach all the normal language milestones in both speech and sign.
One surprising finding is that deaf infants effortlessly distinguish language signs - to which they apply grammatical rules - from routine gestures, even when the two look very much alike. For example, a child uses the word or sign for "open" specifically as a verb, to ask for a jar to be opened. However, a general "twist" gesture is more general - used to mean "open the jar" or refer to the jar itself or to the cookies inside.
"Deaf children do not confuse language with gesture - there is a principled disassociation of the two," Petitto said. "The deaf child has taught us that infants have a basic ability to distinguish structure from other actions that have meaning."
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