by Sue Knapp
babbling, universally uttered by healthy hearing babies when they are about seven months old, is thought to mark the developmental moment when a young child embarks on the road to spoken language. Now, new insight into why this behavior occurs can be found in the hands of hearing babies as they acquire a natural signed language.
According to a study published in the September 6 issue of Nature, Dartmouth researcher Laura Ann Petitto and her associates suggest a fresh approach to how babies begin the remarkable process of acquiring language.
The results of the study, titled "Language Rhythms in Babies' Hand Movements," support the idea that babies are born with sensitivity to highly specific rhythmic patterns naturally found in languages. It is so powerful that a baby can find and produce the rhythms of language even without vocal input from parents. The study further suggests the tantalizing idea that a baby's perception of the rhythmic pattern is a key mechanism that launches the process of human language acquisition.
Petitto and her students and colleagues examined the hand movements of hearing babies born to profoundly deaf parents and compared them to the hand movements of hearing babies with hearing parents.
"Hearing babies with signing deaf parents make a special kind of movement with their hands, with a specific rhythmic pattern, that is distinct from the other hand movements," said Petitto. "We figured out that this kind of rhythmic movement was linguistic. In fact, it was babbling, but with their hands."
Petitto and her colleagues studied six hearing babies. Half of them had no significant exposure to spoken language, only signed language from profoundly deaf parents. The other three were exposed to spoken language. The two groups were equal in all developmental respects, with the only difference being that communication was either by hands or spoken.
The group used a position-tracking system that recorded three-dimensional movements of the babies' hands when they were approximately six, ten and 12 months old. Later, computer programs calculated the speed and cycles of hand movements during the one-hour sessions.
The findings revealed that hearing babies exposed to signed language produce TWO types of hand activity, while the babies hearing spoken language used primarily one type.
All of the babies moved their hands in the familiar pattern of sudden bursts of movement. Speech-exposed babies almost always made about two and a half complete cycles per second. Sign-exposed babies also did that, but had another, slower rhythmic activity, where their hands moved about one complete cycle per second.
The babies who had watched signing also made these slower hand motions within a tightly-restricted space in front of their bodies, corresponding to the location where signs must occur in natural signed languages. Speech-exposed babies produced most of their faster hand activity outside of this crucial linguistic space.
"This dramatic distinction between the two types of hand movements indicates that babies find it important and can make use of the rhythmic patterns underlying human language," said Petitto.
Next, the Petitto team will investigate the physical properties of the sing-song rhythms that parents use to communicate with their babies. The researchers want to learn just how fine-tuned a human baby's sensitivity is to the rhythmic patterns of language their parents use.
Parents and educators can exploit this natural proclivity in children and aid the language learning process. The sing-song way in which delighted parents speak to their baby, and the playful rhyming games common to nursery rhymes at home and in school, could be more important for a child's developing brain than previously imagined, and they provide an important tool for the young child to discover the grammar and structure of his or her native language.
September 5, 2001 (http://www.monitor.net/monitor) All Rights Reserved. Contact firstname.lastname@example.org for permission to use in any format.
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