WEDNESDAY, Sept. 5, 2001 (HealthDayNews) -- Babies born to deaf parents who sign to them "babble" with their hands in a way that mimics the burbling of infants exposed to speech, a new study says.
"It doesn't matter what the language is, the brain just wants highly patterned linguistic information," says Laura Ann Petitto, a Dartmouth College language expert and a co-author of the study, which appears in the Sept. 6 issue of Nature.
Many linguists have assumed that babbling -- that endless stream of gobbledygook that starts around 6 months of age and ultimately leads to baby's first word -- is the result of physical changes in the mouth and jaw that have little if anything to do with language.
Other researchers, including Petitto, have argued that the flood of noises reflects the human infant's inborn sensitivity to the rhythms and patterns of language, particularly syllables, which are its most basic units. And to trigger that part of their brain, they need a structured linguistic environment.
"It isn't just enough to have the means for producing sound. The children have to have systematic language input, and young children are sensitive to the rhythmic glue that underlies language," she says.
What's intriguing about the latest findings is that the glue sticks no matter how it's applied, Petitto says. "It's not critical what modality it is. The brain will take it on the hands or the tongue," she says.
Petitto discovered several years ago that babies exposed to sign language babble with their hands. In the latest work, she and colleagues in the United States and Canada studied six babies with normal hearing, including three raised in homes with profoundly deaf parents. As a result, they had only casual exposure to spoken language.
The researchers used a light-sensing computer called an Optotrak, which recorded the movements of small diodes affixed to the babies' fingertips, to track their hand patterns during one-hour play sessions when they were about 6, 10 and 12 months old. They also videotaped the children during the play periods.
All babies in the study babbled verbally, but those whose parents spoke to them made more systematic noises, Petitto says.
Yet infants with deaf parents had markedly different manual babbling from those spoken to regularly at home. Both groups of babies made short, staccato hand movements. However, babies with deaf parents also made longer gestures of about a second in duration, which they confined to a tight space in front of their torso -- precisely where signers hold their hands while speaking. The other babies' frequent gestures generally occurred outside this zone.
Petitto says less frequenct, prolonged gestures correspond to sounds associated with short words, like "ball" or "cup" and sounds such as "ba" or "da" that are among the first forays babies make into spoken language.
The urge to recognize and repeat rhythmic language patterns "is so powerful it can push itself onto the hands even without sound," says Petitto.
Jana Iverson, a developmental psychologist at the University of Missouri who studies the link between language and hand gestures, says the
latest work "adds something new to our understanding to babies' sensitivity
to the language that surrounds them."
"Sign language is a language," Iverson says, "so it makes sense that
babies exposed to sign would reproduce aspects of the language that they see
in their own hand activity. There's a class of rhythmic hand movements that
all babies produce. They like to do that, that's part of being an infant. But those hand movements [from the sign-exposed babies in the study] take that a step further produce a category that's different" from those of babies
exposed to verbal language.
Richard Meier, a linguist at the University of Texas Children's Research Lab in Austin, says the latest work would be "very important," if it holds up.
What To Do
To find out more about language acquisition, check Laura Petitto's Web site at Dartmouth.
This American Scientist report says spoken language may have evolved from manual gestures.
