Babies' hands move to the rhythm of language
HANOVER, N.H. - Baby 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, 2001 issue of Nature, lead author Laura Ann Petitto, a Professor in the Department of Education and in the Department of Psychological and Brain Sciences at Dartmouth College, suggests a fresh approach to how babies begin the remarkable process of acquiring language.
The results of the study, titled "Language Rhythms in Babies聮 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聮s perception of the rhythmic pattern is a key mechanism that launches the process of human language acquisition.
Petitto, who conducted the study with 捆绑SM社区 (Montreal, Canada) students and colleagues Siobhan Holowka, Lauren Sergio (now an assistant professor at York University) and Professor David Ostry (also at Haskins Laboratories in New Haven, Conn.), studied 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: three received no significant exposure to spoken language, only signed language from profoundly deaf parents, and three were exposed to spoken language. The two groups were equal in all developmental respects, with the only difference found in the form of the language input they received (by hands or by mouth).
The group used an optoelectronic position-tracking system that recorded three-dimensional information of the babies聮 hands when they were approximately six, ten and 12 months old. While the children played in 60-minute sessions, sensors tracked the location and path of light emitting diodes (LEDs) on each of their hands. Then, computer programs calculated the speed and cycles of hand movements over time. Independently, videotapes were made and viewed only after the measurements were calculated. Because Petitto聮s team used this precise method of analysis, they were able to overcome the subjective problems associated with solely viewing videotapes of babies聮 hands that have plagued research on this topic for decades.
The findings revealed that hearing babies exposed to signed language produce two types of hand activity, while the hearing babies exposed to spoken language produce primarily one type. Sign-exposed babies displayed a low-frequency rhythmic activity, where the hands move in undulating bursts of about one complete cycle per second, in addition to another type of high-frequency rhythmic activity, where the hands moved in undulating bursts of around two and a half complete cycles per second. Speech-exposed babies displayed high-frequency actitivity nearly exclusively.
Surprisingly, only the sign-exposed babies produced low-frequency hand activity largely 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 high-frequency hand activity outside of this crucial linguistic location.
"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.
This discovery points to the centrality of the rhythmic patterns that underlie human language. 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聮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.
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聮s sensitivity is to the rhythmic patterns of language their parents use.
