Babies are born with an innate sense of rhythm that is essential for learning a language, according to a pioneering study of children who learnt "silent babbling" using sign language.
Babbling is common to all babies and was once thought to be merely the result of children learning to move their jaws. But research on the children of deaf parents indicates that a baby babbles to develop its inborn rhythm, which is critical for learning a language.
The findings could help children with speech difficulties by providing a better understanding of how infants normally use patterns in the brain's language centres.
Scientists studied the normal, hearing babies of profoundly deaf parents and found that, in addition to the random hand movements made by all babies, the infants demonstrated "silent babbling" using rudimentary signs. By fixing lights to the tips of the babies' fingers and analysing their motion, researchersidentified non-random movements within normal movement.
The scientists, led by Professor Laura Ann Petitto of Dartmouth College, New Hampshire, and McGill University, Montreal, write in Nature: "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. We figured out that this kind of rhythmic movement was linguistic ... It was babbling, but with their hands."
The scientists compared three babies with normal hearing whose parents were profoundly deaf – and who therefore had little exposure to speech – with three babies born to hearing couples who talked to their children. The "silent babbling" seen in the children of deaf parents was a slower, more rhythmic activity performed closer to the body than the ordinary, random hand movements of infants.
Professor Petitto said: "This dramatic distinction between the two types of hand movements indicates that babies ... can make use of the rhythmic patterns underlying human language."
The singsong way many people speak to babies and the patterns of speech in nursery rhymes could be used more effectively in helping handicapped children to speak earlier, the scientists said.