Babies exposed only to sign language learn to babble in sign 鈥� and their hand babble mimics the sign language their parents use, just as verbal babble sounds like speech. The finding supports the idea that children are born with a propensity to learn language, regardless of how that language is mediated.
Laura Ann Petitto at Dartmouth College in Hanover, New Hampshire, and her colleagues studied two groups of hearing babies. Half had hearing parents, the other half had profoundly deaf parents who used sign language. The researchers videotaped each of the babies at six, ten and 12 months and at each session tracked the movements of their hands using LED sensors.
The researchers found that both groups of babies waved their hands around at high frequency. But analysis of the sensor data revealed that only the sign-exposed babes produced low-frequency rhythmic hand activity.
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This low frequency movement is temporally similar to what鈥檚 seen in genuine sign language. What鈥檚 more, the low-frequency hand movements tended to be within the 鈥渟ign phonetic鈥� space in front of the baby鈥檚 body 鈥� just as a signer鈥檚 activity would be 鈥� whereas the high-frequency movements were mostly outside it.
Shrivel and die
The result shows that babies are inherently sensitive to language, says Petitto. 鈥淏abies have a highly-honed sensitivity to the bite-sized rhythmic patterns of natural language,鈥� she says. 鈥淏y finding these attractive, they start to produce them.鈥� This sensitivity, says Petitto, is the 鈥渂ooster rocket鈥� that launches the child into learning language 鈥� regardless of the modality.
All babies are born with the capacity to sign, she says. 鈥淭hey come into the world with a repertoire.鈥�
About three percent of their hand shapes will accidentally hit a real syllabic unit of sign, but with no systematic exposure to the language, the capacity will shrivel and die. Instead, the vocal apparatus will take over.
Journal reference: Nature (vol 413, p 35)