Research conducted several years ago indicated that the seemingly random babbling of babies traverses a sequence of increasingly complex vocal stages, leading to the first spoken words around age 1 (SN: 6/21/86, p. 390). But a new pilot study suggests babies can babble without ever making a sound, thanks to a generalized, innate language capacity in the brain.

Psychologists Laura Ann Petitto and Paula F. Marentette of McGill University in Montreal studied five infants, two of whom were deaf. The deaf babies had deaf parents and acquired American Sign Language as their first language; the three hearing babies had hearing parents who spoke either French or English at home and did not expose their infants to sign language. On three occasions, when the babies reached the ages of about 10, 12, and 14 months, the researchers videotaped the children alone and with their parents, then transcribed each infant's hand movements and vocalizations.

Both hearing and deaf babies engaged in their own brand of babbling, Petitto and Marentette report in the March 22 SCIENCE. Hearing infants initially produced strings of sounds and syllables, emitting their first words by age 1. The two deaf babies babbled with their hands, starting out with basic hand shapes for letters and numbers that they saw their parents use. Hand movements and shapes gradually grew more complex, with the first full-fledged linguistic signs emerging by age 1.

These observations challenge the widespread assumption that babbling requires normal hearing and an ability to speak aloud, the investigators argue. The brain apparently possesses some type of unified capacity for learning both signed and spoken language, they propose.