Developmental milestones: sign language acquisition and motor development.

The sign language and motor development of 11 young children of deaf parents were studied across a 16-month period. The subjects showed accelerated early language development producing, on the average, their first recognizable sign at 8.5 months, their tenth sign at 13.2 months, and their first sign combination at 17.0 months. In contrast, children learning to speak typically do not attain the equivalent spoken language milestones until 2-3 months later. The structure and content of the subjects' 50-sign vocabularies closely resembled those for children at the same stage in previously published studies of spoken language acquisition. The pattern of synchrony between motor and language development previously reported by investigators of children learning to speak was found not to apply to the population of the present study: most of the subjects learning to sign did not slow down in their rate of language acquisition after achieving a new motor milestone, but rather continued to show a gradual increase in the size of their sign language vocabularies.