There is debate about how input variation influences child language. Most deaf children are exposed to a sign language from their non-fluent hearing parents and experience a delay in exposure to accessible language. A small number of children receive language input from their deaf parents who are fluent signers. Thus it is possible to document the…

Children typically acquire their native language naturally and spontaneously at a very young age. The emergence of early grammar can be predicted from children's vocabulary size and composition (Bates et al., 1994; Bates, Bretherton & Snyder, 1998; Bates & Goodman, 1997). One central question in language research is understanding what…