First stage of language acquisition through two modalities in deaf and hearing children.

We consider the earliest stages of language acquisition in both vocal and gestural modalities. The basic hypothesis is that there is a kind of equipotentiality between the two modalities and that the choice between the two depends on the linguistic input to which the child is exposed. We set forth the results of studies conducted in deaf and hearing children who acquire as native language the sign language used by deaf persons (gestural modality) and discuss the data on language acquisition in hearing and deaf children exposed to the American Sign Language (ASL) and in deaf children exposed to the Italian Sign Language (LIS). We go on to present the results of work in deaf children exposed to a bimodal Italian input. Against the background of studies in hearing children exposed to spoken Italian only we discuss the role of the gestural modality in the language acquisition of these children from the holophrastic to the diphrastic period. The comparison of sign language acquisition and spoken language acquisition will enable us to assess which aspects may be considered universal and which modality-related.