Deaf homesigners can create the foundations of phonetics and phonology without an adult linguistic model.

Children who are exposed to minimal linguistic input can nevertheless introduce linguistic features into their communication systems at the level of morphology, syntax, and semantics (Goldin-Meadow, 2003a). However, it is not clear whether they can do so at the level of phonetics and phonology. This study asks whether congenitally deaf children, unable to learn spoken language and living in a hearing family without exposure to sign language, introduce phonology and phonetics into the gestural communication systems they create, called homesigns. We focused on two foundational properties of phonetics and phonology--discreteness of forms, which is defined independently of meaning and thus forms the basis of duality of patterning. We examined index finger and open flat handshapes in deaf children's homesigns and their hearing mothers' co-speech gestures. We found that handshapes in deictic gestures were more discrete in homesign than in co-speech gesture. Moreover, the degree of discreteness depended on meaning (emblems vs. deictics) in co-speech gesture, but not in homesign. Children can thus create discrete forms that are meaning-independent in their homesign systems even without a model for this feature. This finding helps explain why this feature of language is universal in spoken and signed languages.