This working paper introduces a developmental model for studying signed-language writing through four pathways: language input, language output, literacy input, and literacy output. The model separates language development from literacy development. It treats accessible input and expressive output as developmental necessities, and it treats literacy as a durable symbolic layer that can be added after language begins. For signed languages, the research question is not only whether signing is language. It is what changes when a signed language also has durable readable and writable text.
Steve Slevinski (Mon,) studied this question.