Unaided aac interventions such as manual signs appear to facilitate the development of speech. rigorous research is required to establish the effects of aac systems and interventions on speech production across a variety of populations with developmental disabilities

Millar, D. C., Light, J. C., & Schlosser, R. W. (2006). The impact of augmentative and alternative communication intervention on the speech production of individuals with developmental disabilities: A research review. Journal of Speech, Language, and Hearing Research, 49, 248-264. © 2007 Taylor & Francis Group, LLC.