1. Beukelman, D. R., Yorkston, K. M. & Dowden, P. A. (1985). Com-munication augmentation: A casebook of clinical management. San Diego: College Hill Press.
2. Frequency of Word Occurbence in Communication Samples Produced by Adult Communication Aid Users
3. Card, S., Moran, T. & Newell, A. (1983). The psychology of human-computer interaction. Hillsdale, NJ: Lawrence Erlbaum Associates.
4. Derivation of an Efficient Nonvocal Communication System