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AAC for hypothesis testing and treatment of aphasic language production: Lessons from a “processing prosthesis”

Background : The design of augmentative and alternative communication (AAC) technology for aphasic individuals must be informed by a theory of the underlying disorder in order to determine what kind of assistance will be most effective. AAC devices may therefore serve to test competing theories, each predicting the efficacy of a different kind of support for language production. They may also serve as heuristic tools, affording the opportunity to observe language production under radically altered conditions. A communication system that we have termed a “processing prosthesis” was directly inspired by the performance hypothesis, the view that processing factors rather than loss of linguistic knowledge underlie aphasic language production disorders. Unlike AAC technology, which focuses on the provision of direct linguistic support in the form of vocabulary items and pre-stored utterances, this system (referred to here and in previous literature as the “CS”) emphasises indirect support to allow the user to more fully exploit his or her retained language production capabilities. If the CS is effective in facilitating aphasic sentence construction, this may be taken as evidence in support of the performance hypothesis embodied in its design. Aims : We illustrate the interplay between AAC technology and psycholinguistic theory by reviewing studies of the CS, and describe some approaches to language remediation that have emerged from this work. Contributions : We review three published studies and preliminary data from a fourth. These studies demonstrate the efficacy of the CS through “aided” effects (i.e., the extent to which utterances produced on the system are more structured and/or informative than those produced without the system) and treatment effects (i.e., the impact of a period of CS use on the aphasic individual's spontaneous, unaided speech). Conclusions : The CS data suggest that “indirect” support may play an important role in facilitating and treating aphasic sentence production; and, more generally, they demonstrate the bidirectional flow of insight between assistive technology and the psycholinguistic analysis of aphasic disorders.