Aided language and the demands of simultaneous processing: a case of bimodality?

For individuals who use graphic-based augmentative and alternative communication (AAC), language production is never a single-channel process. These individuals receive language input through speech while encoding communicative intentions through a graphic symbol system, an asymmetry that differs fundamentally from typical spoken language development. This forum paper proposes that graphic-based AAC functions as a bimodal production system. We draw on Levelt's model of speech production and Emmorey et al.'s extension for bimodal bilinguals. What has been characterized as impoverished language output in aided AAC, we argue, may instead reflect the simultaneous activation of two parallel language formulators, one verbal and one graphic, each routing output to independent articulatory systems under fundamentally different constraints. The graphic formulator operates without the automaticity of typical speech production, requiring overt symbol selection, display navigation, and deliberate morphological encoding through processes such as post-morphing. This framework reframes documented patterns in AAC output, including morphological omission and reduced syntactic complexity, as consequences of a constrained graphic formulator operating in parallel with a verbal formulator that may have generated a more complete linguistic representation. The framework also offers a foundation for investigating bilingual AAC use and future psycholinguistic studies of aided language production.