Pragmatic presupposition and its impact on the syntax of an AAC user

Pragmatic presupposition is the act of assuming a conversational partner has a high level of understanding regarding the current topic. Non-AAC speakers use this process to determine the content to include in the utterances. Do graphic symbol communicators use it to determine the level of syntactic complexity to produce in an utterance? This study examined the syntax of one AAC user in two contexts: one in which the conversational partner exhibited a high-level of topic awareness and another in which he or she demonstrated a low level. The utterances from the two contexts were analyzed using measurements of syntactic complexity. Results indicate that utterances produced by the AAC user in contexts in which the conversational partner demonstrated a low level of topic awareness were more syntactically complex relative to those produced in high-level contexts. These results may indicate that the AAC user utilized pragmatic presupposition to determine the level of syntactic complexity produced.