Complex syntactic structures may be difficult to recognize when produced using augmentative
and alternative communication (AAC) systems that do not contain grammatical markers. The
present study investigated adult English speakers' production of Subject and Object relative
clause sentences using a picture/symbol-based AAC system with speech output. Most
participants avoided the potential ambiguity that resulted from the absence of grammatical
markers. They followed spoken English word order when encoding Object relative clause
sentences, but altered this order for Subject relative clause sentences. Most participants used
constituent proximity to maintain the distinction between Subject and Object relative clause
sentences. Results indicate the combined effects of underlying syntactic knowledge and pragmatic
variables on the AAC constituent order patterns observed.