  The assumptions we make about a dialogue partner's knowledge and
communicative ability (i.e. our partner models) can influence our language
choices. Although similar processes may operate in human-machine dialogue, the
role of design in shaping these models, and their subsequent effects on
interaction are not clearly understood. Focusing on synthesis design, we
conduct a referential communication experiment to identify the impact of
accented speech on lexical choice. In particular, we focus on whether accented
speech may encourage the use of lexical alternatives that are relevant to a
partner's accent, and how this is may vary when in dialogue with a human or
machine. We find that people are more likely to use American English terms when
speaking with a US accented partner than an Irish accented partner in both
human and machine conditions. This lends support to the proposal that synthesis
design can influence partner perception of lexical knowledge, which in turn
guide user's lexical choices. We discuss the findings with relation to the
nature and dynamics of partner models in human machine dialogue.
