  Perceptions of system competence and communicative ability, termed partner
models, play a significant role in speech interface interaction. Yet we do not
know what the core dimensions of this concept are. Taking a psycholexical
approach, our paper is the first to identify the key dimensions that define
partner models in speech agent interaction. Through a repertory grid study
(N=21), a review of key subjective questionnaires, an expert review of
resulting word pairs and an online study of 356 user of speech interfaces, we
identify three key dimensions that make up a users' partner model: 1)
perceptions toward competence and capability; 2) assessment of human-likeness;
and 3) a system's perceived cognitive flexibility. We discuss the implications
for partner modelling as a concept, emphasising the importance of salience and
the dynamic nature of these perceptions.
