  Voice User Interfaces (VUIs) increasingly leverage 'humanness' as a
foundational design metaphor, adopting roles like 'assistants,' 'teachers,' and
'secretaries' to foster natural interactions. Yet, this approach can sometimes
misalign user trust and reinforce societal stereotypes, leading to
socio-technical challenges that might impede long-term engagement. This paper
explores an alternative approach to navigate these challenges-incorporating
non-human metaphors in VUI design. We report on a study with 240 participants
examining the effects of human versus non-human metaphors on user perceptions
within health and finance domains. Results indicate a preference for the human
metaphor (doctor) over the non-human (health encyclopedia) in health contexts
for its perceived enjoyability and likeability. In finance, however, user
perceptions do not significantly differ between human (financial advisor) and
non-human (calculator) metaphors. Importantly, our research reveals that the
explicit awareness of a metaphor's use influences adoption intentions, with a
marked preference for non-human metaphors when their metaphorical nature is not
disclosed. These findings highlight context-specific conversation design
strategies required in integrating non-human metaphors into VUI design,
suggesting tradeoffs and design considerations that could enhance user
engagement and adoption.
