  Embodied conversational agents (ECAs) are paradigms of conversational user
interfaces in the form of embodied characters. While ECAs offer various
manipulable features, this paper focuses on a study conducted to explore two
distinct levels of presentation realism. The two agent versions are
photorealistic and animated. The study aims to provide insights and design
suggestions for speech-enabled ECAs within serious game environments. A
within-subjects, two-by-two factorial design was employed for this research
with a cohort of 36 participants balanced for gender. The results showed that
both the photorealistic and the animated versions were perceived as highly
usable, with overall mean scores of 5.76 and 5.71, respectively. However, 69.4
per cent of the participants stated they preferred the photorealistic version,
25 per cent stated they preferred the animated version and 5.6 per cent had no
stated preference. The photorealistic agents were perceived as more realistic
and human-like, while the animated characters made the task feel more like a
game. Even though the agents' realism had no significant effect on usability,
it positively influenced participants' perceptions of the agent. This research
aims to lay the groundwork for future studies on ECA realism's impact in
serious games across diverse contexts.
