Ungruh, RobinSchmidt, SusanneNorouzi, NahalSteinicke, FrankJean-Marie NormandMaki SugimotoVeronica Sundstedt2023-12-042023-12-042023978-3-03868-218-91727-530Xhttps://doi.org/10.2312/egve.20231313https://diglib.eg.org:443/handle/10.2312/egve20231313In social interactions, people tend to imitate the behavior of others and to perceive dialogues in which they are imitated to be more natural and smooth. This process of mimicry is not limited to non-verbal behavior, but also involves subtle adaptation of one's own speech style to the communication partner. Although being a natural phenomenon in human-human interaction, it is not yet common for virtual agents to simulate such behavior by adapting their speech style to that of the user. This work presents a user study (N = 48) that explores the participants' perception of a virtual agent mimicking formal and informal speech. The majority of participants preferred agents with a matching speech style over those with a mismatching one. Other positive results of mimicry that were previously found in human-human interaction could not be replicated. To inform other researchers studying subtle agent behavior about possible factors that might dominate participants' perception of an agent, we present the results of a thorough content analysis of qualitative user feedback. From the salient themes, such as mismatched emotionality in language and speech, affordances of agents, and expectations of the agent's role in interactions, we derive recommendations for the design of future user studies of subtle (verbal and non-verbal) agent behavior.Attribution 4.0 International LicenseCCS Concepts: Human-centered computing → Empirical studies in HCI; Natural language interfaces; Computing methodologies → Discourse, dialogue and pragmaticsHumancentered computing → Empirical studies in HCINatural language interfacesComputing methodologies → Discoursedialogue and pragmatics10.2312/egve.2023131353-619 pages