Xiaru Meng, Yulan Ju, Christopher Changmok Kim, Yan He, Giulia Barbareschi, Kouta Minamizawa, Kai Kunze, and Matthias Hoppe. 2025. A Placebo Concert: The Placebo Effect for Visualization of Physiological Audience Data during Experience Recreation in Virtual Reality. In Proceedings of the 2025 CHI Conference on Human Factors in Computing Systems (CHI '25). Association for Computing Machinery, New York, NY, USA, Article 807, 1–16. https://doi.org/10.1145/3706598.3713594 A core use case for Virtual Reality applications is recreating real-life scenarios for training or entertainment. Promoting physiological responses for users in VR that match those of real-life spectators can maximize engagement and contribute to more co-presence. Current research focuses on visualizations and measurements of physiological data to ensure experience accuracy. However, placebo effects are known to influence performance and self-perception in HCI studies, creating a need to investigate the effect of visualizing different types of data (real, unmatched, and fake) on user perception during event recreation in VR. We investigate these conditions through a balanced between-groups study (n=44) of uninformed and informed participants. The informed group was provided with the information that the data visualizations represented previously recorded human physiological data. Our findings reveal a placebo effect, where the informed group demonstrated enhanced engagement and co-presence. Additionally, the fake data condition in the informed group evoked a positive emotional response. https://doi.org/10.1145/3706598.3713594