Preliminary Evidence of Pupillary Response to Unexpectedness in Naturalistic Contexts – A Virtual Reality Study

Abstract: A body of evidence suggests that the pupil dilates in response to expectancy violations and unpredictability, yet evidence from complex and ecologically richer settings remains limited. In this study, we tested whether pupillometry could capture sensitivity to unexpectedness in an immersive virtual reality (VR) environment combining experimental control with greater contextual complexity. Forty-nine participants completed a coin-collection task across two repetitions of the same VR scenario. During the second repetition, participants in the control condition re-entered an unchanged environment, whereas participants in the experimental condition saw the scenario turning upside-down during navigation. Pupil size was recorded through an eye tracker embedded in a head-mounted display and analyzed across two 6-s epochs using linear mixed-effects models and generalized additive mixed models. No difference between conditions was detected before the experimental group had experienced the reversal of the scenario. Yet, pupil trajectories diverged significantly over time after the scenario flipped in the experimental condition, although mean pupil size did not differ between conditions. These results suggest that unexpected events in immersive VR may affect the temporal dynamics of pupil responses, even in the absence of differences in mean dilation. Overall, these findings provide preliminary support for the use of pupillometry in VR-based research on expectancy violation and exploratory cognitive states, while also highlighting the need for further studies to refine and extend this methodological approach.