David Yu¹, Guang Yang¹, David Alais¹, Reuben Rideaux¹, Frans Verstraten¹; ¹The University of Sydney

Typically, motion-sensitivity studies are performed with observers sitting in darkened rooms, often constrained by forehead support and a chinrest. This is fine if one is interested in the sensitivity of the substrates that underlie motion detection and perception. However, it has become increasingly clear that vestibular input when observers are moving plays an important role in the way we perceive the world (see Davidson et al, Nature Communications, 2024). In a series of experiments, we investigated motion sensitivity under conditions where the observer is being moved. We used a CKAS W25R motion simulation platform and had observers perform a left-right motion direction discrimination task (2AFC). The participants were either stationary or were being moved by the motion platform. To make sure the vestibular system was active, the motion platform was accelerating when the task was performed. The stimulus was a random pixel array moving at different speeds. We used a signal-to-noise-ratio paradigm (see Fredericksen et al. Vision Research, 1993), where random pixel noise is added when the observer indicated the correct motion direction 3 times in a row. A single mistake decreased the noise level, resulting in a threshold level of 79% correct. There were 4 main conditions, where the motion platform is either stationary, moving in the same direction as the motion on the display, moving in the opposite direction (either translate or rotate), or moving vertically perpendicular to the stimulus direction. Surprisingly the results show that vestibular input has only little effect, if any, on the motion sensitivity thresholds under these conditions.