Alexander C. Schütz¹ (), Rozana Ovsepian¹, David Souto²; ¹University of Marburg, ²University of Leicester

Smooth pursuit eye movements induce retinal motion. To maintain perceptual stability, this self-induced retinal motion must be cancelled based on some internal reference signal, predicting the sensory consequences of pursuit. Prior studies (Haarmeier et al., 2001, Luna et al., 2021) revealed that with coherent background motion, the reference signal is continuously recalibrated based on the experienced retinal motion. Here, we investigated whether such recalibration depends on the coherence of background motion. The sensorimotor system might either ignore the coherence of motion and simply use the vector average of all retinal motion to assess the sensory consequences of pursuit, or might categorize incoherent motion as object motion in the environment, which is not informative about the sensory consequences of pursuit. Participants executed horizontal smooth pursuit at a velocity of 8.5°/s. In the middle of the trajectory, a random-dot background pattern was presented for 200ms, moving opposite to the eye movement direction (exposure trials). In interleaved test trials, participants reported the perceived direction of the background motion, the velocity of which was varied with an adaptive staircase procedure to estimate the point of subjective stationarity (PSS). Participants were tested in four experimental conditions that varied the coherence (either vertical or horizontal) of the background motion during the exposure and test phases. The background was either coherent or incoherent in exposure trials, paired with either coherent or incoherent motion in test trials. The PSS consistently shifted in the direction of the background speed experienced during the exposure trials, regardless of motion coherence. This shows that the brain recalibrates an internal reference signal using the vector average of the retinal motion. This implies that the brain relies on a prior that the world is stationary on average and that a non-zero average vector is self-induced by smooth pursuit.

Acknowledgements: This work was supported by the “The Adaptive Mind,” funded by the Excellence Program of the Hessian Ministry of Higher Education, Science, Research and Art.