Motor and vestibular self-motion signals drive perceptual alternations of opposed motions in binocular rivalry

Using opposed drifting gratings (left vs. right) to trigger binocular rivalry, we investigated whether motor and vestibular self-motion signals would modulate rivalry alternation dynamics. Rivalry dynamics in vision-only conditions were compared with two observer-rotation conditions – passive and active. Passive: Observers viewed motion rivalry on a motion platform undergoing sinusoidal yaw oscillations (range=±24°, sine period=4s). Active: Observers wore a virtual reality headset and made trunk rotations to reproduce the same sinusoidal oscillations. Perceived direction in rivalry correlated with rotation direction. The 64s trials were modelled by the best-fitting sinewave, then epoched by the sine period and averaged into one cycle. Sinewave fits to epoched data for each participant showed perceived direction in motion rivalry correlated with direction of yaw rotation. Passive data: Group mean sine period was 3.88s, indicating entrainment of rivalry dynamics to the self-motion oscillation. Mean absolute amplitude was 0.37. The sine fit was generally in-phase (perceived motion matched self-motion direction); for 2/10 it was in anti-phase. Active data: All observers showed in-phase oscillations, all had a period very close to 4s (3.98s), and all showed greater amplitude (0.53) than for passive rotation. Rivalling up/down motions showed no effect of yaw rotation (active or passive), ruling out response bias linked to oscillation rate or direction reversals. Head and eye movements: head position was stable throughout trials and timing of any eye movements showed no correlation with rotation profile (turning points or peak velocities) and thus cannot explain the entrainment of dominant rivalry direction to rotation direction. We conclude both motor and vestibular self-motion signals input to vision and can help resolve perceptual ambiguity. The visual uncertainty in rivalry amplifies the role of these crossmodal influences and facilitates their study. In both cases, perceived visual direction follows the rotation direction, with active self-motion (vestibular+motor) signals particularly salient.