Abstract
An optokinetic stimulus rotating about the naso-occipital axis drives torsional eye movements and causes a bias in perception of upright measured with a subjective visual vertical (SVV) task. In addition, a static image with tilted visual cues of gravity orientation will induce optostatic torsion and biases SVV. We posit that a visual gravity cue provided by a frame combined with a torsional optokinetic stimulus would increase measured torsion and further bias SVV. We use a VR headset with eye-tracking to place the subject in a virtual room with circles forming either a rectangular room (frame condition) or a tubular room (no-frame condition). We place a fixation point at the center of the room while the subject performs a SVV task. The room either rotates about the naso-occipital axis at 0.05 Hz, 0.1 Hz, or 0.2 Hz, with an amplitude of ±20°, or has a static tilt of 0° or ±30°. Static frame conditions had the expected bias of SVV and optostatic torsion compared to the control no-frame condition. In sinusoidal rotation conditions, for SVV, there was a significant difference in the amplitude of the response between the frame (5.4 ± 2.6°; mean ± std) and no-frame (3.0 ± 1.3°) condition, while there was no significant difference for torsion, frame (0.8 ± 0.6°) and no-frame (0.7 ± 0.6°). Our results indicate that while perception integrates a moving visual cue into its estimation of upright orientation, the ocular motor system is only affected by those cues when they are static.