Using Eye-tracking to Assess the Relative Importance of Visual and Vestibular Input to Subcortical Motion Processing in the Roll Plane

The present protocol evaluates the relative impact of visual and vestibular inputs during roll plane rotations using optokinetic, vestibular, and combined visuovestibular stimulations. Subjects underwent isolated visual rotations, whole-body vestibular rotations in darkness, and visuovestibular stimulations combining static visual scenes with head rotations. Dynamic and static eye movement gains, absolute amplitudes, velocities, and accelerations were measured alongside perceptual responses. Trials included a baseline rest period before and after movement to stabilize oculomotor fixation. Precise eye- and head-tracking were achieved using the Chronos Eye-Tracking Device (C-ETD), which recorded ocular torsion and head movements across three translational and three rotational dimensions. Eye movements were analyzed for slow-phase velocities and nystagmus frequency, with data quality ensured by averaging torsional outputs from both eyes and excluding frames with artefacts. Real-time gaze alignment monitoring allowed trial repetition as needed, and post-hoc analysis excluded confounding movements. Optokinetic stimulation involved projected visual elements rotating around a fixation point, while vestibular trials employed motorized whole-body rotations in darkness. Visuovestibular trials combined both stimuli, creating relative retinal motion. Data synchronization between eye and head trackers ensured accurate frame-by-frame analysis recorded at 100 Hz. Sensory-specific contributions to gaze stabilization were quantified by comparing slow-phase velocities across trial types. Sensory-specific gains were indexed by dividing visual and vestibular responses by visuovestibular outcomes and validated through comparisons with summed individual responses. Results revealed robust sensory integration, with the relative contributions of visual and vestibular inputs quantified. This protocol offers a detailed framework for evaluating multisensory integration during roll plane rotations. The protocol may therefore serve to elucidate sensory deficits in motion processing, as well as present novel oculomotor biomarkers. It has previously been employed to evaluate how visual clutter and motion accelerations impact motion processing and has highlighted an increased reliance on visual input in concussed patients.