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

Summary

The methodology explored visual and vestibular contributions to gaze stabilization during optokinetic and whole-body rotations. Stimulations were carried out through visual, vestibular, and visuovestibular trials. Torsional eye-movement gain and nystagmus frequencies served as indicators for the subcortical relay of sensory-specific motion information towards the reflexive brainstem response for each trial.

Abstract

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.

Introduction

Motion processing is a fundamental and continuous neural process. In humans, we receive information primarily through our visual and vestibular sensory systems, reflecting external- and self-motion, respectively. These two systems employ complex neural networks across lower- and higher neural regions, but on their most basic level rely on basic subcortical pathways to produce reflexive responses that allow good postural control and gaze-stability^1,2. Proprioception serves as the third sensory contributor to good postural control, and while it has been shown that somatosensation may guide gaze-stabilizing behav....

Protocol

All participants provided informed written consent prior to participation. The study was approved by the regional ethics review board (2018/1768-31/1) and carried out in accordance with the principles outlined in the Declaration of Helsinki. The protocol followed STROBE guidelines.

1. Participant selection

1. Subject all participants to a comprehensive clinical assessment by a medical doctor and a neuropsychologist.
2. Use the following exclusion criteria: ocular motor or gaze dysfunction, vestibular or somatosensory deficits, recent initiation of centrally acting medication (within 3 months), or any neurolo....

Results

A total of 171 trials were conducted, in which all participants underwent visual, vestibular, and combined visuo-vestibular stimulations at three acceleration levels. Eye-tracking assessments were performed on all resulting nystagmus slow phases (n = 223 for nine control participants (seven females); n = 331 for 10 patients (three females)). Statistical analyses were based on the mean values obtained for each participant (n = 19), with data averaged across trials. Healthy controls and patients were matched in terms of ag.......

Discussion

The present protocol offers a validated methodology for assessing subcortical motion processing through torsional gaze-stabilization, a reflex mediated by brainstem circuits²³. By combining visual and vestibular stimulation, the method enables the evaluation of multisensory integration through ocular torsion responses. Prior implementations have demonstrated their sensitivity to acceleration-dependent vestibular contributions¹⁶, visual information density^1.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
AC Brushless Servo Motors / Baldor BSM90C, 400 V	BB Motors and Mechanical, Fort Smith, AK, USA	UPC 781568378342	Used to construct the mechanized sled
Chronos Eye tracking device (C-ETD)	Chronos Vision GmbH, Berlin, Germany	No longer available	Newer models are available from the company, offering higher recording rates.
OriginPro	OriginLab, Northampton, MA, USA	OriginPro 17	Used to visualise and analyse eye-, head-, and chair traces.
SPSS Statististics	IBM, Chicago, IL, USA	SPSS Statistics 28	Used for the statistical analyses