Affiliations: [a] School of Psychology, University of Kent, Canterbury, UK
| [b] School of Psychology, Royal Holloway, University of London, Egham, UK
| [c] Department of Neurology, University Hospital Zurich, Zurich, Switzerland
| [d] Department of Psychological Sciences, Birkbeck University of London, London, UK
| [e] Faculty of Medicine, University of Zurich, Zurich, Switzerland
| [f]
Clinical Neuroscience Center, Zurich, Switzerland
| [g] Department of Otorhinolaryngology, University Hospital Zurich, Zurich, Switzerland
| [h] Department of Ophthalmology, University Hospital Zurich, Zurich, Switzerland
| [i] Institute of Optometry, University of Applied Sciences and Arts Northwestern Switzerland, Olten, Switzerland
Correspondence:
[*]
Corresponding author: Maria Gallagher, School of Psychology, Keynes College, University of Kent, Canterbury, CT27NP, UK. E-mail: m.gallagher@kent.ac.uk.
Abstract: BACKGROUND:The vestibular system provides a comprehensive estimate of self-motion in 3D space. Widely used to artificially stimulate the vestibular system, binaural-bipolar square-wave Galvanic Vestibular Stimulation (GVS) elicits a virtual sensation of roll rotation. Postural responses to GVS have been clearly delineated, however quantifying the perceived virtual rotation vector has not been fully realised. OBJECTIVE:We aimed to quantify the perceived virtual roll rotation vector elicited by GVS using a psychophysical approach on a 3D turntable. METHODS:Participants were placed supine on the 3D turntable and rotated around the naso-occipital axis while supine and received square-wave binaural-bipolar GVS or sham stimulation. GVS amplitudes and intensities were systematically manipulated. The turntable motion profile consisted of a velocity step of 20°/s2 until the trial velocity between 0–20°/s was reached, followed by a 1°/s ramp until the end of the trial. In a psychophysical adaptive staircase procedure, we systematically varied the roll velocity to identify the exact velocity that cancelled the perceived roll sensation induced by GVS. RESULTS:Participants perceived a virtual roll rotation towards the cathode of approximately 2°/s velocity for 1 mA GVS and 6°/s velocity for 2.5 mA GVS. The observed values were stable across repetitions. CONCLUSIONS:Our results quantify for the first time the perceived virtual roll rotations induced by binaural-bipolar square-wave GVS. Importantly, estimates were based on perceptual judgements, in the absence of motor or postural responses and in a head orientation where the GVS-induced roll sensation did not interact with the perceived direction of gravity. This is an important step towards applications of GVS in different settings, including sensory substitution or Virtual Reality.
