Differences Between Physical vs. Virtual Evoked Vestibular Responses

Abstract

Electrovestibulography (EVestG), a technology purported to measure vestibular activity at the vestibular periphery, was used to compare the vestibular responses to two sensory inputs: (1) back-forward physical tilt (with eyes-open and eyes-closed) and (2) virtual reality replica of the back-forward tilt (eyes-open, physically static). Twenty-seven healthy participants (10 females) were tested. From each of the EVestG recordings, two feature curves: (1) average field potential (FP), and (2) distribution of time intervals between the detected FPs were extracted. For the eyes-closed physical tilt, except for the background segment, the FP response curve was generally wider compared to that evoked during the virtual replica tilt (p < 0.05). Moreover, the eyes-closed physical tilt produced longer time intervals between FP’s compared to the virtual stimulus. For this measure, for the background segment, the eyes closed and open physical tilt responses were significantly different (p < 0.05) in both ears (repeated measure experimental design). The results support: (1) both vestibular and visual inputs evoking a measurably different EVestG response, (2) the differences between physical and virtual vestibular responses are dependent on the eyes being either open or closed, and (3) for the stimuli used, the modulation of vestibular afferent activity was measurably smaller for virtual than physical stimulation.

Appendices

Appendix 1

The Neural Pathways Connecting Visual and Vestibular Systems

Photoreceptors in the eyes convert light information received from the surrounding environment to electrical signals. These electrical signals can pass along horizontal, bipolar and or amacrine cells to reach ganglion cells, wherein primary visual processing tasks place (e.g., contrast sensitivity, color perception). The axons of the ganglion cells form the optic nerves, which transmit visual information. The visual system and some of the involved regions have been depicted in the below figure. These regions include the medial superior temporal cortex (MST) and vestibulocerebellar areas (mainly involved in motion information processing), the posterior parietal cortex (responsible for the detection of shapes), and inferotemporal cortex (involved in color perception). These brain regions have connections to the vestibular nuclei, which in turn projects via the efferent vestibular system (pathway) to the peripheral vestibular system (semicircular canals and otolith organs (saccule and utricle)).

On the left: Schematic diagram of the human eye with some key structures labeled and the ‘wiring’ of cells in the human retina.12 Adapted from “How the Retina Works: Much of the construction of an image takes place in the retina itself through the use of specialized neural circuits”, by Helga Kolb, 2003, Am Sci 91 28–35. Adapted with permission. On the right: Visual projections towards the vestibular processing brain regions.

Appendix 2