Quantitative measures of the visually evoked sensation of body movement in space (Vection) using Electrovestibulography (EVestG)

Abstract

Vection is defined as an illusory self-motion sensation induced in stationary observers that can be experienced in a real/virtual world. Vection, as a result of immersion in virtual reality (VR) environments, can subsequently lead to a sense of inability to maintain postural control and cause cybersickness symptoms. The multisensory integration of visual and vestibular (balance) information plays a vital role in vection. The etiology of vection perception, as well as, the vestibular response change while experiencing vection is poorly understood. This study explores vestibular response change following vection in 20 individuals (10 females, 26.45 ± 4.40 (SD) years). Vection was induced in participants using an immersive VR roller-coaster. The vestibular response was measured simultaneously using a noninvasive method called Electrovestibulography (EVestG). The detected field potentials and the time intervals between the field potentials were extracted from the recorded EVestG signals corresponding to four segments of the VR roller-coaster trajectory namely Stationary, Up movement, Down movement, and slopes and turns (Mix). The results show that the Stationary segment is significantly different (P < 0.05) from other dynamic segments when the average field potential of the right and left ear are subtracted. Furthermore, the Stationary segment shows longer time intervals between field potentials compared to those of the other segments in the right ear. These observations suggest that the combined effect of the visually induced sensation of self-motion together with a concurrent/co-occurring stress/anxiety factor can affect the vestibular activity in an excitatory way. Increased excitatory vestibular activity implies increased feeling of imbalance and more likelihood of experiencing cybersickness by the participants.

Appendices

Appendix 1: Transmission of optical information to the vestibular periphery

Human eyes are intricate apparatus that include a number of different structures working together to provide us the visual representation of the surrounding environment. The retina is the light-sensitive component of the eye containing layers of photoreceptors and different cells (amacrine, bipolar, horizontal). In the retina, light photons are converted to electrical signals (following chemical changes in the pigment of the photoreceptors) that are then carried to the optic nerves (axons of ganglion cells). Passing through the optic nerves, these electrical signals reach the optic tract where four major projections diverge; they are the lateral geniculate nucleus (LGN) in the thalamus, superior colliculus, pretectum of the midbrain, and suprachiasmatic nucleus of the hypothalamus (Fig. 1). From these regions, visual information projects to the vestibular nuclei through a number of different neural pathways (Fig. 1). These pathways are different in terms of visual processing time and function (e.g., responsible for elementary and complex visual function). The retino-cortical pathway, through the LGN, projects to the visual cortex wherein delicate visual processing such as the perception of emotions is performed. Based on the results of PET, fMRI and lesion studies (Van Essen et al. 2001), Brodmann’s areas 17–21, 37, 39, and 7 of the visual cortex have been reported to contribute to the sensation of self-motion. These areas send fibers to the cerebellum and more particularly the vestibulo-cerebellum (the flocculus and that part of the vermis connected to it) which have a bi-directional connection to the vestibular nuclei (Burdess 1996). The vestibulocerebellar region receives inputs from the vestibular nuclei and the primary vestibular afferents and project efferents to the vestibular nuclei (Burdess 1996). The processing time through retino-cortical pathway is about 100–150 ms which is longer than that of the other three subcortical visual pathways: the retino-colliculus, the retino-tectal, and the retino hypothalamic pathways (Thorpe et al. 1996; Gerson et al. 2006). Short-latency retino-colliculus pathways involved in primary visual processing tasks, e.g., motion detection and eye movements, has direct connection to the vestibular nuclei, which in turn, projects fibers to extraocular muscles through the abducens, trochlear, and oculomotor nuclei (Fernández and Goldberg 1976); from these regions, three types of voluntary eye movements including smooth pursuit (i.e., tracking a moving object), saccade (i.e., rapid gaze shift toward the object of interest) and vergence (simultaneous movement of both eyes in opposite directions to attain binocular vision) can be controlled (Ito 2012). Processing of the visual information occurs approximately within 80 ms through the retino-collicular pathway (White et al. 2017). The third major projection from the optic tract that sends neurons to the vestibular nuclei is the pretectal area, which is involved in pupillary eye reflex (PLR) and accommodation. Other projections from pretectal areas are to the thalamus, subthalamus, superior colliculus and vestibulo-cerebellum. The last major split originating from the optic tract is the suprachiasmatic nucleus, involved in the regulation of neuronal and hormonal activities, which sends fibers to the hypothalamic nuclei and pineal gland and is responsible for controlling circadian rhythms, reproduction, and human mood disorders (Srinivasan 1989). All these regions, directly or indirectly, have some connections with the vestibular nuclei. Vestibular nuclei send fibers via the efferent vestibular system toward the vestibular periphery, where motion-sensitive sensors (hair cells of semicircular canals and otolith organ) exist.

Appendix 2: SSQ results