A New Angle on Object-Background Effects in Vection

Vision Impairment Provides New Insight Into Self-Motion Perception

Purpose

Leading causes of irreversible blindness such as age-related macular degeneration (AMD) and glaucoma can, respectively, lead to central or peripheral vision loss. The ability of sufferers to process visual motion information can be impacted even during early stages of eye disease. We used head-mounted display virtual reality as a tool to better understand how vision changes caused by eye diseases directly affect the processing of visual information critical for self-motion perception.

Methods

Participants with intermediate AMD or early manifest glaucoma with near-normal visual acuities and visual fields were recruited for this study. We examined their experiences of self-motion in depth (linear vection), spatial presence, and cybersickness when viewing radially expanding patterns of optic flow simulating different speeds of self-motion in depth. Viewing was performed with the head stationary (passive condition) or while making lateral-sway head movements (active conditions).

Results

Participants with AMD (i.e., central visual field loss) were found to have greater vection strength and spatial presence, compared to participants with normal visual fields. However, participants with glaucoma (i.e., peripheral visual field loss) were found to have lower vection strength and spatial presence, compared to participants with normal visual fields. Both AMD and glaucoma groups reported reduced severity in cybersickness compared to healthy normals.

Conclusions

These findings strongly support the view that perceived self-motion is differentially influenced by peripheral versus central vision loss, and that patients with different visual field defects are oppositely biased when processing visual cues to self-motion perception.

Effects of stereopsis on vection, presence and cybersickness in head-mounted display (HMD) virtual reality

Stereopsis provides critical information for the spatial visual perception of object form and motion. We used virtual reality as a tool to understand the role of global stereopsis in the visual perception of self-motion and spatial presence using virtual environments experienced through head-mounted displays (HMDs). Participants viewed radially expanding optic flow simulating different speeds of self-motion in depth, which generated the illusion of self-motion in depth (i.e., linear vection). Displays were viewed with the head either stationary (passive radial flow) or laterally swaying to the beat of a metronome (active conditions). Multisensory conflict was imposed in active conditions by presenting displays that either: (i) compensated for head movement (active compensation condition), or (ii) presented pure radial flow with no compensation during head movement (active no compensation condition). In Experiment 1, impairing stereopsis by anisometropic suppression in healthy participants generated declines in reported vection strength, spatial presence and severity of cybersickness. In Experiment 2, vection and presence ratings were compared between participants with and without clinically-defined global stereopsis. Participants without global stereopsis generated impaired vection and presence similarly to those found in Experiment 1 by subjects with induced stereopsis impairment. We find that reducing global stereopsis can have benefits of reducing cybersickness, but has adverse effects on aspects of self-motion perception in HMD VR.

Relative Visual Oscillation Can Facilitate Visually Induced Self-Motion Perception

Adding simulated viewpoint jitter or oscillation to displays enhances visually induced illusions of self-motion (vection). The cause of this enhancement is yet to be fully understood. Here, we conducted psychophysical experiments to investigate the effects of different types of simulated oscillation on vertical vection. Observers viewed horizontally oscillating and nonoscillating optic flow fields simulating downward self-motion through an aperture. The aperture was visually simulated to be nearer to the observer and was stationary or oscillating in-phase or counter-phase to the direction of background horizontal oscillations of optic flow. Results showed that vection strength was modulated by the oscillation of the aperture relative to the background optic flow. Vertical vection strength increased as the relative oscillatory horizontal motion between the flow and the aperture increased. However, such increases in vection were only generated when the added oscillations were orthogonal to the principal direction of the optic flow pattern, and not when they occurred in the same direction. The oscillation effects observed in this investigation could not be explained by motion adaptation or different (motion parallax based) effects on depth perception. Instead, these results suggest that the oscillation advantage for vection depends on relative visual motion.