Frederick Bonato

Simulated viewpoint jitter shakes sensory conflict accounts of vection.

Sensory conflict has been used to explain the way we perceive and control our self-motion, as well as the aetiology of motion sickness. However, recent research on simulated viewpoint jitter provides a strong challenge to one core prediction of these theories -- that increasing sensory conflict should always impair visually induced illusions of self-motion (known as vection). These studies show that jittering self-motion displays (thought to generate significant and sustained visual-vestibular conflict) actually induce superior vection to comparable non-jittering displays (thought to generate only minimal/transient sensory conflict). Here we review viewpoint jitter effects on vection, postural sway, eye-movements and motion sickness, and relate them to recent behavioural and neurophysiological findings. It is shown that jitter research provides important insights into the role that sensory interaction plays in self-motion perception.

Natural Visual-Field Features Enhance Vection

When a large optic-flow pattern is viewed, induced self-motion perception (vection) can result even for observers who are stationary relative to Earth. Vection is common in optokinetic drums, large-screen cinemas, vehicle simulators, and other virtual environments. However, not all optic-flow patterns are equally effective in producing vection. We hypothesized that visual-field characteristics that typically accompany self-motion are likely to facilitate vection. The two characteristics tested in the current study were color and global visual-field movement consistent with head bob and sway that occurs when a person walks or runs. Stationary observers viewed first-person perspective video clips on a rear-projection screen that depicted forward self-motion. Vection onset and magnitude were measured with a computer-interfaced slide device. In experiment 1, either a grayscale or color video was presented. In experiment 2, the video was shot either from a smooth rolling cart or with a hand-held camera that yielded gait information in addition to global expansion. Vection onset was found to be faster, and stronger in magnitude, when videos containing color and gait movements were viewed. These results suggest that visual-field features that are common during actual self-motion can enhance vection in a virtual environment, resulting in a more realistic experience for viewers.

Vertical display oscillation effects on forward vection and simulator sickness.

BACKGROUND The current study investigated the effects that vertical display oscillation had on the development of both vection and simulator sickness. METHODS There were 16 subjects who were exposed to optic flow displays which simulated either: 1) constant velocity forward self-motion (pure radial flow); or 2) combined constant velocity forward and vertically oscillating self-motion (radial flow with vertical oscillation at one of three frequencies: 1.8, 3.7, or 7.4 Hz). During each 10-min display exposure, subjects rated the strength of their vection and eight symptoms listed on the Subjective Symptoms of Motion Sickness (SSMS) scale at 2-min intervals. Subjects also completed the Simulator Sickness Questionnaire (SSQ) designed by Kennedy and colleagues before and after each trial, which generated a total SSQ score and three SSQ subscores (nausea, oculomotor symptoms, and disorientation). RESULTS Vertically oscillating displays (mean = 5.51; SD = 2.5) were found to produce significantly stronger vection ratings than non-oscillating displays (mean = 3.56; SD = 2.1). Vertically oscillating displays (mean = 58.18; SD = 32.2) were also found to produce significantly more severe sickness (as rated by total SSQ scores) than non-oscillating displays (mean = 29.67; SD = 24.7). Both vection and sickness symptoms increased in magnitude with prolonged exposure to optic flow. CONCLUSIONS Our findings appear to represent a special case in visual self-motion perception where high-frequency vertical oscillation both enhances vection and increases simulator sickness when it is incorporated into an optic flow display simulating constant velocity self-motion in depth.

Expanding and Contracting Optic-Flow Patterns and Vection

When stationary observers view an optic-flow pattern, visually induced self-motion perception (vection) and a form of motion sickness known as simulator sickness (SS), can result. Previous results suggest that an expanding flow pattern leads to more SS than a contracting pattern. Sensory conflict, a possible cause of SS, may be more salient when an expanding optic-flow pattern is viewed. An experiment was conducted to test if a more salient sensory conflict accompanying expanding flow patterns might inhibit vection. Participants (n = 15) viewed a pattern of blue squares, either steadily expanded or contracted, on a large rear-projection screen. Vection onset and magnitude were measured for 30 s with a computer-interfaced slide device. Vection onset was significantly faster, and vection magnitude stronger, when a contracting pattern was viewed. We propose that our extensive experience with forward self-motion may form a neural expectancy (exposure-history) about the sensory inputs which typically accompany expanding flow. However, since backward self-motion is less common, there may be a weaker exposure-history for contracting flow, and as a result these patterns generate less salient sensory conflict and subsequently less vection.

Combined pitch and roll and cybersickness in a virtual environment.

BACKGROUND Stationary subjects who perceive visually induced illusions of self-motion, or vection, in virtual reality (VR) often experience cybersickness, the symptoms of which are similar to those experienced during motion sickness. An experiment was conducted to test the effects of single and dual-axis rotation of a virtual environment on cybersickness. It was predicted that VR displays which induced illusory dual-axis (as opposed to single-axis) self-rotations in stationary subjects would generate more sensory conflict and subsequently more cybersickness. METHODS There were 19 individuals (5 men, 14 women, mean age = 19.8 yr) who viewed the interior of a virtual cube that steadily rotated (at 60 degrees x s(-1)) about either the pitch axis or both the pitch and roll axes simultaneously. Subjects completed the Simulator Sickness Questionnaire (SSQ) before a trial and after 5 min of stimulus viewing. RESULTS Post-treatment total SSQ scores and subscores for nausea, oculomotor, and disorientation were significantly higher in the dual-axis condition. CONCLUSIONS These results support the hypothesis that a vection-inducing VR stimulus that rotates about two axes generates more cybersickness compared to aVR stimulus that rotates about only one. In the single-axis condition, sensory conflict and pseudo-Coriolis effects may have led to symptoms. However, in the dual-axis condition, not only was perceived self-motion more complex (two axes compared to one), the inducing stimulus was consistent with twice as much self-motion. Hence, the increased likelihood/magnitude of sensory conflict and pseudo-Coriolis effects may have subsequently resulted in a higher degree of cybersickness in the dual-axis condition.

Vection change exacerbates simulator sickness in virtual environments

The optic flow patterns generated by virtual reality (VR) systems typically produce visually induced experiences of self-motion (vection). While this vection can enhance presence in VR, it is often accompanied by a variant of motion sickness called simulator sickness (SS). However, not all vection experiences are the same. In terms of perceived heading and/or speed, visually simulated self-motion can be either steady or changing. It was hypothesized that changing vection would lead to more SS. Participants viewed an optic flow pattern that either steadily expanded or alternately expanded and contracted. In one experiment, SS was measured pretreatment and after 5 min of viewing using the Simulator Sickness Questionnaire. In a second experiment employing the same stimuli, vection onset and magnitude were measured using a computer-interfaced slide indicator. The steadily expanding flow pattern, compared to the expanding and contracting pattern, led to: 1) significantly less SS, 2) lower subscores for nausea, oculomotor, and disorientation symptoms, 3) more overall vection magnitude, and 4) less changing vection. Collectively, these results suggest that changing vection exacerbates SS.

Perceived area and the luminosity threshold

Observers made forced-choice opaque/luminous responses to targets of varying luminance and varying size presented (1) on the wall of a laboratory, (2) as a disk within an annulus, and (3) embedded within a Mondrian array presented within a vision tunnel. Lightness matches were also made for nearby opaque surfaces. The results show that the threshold luminance value at which a target begins to appear self-luminous increases with its size, defined as perceived size, not retinal size. More generally, the larger the target, the more an increase in its luminance induces grayness/blackness into the surround and the less it induces luminosity into the target, and vice versa. Corresponding to this luminosity/grayness tradeoff, there appears to be an invariant: Across a wide variety of conditions, a target begins to appear luminous when its luminance is about 1.7 times that of a surface that would appear white in the same illumination. These results show that the luminosity threshold behaves like a surface lightness value—the maximum lightness value, in fact—and is subject to the same laws of anchoring (such as the area rule proposed by Li & Gilchrist, 1999) as surface lightness.

Space motion sickness and motion sickness: symptoms and etiology.

The adverse symptoms of space motion sickness (SMS) have remained problematic since the beginning of manned spaceflight. Despite over 50 yr of research SMS remains a problem that affects about half of all space travelers during the first 24-72 h of a spaceflight. SMS has been treated as another form of motion sickness (MS) despite distinct differences in symptomology. In this review SMS and MS differences are examined and documented based on available data. Vestibular biomechanics that occur during weightlessness coupled with theoretical assertions regarding human evolution have led us to propose a two-component model of SMS. The first component involves conflicting sensory signals inherent to the otolith organs that occur during weightlessness. The second component is a bimodal conflict between the otoliths and semicircular canals that can occur during normal head movements in weightlessness. Both components may inadvertently, and mistakenly, signal that a vestibular malfunction has occurred, hence initiating a protective mechanism that may produce symptoms that discourage activity.

Chromaticity, Spatial Complexity, and Self-Motion Perception

The effects of visual field color and spatial complexity on self-motion perception were investigated by placing observers inside a large rotating cylinder (optokinetic drum). Under optokinetic-drum conditions visually induced self-motion (vection) is typically perceived within 30 s, even though all forms of sensory input (eg vestibular, proprioceptive, auditory), except vision, indicate that the observer is stationary. It was hypothesized that vection would be hastened and vection magnitude increased by adding chromatic colors and spatial complexity to the lining of an optokinetic drum. Addition of these visual-field characteristics results in an array that shares more visual-field characteristics with our typical environment that usually serves as a stable frame of reference regarding self-motion perception. In the color experiment, participants viewed vertical stripes that were: (i) black and white, (ii) various gray shades, or (iii) chromatic. In the spatial complexity experiment, participants were presented with: (i) black-and-white vertical stripes, or (ii) a black-and-white checkerboard pattern. Drum rotation velocity was 5 rev. min−1 (30° s−1), and both vection onset and magnitude were measured for 60 s trials. Results indicate that chromaticity and spatial complexity hasten the onset of vection and increase its perceived magnitude. Chromaticity and spatial complexity are common characteristics of the environments in which our visual system evolved. The presence of these visual-field features in an optic flow pattern may be treated as an indicator that the scene being viewed is stationary and that the observer is moving.

Simulated Angular Head Oscillation Enhances Vection in Depth

Research has shown that adding simulated linear head oscillation to radial optic flow displays enhances the illusion of self-motion in depth (ie linear vection). We examined whether this oscillation advantage for vection was due to either the added motion parallax or retinal slip generated by insufficient compensatory eye movement during display oscillation. We constructed radial flow displays which simulated 1 Hz horizontal linear head oscillation (generates motion parallax) or angular head oscillation in yaw (generates no motion parallax). We found that adding simulated angular or linear head oscillation to radial flow increased the strength of linear vection in depth. Neither type of simulated head oscillation significantly reduced vection onset latencies relative to pure radial flow. Simultaneous eye-movement recordings showed that slow-phase ocular following responses (OFRs) were induced in both linear and angular viewpoint oscillation conditions. Vection strength was significantly reduced by active central fixation when viewing displays which simulated angular, but not linear, head oscillation. When these displays with angular oscillation were viewed without stable fixation, vection strength was found to increase with the velocity and regularity of the OFR. We conclude that vection improvements observed during central viewing of displays with angular viewpoint oscillation depend on the generation of eye movements.