Donald E. Parker

Conflicting motion cues to the visual and vestibular self-motion systems around 0.06 Hz evoke simulator sickness.

The basic question this research addressed was, how does simulator sickness vary with simulated motion frequency? Participants were 11 women and 19 men, 20 to 63 years of age. A visual self-motion frequency response curve was determined using a Chattecx posture platform with a VR4 head-mounted display (HMD) or a back-projected dome. That curve and one for vestibular self-motion specify a frequency range in which vestibular and visual motion stimuli could produce conflicting self-motion cues. Using a rotating chair and the HMD, a third experiment supported (p < .01) the hypothesis that conflicting cues at the frequency of maximum “crossover” between the curves (about 0.06 Hz) would be more likely to evoke simulator sickness than would conflicting cues at a higher frequency. Actual or potential applications of this work include a preliminary design guidance curve that indicates the frequency range of simulated motion that is likely to evoke simulator or virtual reality sickness; for simulators intended to operate in this frequency range, appropriate simulator sickness interventions should be considered during the design process.

Spatial orientation: Visual-vestibular-somatic interaction

We are able to orient lines with respect to environmentally or egocentrically defined reference axes. To do this we must be able to compensate for disturbances produced by displacement of our eyes relative to other parts of our bodies and for visual disturbances such as tilted frames or moving visual fields. Compensation signals from somatosensory and vestibular receptors were examined in this investigation. Disturbances were produced by tilting the head and by rotating a large visual display. Compensation signals associated with gravity were manipulated by placing the observers horizontally on a board or seating them verticatly. Experiment 1 examined effects of visual disturbance on the ability of supine observers to set a line to the longitudinal body axis while the head was tilted toward one shoulder or while the head was straight. Effects of the visual disturbance were greater when the head was tilted than when it was straight. This indicates that the effects of visual disturbance were greater for a task that required compensation. Experiment 2 compared the performance of supine and erect observers. No differences between the performance of observers on a task requiring the use of compensation signals were obtained under these two conditions. This suggests that enrichment of compensatory signals did not reduce the effects of visual disturbance. Experiment 2 did replicate the result from Experiment 1 that the effects of visual disturbance were greater when observers performed a task that required them to use compensation signals. Finally, Templeton’s (l973) previous report that supine observers undercompensate for head tilt was replicated.

Preflight Adaptation Training for Spatial Orientation and Space Motion Sickness

Two part‐task preflight adaptation trainers (PATs) are being developed at the NASA Johnson Space Center to preadapt astronauts to novel sensory stimulus conditions similar to those present in microgravity to facilitate adaptation to microgravity and readaptation to Earth. This activity is a major component of a general effort to develop countermeasures aimed at minimizing sensory and sensorimotor disturbances and Space Motion Sickness (SMS) associated with adaptation to microgravity and readaptation to Earth. Design principles for the development of the two trainers are discussed, along with a detailed description of both devices. In addition, a summary of four ground‐based investigations using one of the trainers to determine the extent to which various novel sensory stimulus conditions produce changes in compensatory eye movement responses, postural equilibrium, motion sickness symptoms, and electrogastric responses are presented. Finally, a brief description of the general concept of dual‐adapted states that underly the development of the PATs, and ongoing and future operational and basic research activities is presented.

Inertial acceleration as a measure of linear vection: An alternative to magnitude estimation

The present study focused on the development of a procedure to assess perceived self-motion induced by visual surround motion—vection. Using an apparatus that permitted independent control of visual and inertial stimuli, prone observers were translated along their headx-axis (fore/aft). The observers’ task was to report the direction of self-motion during passive forward and backward translations of their bodies coupled with exposure to various visual surround conditions. The proportion of “forward” responses was used to calculate each observer’s point of subjective equality (PSE) for each surround condition. The results showed that the moving visual stimulus produced a significant shift in the PSE when data from the moving surround condition were compared with the stationary surround and no-vision condition. Further, the results indicated that vection increased monotonically with surround velocities between 4 and 40°/sec. It was concluded that linear vection can be measured in terms of changes in the amplitude of whole-body inertial acceleration required to elicit equivalent numbers of “forward” and “backward” self-motion reports.

An “independent visual background” reduced balance disturbance envoked by visual scene motion: implication for alleviating simulator sickness

Simulator sickness (SS) / virtual environment (VE) sickness is expected to become increasingly troublesome as VE technology evolves [20]. Procedures to alleviate SS / VE sickness have been of limited value [12]. This paper investigated a possible procedure to reduce SS and VE sickness. Postural disturbance was evoked by visual scene motion at different frequencies. Differences in disturbance were examined as a function of simultaneous exposure to an “independent visual background” (IVB). Eight subjects were tested at two scene motion frequencies and three different IVB conditions using a within-subjects design. An expected statistically significant interaction between IVB condition and frequency was observed. For low frequency scene movements, subjects exhibited less balance disturbance when the IVB was presented. We suggest that an IVB may alleviate disturbance when conflicting visual and inertial cues are likely to result in simulator or VE sickness.

Foreground/Background Manipulations Affect Presence:

A possible relation between vection and presence is discussed. Two experiments examined the hypothesis that “presence” is enhanced by manipulations which facilitate interpreting visual scenes as “background.” A total of 39 participants in two experiments engaged in a pursuit game while in a virtual visual environment generated by an HMD and rated their experience of “presence” on 5 questions. Experiment 1 compared two viewing conditions: visual scene masking at the eye and a paper mask mounted on the screen with the same 60° FOV, and showed that presence was enhanced by eye masking relative to screen masking. Experiment 2 replicated these findings with a double-blind experimental design.

Effects of characteristics of image quality in an immersive environment

Image quality issues such as field of view (FOV) and resolution are important for evaluating presence and simulator sickness (SS) in virtual environments (VEs). This research examined effects on postural stability of varying FOV, image resolution, and scene content in an immersive visual display. Two different scenes (a photograph of a fountain and a simple radial pattern) at two different resolutions were tested using six FOVs (30, 60, 90, 120, 150, and 180 deg.). Both postural stability, recorded by force plates, and subjective difficulty ratings varied as a function of FOV, scene content, and image resolution. Subjects exhibited more balance disturbance and reported more difficulty in maintaining posture in the wide-FOV, highresolution, and natural scene conditions.

An independent visual background reduced simulator sickness in a driving simulator

Simulator sickness (SS)-virtual environment (VE) sickness is expected to become increasingly troublesome as VE technology evolves. This paper investigated using an independent visual background (IVB) to reduce SS and VE sickness. The IVB is a visual scene component that provides visual motion and orientation cues that match those from the vestibular receptors. In this study, the IVB was stationary, fixed with respect to inertial space. Two experiments were conducted. The first experiment examined the differences in visual motion-induced postural disturbance as a function of simultaneous exposure to an IVB. Subjects exhibited less balance disturbance when the IVB was presented. An expected statistically significant interaction between IVB presence-absence and visual scene motion oscillation frequency was observed. In the second experiment, subjects reported less SS when the IVB was presented during the VE exposure. We suggest that an IVB may alleviate disturbance when conflicting visual and inertial cues evoke SS.

Human vestibular function and weightlessness.

This article presents the concept of a spatial orientation/motion perceptual system, the contributions of the vestibular receptors to this system, and apparatus and training procedures and observations to allow astronauts to preadapt to weightlessness. The author also discusses perceptual reactions to prolonged weightlessness.

Visual field displacements in human beings evoked by acoustical transients

Sixty-two of 133 subjects reported visual-field displacements when they were exposed to intense (125 dB SPL) repetitive audiofrequency transients. This phenomenon was investigated in three experiments. Frequency (100-5000 Hz) was varied in experiment I; repetition rate (0.5/s--6.0/s) was varied in experiment II; acoustical transient onset/offset time (0.2--25 ms) was examined in experiment III. The results of these three experiments indicated that the largest proportion of displacement reports and the largest perceived motion magnitudes followed stimulation in the 500- to 1000-Hz frequency range at repetition rates of about 1/s. Response differences as a function of onset/offset time were erratic. The pattern of results obtained in this study, in conjunction with the results of previous investigations of acoustical vestibular stimulation, suggests that the visual-field displacments resulted from stimulation of the receptors of the vestibular system. These experiments may account for discrepancies in reports of infrasound-evoked eye movements. Finally, it is suggested that intense sound exposure may damage the vestibular receptors with or without concomitant damage to the auditory portion of the membranous labyrinth.