R.H.Y. So

Cybersickness in the presence of scene rotational movements along different axes

Compelling scene movements in a virtual reality (VR) system can cause symptoms of motion sickness (i.e., cybersickness). A within-subject experiment has been conducted to investigate the effects of scene oscillations along different axes on the level of cybersickness. Sixteen male participants were exposed to four 20-min VR simulation sessions. The four sessions used the same virtual environment but with scene oscillations along different axes, i.e., pitch, yaw, roll, or no oscillation (speed: 30 degrees/s, range: +/- 60 degrees). Verbal ratings of the level of nausea were taken at 5-min intervals during the sessions and sickness symptoms were also measured before and after the sessions using the Simulator Sickness Questionnaire (SSQ). In the presence of scene oscillation, both nausea ratings and SSQ scores increased at significantly higher rates than with no oscillation. While individual participants exhibited different susceptibilities to nausea associated with VR simulation containing scene oscillations along different rotational axes, the overall effects of axis among our group of 16 randomly selected participants were not significant. The main effects of, and interactions among, scene oscillation, duration, and participants are discussed in the paper.

A Metric to Quantify Virtual Scene Movement for the Study of Cybersickness: Definition, Implementation, and Verification

This paper presents a metric to quantify visual scene movement perceived inside a virtual environment (VE) and illustrates how this method could be used in future studies to determine a cybersickness dose value to predict levels of cybersickness in VEs. Sensory conflict theories predict that cybersickness produced by a VE is a kind of visually induced motion sickness. A comprehensive review indicates that there is only one subjective measure to quantify visual stimuli presented inside a VE. A metric, referred to as spatial velocity (SV), is proposed. It combines objective measures of scene complexity and scene movement velocity. The theoretical basis for the proposed SV metric and the algorithms for its implementation are presented. Data from two previous experiments on cybersickness were reanalyzed using the metric. Results showed that increasing SV by either increasing the scene complexity or scene velocity significantly increased the rated level of cybersickness. A strong correlation between SV and the level of cybersickness was found. The use of the spatial velocity metric to predict levels of cybersickness is also discussed.

EFFECTS OF NAVIGATION SPEED ON MOTION SICKNESS CAUSED BY AN IMMERSIVE VIRTUAL ENVIRONMENT

This study investigated the effects of navigation speed on the level of motion sickness during and after a 30-min head-steered virtual environment. Root-mean-squares for 8 speeds in the fore-and-aft axis were 3, 4, 6, 8, 10, 24, 30, and 59 m/s. Participants were 96 Chinese men. Both the nausea and vection ratings increased significantly with speeds increasing from 3 m/s to 10 m/s. At speeds exceeding 10 m/s, the ratings stabilized. Navigation speeds were found to significantly affect the onset times of vection and nausea but did not affect their rates of increase with duration of exposure. For the various Simulator Sickness Questionnaire scores, navigation speed had a significant influence on only the oculomotor subscore. Actual or potential applications of this research include the prediction of sickness associated with simulation tours in a virtual environment at different navigation speeds.

Compensating Lags in Head-Coupled Displays Using Head Position Prediction and Image Deflection

Images on head-coupled systems are delayed by latencies in measuring head position and generating computer graphics. The objectives of this study were 1) to investigate the effects of time delays on head tracking performance; 2) to evaluate the use of an image deflection technique to reduce deleterious effects of delayed images; and 3) to investigate the application of a head position prediction algorithm to enhance the benefits of image deflection. There were significant decreases in head tracking performance when lags of 40 ms or more were added to a system with an inherent 40 ms lag. Lag compensation by image deflection significantly improved tracking performance with lags up to 380 ms. However, by deflecting the delayed image back to its prelag angular position, part of the picture was displaced beyond the edge of the screen. The amount of deflection required was reduced by a simple means of predicting the position of the head before applying deflection. Improved means of predicting head position would further reduce the required image deflection.

Sensation of presence and cybersickness in applications of virtual reality for advanced rehabilitation.

Around three years ago, in the special issue on augmented and virtual reality in rehabilitation, the topics of simulator sickness was briefly discussed in relation to vestibular rehabilitation. Simulator sickness with virtual reality applications have also been referred to as visually induced motion sickness or cybersickness. Recently, study on cybersickness has been reported in entertainment, training, game, and medical environment in several journals. Virtual stimuli can enlarge sensation of presence, but they sometimes also evoke unpleasant sensation. In order to safely apply augmented and virtual reality for long-term rehabilitation treatment, sensation of presence and cybersickness should be appropriately controlled. This issue presents the results of five studies conducted to evaluate visually-induced effects and speculate influences of virtual rehabilitation. In particular, the influence of visual and vestibular stimuli on cardiovascular responses are reported in terms of academic contribution.

Isolating the Effects of Vection and Optokinetic Nystagmus on Optokinetic Rotation-Induced Motion Sickness

Objective: This study investigates isolated effects of vection and optokinetic nystagmus (OKN) on visually induced motion sickness (VIMS) provoked by rotating optokinetic drum patterns. Background: VIMS was the subject of recent standardization activities, but the effects of OKN have not been studied in the absence of vection. Method: Experiment 1 suppressed OKN by eye fixation and examined VIMS severity (both ordinal and ratio scale) and time spent in saturated vection at four pattern rotating velocities of 0, 2, 14, and 34 degrees per second (dps). Experiment 2 suppressed vection by adding a peripheral visual field rotating in the opposite direction to the rotating patterns. VIMS severity and OKN slow-phase velocity were studied at four rotating velocities of 0, 30, 60, and 90 dps. Results: Results from Experiment 1 indicated that VIMS severity increased as the pattern velocity increased from 0 dps to 34 dps. Results from Experiment 2 indicated that as the velocity of the rotating pattern increased, the slow-phase velocity of OKN and the severity of VIMS increased and peaked in the 60-dps condition. In both experiments, ratio-scaled nausea data significantly correlated with ordinal-scaled nausea ratings. Conclusion: VIMS can still occur in the absence of either vection or OKN. Interestingly, the profile of the summed results of the two experiments matches nicely with the profile reported by Hu et al. in which neither OKN nor vection were controlled. Application: Potential applications include modeling and reduction of VIMS in computer gaming environments.

Cybersickness: an experimental study to isolate the effects of rotational scene oscillations

Head-coupled virtual reality systems can cause symptoms of sickness (cybersickness). A study has been conducted to investigate the effects of scene oscillations on the level and types of cybersickness. Sixteen male subjects participated in the experiments. They were exposed to four 20-minute virtual simulation sessions, in a balanced order with 10 days separation. The 4 simulation sessions exposed the subjects to similar visual scene oscillation in different axis: pitch axis, yaw axis, roll axis and no oscillation (speed: 30/spl deg//s, range: +/-60/spl deg/). Verbal ratings of nausea level were taken at 5-minute intervals and sickness symptoms were measured before and after the exposure using the Simulator Sickness Questionnaire (SSQ). Significant differences were found between the no oscillation condition and the oscillating conditions. With scene oscillation, nausea ratings increased significantly after 5-minute exposure for all the oscillation axes (pitch, yaw, and roll axes). Total sickness scores were obtained from the SSQ and their profiles with different scene oscillation axes were presented.

Detection of random alterations to time-varying musical instrument spectra.

The time-varying spectra of eight musical instrument sounds were randomly altered by a time-invariant process to determine how detection of spectral alteration varies with degree of alteration, instrument, musical experience, and spectral variation. Sounds were resynthesized with centroids equalized to the original sounds, with frequencies harmonically flattened, and with average spectral error levels of 8%, 16%, 24%, 32%, and 48%. Listeners were asked to discriminate the randomly altered sounds from reference sounds resynthesized from the original data. For all eight instruments, discrimination was very good for the 32% and 48% error levels, moderate for the 16% and 24% error levels, and poor for the 8% error levels. When the error levels were 16%, 24%, and 32%, the scores of musically experienced listeners were found to be significantly better than the scores of listeners with no musical experience. Also, in this same error level range, discrimination was significantly affected by the instrument tested. For error levels of 16% and 24%, discrimination scores were significantly, but negatively correlated with measures of spectral incoherence and normalized centroid deviation on unaltered instrument spectra, suggesting that the presence of dynamic spectral variations tends to increase the difficulty of detecting spectral alterations. Correlation between discrimination and a measure of spectral irregularity was comparatively low.

Visually induced motion sickness, visual stress and photosensitive epileptic seizures: What do they have in common? - Preface to the special issue

Prolonged exposure to computer animation can cause undesirable side effects (e.g., the Pokémon incident: Takahashi and Tsukahara (1998) and motion sickness with computer games: de Waard et al., 2003). In 2005, the International Organization for Standardization (ISO) published the ISO workshop agreement 3 (IWA 3) that called for more guidelines on image safety. In particular, measures to reduce incidents of visually induced motion sickness (VIMS), visual stress (VS), and photosensitive epileptic seizures (PES) were on the top of the workshop’s agenda. Subsequent to the workshop, both the ISO and the Commission Internationale de ĺEclairage (CIE) have commissioned two technical study groups to draft guidelines concerning the quantification and prevention of VIMS, VS, and PES (ISO/TC159/SC4/SGISO and CIE TC-167: Ujike, 2007). Among the three disorderly conditions, PES is most clearly defined. A PES is an abnormal brain activity triggered by viewing certain visual stimuli. Its symptoms are clearly measurable by EEG recordings and about 1 in 4000 persons in the United Kingdom are susceptible (Harding and Harding, 2007). The type of visual stimuli that will cause PES has been the subject of many studies (see Harding’s article in this special issue) and its understanding has led to the development of an ITC guideline (ITC, 2001). Despite decades of research, VIMS (also known as cinema sickness: Griffin, 1990; cybersickness: McCauley and Sharkey, 1992; vection induced MS: Hettinger et al., 1990; and simulator sickness: Kennedy et al., 1990), the etiology of VIMS is still unknown. It is a condition in which viewers experience symptoms of nausea and eye fatigue during or after viewing visual stimuli with compelling ego-motion inappropriate to their physical body motion (Reason, 1978). Hettinger et al. (1990) reported correlations between levels of vection (illusion of self-motion) and levels of VIMS. They predicted that the VIMS is induced by sensations of vection (illusion of self-motion). Stoffregen and Smart (1998) further predicted that the illusion of self-motion causes postural instability and VIMS is a disorderly condition associated with prolonged postural instability. Stoffregen and his colleagues found that VIMS is preceded by postural instability. Similar to this line of thoughts, Bos and Bles (1998) predicted that VIMS is caused by a kind of disorientation in which ego-motion stimuli promote a subjective sense of vertical axis that is different from the vertical axis aligned with the gravitation force. Bos and Bles (1998) reported that VIMS commonly induced by watching a rotating drum could be eliminated by aligning the drum and

Effects of a target movement direction cue on head-tracking performance

A review of the literature has shown that most investigations of head-tracking performance have used symmetrically shaped targets. This paper identifies a problem in using circular targets to represent the movement of complex targets (i.e. targets giving directional cues). Two experiments investigated the effects of a target direction cue on head-tracking performance. In the first experiment, practice did not improve performance when tracking either with or without a ‘look-ahead trace’ showing all target positions 160 ms into the future. A second experiment utilized a ‘look-ahead trace’ showing target positions with eight different lead-times (0-560 ms). With lead-times of 160 ms or more, significant improvements in tracking performance and subjective difficulty ratings were obtained. Tracking responses were also significantly affected. The results suggest caution when performance data obtained with a symmetrical target are generalized to predict tracking performance with a real target giving cues to the direction of movement. The look-ahead trace offers a systematic means of bridging the gap between a symmetrical target and a real target having direction of movement cues.