Behrang Keshavarz* Stereoscopic Viewing Enhances Heiko Hecht Department of General Visually Induced Motion Sickness Experimental Psychology but Sound Does Not Johannes Gutenberg-University 55099 Mainz, Germany

Abstract

Optic flow in visual displays or virtual environments often induces motion sickness (MS). We conducted two studies to analyze the effects of , background sound, and realism (video vs. simulation) on the severity of MS and related feelings of immersion and vection. In Experiment 1, 79 participants watched either a 15-min-long video clip taken during a real roller coaster ride, or a precise simulation of the same ride. Additionally, half of the participants watched the movie in 2D, and the other half in 3D. MS was measured using the Simulator Sickness Questionnaire (SSQ) and the Fast Motion Sickness Scale (FMS). Results showed a significant interaction for both variables, indicating highest sickness scores for the real roller coaster video presented in 3D, while all other videos provoked less MS and did not differ among one another. In Experiment 2, 69 subjects were exposed to a video captured during a bicycle ride. Viewing mode (3D vs. 2D) and sound (on vs. off) were varied between subjects. Response measures were the same as in Experiment 1. Results showed a significant effect of stereopsis; MS was more severe for 3D presentation. Sound did not have a significant effect. Taken together, stereoscopic viewing played a crucial role in MS in both experiments. Our findings imply that stereoscopic videos can amplify visual dis- comfort and should be handled with care.

1 Introduction

Over the past decades, the technological progress in entertainment sys- tems has grown rapidly. Looking at console video games, for example, the graphical design of virtual environments (VE) has changed dramatically toward more realism. High-resolution monitors, high-definition projectors, and powerful computer systems offer the possibility to enjoy the impressive sensa- tion of virtual worlds. Not only does the entertainment industry benefit from such developments, but modern simulators and virtual systems are of para- mount importance in rehabilitation and training. Flight and driving simulations for trainees are an efficient, time-saving, as well as cost and risk minimizing tool, and are widely accepted in different fields in research and education. Despite this imposing progress in technology, visually induced motion sickness (AKA, simulator sickness or cybersickness; Cobb, Nichols, Ramsey, & Wilson, 1999; McCauley & Sharkey, 1992) is still a major problem in such virtual systems.

Presence, Vol. 21, No. 2, Spring 2012, 213–228 ª 2012 by the Massachusetts Institute of Technology *Correspondence to [email protected].

Keshavarz and Hecht 213

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Visually induced motion sickness (MS) is a phenom- observer’s feeling of being there in a virtual environment enon similar to other forms of MS, with the exception (for an overview see Sadowski and Stanney, 2002). that visually induced MS does not require physical There are several theories on the construct of immersion motion (Hettinger & Riccio, 1992; McCauley & and its subcomponents (Witmer & Singer, 1998; Sharkey, 1992). Typical symptoms are nausea, dizziness, Heeter, 1992). Immersion itself is influenced by several pallor, cold sweat, or oculomotor problems. Sensory factors, such as pictorial realism or inter-individual inter- conflict theory (Reason, 1978; Reason & Brand, 1975; nal factors. Although the role of vection has been dis- Oman, 1990) may be the best explanation for visually cussed frequently in the current literature, not much induced MS, which proposes that there is a conflict has been paid to the relationship between among the visual, the vestibular, and/or the propriocep- immersion and visually induced MS. If vection is tive systems. The visual system senses self-motion (e.g., involved in feeling sick, and vection is needed to enhance vection; Dichgans & Brandt, 1973), whereas the vestib- the level of immersion, then immersion and MS should ular organs do not signal corresponding accelerations. correlate positively (Lawson, Graeber, Mead, & Muth, From an evolutionary point of view, the sensory conflict 2002). However, there are only very few studies that and the resulting MS-typical symptoms are to tried to analyze the relationship between immersion and simulate the effect of a contamination of the gastrointes- visually induced MS. Surprisingly, both studies that did, tinal tract with toxins. As a natural reaction, the orga- found negative correlations between immersion and MS nism tries to withdraw the toxins by retching and even (Nichols, Haldane, & Wilson, 2000; Witmer & Singer). vomiting as ultimate reaction (a poison theory by Treis- The aim of our study was to examine three aspects of man, 1977). visually induced MS: (1) the role of stereoscopic viewing Several factors influence the degree of visually induced on visually induced MS, (2) the comparison between MS. Most importantly, vection has been linked to visu- reality-captured video footage and computer simula- ally induced MS (Hettinger, Berbaum, Kennedy, tions, and (3) the role of background sound on MS. All Dunlap, & Nolan, 1990; McCauley & Sharkey, 1992); three aspects are briefly described in the following. and may be a precondition for visually induced MS (Crampton & Young, 1953; Smart, Stoffregen, & Bardy, 2002), as most users of virtual simulators who 1.1 Stereoscopic Viewing. We wanted to mea- report sickness also experience vection (Hettinger et al.). sure the effect of stereoscopic viewing on visually Vection itself is determined by a number of other induced MS, if present at all. Although 3D movies have factors, such as the participant’s field of view (Brandt, existed for a long time, they are only now becoming Dichgans, & Koenig, 1973; IJsselsteijn, de Ridder, readily available. With the introduction of digital projec- Freeman, Avons, & Bouwhuis, 2001) or even the tion systems and shutter glasses or polarized filter lenses, color of the visual stimulus (Bonato & Bubka, 2006; stereoscopic entertainment is becoming mainstream. In Seno, Sunaga, & Ito, 2010). Apart from the role of the 2009, when James Cameron’s Avatar was released in field of view, only a few studies have investigated the cinemas, a certain 3D-movie euphoria was initiated. Its relationship between stereopsis and vection and found effects with regard to MS are, however, largely heterogeneous results. While IJsselstein et al. reported unknown, barring some anecdotal reports of MS-like no effect of stereopsis on the degree of vection, Palmisa- symptoms when watching 3D movies either in cinemas no’s data (1996) indicated shorter latencies of vection or at home. when the stimuli (random-dot clouds) were presented There is some indication in the current literature that stereoscopically. stereoscopic viewing enhances feelings of immersion A further phenomenon closely linked to vection is the (Banos, Botella, Rubio, Quero, Garcia-Palacios, & feeling of immersion or presence (see Hettinger, 2002, Alcan˜iz, 2008; IJsselsteijn et al., 2001; IJsselsteijn, for an overview). In short, immersion describes the de Ridder, Hamberg, Bouwhuis, and Freeman, 1998).

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However, to our knowledge, there is a lack of data deal- 1.3 Sound. Music has been used as a counter- ing with the influence of stereopsis on visually induced measure to decrease MS in a few studies, with mixed suc- MS, even though potential hazards of stereoscopic view- cess (Yen Pik Sang, Billar, Golding, & Gresty, 2003; ing have been discussed recently (see Howarth, 2011). Dozza et al., 2005), but the role of realistic background IJsselsteijn et al. (2001) collected data on MS while pre- sound has only been vaguely discussed before (Nichols, senting video footage on a large screen to their partici- et al., 2000). To fill this gap, we took a closer look at the pants for a short interval. The stimuli were shown either role of realistic background sound on visually induced in 3D or 2D, and the results showed no difference MS, as well as on immersion and vection. between the groups. The stimulus—a 100-s long video Additionally, we wanted to take a closer look at possi- taken out of a driving car—most likely was too short and ble after-effects on visually induced MS. It is well known too weak to provoke any kind of visually induced MS. that MS can last up to several hours or even days after Furthermore, the authors chose a within-subjects design, the experiment is terminated (Muth, 2010; Stanney, which might have produced some habituation, a well- Hale, Nahmens, & Kennedy, 2003; Stanney & Salvendy, known phenomenon in MS (Hill & Howarth, 2000). 1998). However, we gathered data up to 5 hr after the MS was not the focus of that study, but merely a by- experiment to see if stereopsis prolongs the recovery pro- product which the authors did not even discuss. cess. We conducted two separate experiments to answer 1.2 Real-World Footage versus Computer these questions. In Experiment 1, a 2 [video type (real, Simulation.1 Computer simulations are widely used simulation)] 2 [viewing mode (bi-ocular 2D, stereo- in training, rehabilitation, entertainment, and psycho- scopic 3D)] between-subjects design was chosen. We cap- logical studies, but have not yet been tested for ecologi- tured a video sequence of a real roller coaster ride using cal validity with respect to the genesis of MS. Are simula- stereo cameras. We additionally used a computer-simula- tions as realistic as real videos, and can they be used as tion of the same ride to compare the difference between one-on-one substitutes when it comes to their ability to real and simulated stimuli. Both videos were either pre- create MS symptoms? To our knowledge, reality- sented stereoscopically or in bi-ocular mode. In Experi- captured videos have never been compared to computer- ment 2, we again decided to run a between-subjects generated stimuli to validate research on visually induced design, this time including the two factors viewing mode MS (VIMS). This might be due to the fact that reality- (bi-ocular 2D, stereoscopic 3D) and sound (no sound, captured stimuli cannot (or can only partially) be con- background sound). A 15-min-long bicycle ride (including trolled and systematically varied by the experimenter. environmental sounds) through the city of Mainz, Ger- Since the main purpose of our study was to assess the many, was recorded and the sound was switched on or off influence of stereopsis on visually induced MS, we had between the groups during stimulus presentations. no need for stimulus variations that would preclude the We hypothesized that stereopsis should increase the use of video footage. Thus, we deliberately used reality- severity of visually induced MS in general. Regarding the captured video material such that we could use 3D and other two variables—the video type and the background 2D versions of this more realistic video footage. Addi- sound—we did not have a well-founded hypothesis, as tionally, we wanted to make a first comparison between neither the theoretical background nor existing studies reality-captured stimuli and computer simulations. suggest a particular result. However, one might hypothesize that real footage is a more powerful stimulus than the computer simulation, owing to greater detail 1. Note that we deliberately prefer the term simulation to animation in our case. We do so because the computer-generated movie was a and more realistic dynamics. Sound should increase the physically and mathematically correct replication of the real-world realism of the video and thereby potentially increase the roller coaster—within the limits of simulation. In contrast, the term animation designates motion sequences that may ignore or even defy conflict with the vestibular information, but the question the laws of physics. whether this changes MS is rather exploratory.

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Table 1. Number of Participants Per Group, Mean Age, and Standard Deviation by Gender for Experiment 1

Male Female Total

NMage (SD) NMage (SD) NMage (SD)

Real, 2D 5 22.40 (0.89) 15 22.40 (2.13) 20 22.40 (1.88) Real, 3D 4 18.75 (9.00) 15 25.07 (5.59) 19 25.85 (6.34) Sim, 2D 5 22.75 (2.22) 15 25.93 (8.59) 20 25.26 (7.74) Sim, 3D 5 25.60 (4.04) 14 23.46 (2.67) 19 24.06 (3.13) Total 19 24.78 (5.07) 59 24.24 (5.51) 78 24.37 (5.38) NOTE: Real ¼ real video footage; Sim ¼ computer-simulated video.

2 Experiment 1 HC23E) were mounted on top of a head-fixed helmet so as to mimic the positions of the left and the right 2.1 Methods human eyes. The cameras were synchronized by a cus- 2.1.1 Participants. Seventy-nine mostly under- tom-made device. The distance between the camera graduate psychology students participated in the study. lenses was at 60 mm, and a resolution of 800 600 Prior to the experiment, all subjects gave written consent pixels was chosen for each camera. One round on the G- to their participation and asserted that they were in a Force lasted for 1 min 48 s and was repeated eight times normal state of health. Before stimulus presentation without a break (total length of 14 min 24 s). Next, an began, participants filled in the Simulator Sickness Ques- existing simulation of the G-Force course was adapted tionnaire (SSQ; Kennedy, Lane, Berbaum, & Lilienthal, for our purposes. It was available at the Software Achter- 1993) to make sure that the baselines did not differ bahn Simulator 2009 (Astragon Software GmbH) and between the groups. Due to abnormally high SSQ-rat- represented a very precise replication of the real G-Force ings prior to the experiment (SSQ; nausea score above roller coaster ride. One simulated round was captured 60), one subject had to be eliminated from data analysis. twice by two virtual camera positions separated by 60 Table 1 shows the final distribution of subjects’ gender mm. Thus, we were able to produce identical video and age separated by group. Participants were naı¨ve with sequences for the left and the right eye, which only dif- respect to the purposes of the study and received either fered due to the virtual position of the camera. Again, partial course credit or were rewarded with 5 €. The the resolution was restricted to 800 600 pixels. The stimuli were administered in accordance with the Decla- only discernable difference in timing between the real ration of Helsinki, which represents a set of principles to ride and the simulation was a prolonged finish in the real ensure research ethics in human experimentation. Partic- video (when the roller coaster returned to the starting ipants were free to abort the experiment at any time position after the main ride); the simulated round was without negative consequences. Five subjects chose to somewhat shorter and lasted for 1 min 25 s. Thus, the abort before stimulus offset due to severe sickness. simulation was repeated 10 times to reach a total of 14 min 4 s. Figure 1 depicts two pairs of matching screen 2.1.2 Apparatus and Stimuli. To fit the pur- shots from the real and the simulated G-Force ride. pose of the study, a real and a simulated video sequence Participants were positioned in a height-adjustable of the same roller coaster line were generated. The real chair 200 cm in front of a large projection screen (300 video was captured at Holiday Park (Haßloch, Germany) 196 cm) with a resulting field of view of 608 horizontally during a ride on the G-Force roller coaster in the very and 438 vertically. To restrict head movements, partici- first row of seats. Two digital movie cameras (Sony DCR pants rested their heads in a chin rest, which was posi-

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2011b). The FMS is an easy-to-administer verbal rating scale ranging from 0 (no sickness at all) to 20 (frank sick- ness). The time course of MS can be captured by asking participants to rate their severity of MS once every mi- nute. Additionally, the SSQ (Kennedy et al., 1993) was used to get a detailed insight in the symptom cluster of MS. The SSQ is a standardized tool to capture simulator sickness and consists of 16 items on separate 4-point rat- ing scales. Scores for three subscales, including nausea (N), oculomotor (O), and disorientation (D), as well as a total-score (TS) can be calculated. Note that the SSQ sub- scores as well as the SSQ total-score showed high correla- tions with the peak FMS-score in a previous validation study (Keshavarz & Hecht, 2011b). The SSQ had to be filled in three times during Experiment 1. The first SSQ Figure 1. Corresponding screen shots from videos of the real G-Force (SSQ ) was given to the participants prior to stimulus pre- roller coaster (upper panels) and the matching computer-simulation I (lower panels). The screenshots show a still frame of the video captured sentation and served as a baseline measurement. In this with the left camera (representing the left human eye). way, we could ensure that participants felt well at the be- ginning of the study. The second SSQ (SSQII) had to be filled in immediately after stimulus offset and captured the tioned 145 cm above the floor such that the observer’s severity of visually induced MS with respect to the pre-

eye-height corresponded to the middle of the projection sented videos. The purpose of the third SSQ (SSQIII)was screen (160 cm above the floor). Participants were free to to deliver insights into possible aftereffects of the experi-

adjust the height of the chair to find the most comfortable ment. Thus, participants took the SSQIII home and were posture compatible with the fixed position of the chin asked to fill it in 5 hr after leaving the laboratory. Immer- rest. No complaints regarding the comfort of the seat and sion and vection were measured after stimulus presenta- chin rest were reported. Stimuli were presented using a tion via a short self-created questionnaire. Participants desktop computer (Dell Precision 390 with NVIDIA had to rate their level of vection on a 4-point scale (‘‘How Quattro FX 5500 graphics), a stereoscopic projector (pro- often did you have the feeling of self-movement?’’ 0 ¼ jectiondesign F10 AS3D), and LCD shutter glasses never, 1 ¼ sometimes, 2 ¼ often, 3 ¼ always). To ensure (XPAND X102). The real video was captured with a that participants were able to make correct judgments of frame rate of 25 fps, while the frame rate for the computer vection, they were informed prior to the experiment simulation was somewhat lower (15 fps). This was due to about the phenomenon of illusory self-motion. Immer- limitations of the roller coaster software, which was not sion was measured using self-ratings of immersion (‘‘Did capable of producing videos of higher rates. Despite the you feel like being in the scene?’’). Additionally, the level comparatively slow frame rate, we opted not to add of video realism was captured (‘‘How realistic was the motion blur. Both videos came across as very sharp and video-clip?’’). Participants answered both questions using smooth. To create the bi-ocular mode, the video taken a 4-point Likert scale (0 ¼ not at all, 1 ¼ little, 2 ¼ nota- with the left camera (both for the real video and the simu- bly, 3 ¼ very much). lation) was presented on both eyes. 2.1.4 Procedure. Participants were randomly 2.1.3 Response Measures. Visually induced assigned to one of the four groups. Prior to the experi- MS was measured during stimulus presentation using the ment, the subjects were informed about possible nega- Fast Motion Sickness Scale (FMS; Keshavarz & Hecht, tive side effects such as sickness or vertigo. In addition,

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Figure 2. SSQ scores separated by viewing mode and video type. The left part illustrates the SSQ score prior to stimulus exposure (SSQ-I); the middle part illustrates the SSQ scores after stimulus offset (SSQ-II); and the right part depicts the results of the SSQ during the postexperimental period (SSQ-III). SSQ-N ¼ SSQ-Nausea, SSQ-O ¼ SSQ-Oculomotor, SSQ-D ¼ SSQ-Disorientation, SSQ-TS ¼ SSQ-Total score, real ¼ real video, sim ¼ simulated video. Error bars represent SEM.

they were encouraged to abort the experiment at any the fifth hour, looking back on the very first hour after time should they feel uncomfortable, in particular, when the experiment. Before participants left the laboratory, MS symptoms became too severe. Before stimulus pre- they were informed about possible aftereffects of MS

sentation began, participants first filled in the SSQI and gave their written consent not to drive any vehicle and were afterward tested for vestibular dysfunctions until all MS symptoms had disappeared. (Romberg Test) and stereo acuity (Titmus Test). All For data analysis, SPSS (Statistical Package for Social subjects passed both tests successfully. Then, participants Sciences, Version 15) was used. The a priori significance were guided to the experimental chair and put on the was set to a ¼ 0.05 for all statistical procedures. stereoscopic LCD glasses. Note that the observers in all four groups had to undergo the same procedure and had 2.2 Results to wear the stereoscopic glasses, regardless of whether 2.2.1 MS Measurements. A one-way ANOVA the video was shown in 3D or 2D. Shortly before the including the factor group (3D real, 3D simulation, 2D video was started, participants were asked to report the real, 2D simulation) was conducted to analyze group first FMS score. This score served as a baseline measure differences prior to stimulus presentation. The results and ensured that the subjects understood the procedure showed that the groups did not vary significantly in the of the FMS. 2 SSQI subscores nausea (SSQI-N), F(3, 74) ¼ 2.325, Immediately after the stimulus presentation was fin- 3 p ¼ .082, oculomotor (SSQI-O), F(3, 74) ¼ 1.509, ished, participants filled in the SSQII followed by the p ¼ .267, disorientation (SSQI-D), F(3, 74) ¼ 2.708, questions regarding immersion and vection. Finally, par- p ¼ .059, and also not in the total score (SSQI-TS), F(3, ticipants were given an additional questionnaire to take 74) ¼ 2.633, p ¼ .056. Figure 2 illustrates all SSQ home, in which they were asked to note an FMS-score scores. every 60 min up to 5 hr after the experiment. The SSQ III A 2 [video type (real, simulation)] 2 [viewing mode was attached to that questionnaire and had to be filled in (bi-ocular 2D, stereoscopic 3D)] MANOVA including at the end of the postexperimental period retrospec- the SSQII-N, SSQII-O, SSQII-D, and SSQII-TS scores tively, referring to the moment they felt worst during

the 5-hr postexperimental period. That is, if MS was 2. Robust test of means, Brown-Forsythe corrected. strongest after 1 hr, participants filled in the SSQIII after 3. Robust test of means, Brown-Forsythe corrected.

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Figure 3. Time course of the FMS scores including viewing mode (3D Figure 4. Mean ratings for feelings of immersion (Did you feel like vs. 2D) and video type (real vs. simulation) during stimulus presentation. being in the scene?), realism (How realistic was the video-clip?), and vec- Error bars represent SEM. tion (How often did you have the feeling of self-movement?) measured after stimulus offset via questionnaire for Experiment 1. Ratings were scored on a 4-point scale (0 ¼ not at all, 3 ¼ very much). Due to incom- was calculated. The mean SSQII scores are presented in plete questionnaires, 13 realism judgments were missing. Real ¼ real Figure 2. Additionally, the peak FMS score reported video; Sim ¼ computer-simulated video. Error bars represent SEM. during stimulus presentation was also included in the MANOVA. Note that the baseline FMS scores that var- 2 ied from zero were subtracted from the peak FMS score. .001, gp ¼ .423, indicating increased visually induced This was the case for 14 participants (baseline scores MS with prolonged stimulus presentation. The Time ranging from 1–3) and was done to ensure that changes Viewing Mode interaction, F(15, 1050) ¼ 2.984, p ¼ 2 in MS could be traced back solely to the stimuli. The .035, gp ¼ .041, as well as the Time Video Type inter- 2 mean peak FMS scores were M ¼ 9.90 (SD ¼ 5.78) for action, F(15, 1050) ¼ 3.928, p ¼ .011, gp ¼ .053, the real 3D group, M ¼ 5.15 (SD ¼ 3.23) for the real turned out to be significant. Figure 3 depicts the time 2D group, course of the FMS scores for the interactions. M ¼ 5.42 (SD ¼ 4.25) for the simulation 3D group, and M ¼ 4.30 (SD ¼ 4.14) for the simulation 2D group. 2.2.2 Vection, Immersion, and Realism. The The analysis revealed a significant interaction for video distribution of immersion and realism, as well as the vection 2 type and viewing mode, F(5, 71) ¼ 2.345, p ¼ .05, gp ¼ judgments, are shown in Figure 4. A Kruskal-Wallis test for .142, indicating increased visually induced MS for 3D nonparametric measures was performed. Results indicated a presentation in the real-video group, but not in the sim- significant difference in the realism judgment, H(3) ¼ ulation-video group. No main effects of viewing mode 15.670, p ¼ .001. Single Mann-Whitney comparisons for or video type were found. each group were run to qualify the results. They revealed To analyze the time course of the FMS scores during significantly less realism in the simulated 2D group. All stimulus presentation, a repeated-measures ANOVA other groups did not differ significantly. There were no including the factor time and the between-subjects varia- effects of group for vection, H(3) ¼ 5.271, p ¼ .153, or bles video type and viewing mode was calculated. As five immersion, H(3) ¼ 3.503, p ¼ .320. participants aborted the experiment prior to stimulus offset (four in the real 3D group, one in the real 2D 2.2.3 MS Aftereffects. Twelve participants did group), they had to be excluded from the ANOVA. The not return the questionnaire and had to be excluded results were Huynh-Feldt corrected (e ¼ .190) and from data analysis (two in the real 3D group, two in the showed an effect of time, F(15, 1050) ¼ 51.382, p < real 2D group, five in the simulated 3D group, and 3 in

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ing a real roller coaster ride and compared it to its simu- lated complement. All four videos produced MS to a nota- ble extent, given the rather short stimulus presentation.

Both the mean peak FMS score and the SSQII subscores gathered during the stimulus presentation revealed an interaction between stereoscopic viewing and video type for all collected MS measurements. As predicted, MS was strongest when the real roller coaster ride was presented in 3D. However, stereopsis and simulation did not produce independent main effects. Only in combination did 3D and real footage increase MS. The other three videos all had similar effects on MS and did not vary from each other Figure 5. Time course for the FMS scores during the postexperimental significantly. Several factors might explain this result, period separated by group. Error bars represent SEM. including the level of video detail or differential effects of vection and immersion. We will discuss some of these fac- the simulated 2D group). A repeated-measures ANOVA tors in the general discussion section. including the within-subjects factor time and the Additionally, our results showed that computer- between-subjects variables video and viewing mode was simulated stimuli and reality-captured 2D video clips calculated for the FMS scores captured every 60 min. produce similar magnitudes of MS. This implies that Results revealed a significant effect of time, F(4, 252) ¼ simulations may generally be quite useful substitutes for 13.455, p < .001, g2 ¼ .176, which showed decreasing reality, but they have clear limitations. This is supported MS over the duration of the postexperimental period. by a study conducted by Webb and Griffin (2002). The Additionally, an effect of viewing mode surfaced as well, authors compared a real optokinetic drum with a virtu- F(1, 63) ¼ 4.239, p ¼ .044, g2 ¼ .063, indicating ally designed drum. Optokinetic drums are typically slightly stronger MS aftereffects in the 3D condition. painted with a pattern of alternating color stripes, which Other main effects or interactions were not significant. surround the stationary observer. As the drum starts to Figure 5 shows the time course for the postexperimental turn, the observers get the feeling of self-motion in the period separated by the experimental groups. opposite direction of the drum’s movement. This

The mean scores for the SSQIII are presented in method is known to be very nauseating and is frequently Figure 2. A 2 [Video Type (real, simulation)] used to study vection. As the authors could show, there 2 [viewing mode (bi-ocular 2D, stereoscopic 3D)] was no difference between the real and the virtual rotat- MANOVA including the peak FMS-score (during the ing drum regarding the severity of sickness.

postexperimental period) and the SSQIII-scores was run. Note that we are aware of the fact that our stimuli Again, the Video Type Viewing Mode interaction were not only highly provocative in a virtual environ- turned out to be significant, F(5, 58) ¼ 2.395, p ¼ .048, ment, but might already be so in the real world. Motion 2 gp ¼ .171, revealing stronger visually induced MS for sickness during real roller coaster rides is not out of the 3D presentation only in the real-video group. The simu- ordinary. We do not know whether our stimuli would lated video condition was not affected by stereopsis. have been nauseating in the real world, as we did not gather MS data on the physical roller coaster. A compari- son between a real roller coaster ride and its virtual coun- 2.3 Discussion terpart is very desirable for future studies, and to our The aim of Experiment 1 was to explore the effect of knowledge, there is no experiment so far that has investi- stereoscopic viewing in the genesis of visually induced MS. gated these differences between real and virtual stimuli Additionally, we compared a video sequence captured dur- with respect to MS. The physical stimulus of Experiment

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Table 2. Subjects’ Distribution to the Four Groups of Experiment 2

Male Female Total

NMage (SD) NMage (SD) NMage (SD)

3D w sound 10 23.00 (3.65) 9 21.22 (2.11) 19 22.16 (3.08) 3D w/o sound 8 25.00 (3.89) 10 21.20 (1.23) 18 22.89 (3.29) 2D w sound 9 23.78 (3.87) 7 22.57 (2.64) 16 23.25 (3.34) 2D w/o sound 8 21.38 (3.58) 8 26.25 (8.56) 16 23.81 (6.82) Total 35 23.29 (3.80) 34 22.68 (4.76) 69 22.99 (4.28)

2, where we mounted two cameras on the handlebars of All subjects gave written consent to participation and a bicycle, is less likely to cause MS. However, the video asserted that they were in a normal state of health. Partici- footage may have included somewhat more abrupt angu- pants were naı¨ve with respect to the purposes of the study lar accelerations than would be expected from a head- and were informed that they could abort the experiment mounted camera. at any time they wanted to. Indeed, five subjects termi- In sum, stereoscopic viewing is not more nauseating nated before stimulus offset, due to severe sickness (two per se than the bi-ocular presentation of the same stim- in the 3D without sound group, one in the 2D with uli. Instead, the combination of 3D and realistic video sound group, two in the 2D without sound group). footage seems to be highly provocative, and thus, stereo- psis seems to play a subordinate role in less detailed com- 3.1.2 Apparatus, Stimuli, Response Measures, puter simulations. Based on this consideration, we con- and Procedure. The laboratory equipment and the ducted a second experiment in which we further procedure (including Romberg test and Titmus test) enhanced the level of realism by adding realistic back- were the same as in Experiment 1. Stimuli were gener- ground sound to the video. This would enable us to rule ated using two Sony Handycam DCR-HC17E cameras, out that uncontrolled sound effects only present in the which were mounted on the handlebars of an ordinary video influenced the severity of visually induced MS. bicycle. As before, the distance between the two camera lenses was set to an average inter-pupillary distance of 3 Experiment 2 60 mm. The respective videos were presented with a re- solution of 600 480 pixels (frame rate of 25 fps) and Experiment 2 was conducted to analyze the role of lasted for 14 min 21 s. The recorded stereo sound background sound on visually induced MS, as well as its (approximately 90 dB) was presented via two speakers relationship to vection, immersion, and realism. We cap- which were positioned at the right and left side of the tured a real bicycle ride using a and addi- screen facing the participants. The chin rest was posi- tionally recorded the environmental background sound. tioned 300 cm away from the 300 196 cm projection We chose a 2 [viewing mode (bi-ocular 2D, stereoscopic screen, which resulted in a field of view of 418 horizon- 3D)]2 [sound (with sound, without sound)] between- tally and 288 vertically.4 Again, an FMS rating was subjects design for this purpose.

4. Note that the distance between screen and observer was delibera- 3.1 Methods tively increased by 100 cm compared to Experiment 1. A preliminary testing, including three volunteers with an observer–screen distance of 3.1.1 Participants. Sixty-nine volunteers par- 200 cm, revealed extremely high visually induced MS scores. To pre- ticipated in the second experiment and were randomly vent a ceiling effect, which could have eliminated any differences between the experimental groups regarding visually induced MS, we assigned to one of the four experimental groups crossing decided to reduce the field of view by increasing the distance between the addition of sound with 2D versus 3D (see Table 2). screen and observer by 100 cm.

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Figure 6. SSQ scores separated by viewing mode and video type. The left side illustrates the SSQ scores prior to stimulus exposure (SSQ-I); the right side illustrates the SSQ scores after stimulus offset (SSQ-II). SSQ-N ¼ SSQ-Nausea, SSQ-O ¼ SSQ-Oculomotor, SSQ-D ¼ SSQ-Disorientation, SSQ-TS ¼ SSQ-Total score, w ¼ with, w/o ¼ without. Error bars represent SEM.

assessed every minute and the SSQ had to be filled in participants, ranging from 1–8), and all four SSQII once prior to stimulus presentation (SSQ-I) and once af- scores. The FMS data showed increased sickness under ter stimulus offset (SSQ-II). Note that postexperimental stereoscopic presentation (3D with sound: M ¼ 8.21, aftereffects were not measured in Experiment 2. SD ¼ 4.17; 3D without sound: M ¼ 9.44, SD ¼ 5.57; 2D with sound: M ¼ 6.69, SD ¼ 5.04; 2D without

sound: M ¼ 6.38, SD ¼ 6.63), while the SSQII scores 3.2 Results did not differ obviously betweenthegroups(seeFigure6). However, the MANOVA revealed a significant effect of A one-way ANOVA including group (3D with viewing mode, F(5, 61) ¼ 2.392, p ¼ .048, g2 ¼ .164, sound, 3D without sound, 2D with sound, 2D without p indicating more severe MS when the video was presented sound) and the SSQI scores was conducted to make sure stereoscopically. Sound had no effect, F(5, 61) ¼ 1.524, that our subjects did not vary in their MS ratings before p ¼ .196, g2 ¼ .111, and neither was there an interac- the experiment began. No significant results were found p 5 tion between viewing mode and sound, F(5, 61) ¼ for any of the SSQI scores, including SSQI-N, F(3, 64) ¼ 2 0.282, p ¼ .921, gp ¼ .023. 1.257, p ¼ .271, the SSQI-O, F(3, 64) ¼ 0.581, p ¼ 6 A repeated-measures ANOVA was conducted to ana- .630, the SSQI-D, F(3, 64) ¼ 0.952, p ¼ .428, and the lyze the time course of the MS. Time was chosen as a SSQI-TS, F(3, 64) ¼ 1.242, p ¼ .302. Figure 6 shows within-subjects factor and viewing mode and sound as the pre-experimental SSQI scores. between-subjects factors. Again, the five participants To analyze visually induced MS differences during who aborted Experiment 2 prior to stimulus offset were stimulus presentation, a 2 2 MANOVA with the excluded from the data analysis. The results were between-subjects factors viewing mode (bi-ocular 2D, Huynh-Feldt corrected (e ¼ .210) and showed a signifi- stereoscopic 3D) and sound (with sound, without cant effect of time, F(15, 900) ¼ 49.130, p < .001, g2 ¼ sound) was calculated. Dependent variables included the p .450, indicating higher MS scores the longer the video mean peak FMS score (with subtracted baseline for 14 lasted. The Time Viewing Mode interaction missed g2 5. Robust test of means, Brown-Forsythe corrected. significance, F(15, 900) ¼ 3.157, p ¼ .063, p ¼ .039, 6. Robust test of means, Brown-Forsythe corrected. suggesting a trend for visually induced MS to be stron-

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Figure 7. Time course of the FMS scores plotted by viewing mode (3D vs. 2D, left panel) and sound (with sound vs. without sound, right panel) during stimulus presentation. Error bars represent SEM.

ther for immersion, H(3) ¼ 1.980, p ¼ .577, nor for re- alism, H(3) ¼ 1.234, p ¼ .745, nor vection judgments, H(3) ¼ 1.041, p ¼ .791. Nonparametric correlations (Spearman) revealed only a nonsignificant trend for

immersion to be related to the peak FMS scores (rs ¼

.197, p ¼ .084). Vection (rs ¼ .182, p ¼ .111) and real-

ism (rs ¼ .094, p ¼ .444) had no relation to the peak FMS scores.

3.3 Discussion

Experiment 2 revealed a significant effect of stereo- psis on visually induced MS. Participants who watched the Figure 8. Mean ratings for feelings of immersion (Did you feel like being in the scene?), realism (How realistic was the video?), and vection bicycleridein3DreportedmoreMSthanparticipantsin (How often did you have the feeling of self-movement?) measured after the 2D condition did. This finding perfectly emphasizes stimulus offset via questionnaire for Experiment 2. Ratings were scored the results of Experiment 1, where 3D was also efficient in on a 4-point scale (0 ¼ not at all, 3 ¼ very much). W ¼ with sound, increasing visually induced MS in the real video footage. w/o ¼ without sound. Error bars represent SEM. On the other hand, sound turned out to have no effect on visually induced MS in our experiment. Several reasons ger when the video was presented stereoscopically. The might be responsible for this finding, and we will discuss interaction between time and sound did not become sig- two of them briefly in the following general discussion. 2 nificant, F(15, 900) ¼ 0.237, p < .880, gp ¼ .004. Figure 7 depicts the time courses of the FMS separated 4 General Discussion by viewing mode and sound. 4.1 The Role of Stereopsis The distribution of immersion and realism, as well as the vection judgments, are shown in Figure 8. A In both our experiments, stereopsis significantly Kruskal-Wallis test for nonparametric measures was per- increased the level of visually induced MS only in combi- formed. The results indicated significant differences nei- nation with highly realistic video footage. In the less-

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detailed computer simulations of Experiment 1, stereo- could also conceive that the 2D presentation could be psis did not make a difference. Why was this the case? negating the reality tag. In the case of a very sophisti- Two things might be responsible for this power of picto- cated simulation, stereopsis as the only remaining visual rial detail which extends to vection and immersion. indicator pointing to the virtuality of the scene may Hypothesis 1 is that it might provide a tag for the scene amount to a veto when absent. The notion of a visual to be real. Hypothesis 2 is that it could increase immer- tag as real or unreal would imply a step function rather sion and thereby boost MS. Both hypotheses will be than a gradual increase of MS with improved fidelity of expanded upon in the following. the simulation. The well-known idiosyncrasies of video footage may Hypothesis 2 implicates feelings of vection, immer- serve as a tag that tells the visual system that the scene is sion, and realism triggered by the display. These feelings real. There are many cues that betray to the observer that could mediate MS, as the level of detail, the resolution a given movie has been produced with a video camera of the display, and stereopsis should all contribute to rather than a computer simulation. For instance, there is immersion, vection, and realism. An increase in one or slight jitter when the camera is handheld or head- more of these subjective variables could trigger MS. We mounted. Such jitter is absent in simulation and cannot recorded data on all three variables and supposed that easily be simulated. A stimulus may have to be tagged as vection and immersion, in particular, play a crucial role real before the effect of stereopsis can come to bear. In in the genesis and severity of visually induced MS. the case of the computer simulations, this tag is missing. However, our vection ratings did not vary significantly The simulation does not have some critical cues that are between the groups. It thus seems unlikely that differen- necessary to earn the reality tag. Without this tag, stereo- tial vection is the reason for the different levels of MS in psis by itself is not sufficient to lead the system to take our study. Note, however, that vection appears to be the visual information as seriously. Although the com- linked with MS: All our four groups showed increased puter simulation used in Experiment 1 seems rather real- MS scores (compared to the baseline) and almost every istic when viewing it, upon closer inspection, its level of participant reported vection at some point during the detail is rather limited. This tagging mechanism might experiment. Similarly, different degrees of immersion fail also reconcile two seemingly contradictory findings to explain the particularly nauseating nature of 3D view- regarding the effect of stereopsis on MS. Ha¨kkinen, ing combined with real video footage. We would have Po¨lo¨nen, Takatalo, and Nyman (2006) analyzed the expected stereopsis to increase the level of immersion influence of stereopsis on gaming sickness. Their partici- since there is some evidence for this assumption (see pants played a car-race game wearing a head-mounted Banos et al., 2008; IJsselsteijn et al., 2001, 1998). How- display (800 600 pixels) for 40 min either in 2D or ever, in Experiment 1, immersion did not vary signifi- 3D. The data showed a strong trend toward increased cantly between groups and can be excluded as a potential sickness scores in the stereoscopic condition, but the explanation for our findings. Note that, unfortunately, results failed to reach statistical significance. A recent our data do not allow for a more detailed analysis of the study by Ujike and Watanabe (2011) found a more sub- relationship between vection, immersion, and MS over stantial main effect of stereopsis. The authors projected a time. More finely graded immersion and vection mea- rather sophisticated computer simulation of a car ride surements (instead of the 4-point scale we used) would through a virtual scene and presented their stimuli either be needed. Interestingly, the bi-ocular video of the roller stereoscopically or bi-ocularly. Unfortunately, they did coaster simulation was judged to be less realistic than the not report the resolution of the display. They found sig- videos in the other three groups. Although the MS nificantly higher SSQ-nausea scores in the stereoscopic scores were not lower in this particular group, the real- condition compared to the 2D condition. Thus, it seems ism judgments showed that stereopsis did indeed have a plausible that the more sophisticated the computer simu- positive influence on the level of realism in the simula- lation, the more likely it is to receive a reality tag. One tion condition.

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Note that, conceivably, the higher frame rate used in sory self-motion and seem to enhance vection (for a the video sequences might be responsible for increased review see Va¨ljama¨e, 2009). The lack of such power in the MS. However, this should have produced a main effect induction of motion sickness may be related to the visual of video versus simulation. Also, observers judged the system being very dominant when conflicting auditory motion to be smooth both in the video and in the simu- cues are present. This is the case in localization tasks such lation. Thus, we believe that the differences in frame rate as the ventriloquism effect (see Storms, 2002), where vis- due to technical constraints were not the cause for the ual signals largely overrule auditory cues. differences in MS. Based on these findings, it seems quite plausible that To further test which of these two interpretations sound did not affect visually induced MS, or that its (realism tag vs. mediation via immersion or vection) is effect was too weak to be noticeable. Note that we used more adequate, future experiments should vary the level very dominant and imposing visual stimuli in our experi- of pictorial detail in a finely graded fashion, for instance, ments, which might have overruled any possible effect of by independently changing the level of rendered detail auditory cues in the genesis of vection or visually and the resolution of the stimuli. If stereopsis is only induced MS. Reducing the dominance of the visual stim- more nauseating by mediation of feelings of immersion, uli and thus increasing the importance of the auditory then the level of visually induced MS should increase inputs might change the pattern and show the effects of gradually with the sophistication of the simulation. But sound on MS. note that in light of the current findings, the tag hypoth- The possibility remains that we were simply not able esis is more likely, as ratings of immersion and MS were to find an effect of sound due to limitations of our not correlated with an according strength. equipment. Unfortunately, our sample size and the resulting statistical power of our experimental design were too low to be able to make a final statement on this 4.2 The Role of Background Sound nonsignificant finding. To finally answer this question In Experiment 2, we analyzed a potential effect of and to rule out the role of background sound in the gen- background sound on MS, but found no significant dif- esis and severity of visually induced MS, further studies ferences between the groups who watched the bicycle are needed and desirable. ride either with or without sound. Two explanations for Additionally, sound did not influence the amount of the lack of such an effect can be entertained. Firstly, au- immersion, vection, or realism, which contradicts a study ditory cues just might not be of importance in the area by Nichols et al. (2000). In their study, the authors pre- of visually induced MS. Secondly, some experimental sented a console video game to their participants, once shortcomings might explain the null effect of sound. with sound and once without. Although the sound of The microphones recording the sound were not of top the video game was more artificial than realistic, sound professional quality and might have prevented some turned out to increase the feelings of perceived immer- nuances from appearing on the sound track. The speak- sion. Thus, we once again recommend further studies to ers in the lab were of good quality and provided stereo shed some light on this inconsistent finding. sound. High-end surround sound was not within our means. We believe, however, that sound is not relevant 4.3 MS Aftereffects in the genesis of MS. It does not seem to factor into the sensory conflict responsible for generating visually In Experiment 1, we captured MS data up to 5 hr induced MS. Despite the cross-modal power of percep- after stimulus presentation. Our results support the tion in other circumstances, acoustic cues might just not assumption that visually induced MS can last up to several have the power to validate and enhance the visual cues in hours and does not generally decrease quickly. This is in the context of a visual-vestibular conflict. However, au- accordance with several other studies that found similar ditory cues are known to exert a facilitating effect on illu- results (Muth, 2010; Stanney et al., 2003; Stanney &

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Salvendy, 1998; Keshavarz & Hecht, 2011a). The FMS in virtual environments: The influence of . time courses during the 5-hr period after our experiment CyberPsychology & Behavior, 11(1), 1–8. doi:10.1089/ showed that stereopsis seemed to prolong the duration cpb.2007.9936 and the severity of MS aftereffects. This finding confirms Bonato, F., & Bubka, A. (2006). Chromaticity, spatial com- our hypothesis that stereopsis increases MS not just dur- plexity, and self-motion . Perception, 35(1), 53– ing the experiment, but also afterward. Again, we found 64. doi:10.1068/p5062 Brandt, T., Dichgans, J., & Koenig, E. (1973). Differential the same interaction between viewing mode and video effects of central versus on egocentric and type for all SSQ subscores during and after stimulus ex- exocentric . Experimental Research, posure. The same pattern of MS persisted and is likely to 16(5), 476–491. carry on through the recovery process. Cobb, S. V. G., Nichols, S., Ramsey, A., & Wilson, J. R. (1999). -induced symptoms and effects 5. Summary and Conclusion (VRISE). Presence: Teleoperators and Virtual Environments, 8(2), 169–186. doi:10.1162/ The relationship between stereoscopic viewing and 105474699566152 visually induced sickness seems to be rather complex. In Crampton, G. H., & Young, F. A. (1953). The differential Experiment 1, we found strong evidence for an effect of effect of a rotary visual field on susceptibles and nonsuscepti- stereopsis in real-life videos, but not in simulations, bles to motion sickness. Journal of Comparative and Physio- which is somehow surprising. Obviously, neither the logical Psychology, 46(6), 451–453. viewing condition (3D vs. 2D), nor the origin of the Dichgans, J., & Brandt, T. (1973). Optokinetic motion sick- video footage (reality-captured vs. computer simulated) ness and pseudo-Coriolis effects induced by moving visual stimuli. Acta Oto-laryngologica, 76(1–6), 339–348. had an exclusive and extensive impact on the severity of doi:10.3109/00016487309121519 visually induced MS. Instead, the combination of both Dozza, M., Chiari, L., Chan, B., Rocchi, L., Horak, F. B., & factors seems to be the crucial aspect which influences Cappello, A. (2005). Influence of a portable audio-biofeed- MS dramatically. In Experiment 2, we found further back device on structural properties of postural sway. Journal support for the effect of stereopsis on visually induced of NeuroEngineering and Rehabilitation, 2(1), 13. MS. 3D viewing combined with real video significantly doi:10.1186/1743-0003-2-13 increased the sickness ratings in this experiment as well. Ha¨kkinen, J., Po¨lo¨nen, M., Takatalo, J., & Nyman, G. (2006). Taking both results together, the effect of stereoscopic Simulator sickness in virtual display gaming. In M. Nieminen presentation on visually induced MS seems to be quite &M.Ro¨ykkee (Eds.), Proceedings of the 8th Conference on robust in realistic videos. Human-Computer Interaction with Mobile Devices and Serv- In sum, viewing conditions seem best understood as ices (pp. 227–229). tags that may indicate a real situation. They do so when Heeter, C. (1992). Being there: The subjective experience of stereo is present and fidelity is high. Only in those cases presence. Presence: Teleoperators and Virtual Environments, is vision powerful enough to overrule the vestibular out- 1(2), 262–271. put and produce substantial motion sickness. The more Hettinger, L. J. (2002). Illusory self-motion in virtual environ- ments. In K. M. Stanney (Ed.), Handbook of virtual environ- sophisticated that and 3D computer gam- ments. Design, implementation, and applications (pp. 471– ing become, the more we have to be concerned about 491). Mahwah, NJ: Lawrence Erlbaum. episodes of visually induced MS. Hettinger, L. J., Berbaum, K. S., Kennedy, R. S., Dunlap, W. P., & Nolan, M. D. (1990). Vection and simulator sick- ness. Military Psychology, 2(3), 171–181. doi:10.1207/ References s15327876mp0203_4 Hettinger, L. J., & Riccio, G. E. (1992). Visually induced Ban˜os, R. M., Botella, C., Rubio´, I., Quero, S., Garcı´a- motion sickness in virtual environments. Presence: Teleopera- Palacios, A., & Alcan˜iz, M. (2008). Presence and emotions tors and Virtual Environments, 1(3), 306–310.

Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/PRES_a_00102 by guest on 01 October 2021 Keshavarz and Hecht 227

Hill, K., & Howarth, P. (2000). Habituation to the side effects ments. International Journal of Human–Computer Studies, of immersion in a virtual environment. Displays, 21(1), 25– 52(3), 471–491. doi:10.1006/ijhc.1999.0343 30. doi:10.1016/S0141-9382(00)00029-9 Oman, C. M. (1990). Motion sickness: A synthesis and evalua- Howarth, P. A. (2011). Potential hazards of viewing 3-D ster- tion of the sensory conflict theory. Canadian Journal of eoscopic television, cinema and computer games: A review. Physiology and Pharmacology, 68(2), 294–303. Ophthalmic and Physiological Optics, 31(2), 111–122. Palmisano, S. (1996). Perceiving self-motion in depth: The doi:10.1111/j.1475-1313.2011.00822.x role of stereoscopic motion and changing-size cues. Percep- IJsselsteijn, W., de Ridder, H., Hamberg, R., Bouwhuis, D., & tion & Psychophysics, 58(8), 1168–1176. doi:10.3758/ Freeman, J. (1998). Perceived depth and the feeling of pres- BF03207550 ence in 3DTV. Displays, 18(4), 207–214. doi:10.1016/ Reason, J. T. (1978). Motion sickness adaptation—Neural mis- S0141-9382(98)00022-5 match model. Journal of the Royal Society of Medicine, IJsselsteijn, W., de Ridder, H., Freeman, J., Avons, S. E., & 71(11), 819–829. Bouwhuis, D. (2001). Effects of stereoscopic presentation, Reason, J. T., & Brand, J. J. (1975). Motion sickness. New image motion, and screen size on subjective and objective York: Academic Press. corroborative measures of presence. Presence: Teleoperators Sadowski, W., & Stanney, K. M. (2002). Presence in virtual and Virtual Environments, 10(3), 298–311. doi:10.1162/ environments. In K. M. Stanney (Ed.), Handbook of virtual 105474601300343621 environments. Design, implementation, and applications (pp. Kennedy, R. S., Lane, N. E., Berbaum, K. S., & Lilienthal, M. 791–806). Mahwah, NJ: Lawrence Erlbaum. G. (1993). Simulator Sickness Questionnaire: An enhanced Seno, T., Sunaga, S., & Ito, H. (2010). Inhibition of vection method for quantifying simulator sickness. The International by red. Attention, Perception, & Psychophysics, 72(6), 1642– Journal of Aviation Psychology, 3(3), 203–220. doi:10.1207/ 1653. doi:10.3758/APP.72.6.1642 s15327108ijap0303_3 Smart, L. J., Stoffregen, T. A., & Bardy, B. G. (2002). Visually Keshavarz, B., & Hecht, H. (2011a). Axis rotation and visually induced motion sickness predicted by postural instability. induced motion sickness: The role of combined roll, pitch, Human Factors: The Journal of the Human Factors and Ergo- and yaw motion. Aviation, Space, and Environmental nomics Society, 44(3), 451–465. doi:10.1518/ Medicine, 82(11), 1023–1029. doi:10.3357/ 0018720024497745 ASEM.3078.2011 Stanney, K. M., Hale, K. S., Nahmens, I., & Kennedy, R. S. Keshavarz, B., & Hecht, H. (2011b). Validating an efficient (2003). What to expect from immersive virtual environment method to quantify motion sickness. Human Factors: The exposure: Influences of gender, body mass index, and past Journal of the Human Factors and Ergonomics Society, 53(4), experience. Human Factors: The Journal of the Human Fac- 415–426. doi:10.1177/0018720811403736 tors and Ergonomics Society, 45(3), 504–520. doi:10.1518/ Lawson, B. D., Graeber, D. A., Mead, A. M., & Muth, E. R. hfes.45.3.504.27254 (2002). Signs and symptoms of human sysndromes associ- Stanney, K., & Salvendy, G. (1998). Aftereffects and sense of ated with synthetic experiences. In K. M. Stanney (Ed.), presence in virtual environments: Formulation of a research Handbook of virtual environments. Design, implementation, and development agenda. International Journal of Human– and applications (pp. 589–618). Mahwah, NJ: Lawrence Erl- Computer Interaction, 10(2), 135–187. doi:10.1207/ baum. s15327590ijhc1002_3 McCauly, M. E., & Sharkey, T. J. (1992). Cybersickness: Storms, R. L. (2002). Auditory-visual cross-modality interac- Perception of self-motion in virtual environments. Presence: tion and illusions. In K. M. Stanney (Ed.), Handbook of Teleoperators and Virtual Environments, 1(3), 311–318. virtual environments. Design, implementation, and Muth, E. R. (2010). The challenge of uncoupled motion: applications (pp. 589–618). Mahwah, NJ: Lawrence Duration of cognitive and physiological aftereffects. Erlbaum Associates. Human Factors: The Journal of the Human Factors and Treisman, M. (1977). Motion sickness: An evolutionary hy- Ergonomics Society, 51(5), 752–761. doi:10.1177/ pothesis. Science, 197(4302), 493–495. doi:10.1126/ 0018720809353320 science.301659 Nichols, S., Haldane, C., & Wilson, J. R. (2000). Measure- Ujike, H., & Watanabe, H. (2011). Effects of stereoscopic pre- ment of presence and its consequences in virtual environ- sentation on visually induced motion sickness. Proceedings of

Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/PRES_a_00102 by guest on 01 October 2021 228 PRESENCE: VOLUME 21, NUMBER 2

SPIE-IS&T Electronic Imaging 7863, 786314. doi:10.1117/ Witmer, B. G., & Singer, M. J. (1998). Measuring presence in 12.873500 virtual environments: A presence questionnaire. Presence: Va¨ljama¨e, A. (2009). Auditorily-induced illusory self-motion: Teleoperators and Virtual Environments, 7(3), 225–240. A review. Brain Research Reviews, 61(2), 240–255. doi:10.1162/105474698565686 doi:10.1016/j.brainresrev.2009.07.001 Yen Pik Sang, F. D., Billar, J. P., Golding, J. F., & Gresty, Webb, N. A., & Griffin, M. J. (2002). Optokinetic stimuli: M. A. (2003). Behavioral methods of alleviating motion Motion sickness, visual acuity, and eye movements. Aviation, sickness: Effectiveness of controlled breathing and a music Space, and Environmental Medicine, 73(4), 351–358. audiotape. Journal of Travel Medicine, 10(2), 108–111.

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