Analysis of Simulator Sickness in IVE by PCA
Chompoonuch Jinjakam 1 and Kazuhiko Hamamoto 2121

Graduate School of Science and Technology, Tokai University, Japan
School of Information and Telecommunication Engineering, Tokai University, Japan

Introduction

Virtual environment persuaded users feeling similar within
the real world. Unfortunately, it also induces simulator sickness
for some users. Kennedy and Fowlkes state that the prevalenceof sickness symptoms in simulator users ranges from 20% in the“best” simulator to 60% in the “worst” [1]. The impact ofinfluential factors on virtual reality-induced symptoms andeffects are virtual reality system, virtual environment, andindividual participant characteristics [2]. There are researches
published the sickness related as the older participants had agreater likelihood of simulator sickness than younger
participants [3], subjects exhibited more postural disturbancewith increasing field-of-view [4], parallax and number ofdisplay screens effect to simulator sickness [5]. Even thoughseveral factors effect to simulator sickness but they are notpresent what is the most important factor of sickness.
Therefore, main purpose of this paper is to analyze simulator
sickness results for specify the important influential factors ofsickness, then proposal for safety immersive virtual environment.
2

Method and Results of Experiment 1

The immersive virtual environment is tested by three-screen(front-right-floor) HoloStageTM system in Tokai University,
Takanawa Campus. The condition is one group of three subjects
stand in left, center, and right position by randomly assigned,
but grouped entirely male or female first, then mixed theresidual. The center subject called driver wears controlled
glasses that synchronize scene movement related with their head
movement. The left and right subjects called passengers wear
stereo glasses that can see the 3D but not control the scene
movement. The subjects standing are shown in Fig.1. All
subjects were healthy, as determined by health questionnaireand had normal or corrected to normal vision. They were not ate
food or drunk caffeine at least 2 hours prior the experiment. We
explained content details and obtained consent from all subjects
prior to the experiment. One subject was tested for only one
experiment in order to avoid familiarity of the scene due torepeated exposure and also people habituate to the visualappearance of motion [6].
After virtual content experimented with no audio, subjects
are request to answer Simulator Sickness Questionnaire (SSQ)
within 5 minutes. The SSQ was proposed by Kennedy et al.[7]consisted of sixteen symptoms; general discomfort, fatigue,headache, eyestrain, difficulty focusing, increased salivation,
sweating, nausea, difficulty concentrating, fullness of head,blurred vision, dizzy (eyes open), dizzy (eyes closed), vertigo,
stomach awareness, and burping. The SSQ results weremeasured only post-test experiment because simulator sickness
after immersion in a virtual environment are much greater whenboth pre- and post- questionnaires are given than when only apost-test questionnaire is used.
All subjects were asked to do not move their heads during
the experiment and allow eliminating anytime when they feel
too severe sickness

(b)

(a)
(c)
Fig. 1. Subject positions in HoloStageTM experiment.
(b) controlled glasses (c) stereo glasses.
2.1Experiment 1
The simulator sickness affects by different parallax was used
VR4MAX software to set the parallax as distance between eyesin the scene period. The parallax are set as 2.0 cm (commonparallax for 3D image in commercial cameras), 6.5 cm (normaldistance between human left and right eyes), and 9 cm (severeparallax) for three-screen HoloStageTM system with wide-road
animation content as shown in Fig. 2 for 4 minutes long.

Fig. 2. The 1st experiment with wide road content.
Subjects are twenty-eight students and lecturers from Tokai
University, Japan and KMITL, Thailand in age between 19-37years old (avg.=23.61years, variance=25.34), 20 males and 8
females, height 152-181 cm (avg.=168.89 cm, variance=57.84),
14 Japanese and 14 Thai, and they are 16 experienced and 12
non-experienced in HoloStageTM system.
2.2

Experiment Results 1
The elder subject prone to sickness more than younger one,however, the moderate group (26-30 years old) also has highsickness. Passenger that taller than driver, prone to get higher
sickness than the shorter one. Gender and nationality are nosignificant difference and experience affect in immersive virtualenvironment is significant difference. Simulator sickness fromparallax affect in nausea, oculomotor, and disorientation (NOD)
are presented by ascending order as 6.5 cm<2.0 cm<<9.0 cm.
Furthermore, the most important effect factors of Age, Tall_diff(tall difference between passenger and driver), Position, andParallax are analysis by principal component analysis (PCA).

2.3

Result 1 Analysis by PCA

3.3

Result 2 analysis by PCA
The Eigenvalue of factors in descending order are Position(71.59%), Tall_diff (22.01%), and Age (6.40%). Then, the mostimportant factors of sickness are Position and Tall_diff in total
93.60%. Figure 5 shows comparing of each factor, that rightposition, higher passenger than driver, and elder subject prone tohigher sickness.

Fig. 3. PCA of 1st experiment results.
The Eigenvalue of factors in descending order are Parallax(33.38%), Position (27.42%), Tall_diff (22.72%), and Age(16.48%). Then, the most important factors of sickness areParallax, Position and Tall_diff, respectively, in total 83.52%.
Figure 3 shows comparing of each factor, that higher parallax,
right position, higher passenger than driver, and elder subject
prone to higher sickness.
3

Method and Results of Experiment 2

3.1

Experiment 2
Simulator sickness affect by different positions are repeatedexperimented with new subject group in three-screen
HoloStageTM system. The content was changed to narrow roadanimation walkthrough as shown in Fig. 4 that added more nearroad details and color, testing for 5 minutes long.
Subjects are fifteen students from Tokai University in age
between 22-34 years old (avg. =24.13 years, variance=6.88), 11males and 4 females, 12 Japanese, 2 Thai, and 1 Indonesian,height 154-178 cm (avg. =168.47 cm, variance=45.63) and they
are 13 experienced and 2 non-experienced in HoloStageTM
system. The author explained purpose and obtained consent
from all subjects before the experiment.

Fig. 5. PCA of 2nd experiment results.
4

From experiment results analysis by PCA, the mostimportant factor for simulator sickness is parallax, that highparallax as 9.0 cm induced higher sickness than less parallax. If
irrespective of parallax, from both experiment 1’s and 2’s results,
the next important factors are position and then tall difference
between passenger and driver, respectively. Right position
suffers higher sickness. The subjects in right position thatstanding near three borders of screen is the worst or prone to gethigher sickness. Finally, passenger who is taller than driver
sustains higher sickness than shorter passenger.
Proposal for safety IVE are set parallax as 6.5 cm, setpassenger that shorter or similar with driver’s height, or better
set for bird’s eyes view and avoid the position that nearconnected several borders. The relation of convergence andsimulator sickness will research in future work.
References
[1]

[2]

[3]

[4]

[5]

Fig. 4. The 2nd experiment with narrow road content.
Experiment Result 2
The passenger taller than driver prone to has got higher
sickness. The elder subject prone to has got higher sickness than
younger one. Simulator sickness in positions center<left<<right.
Moreover, the most important effect factors of Age, Tall_diff
and Position are analysis by principal component analysis(PCA).

Conclusion

[6]

3.2

[7]

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