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Enhancing User Experience through Immersive Virtual
Reality: An Experimental Study Using EEG Data
Guan Wang
School of Creative Media, City University of Hong Kong
Wenying Gu
School of Creative Media, City University of Hong Kong
Ayoung Suh
School of Creative Media, City University of Hong Kong
Abstract
Immersive virtual reality (VR) has been widely adopted to enhance user experience in diverse
contexts. While immersive VR with a head-mounted display has the potential to create new value
in generating the sense of presence, it also causes cybersickness which hinders user experience.
Despite increasing scholarly and practical attention to immersive VR, the question of how to
enhance the user experience by increasing presence and inhibiting cybersickness has yet to be
answered. Hence, this study seeks to fill the gap by examining the effects of motion orientation
and posture state on presence and cybersickness using both subjective and electroencephalogram
(EEG) data during a laboratory experiment. This study discusses how a user’s immersive VR
experience is influenced by the two key factors (motion orientation and posture state) that derive
presence and cybersickness. By explaining the underlying mechanisms for presence and
cybersickness, this study contributes to resolving previous inconsistent findings regarding the
effect of immersive VR on user experience.
Keywords: Presence, cybersickness, visual motion orientation, posture state, posture-scenario
incoherence.
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1. Introduction
Virtual reality (VR) refers to technology that generates an interactive virtual environment designed
to simulate a real-life experience (H.-G. Lee et al., 2013; Wojciechowski & Cellary, 2013). In
recent years, VR has become increasingly popular in many contexts, including education
(Cochrane et al., 2017; S. H. Lee et al., 2017), entertainment (Jung et al., 2018), marketing
(Ebbesen & Ahsan, 2017), and clinical training (Huber et al., 2017). As one of the key features of
VR technology, immersion is defined as the capability to simulate and surround a user with layers
of sensory information (Witmer & Singer, 1998). While non-immersive VR displays content via
traditional devices such as a desktop, immersive VR is typically facilitated by several additional
devices, such as a head-tracking sensor, a head-mounted display (HMD), three-dimensional (3D)
sound effects, and an input device (Hoffman et al., 2003; Witmer & Singer, 1998).
Immersive VR enhances the user experience by increasing the sense of presence, which leads to
an increase in perceived enjoyment (Sánchez Laws, 2017; Shin & Biocca, 2017). Presence refers
to the extent to which a user feels that he or she is in a particular place, even while physically
situated in the other place (Huang & Liu, 2014). However, user experience with a high level of
immersion is not uniformly positive. A troublesome problem with immersive VR is that users
rapidly transit from a pleasurable sense of presence to a highly aversive sense of discomfort,
disorientation, and nausea. These symptoms are similar to the common symptoms found when
people get motion sick. When users exhibit these motion sickness-like symptoms while using an
immersive VR, researchers specially call them cybersickness. HMDs usually produce the strongest
presence. At the expense of the high level of immersion, the use of HMDs causes cybersickness.
It has been known that all types of VR displays cause cybersickness but it is much more prevalent
and severe with HMDs than other displays. This is because that HMDs enable viewers to change
their orientations in seconds in a highly immersive condition (Broeck et al., 2017). There are a
number of consequences of cybersickness in immersive VR environments. One of the serious
issues is that cybersickness can possibly linger for hours or even days following the immersive
VR experience. Apart from such after-effects, cybersickness also implies a decreased amount of
VR usage when people try to avoid getting sick by stopping using HMDs or by consuming no
more VR content (Fernandes & Feiner, 2016).
To harness the benefits of immersive VR technology to enhance the user experience, it is important
to understand how to reduce cybersickness without sacrificing high levels of presence. The factors
causing presence or cybersickness usually include technological, content, and user factors (Davis
et al., 2014). Most previous studies have tested various types of technological factors (e.g., the size
of display) and proved that certain technological features of immersive VR have significant
influences on presence and cybersickness (Coelho et al., 2006; Rebenitsch & Owen, 2016). It is
worth noting that technological characteristics become less important as antecedents of presence
or cybersickness in contemporary VR (Schultze, 2010). It has been also found that an effective
design for VR content (e.g., motion simulation) creates an opportunity to enhance the user
experience by increasing the vividness and realism of virtual environments (Freeman et al., 2000).
However, practitioners (e.g., developers of VR entertainment or business) found it difficult to
achieve a natural and real life-like motion, such as walking up stairs, jumping, without causing
cybersickness. In an effort to reduce cybersickness, researchers have tested how user factors (e.g.,
posture) play a role in increasing VR experience (Alsina-Jurnet & Gutiérrez-Maldonado, 2010;
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Davis et al., 2014). According to the postural instability theory (Riccio & Stoffregen, 1991),
playing from a seated position rather than standing can alleviate the cybersickness. In this sense,
researchers have called for research on the effects of a user’s posture state on cybersickness in
immersive VR environments.
To date, the underlying mechanisms that cause presence and cybersickness are still not completely
understood. While most previous studies focused on technological factors that cause presence and
cybersickness, relatively little effort has made in understanding the effects of content and user
characteristics. Furthermore, previous studies have not consolidated the two aspects (content and
user characteristics) to examine user experience. One example is the existence of posture-scenario
incoherence (i.e., a sense of the incoherence between a user’s physical posture and simulated VR
scenario), which can decrease the naturalness and realism of a virtual environment, and ultimately
inhibit the user’s sense of presence. These separate research streams do not inform one another,
which has limited our comprehensive understanding of why immersive VR often fail to satisfy
users. Recognizing that little effort has been made toward exploring how different visual motion
orientation and posture state influence presence and cybersickness in immersive VR, the present
study seeks to answer the following questions:
RQ1: How does visual motion orientation influence presence and cybersickness in immersive VR?
RQ2: How does posture state influence presence and cybersickness in immersive VR?
RQ3: How do visual motion orientation and posture state jointly influence presence and
cybersickness in immersive VR?
To answer these questions, this research-in-progress develops hypotheses regarding the influences
of motion orientation and posture state on presence and cybersickness. To test the proposed
hypotheses, this study conducts a between-subjects experiment with visual motion orientation and
posture state as between-subjects factors. An EEG method will be used to capture the cortical
mechanisms of presence and cybersickness. Our results are expected to show how both visual
motion orientation and posture state influence presence and cybersickness. This study extends our
understanding of the underlying mechanisms of presence and cybersickness in several ways. The
study complements and extends the existing literature, which has yet to empirically and thoroughly
test the of different visual motion orientations on presence and cybersickness. The study also
examines how posture state influences presence and cybersickness. The study provides useful
insights that could help content creators and engineers better understand immersive VR by
considering the joint influences of visual motion orientations and posture state in various scenarios.
2. Related Work
2.1 Theories of Presence
Researchers have developed different theories to explain how presence is generated in virtual
environments. A common agreement from the previous studies is that immersion is the most
important force that derives the sense of presence (Linder, 2017). Slater and Wilbur (1997) argue
that presence is a state of consciousness that may be concomitant with immersion. As a technical
capability, immersion can be objectively assessed as the extent to which a display system can
deliver an inclusive, extensive, surrounding and vivid illusion of virtual environment to a
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participant (Slater & Wilbur, 1997). People in a high immersion condition (e.g., using HMDs as
the display device) feel high levels of presence (Broeck et al., 2017; Fonseca & Kraus, 2016; Rupp
et al., 2016). For example, HMDs with a wide field of view increase the authenticity and realism
of the viewing experience in immersive VR environment (IJsselsteijn et al., 2001; Lin et al., 2002;
Prothero & Hoffman, 1995). HMDs also enhances presence in immersive VR environment by
enabling viewers to rotate their views naturally to look anywhere around them (Broeck et al., 2017;
Philpot et al., 2017; Sheikh et al., 2016; Sundar et al., 2017).
Although there are various theories of how presence is generated, it’s important to note that the
antecedents of presence are overlapped among these different theoretical lenses. Among the
presence’s antecedents, the virtual environment’s realness, such as sensory fidelity and behavioral
fidelity, has been mentioned repeatedly (Bystrom et al., 1999; Schultze, 2010). Sensory fidelity is
the degree to which displays of information in the virtual worlds is similar to that in the actual
world (Bystrom et al., 1999). Behavioral fidelity refers to judgment of the virtual environment’s
realness as it related to the user’s actions and interactions within the virtual world (Schubert et al.,
2001).
2.2 Theories of Cybersickness
Cybersickness, as a subset of motion sickness, can be experienced by users of VR where they
appear to be moving in the virtual scene while actually remaining stationary (LaViola Jr, 2000).
The typical symptoms of cybersickness include nausea, disorientation, tiredness, headaches, eye
strain and dizziness (LaViola Jr, 2000). Previous studies suggest that different display devices can
cause different levels of cybersickness in an immersive VR environment (Kelaiah et al., 2014).
Users in high-immersion conditions have more severe symptoms (Howarth & Costello, 1997;
Muhammad et al., 2017). Specifically, cybersickness is common when using contemporary HMD
systems (Coxon et al., 2016; Munafo et al., 2017). The visual motions displayed through HMDs
may not be aligned with users’ physical motion, which can exhibit some degree of cybersickness
(McGill et al., 2017). Cybersickness may also occur in cases of detectable lags between head
movements and the recomputation and presentation of the visual HMD display (Hettinger & Riccio,
1992).
2.2.1 Sensory Conflict Theory
The most longstanding and popular explanation for cybersickness is known as sensory conflict
theory (Cobb et al., 1999; LaViola Jr, 2000). Sensory conflict theory describes the conflicts of two
sensory systems engaged in VR namely the visual and vestibular systems (Kolasinski, 1995). The
theory is based on the premise that these sensory systems provide information about an
individual’s perceived motion and orientation, and the discrepancies between the senses can
frequently occur in VR. For example, the vestibular system may tell the user that his/her body is
stationary while the visual system tells them that their body is moving, causing a sensory conflict
(Howarth & Costello, 1997). Such a conflict between vestibular and visual cues is a possible cause
for cybersickness.
2.2.2 Posture Instability Theory
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There has been evidence to support that the sensory conflict theory is inadequate to explain
cybersickness (Riccio et al., 1992). As an alternative, postural instability theory parallels the
sensory conflict theory in many ways especially in terms of cybersickness. Postural stability is
defined as the state in which uncontrolled movements of the perception and action systems are
minimized (Riccio & Stoffregen, 1991). When the environment changes in a significant way,
postural control strategies will be not available due to lack of experience. Then the individual will
lose postural control and be in a state of postural instability. The postural instability theory states
that instabilities in the control of body orientation is necessary and sufficient for the occurrence of
cybersickness (Riccio & Stoffregen, 1991). When VR scenarios are designed to be unrelated to
the real-world constrains on control of the body, postural control strategies for gaining postural
stability will not work (LaViola Jr, 2000).
2.3 Contributing Factors to Presence and Cybersickness in immersive VR
2.3.1 Vection
Vection refers to the sensation of illusory self-motion in the absence of physical movement through
space (Palmisano et al., 2015). Visual cues about self-motion can be provided by optic flow. In an
immersive VR environment, the optical flow patterns of the virtual environment move past the
user's periphery and give him/her a sense of vection (DiZio & Lackner, 1992). Vection may be
related to both presence and cybersickness (Bonato et al., 2008; Nichols & Patel, 2002). Vection
can enhance presence in immersive VR. The visual system tells the user a variety of information
which includes that he/she is moving in a certain direction, and thus provides extra information to
make the users feel that they are acting in the virtual environment (i.e., the realness). If the visual
motion cues simulated in VR are unable to evoke a natural perception and vection, the overall
believability of the VR simulation and presence may also be reduced.
According to the sensory conflict theory, the cause of cybersickness is the conflict between the
visual motion information transmitted by the VR content and the user’s real-world perceptions
(Kasahara et al., 2015). As the user is not actually moving, the vestibular sense fails to provide a
proportional sense of linear or angular motion. Then a conflict occurs and cybersickness may ensue.
The coexistence of the stationary reality and the visual information specifying self-motion
generates vection, and large visuo-vestibular cue conflicts can lead to the occurrence of
cybersickness. Thus vection is often accompanied by cybersickness and can possibly exacerbate
it in some cases (Bonato et al., 2008).
2.3.2 Visual Motion: Orientation
Previous studies have found that visual motions offer a superior viewing experience (Broeck et al.,
2017) by supporting a fast and great sense of depth and sharpness (Palmisano, 2002; Palmisano et
al., 2015; Tam et al., 1998). The overall believability of the motion simulation might result in
presence and involvement in the simulated VR scene. There are a number of important moving
stimulus factors that could determine the strength of vection illusions. In this study, we focus on
the direction of the visual stimulus, especially forward-backward and up-down motion. Visual
motion orientation refers to the situation that the visual system informs the subject that he/she is
moving in a certain direction. It has been argued that certain types of visual motion orientation in
a VR environment can influence users’ immersive experience. An extreme downward motion
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orientation, as opposed to a forward orientation, can markedly increase presence as well as
cybersickness (Ruddle, 2004), especially when a VR scene contains rapid motions (So et al., 2001).
Such motion orientation can create different visual motion cues like optic flow, which can elicit
the distinguished experience of vection. Prior studies have compared different motion orientations
and found that up-down motion performed better than front-back motion in evoking the sense of
vection (Trutoiu et al., 2009). This can be explained by that up-down movements are aligned with
the direction of gravity for upright users. Considering the velocity of visual stimulus, the optical
flow rate is a contributing factor to inducing vection. A faster flow rate can increase the perceived
motion's speed and make the illusion more intense. Downward orientation in a natural VR scenario
usually adopts a faster flow rate than upward orientation because of the gravity simulation.
Presence has been shown to correlate with vection (Riecke & Schulte-Pelkum, 2015; Riecke et al.,
2004). Accordingly, we propose the following hypothesis:
H1: Different visual motion orientations have different impacts on presence; especially, downward
orientation elicits the greatest degree of presence than other orientation types.
When orientation signals that are transmitted by the eyes and the vestibular organs do not match,
people experience sensory conflict (Hale & Stanney, 2014). When a large sensory conflict exists
between the physical motions and visual motions, the occurrence of vection can be correlated with
undesirable side-effects like cybersickness (Riecke, 2010). Visually simulated self-motion can be
either steady or changing. Prior studies argued that changing vection could lead to more
cybersickness (Bonato et al., 2008). Changes in the pitch of simulated up-down motion could make
a large contribution to symptoms of cybersickness. Compared with front-back orientation, the
vestibular cues can be significantly changed because of head movements during watching up-down
motion scenarios. For example, prior studies discovered that nausea was particularly severe when
users had to spend substantial amounts of time looking steeply downwards (Ruddle, 2004). To
overcome the cybersickness, vertical head movements for the majority of users become very slow
(Ruddle, 2004). Considering visually upward motion can create the largest sensory conflicts
between the visual and vestibular systems, we propose the following hypotheses:
H2: Different visual motion orientations have different impacts on cybersickness; especially,
upward orientation elicits the greatest degree of cybersickness than other orientation types.
2.3.2 Physical Motion: Posture state
Posture is known to influence motion sickness susceptibility in various reality context (e.g., ships,
vehicles) (Money, 1970). Positioning the user in the immersive VR can also play a role in the
susceptibility to cybersickness. When users play the immersive VR, they are usually sitting or
standing. Prior studies found that playing from a seated position rather than standing can alleviate
the sickness (Merhi et al., 2007). Since in many immersive VR scenarios, there are simulated
motions that are impossible in the real world because of body constraints, postural control
strategies will not work. Sitting posture can reduce the demands on postural control. Based on the
postural instability theory (Riccio & Stoffregen, 1991), sitting appears to be a better posture in
which to reduce cybersickness symptoms.
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Hypothesis 3: Different posture states have different impacts on cybersickness; especially,
standing posture elicits a greater degree of cybersickness than sitting posture.
The experience of vection and presence is not only determined by the technological parameters of
the fast-moving stimulus, but also influenced by posture-scenario incoherence. In particular,
people are typically aware whether a simulated motion is possible in immersive VR environment.
A coherence between the actual posture and scenario posture can prime users to suspend disbelief
from a cognitive-perceptual level. For example, a sitting posture can make the believability of
motion simulation challenged in a virtual skiing scenario. The existence of posture-scenario
incoherence constrains the sense of proprioceptive matching between the perception in VR and
real world (Slater & Wilbur, 1997). Such incoherence has a considerable effect on the vection and
consequently on the overall believability and effectiveness of a simulation. Although sitting
posture can help reduce cybersickness, it may reduce presence if there exists the posture-scenario
incoherence.
Hypothesis 4: Posture-scenario incoherence elicits a smaller degree of presence.
3. Methods
3.1 Participants
This study will get the approval from the local ethical committee of the university and government.
Before the experiment, all participants will be required to sign a written informed consent to make
sure that they know they have the right to abort this experiment at any time. We expect to recruit
80 participants to attend our four experimental conditions. Prior to their inclusion in the study, the
participants should not have a history of neurological or psychiatric disorders, visual and vestibular
impairment, muscles and joints diseases or equilibrium disorder.
3.2 Device
We will employ 2017 HTC Vive® (High Tech Computer Corp., Taiwan) as the HMD device to
offer the fully immersive experience during the experiment (see Figure 1a). Vive headset can
facilitate total 110° degrees field-of-view (FOV). The resolution of this HMD is 1080 × 1200 pixels
per eye with 90 Hz refresh rate. Two handheld motion controllers which fit with the headset will
be provided for interaction with VR stimuli. Also, Vive headset will track head movement across
gyroscope and accelerometer sensors to establish a head orientation of participants.
The EEG signal will be recorded by Emotiv EPOC, a wireless portable EEG equipment
(www.emotiv.com). The headset enables access to 14 data channels and 9-axis inertial motion
sensors. 14 EEG channels are placed at positions AF3, F7, F3, FC5, T7, P7, O1, O2, P8, T8, FC6,
F4, F8, AF4 based on 10-20 International System (Jasper, 1958) (see Figure 1b). Two bipolar
reference electrodes (CMS/DRL) are located above participants' ears in the P3/P4 locations.
Emotiv EPOC operates at a resolution of 14 bits per channel with the frequency response between
0.16–43 Hz. The EEG equipment is selected because of its portability for combining with HMD
(Ghali et al., 2017). First, the wireless function will ensure the study performed without
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interference in the virtual reality. Next, possible head movements can be detected with 9-axis
inertial motion sensors, and noise from head movement can be filtered out. Furthermore, Badcock
et al. (2013) suggested the validation of Emotiv EPOC EEG system as an alternative use of clinical
EEG devices, such as Neuroscan.
a) HTC Vive with Emotiv EPOC b) EPOC electrode positions
Figure. 1. Devices used in the experiment
a) Upward, roller coaster b) Downward, skiing
Figure. 2. Screenshots of the two VR scenarios
3.3 Design
To test our hypotheses, separate groups of participants will play the two games (see Figure 2) while
sitting and standing. In total, there are four experimental conditions: 1) standing, roller coaster; 2)
standing, skiing; 3) sitting, roller coaster and 4) sitting, skiing. Each participant will be randomly
assigned to a single condition.
3.4 Instruments
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Two types of instruments (psychological and physiological) will be used in this study to measure
the participants’ experience during the exposure session. Subjective measurement items for all
constructs will be adapted from prior research and designed to investigate the effects of visual
motion orientation and posture state. Measures of presence will be adapted from the work of
(Huang & Liu, 2014; Slater et al., 1994). Measures of cybersickness were adapted from (Cho &
Kang, 2012). All items will be measured on a 7-point Likert scale (from 1 = strongly disagree to
7 = strongly agree).
3.5 Procedure
Before the experiment, participants will sign an ethic form which contains the explanation of
research purposes. We will warn the participants that they may become ill and ask them to
discontinue play immediately if they experience any severe symptoms of cybersickness. After that,
HTC Vive and Emotiv EPOC headsets will be introduced to participants to ensure familiarity.
Also, a tutorial will be offered to present the basic functions of experiment devices. After the
tutorial, tasks that designed for this study will be explained to the participants. Both the tutorial
and the tasks will be reiterated verbally by the experimenter. The participants will be asked to
answer a pre-test questionnaire containing questions related to demographic information and their
familiarity with VR and HMDs. After the participants completed the pre-test questionnaire, they
will be first equipped with Emotiv EPOC headset, and then HTV Vive. Before the virtual exposure,
two minutes of resting EEG activity will be recorded (Baseline 1). Afterward, the experimenter
will ask the participants to play the VR game in either sitting or standing posture. At the end of the
virtual experience, two minutes of resting EEG activity will be recorded again (Baseline 2). Finally,
the experimenter will remove all devices from the head of the participants, and the participants
will complete a post-questionnaire containing subjective measures. Upon completion of the study,
each participant will be offered the incentive for participating.
4. Potential Applications
Our study intends to contribute to the knowledge of immersive VR by testing the joint effects of
viewing orientation and posture state on presence and cybersickness. We propose two underlying
mechanisms: sensory conflict mechanism and postural instability mechanism can both explain the
effects of these contributing factors. The system developers should pay attention to the design of
scenarios. For example, considering the effect of posture-scenario incoherence, a standing scenario
(e.g., walking) followed by a sitting scenario (e.g., riding) can create a challenge by decreasing
presence.
Acknowledgement
This research was supported by grant from the Centre for Applied Computing and Interactive
Media (ACIM) and the Teaching Development Grant (No. 6000666) from the City University of
Hong Kong awarded to the third author. This research was supported in part by grant No. CityU
11507815 from the Research Grants Council of the Hong Kong SAR.
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