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VRET REVIEW AND STUDY PRELUDE 1
Virtual Reality Exposure Therapy Literature Review and Study Prelude
Samuel Borchart
Ohio Wesleyan University
VRET REVIEW AND STUDY PRELUDE 2
Virtual Reality Exposure Therapy Literature Review and Study Prelude
Out of a variety of treatments for anxiety disorders such as specific phobia(s), social
phobia, panic disorder, post-traumatic stress disorder (PTSD), and obsessive compulsive disorder
(OCD), a form of behavioral therapy often used is exposure therapy (Rachman, 2009).
Exposure therapy has its roots in the research of Mary Cover Jones (1924, as cited by
Rachman, 2009). After testing a number of potential methods by which to reduce fear in
children, one of the methods that she settled on was direct conditioning in which a feared object
or stimulus is repeatedly presented at a gradually increasing proximity to the subject and
negative reactions are reduced by the association of the stimulus with a pleasurable stimulus that
is incompatible with the negative feelings of fear; in this case, eating. That exposure to the feared
stimulus, graded and gradual, which was a key element in Jones’s direct conditioning method,
remains a central component in current exposure and response prevention treatments (Rachman,
2009).
Two pioneers of cognitive therapy, which, along with behavioral therapy, make up the
well supported method of cognitive behavioral therapy (CBT), are Aaron Beck and Albert Ellis.
Beck and Ellis both shared the view that most psychological disturbances arise from flawed
cognitions and flawed cognitive processing, and that these disturbances can be treated by
correcting appraisals of stimuli and correcting cognitions within the client (Rachman, 2009).
Exposure therapy seeks to be one method useful in correcting these flawed cognitions.
The background and current implementation of exposure therapy in all forms aligns well with the
emotion-processing model of fear. This model hinges upon the proposed existence of a “fear
structure” which is a cognitive network that includes information about stimuli and information
about responses to those stimuli. This network is different from other information processing
VRET REVIEW AND STUDY PRELUDE 3
structures most importantly because the fear network attaches meanings to the stimuli within the
network as dangerous. Running ahead of a competitor in a race involves similar stimuli and
response cognitions to running away from a man with a knife; the difference is in the meaning
attached to the stimuli and to the response and the desire to escape from the threat. In order to
treat and alter this fear network when it is pathological and disruptive to a client’s life, two
conditions are necessary. The first of these conditions is that fear-relevant information (feared
stimuli) must be presented in a way that activates the fear network. Secondly, the information
that is presented must include elements that are incompatible with information already within the
fear network (Foa & Kozak, 1986). For example, if the fear network includes the cognition of
“the banging sound happened right before my Humvee was attacked. When I hear that sound,
I’m about to be attacked and killed”, then presentation of that banging sound followed by the
client not being attacked or harmed can modify the fear network through extinction because the
fear of being attacked is incompatible with not being attacked at all. Exposure therapy comes in a
variety of forms. The most intuitively obvious form, exposure to real, physical manifestations of
stimuli or scenarios that elicit fear responses and cause anxiety is called in vivo exposure therapy
(IVET). IVET has a great deal of empirical support behind its effectiveness for many disorders,
so much so that the American Psychological Association (APA), the National Institute of Mental
Health (NIMH), and the National Institute for Health and Clinical Excellence (NICE) all
recommend CBT and exposure-based behavioral therapy as an effective treatment for people
with specific phobias and panic disorder (Woody & Sanderson, 1998; Rachman, 2009). The
same entities as well researchers in the field also recommend CBT including exposure and
response prevention (ERP) for the treatment of OCD (Woody & Sanderson, 1998; Rachman,
2009; Franklin & Foa, 2011). Continuing research also supports the effectiveness of exposure
VRET REVIEW AND STUDY PRELUDE 4
therapy for the treatment of PTSD in combat veterans, sexual assault victims, and other
populations as well (Barlow, 1993; Rothbaum, 2002).
The biggest limitation of IVET is not its clinical effectiveness when used as a treatment,
but its acceptance by clients and patients when used for treatment. For example, despite the fact
that phobias are among the most common mental disorders in all populations, a remarkably high
proportion of those suffering from them do not even get treated, and of those who do seek
treatment, approximately 25% refuse in vivo exposure therapy once they are informed about
what it entails, or drop out of therapy entirely (Garcia-Palacios, Botella, Hoffman, & Fabregat,
2007). Beyond the intensity of the feared stimulus causing people to withdraw from treatment,
some individuals also find in vivo exposure undesirable because of a potential loss of
confidentiality if therapy involves them being in public and because of the longer amount of time
involved in each treatment session (Wiederhold, Jang, Gervirtz, Kim, Kim, & Wiederhold,
2002). Furthermore, some are concerned about added expense required for in vivo treatment
protocols. Similarly problematic effects exist for people suffering from OCD. Of those seeking
treatment for OCD and who do not respond to or become sufficiently engaged in in vivo ERP,
nearly 20% refuse or drop out of therapy (Belloch, Cabedo, Carrió, Lozano-Quilis, Gil-Gómez,
& Gil-Gómez, 2014). In light of these facts, further work is needed to increase the proportion of
people who are suffering from phobias and other anxiety disorders that seek out and can benefit
from exposure therapy. When IVET is not appropriate, due to financial or physical limitations or
to client preference, one alternative version of exposure therapy is imaginal exposure therapy
(IET). In IET, instead of being actually physically exposed to the stimulus that is provoking
anxiety, the client or patient is instead tasked with imagining a scenario or narrative of a situation
as it is described aloud in detail by a therapist. Studies have shown that IET does effectively
VRET REVIEW AND STUDY PRELUDE 5
reduce anxiety symptoms to a statistically significant degree for phobias such as the fear of
flying (Rus-Calafell, Gutiérrez-Maldonado, Botella, & Baños, 2013; Wiederhold, Jang, Gervertz,
Kim, Kim, & Wiederhold 2002). This allows us to conclude that, if IVET cannot be performed
because of some limitation, IET can still be used to treat at least some phobias. However, like
IVET, IET comes with its own set of weaknesses and limitations. Furthermore, in their study on
the fear of flying, Wiederhold et al. (2002) found that, while both groups improved at a
statistically significant level on symptomatic measurements, a small percentage of participants in
the IET treatment group completed the post-treatment real flight protocol without anxiolytic
medication or alcohol (10%), while a large majority of the other treatment group completed the
same protocol (80%). Rus-Calafell et al. (2013) found that participants who were treated with
IET did not continue to improve on some measures of fear-related symptomology at follow-up
relative to post-treatment, while those in the other treatment group did continue to improve
relative to post-treatment. One potential reason as to why IET might suffer from these
deficiencies is that some clients or patients may not possess the ability to feel present in the
feared situation and/or to re-experience the feared stimuli, and if you cannot activate the fear
network you cannot change it (Wiederhold et al., 2002). Another promising alternative form of
exposure therapy beyond IVET is virtual reality exposure therapy (VRET). In VRET, in contrast
to both IVET and IET, clients or patients are not exposed to real, physical manifestations of
feared scenarios or stimuli; they are instead exposed to these stimuli in an electronically-
generated virtual environment. In VRET, clients are presented with virtual counterparts of real
world stimuli such as spiders, tall buildings, airplanes, cramped spaces, public speaking, etc., that
elicit anxiety (Powers & Emmelkamp, 2008). VRET setups utilize multi-sensory computer
generated environments that are experienced by the client through a series of technological
VRET REVIEW AND STUDY PRELUDE 6
devices such as head mounted displays and audio equipment. Virtual reality (VR) environments
generated by the equipment may be two-dimensional (2D) or three-dimensional (3D), with 3D
environments being more common. Clients then interact with these environments using a
joystick, a video game controller, or through a body movement tracking system so that the
environment adapts to the user’s behavior within it (David, Matu, & David, 2013).
One of VRET’s greatest strengths is that it addresses the limitations found in IVET as
well as IET. To begin, the greatest limitation and weakness in IVET is the high rates of attrition
found in in vivo exposure programs. VRET addresses this weakness because, unlike in IVET
treatments, confrontation of the feared stimulus, while still “real”-feeling and anxiety provoking
(therefore enabling alteration of the fear network), actual danger coming from the stimulus is
physically impossible in virtual reality. Garcia-Palacios et al. (2007) conducted a study in which
150 participants, each diagnosed with either specific phobia: animal phobias (i.e. spiders, rats,
cockroaches), situational phobia (i.e. claustrophobia), natural environment phobia (i.e. heights),
or social phobia (i.e. public speaking), were tasked with completing a survey in which they rated
their willingness (on a scale of one to seven) to participate in either IVET or VRET treatment.
Results of the survey found a statistically significant difference between the means for IVET and
VRET conditions, with participants preferring VRET over IVET (M = 6.08, SD = 1.31 on a 7-
point scale for VRET, M = 3.97, SD = 1.89 for IVET). Additionally, because this survey was the
prelude to all participants undergoing actual treatment for their phobias either through IVET or
VRET, researchers examined which form of treatment participants chose and/or refused. Of
those surveyed, 27% of participants refused to undergo IVET, while only 3% of participants
refused VRET treatment. Furthermore, when ultimately given a choice about which treatment to
undergo, 76% of participants chose VRET, leaving only 23.7% choosing IVET. Analysis
VRET REVIEW AND STUDY PRELUDE 7
revealed that this difference in percentages was statistically significant. Finally, of those
participants who chose VRET treatment, a large majority (90.4%) said that they chose VRET
over IVET because they were too afraid of confronting the real, physical feared object or
situation. This result confirms many predictions that a large factor in IVET’s problem with
attrition may lie in the fear of confronting the true, real, corporeal form of one’s fear. Now that it
has been shown that participants strongly prefer VRET over IVET when given a choice, the next
logical question is whether VRET achieve similar results to IVET which, for all its faults,
remains the gold standard for exposure therapy, one of the most efficacious techniques in clinical
psychology (Garcia-Palacios et al., 2007)? Immediate intuition may lead one to predict that
VRET would have smaller effect sizes or generally would not effectively improve fear-related
symptoms because of the disbelief that can accompany the presentation of a stimulus in what
colloquially amounts to a video game-like setting. That prediction, however, would be mistaken;
both individual studies and meta-analyses of VRET’s efficacy find it to be equally as effective as
the gold standard.
Anderson, Price, Edwards, Obasaju, Schmertz, Zimand, and Calamaras (2013) recently
performed the first randomized controlled trial comparing VRET to IVET for the treatment of
social anxiety disorder. In this study, ninety-seven participants, all of whom met diagnostic
criteria for social anxiety disorder, were randomly assigned to one of three groups: the VR
condition (called VRE in the study, hereafter referred to as VRET), the exposure group therapy
condition (called EGT in the study, hereafter referred to as IVET), or a wait list control
condition. Participants were assessed through a behavioral task in which they prepared notes on
controversial speech topics, gave a ten minute speech on the topic, and then rated themselves on
how well they felt they performed and how anxious they felt. Throughout treatment in the study,
VRET REVIEW AND STUDY PRELUDE 8
each condition lost some participants to attrition for various reasons. Interestingly, and in line
with other examinations of attrition rates between VRET and IVET, more than twice as many
participants in the IVET condition either dropped out beforehand or did not complete treatment
(twenty-two participants) compared to the VRET condition (ten participants). Results of this trial
indicated a significant difference both in self-report measure scores and in behavioral avoidance
between VRET and wait list conditions and between IVET and wait list conditions, but no
significant differences between VRET and IVET conditions themselves. Analysis of participants
at a three month follow-up assessment revealed no significant difference between VRET and
IVET conditions in the rates of full remission, partial remission, or people continuing to meet
diagnostic criteria. All of these results display the equal efficacy of VRET and gold standard
IVET treatments.
Another study using random assignment and controls that compared VRET and IVET in
treatment of a very common specific phobia (10-25% of the population), the fear of flying, was
conducted by Rothbaum, Hodges, Smith, Lee, and Price (2000). Forty-nine participants, all
meeting diagnostic criteria for specific phobia: fear of flying or panic disorder with agoraphobia,
were randomly assigned to the virtual reality condition (called VRE in the study, hereafter
referred to as VRET), the condition that used actual exposure to a real plane in a real airport as
well as a brief period of IET (imagining turbulence, take-off, landing, etc.) in the final treatment
session (called SE in the study, hereafter referred to as IVET), or a wait list control condition.
Participants received eight sessions of treatment in their respective condition over a period of six
weeks. Post-treatment, participants were asked to undergo a real, round-trip flight accompanied
by a therapist. In the results of this study, both the VRET and IVET groups were superior to the
wait list condition in the decrease of symptoms as measured by standardized questionnaires and
VRET REVIEW AND STUDY PRELUDE 9
also in the number of participants able to successfully complete a post-treatment flight on a real
airplane. Anxiety ratings during the real flight indicated that VRET and IVET participants felt
equally comfortable and both groups felt more comfortable than participants in the wait list
condition. All of these measured improvements were maintained in both the VRET and IVET
groups in a six month follow-up. Finally, when ultimately given a choice, only one participant in
the wait list group chose IVET treatment, while the other fourteen participants chose VRET, an
overwhelming majority. These results continue to showcase the tendency of VRET and IVET to
have equal efficacy in treating specific phobias and also that VRET is preferred over IVET by a
large majority of people when given a choice.
Extending beyond phobias, research is beginning to be performed in order to assess
VRET’s capability to treat other types of anxiety disorders such as PTSD and OCD. For OCD, a
go-to method of treatment is ERP. In this method, clients are treated with prolonged exposure to
obsessional cues (such as a dirty environment evoking the feeling of disgust and filthiness) and
then are prevented from engaging in ritualistic behaviors which are performed in an attempt to
reduce anxiety (avoidance behavior). This treatment, as with all exposure therapies, works so
long as the incoming stimuli evoke enough anxiety that the fear network can be activated and
altered (Barlow, 1993). In a study attempting to asses VRET’s utility in future treatments of
OCD, four women diagnosed with OCD assessed their subjective sense of presence, emotional
engagement, reality judgment, and, importantly, levels of anxiety and disgust coming from the
stimuli (dirtiness and contamination) in a VR environment. Results of this study showed that, as
stimuli in the VR environment increased in dirtiness and contamination, the anxiety and disgust
levels of all subjects increased significantly and that these increased levels of anxiety were
associated with higher levels of emotional engagement and sense of presence experienced during
VRET REVIEW AND STUDY PRELUDE 10
the VRET intervention. The results of this study, being one of the very first to examine VRET’s
utility as a potential OCD treatment alternative to IVET, are very promising for proponents of
VRET interventions (Belloch et al., 2014).
With multiple individual studies comparing VRET’s efficacy to IVET for individual
disorders, the literature on VRET treatment has grown large enough that meta-analyses of effect
sizes of VRET results are beginning to be published. One such analysis, one of the first of its
kind, was conducted in order to assess VRET’s utility as an alternative treatment to IVET for
PTSD. This analysis looked through multiple databases and found six studies with experimental
or quasi-experimental designs that used VRET interventions for active duty service members or
veterans, all who had been diagnosed with combat-related PTSD. This meta-analysis’s results
showed positive effects for VRET’s treatment of combat-related PTSD, but noted that much
more research in this particular area is needed (Nelson, 2012).
A second meta-analysis that examined effect sizes from the results of twenty-one studies
(with a total of 300 participants) utilizing VRET treatment in the domains of PTSD, social
phobia, arachnophobia, acrophobia, panic disorder with agoraphobia, and aviophobia is Parsons
and Rizzo (2008). This analysis found statistically large effect sizes (very near or above one full
standard deviation) in VRET’s treatment of all six domains examined in the twenty-one studies,
further demonstrating VRET’s efficacy in treating a variety of anxiety disorders.
Yet a third meta-analysis, Powers and Emmelkamp (2008), also examined effect sizes
from several studies utilizing VRET treatment, but this analysis also compared VRET to IVET
across several studies at once. The results of this analysis first assessed the effect sizes in VRET
conditions compared to control conditions and found that, across the thirteen studies used in this
analysis (with a total of 397 participants), there was a large, significant effect for VRET
VRET REVIEW AND STUDY PRELUDE 11
interventions relative to controls. The analysis then compared effect sizes found in VRET
interventions and those found in IVET interventions and found both interventions be similar and
highly effective over controls, but with a small effect size difference favoring VRET over IVET
in the thirteen studies.
The meta-analyses, along with several individual studies assessing VRET ability to treat
a wide variety of anxiety disorders such as specific phobias, panic disorder, and even PTSD and
OCD, lead to the conclusion that VRET can be just as effective as the gold standard exposure
treatment of IVET.
The greatest limitations of IET, considered a sufficient alternative treatment to IVET, lie
in IET’s questionable ability or lack of ability to truly activate the fear network (and therefore
open it to alteration) in clients and its somewhat poor support for the maintenance of treatment
effects at follow-up. Lackluster improvement maintenance in IET treatment may in fact be a
result of IET not sufficiently activating the fear network, however (Wiederhold et al., 2002).
Regardless, VRET effectively addresses these shortcomings and achieves greater effects than
IET in several studies.
In Wiederhold et al. (2002), which was previously used here to identify IET’s limitations,
researchers conducted a controlled study comparing IET and VRET for use in treating the fear of
flying. In this study, thirty participants, who were confirmed to meet DSM-IV criteria for a
diagnosis of specific phobia for the fear of flying, were randomly assigned into one of three
groups: virtual reality graded exposure therapy (called VRGET in the study, referred to hereafter
simply as VRET) with physiological feedback, VRET without physiological feedback, and
systematic desensitization through IET. Each group received eight sessions of the treatment,
once per week and results were measured using subjective ratings of anxiety (SUDs),
VRET REVIEW AND STUDY PRELUDE 12
physiological measures such as heart rate and respiration rate, and a post-treatment assessment of
flying on an actual flight without anxiolytic medication or alcohol. All three groups showed
improvement in SUDs ratings over time. However, an interesting effect was noticed: participants
in the IET group never reported anxiety levels on a level as high as those reported by the two
VRET groups, never displayed as much of a decline in anxiety compared to VRET participants,
and never became nearly as physiologically aroused as in the VRET groups. This difference in
elicited anxiety may be a result of IET not activating the fear network, which, as previously
stated, is a necessary condition for exposure therapy to work, at the same level as VRET, which
could explain the lack of behavioral improvement in this particular study. In that behavioral
measure, the post-treatment real flight, only one participant (10%) in the IET group was able to
complete the flight without the aid of alcohol of anxiolytic medications. In stark contrast, eight
participants (80%) in the VRET without physiological feedback group completed their flight,
and a full 100% (ten participants) of the VRET with physiological feedback group were able to
complete the flight. Although the sample sizes in this study are relatively small, they still display
a significant difference in treatment outcome for IET and VRET group participants.
Similar results were found in Rus-Calafell et al. (2013), which also examined the
comparison of VRET and IET in the fear of flying. Fifteen participants who met diagnostic
criteria for the fear of flying were randomly assigned to either VRET (called VR in the study,
hereafter referred to as VRET) or IET groups and each group received eight sessions of
treatment. During each exposure session, participants’ anxiety was rated on a SUDs scale and
recorded every five minutes. Just as with Wiederhold et al., (2002) the post-treatment assessment
was the completion of a real flight by each participant, however this study also reexamined each
participant in a six month follow-up. Results of this study are similar to Wiederhold et al.
VRET REVIEW AND STUDY PRELUDE 13
(2002)’s results; six of the eight participants in the IET group were able to complete the real
flight without anxiolytic medication while the full seven participants in the VRET group
completed their flight without medication. Additionally, when looking at self-report measures,
participants from the VRET group experienced significantly less anxiety during the real flight at
post-treatment than did participants in the IET group. The six month follow-up procedure also
revealed an interesting result; two of the eight participants in the IET group still met diagnostic
criteria for specific phobia (fear of flying), while not a single participant in the VRET group
continued to meet such criteria. This study, similarly to Wiederhold et al., (2002) displayed a
significant difference between VRET and IET treatment results despite small sample sizes.
The support for VRET’s effectiveness as an intervention and VRET’s coverage of IVET
and IET’s weaknesses is extensive. VRET does have its own limitations and potential
weaknesses, however. The largest of these weaknesses is VR environment immersion level
(Pallavicini et al., 2013), monetary cost (Nelson, 2012), and technological acceptance in certain
populations (Nelson, 2012; Garcia-Palacios et al., 2007).
First and foremost, VRET still has the capability to encounter the fatal flaw of all
exposure therapies; the inability to activate a subject’s fear network and therefore be unable to
alter it. As suggested by the results in Belloch et al. (2014), in which the realistic presentation of
dirty stimuli in a VR environment evoked anxiety in subjects suffering from OCD, VR
environments that appear realistic and feel “real” to the client can evoke the levels of anxiety
necessary for activation and therefore alteration of the fear network. But what if the technology
involved in the VR environment suffers a glitch or is poorly executed? Will that break in
immersion disrupt VRET’s ability to evoke anxiety? To answer this question, Pallavicini et al.
(2013) designed an experiment in which thirty-nine undergraduate students were exposed to an
VRET REVIEW AND STUDY PRELUDE 14
academic exam situation, a scenario that is almost universally considered an aversive real-life
stressor. The participants were exposed to this scenario in one of four conditions: text, audio,
video, and VR. Additionally, in the VR condition, researchers implemented artificial
technological breakdowns (VR headset head tracking was reversed for 20 seconds and students
in the VR environment’s lips did not move in sync with their voice) in order to intentionally
attempt to break down the participants’ subjective feeling of immersion in the VR environment.
The study’s results showed that, when VR environments have sufficient technological
breakdowns of any kind that disable the subject’s ability to feel that the environment is “real”,
VR environments are not even as effective as listen to an audio recording of a narration of a
scenario. These results identify the most significant limitation of VRET when held in comparison
to IET and IVET; IET may not provoke enough anxiety to activate the fear network to a
sufficient level, IVET has significantly disappointing attrition rates, and VRET VR environments
must feel immersive and “real” to subjects in order to provoke sufficient anxiety for fear network
alteration.
The second chief limitation of VRET’s utility is monetary cost of the technology required
to perform VRET interventions. Although the costs of acquiring technology sufficiently
advanced to use VRET has dramatically decreased over the years and the quality of the VR
environments themselves has steadily increased (David et al., 2013), technology sufficiently able
to generate these VR environments can still be expensive. In the meta-analysis of VRET’s utility
in treating PTSD performed by Nelson (2012), the estimated total cost of the equipment needed
to set up a VR therapy environment was US$15,000, which is a high enough cost that it is
exclusionary of many clinical settings, let alone private counseling settings.
VRET REVIEW AND STUDY PRELUDE 15
A third, possibly tertiary limitation of VRET’s utility as a therapeutic intervention for
many populations is the attrition of the treatment in certain populations, most notably older
adults. In Nelson’s (2012) meta-analysis of VRET in PTSD, Belloch et al.’s (2014) study on the
utility of VRET in treating OCD, as well as in Garcia-Palacios et al.’s (2007) study comparing
acceptance rates of IVET and VRET in subjects suffering from specific phobias, older
participants dropped out of, did not choose, or reported distress related to VRET conditions and
VRET technology in general much more frequently than did younger participants. This effect has
not been examined thoroughly in its own right, and future research should look into this effect in
order to determine if this is a persistent limitation of VRET interventions.
We know that VRET can produce similar effect sizes to IVET, the gold standard of
exposure therapy, in populations of a wide variety of anxiety disorders such as specific phobias,
panic disorder, PTSD, and OCD. We also know that VRET can produce similar if not superior
effect sizes to IET, considered an acceptable alternative treatment to IVET, in populations with
specific phobias. Bearing in mind the potential limitations of VRET’s effectiveness stemming
from technological breakdowns and monetary cost, the logical next step that research into VRET
should take is to find affordable VR technologies and equipment and to test those technologies in
order to determine if they can create VR environments that can sufficiently activate a client’s
fear network, opening it to alteration.
An example of emerging, affordable VR equipment/technology is the Oculus Rift®
(Oculus VR, LLC, 2014), a VR peripheral developed for use in video gaming. The Oculus Rift is
currently available only in a developer kit phase of its production, and is not yet in its final
commercially-ready form. It is, however, incredibly affordable when held to other VR equipment
standards, as it costs only US$350 per unit from the creators and works on any computer running
VRET REVIEW AND STUDY PRELUDE 16
Windows, Mac OS, or Linux. Research into whether products like the Oculus Rift can
adequately evoke anxiety and activate a subject’s fear network could be incredibly rewarding. If
affordable equipment like the Oculus Rift works for exposure therapy purposes, its price opens it
up to being available for clinical and private counseling orientations, helping to fight against the
dissemination crisis currently facing the field of mental health care.
VRET REVIEW AND STUDY PRELUDE 17
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