International Journal of
Environmental Research
and Public Health
Article
The Influence of Virtual Forest Walk on Physiological and
Psychological Responses
Emad Alyan 1,* , Theo Combe 1 , Dayang Rohaya Awang Rambli 1,*, Suziah Sulaiman 1 , Frederic Merienne 2
and Nadia Diyana 3
1 Department of Computer and Information Sciences, University Teknologi PETRONAS,
Seri Iskandar 32610, Perak, Malaysia; combetheo@gmail.com (T.C.); suziah@utp.edu.my (S.S.)
2 Arts et Metiers Institute of Technology, LISPEN, HESAM Université, F-71100 Chalon-sur-Saône, France;
frederic.merienne@ensam.eu
3 School of Multimedia Technology and Communication, University Utara Malaysia,
Sintok 06010, Kedah, Malaysia; nadia.diyana@uum.edu.my
* Correspondence: emad.alyan@utp.edu.my (E.A.); dayangrohaya.ar@utp.edu.my (D.R.A.R.)
Citation: Alyan, E.; Combe, T.;
Awang Rambli, D.R.; Sulaiman, S.;
Merienne, F.; Diyana, N. The
Influence of Virtual Forest Walk on
Physiological and Psychological
Responses. Int. J. Environ. Res. Public
Health 2021, 18, 11420. https://
doi.org/10.3390/ijerph182111420
Academic Editor: Paul B. Tchounwou
Abstract: The authors of this paper sought to investigate the impact of virtual forest therapy based
on realistic versus dreamlike environments on reducing stress levels. Today, people are facing an
increase in stress levels in everyday life, which may be due to personal life, work environment,
or urban area expansion. Previous studies have reported that urban environments demand more
attention and mental workload than natural environments. However, evidence for the effects of
natural environments as virtual forest therapy on stress levels has not yet been fully explored. In this
study, a total of 20 healthy participants completed a letter-detection test to increase their stress level
and were then randomly assigned to two different virtual environments representing realistic and
dreamlike graphics. The participants’ stress levels were assessed using two physiological methods
that measured heart rate and skin conductance levels and one psychological method through the
Profile of Mood States (POMS) questionnaire. These indicators were analyzed using a sample t-test
and a one-way analysis of variance. The results showed that virtual forest environments could have
positive stress-relieving effects. However, realistic graphics were more efficient in reducing stress.
These findings contribute to growing forest therapy concepts and provide new directions for future
forest therapy research.
Keywords: virtual reality (VR); stress; forest therapy; psychophysiological response
Received: 21 September 2021
Accepted: 13 October 2021
Published: 29 October 2021
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1. Introduction
Stress is a situation that develops when an individual perceives a mismatch between
the demands of a circumstance and his/her biological, psychological, or social resources [1].
According to the literature, prolonged stress can negatively and severely influence health [2].
Stress is linked to a variety of mental illnesses and cardiovascular problems [3,4]. The envi-
ronment plays an essential role in our capacity to deal with stress factors. The environment
can improve or decrease people’s coping strategies in the face of stressful situations [5–7].
For instance, the urban environment is visually complex and requires more attention than
natural environments [8]. Therefore, spending time in a non-urban area, where attention
is in its natural environment, can help to alleviate urban stress. From a psychological
perspective, Ulrich, et al. [9] presented the stress relief theory, which claims that exposure
to nature can relieve stress and directly impact cognitive restoration.
The association between interaction with forests and public health has long been
argued and extensively demonstrated. The literature suggests that forests may improve
health status more than urban environments [10,11]. Individuals exposed to stimuli derived
from a forest can experience preventive medical effects, acquire physiological relaxation,
and boost immune system weakness [12,13]. The term “forest therapy” refers to a form
Int. J. Environ. Res. Public Health 2021, 18, 11420. https://doi.org/10.3390/ijerph182111420
https://www.mdpi.com/journal/ijerph
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of alternative therapy that helps to strengthen the immune system and enhance mental
health by attaining a state of physiological relaxation [10,14].
There have been many studies on the impacts of forest exposure, mainly focusing on
the psychological and physiological implications of forest therapy. It has been claimed
that visiting forests can reduce one’s cortisol levels, blood pressure, respiratory rate, and
heart rate [12,15,16], which can contribute to alleviating mental symptoms (such as anxiety,
nervousness, stress, and fatigue) and improve mood and cognitive states [17–19]. Another
nature-based well-being practice called forest bathing or “Shinrin-yoku” has been proven
to reduce undue stress and potential burnout [20]. According to several studies, visiting a
forest can prevent disease and strengthen immunity [21].
Despite significant evidence demonstrating the benefits of forest visits, it is difficult
for people in urban cities to regularly visit forests and experience their positive effects.
However, instead of stepping outside, an emerging technology based on virtual reality
(VR) has been developed to provide an immersive environment to simulate interactions
with real nature. For example, a head-mounted display (HMD) can be used to give a
feeling of deep immersion that is very close to the real situation [22]. Recently, VR systems
have rapidly grown and confirmed their effectiveness in mimicking natural forests for
applications of healthcare and psychology disorders [23] such as stress [24], anxiety [25],
and social phobia [26]. Different psychiatric patients have reported that VR environments
can alter their anxiety, cognition, depression, and social functions [27]. For example,
Ahmadpour, Keep, Janssen, Rouf and Marthick [25] suggested that VR could be a practical
solution for pain and anxiety management in various medical procedures. Furthermore,
other studies have demonstrated the ability of VR to reduce posttraumatic stress disorder
(PTSD) symptoms [23] and suggested its use in treating PTSD. Although few studies
have examined the impact of the forest environment on human physiological and mental
health [24,28], the research in this field is still in its infancy.
Consequently, the authors of the present study sought to contribute new knowledge
to forest therapy and to examine the physiological stress level resulting from the effects
of exposure by measuring skin conductance and heart rate. Previous studies have linked
declines in skin conductance [29–31] and heart rate [24,32] to decreased stress levels. Our
aim was to quantify participants’ moods after viewing different forest environments used to
reduce psychological stress through a well-standardized scale—the Profile of Mood States
(POMS) questionnaire, which is extensively used in many situations, including past studies
that assessed mood in people exposed to various virtual forest environments [24,33].
2. Materials and Methods
2.1. Demographics
The sociodemographic information of the participants in this research is reported in
Table 1. The authors of this study enrolled 20 healthy university students comprised of
10 males and 10 females who had normal vision or corrected normal vision and no history
of cardiovascular disease, cognitive impairment, or psychiatric disorders. The average
age of all participants was 21.8 ± 2.2 years old. The participants were instructed to obtain
plenty of sleep (>8 h) and to avoid coffee, smoking, drugs, alcohol, and strenuous physical
activity on the experiment day.
2.2. Study Site and Stimuli
2.2.1. Stress Induction Method
We developed a computerized task based on the letter-detection test (LDT) to provoke
stress in the lab environment [34]. The task involved a sequence of letters displayed on a
computer screen, as shown in Figure 1. Participants had to press the correct keyboard key
as fast as possible. This was a challenging task because the letters were moving so quickly.
Additionally, participants received negative auditory feedback when they pressed the
wrong key. The duration between the two actions shortened every 30 s (from 1 s between
Int. J. Environ. Res. Public Health 2021, 18, 11420
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two letters to 0.25 s), and a stressful noise occurred when the remaining time was less than
a minute.
Table 1. List of the sociodemographic characteristics of the study participants.
N
Gender
Male
Female
Age Group
18–25
Education
University Degree
RE
10
5
5
23 (1.1)
10
Total Sample
DE
10
5
5
20.6 (2.4)
10
Figure 1. Letter-detection test.
2.2.2. Design and Equipment
To examine exposure to the forest environment, we created two virtual environments,
one realistic and the other dreamlike. The dreamlike environment (DE) can be described
as an illusory atmosphere that lacked reality compared to the realistic environment (RE)
(refer to Figure 2). The virtual environments were specifically developed to help reduce
the physiological and psychological stress via improved engagement provided through
virtual immersion in a forest environment with bubbles that disappeared when touched.
These bubbles were incorporated into the environment to capture participants’ attention
and motivate them to complete the task. During the experiment, the participants had to
explore the environments by touching bubbles using a touchpad, looking around, and
hearing various sounds of nature such as birds and waterfalls. Both environments, realistic
and dreamlike, had the same terrain, interactions, and sounds.
The assets for the virtual environments were designed in 3DS Max and compiled in
Unity using Visual Studio. VR equipment included the HTC Vive with a 1440 × 1600 pixel-
per-eye display at 110 degrees tethered viewing angle.
2.3. Measures
2.3.1. Physiological Index
The heart rate (HR) and skin conductance level (SCL) have been utilized as biomarkers
to indicate short-term stress response by non-invasively monitoring individuals’ autonomic
nervous system reactions, particularly when comparing pre and post-experiment data.
Here, the SCL was sampled at 32 Hz using sensors (Model SA9309M, Thought Technol-
ogy) attached to the index and ring fingers to measure skin conductivity in MicroMho
(0–30 MΩ) because MicroMho rises in response to an increase in anger-related arousal [35].
Additionally, the HR was recorded at a sampling rate of 32 Hz through a blood volume
pulse (BVP) sensor (Thought Technologies, model SA9308M) placed on the index finger to
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assess heart rate in beats per minute (bpm). That is, an infrared sensor was used to detect
the participant’s blood cell reflection. The signal reflected by each blood cell was processed
and used to compute the participants’ cardiovascular change based on their pulse and
blood circulation speed. According to previous research, variations in the BVP amplitude
and SCL value imply sympathetic arousal that increases under stress and decreases in a
pleasant environment [36,37].
(a)
(b)
Figure 2. Representation of designed virtual environments: (a) realistic and (b) dreamlike.
2.3.2. Psychological Index
The POMS questionnaire was utilized to monitor mood changes, particularly partici-
pants’ psychological stress [38]. Many studies have demonstrated that POMS is a validated
self-report survey that possesses adequate psychometric properties in clinical psychology,
psychotherapy, and medicine to assess psychological distress and distinct subjective mood
states. It is sensitive to mood-related emotional changes. For instance, Zhang, et al. [39]
used POMS to examine people’s psychological response to an enclosed wooden area. Yu,
Lee,
and
aanndurLbuaon [a1r1e]aΩa. lso
used
this
scale
to
investigate
the
psychological
effects
of
a
VR
forest
This scale consists of 40 options that define subjective feelings in six different mood
states (T: tension; D: depression; A: anger; F: fatigue; C: confusion; and V: vigor). A 5-point
Likert scale, ranging from 0 (Not at all) to 4 (Extremely), was used for each item. The
higher the score, the more pronounced the participant’s emotion was. After the experiment,
participants were asked to fill out the scale based on their emotional states. The total
mood disturbance (TMD) was computed by summing the negative mood state scales and
subtracting V (a positive mood state scale):
TMD = (T + D + A + F + C) − (V)
(1)
In which an increase in the mean value of TMD could imply a deterioration in partici-
pants’ mood.
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2.4. Experimental Procedure
Participants were first briefly introduced to the experiment to allow them to become
accustomed to the environment. This included the purpose and stages of the experiment,
the hardware to be used, and the questionnaires to be filled. Before the experiment, partic-
ipants were required to fill out a consent form for participation. During the experiment,
participants were initially measured as baselines for HR and SCL to ensure they were in
normal states and to allow them to become practically accustomed to the device.
The LDT was then conducted, and the participants were instructed to perform a 2 min
letter detection task. The LDT was designed to induce stress levels in every participant.
After the LDT, the pre-testing of HR and SCL was conducted, reflecting the participants’
stress levels prior to the VR experiment. For 5 min, participants were then randomly
assigned to either a realistic or a dreamlike virtual environment (RE or DE, respectively),
assuming that this could reduce stress to some extent. This was followed by the post-tests,
including the POMS and previous tests (of HR and SCL), demonstrating stress levels after
experiencing the virtual forest environments. The timeline of the process is illustrated
in Figure 3.
Figure 3. Timeline of the experimental process (LDT = letter-detection test; VR = virtual reality;
HR = heartrate; SCL = skin conductance level; POMS = Profile of Mood States).
2.5. Statistical Analysis
A statistical analysis of the experimental data was carried out using MATLAB and
SPSS version 24.0. (SPSS Inc., Chicago, IL, USA). Two analytical methods were used:
(1) for the HR and SCL data before and after the LDT, related paired t-tests were carried
out to verify whether the LDT played a role in increasing stress levels, and (2) for the
same indicators (HR and SCL), the differences between the pre- and post-test for RE and
DE were used to determine whether these environments played a role in relieving stress.
Additionally, a one-way analysis of variance (ANOVA) with Bonferroni correction was
used to evaluate the effects of the two tested environments (RE and DE) on relieving
psychological stress levels. The effect size was calculated using Cohen’s d and partial eta
squared (ηp2). The significance levels were set at * p < 0.05, ** p < 0.01, and *** p < 0.001.
The data are presented as means and standard deviations (SDs).
η
3. Results
3.1. Physiological Response to Virtual Environments
Figure 4 depicts the mean levels of HR and SCL for the twenty participants, along with
the measurements taken before and instantly after the LDT. Paired t-tests were conducted
to examine the change in HR and SCL levels associated with the LDT (refer to Table 2).
The results showed that for participants who completed the LDT, their HR (mean = 93.9,
SD = 17.5) and SCL (mean = 5.8, SD = 3.7) levels were higher than they were at baseline
(HR: mean = 84.9, SD = 15.6; SCL: mean = 3.9, SD = 3.2). Both physiological indexes (HR:
t(1,19) = 3.5, p < 0.01, d = 0.54; SCL: t(1,19) = 7.3, p < 0.001, d = 0.55) showed statistically
significant differences between pre- and post-LDT.
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(a)
(b)
Figure 4. Mean values of (a) HR and (b) SCL for pre- and post-LDT. The error bars indicate the SD,
and the red stars indicate significant differences (** p < 0.01 and *** p < 0.001).
Table 2. The statistical results of physiological indexes (HR and SCL) for pre- and post-test of the
LDT, RE, and DE.
Index
Pre
Mean
SD
Post
Mean
SD
Paired t-Test
t-Value p-Value Cohen’s D
HR
LDT
84.9
15.6
93.9
17.5
RE
93.5
20.0
79.7
16.5
DE
94.2
15.8
86.0
10.8
SCL
LDT
3.9
3.2
5.8
3.7
RE
4.2
2.3
1.8
1.1
DE
7.3
4.3
5.5
5.6
3.5
0.001 **
0.54
3.3
0.005 **
0.75
3.1
0.006 **
0.59
7.3
0.000 ***
0.55
5.3
0.000 ***
1.20
2.5
0.016 *
0.33
SD: standard deviation, HR: heart rate, SCL: skin conductance level, *: p < 0.05, **: p < 0.01, ***: p < 0.001.
Furthermore, the HR and SCL data of the pre- and post-test of the real and dreamlike
environment groups were assessed using paired t-tests. The pre- and post-test data for both
types of virtual environments showed statistically significant differences. Figure 5a,b—for
the HR and SCL data, respectively—indicate that the RE and DE were able to help reduce
the stress levels of the participants. However, the RE (HR: t(1,9) = 3.3, p < 0.01, d = 0.75; SCL:
t(1,9) = 5.3, p < 0.001, d = 1.20) was highly significant in reducing stress levels compared to
the DE (HR: t(1,9) = 3.1, p < 0.01, d = 0.59; SCL: t(1,9) = 2.5, p < 0.05, d = 0.33).
3.2. Psychological Response to Virtual Environments
The mean TMD scores of both virtual environments, RE and DE, are illustrated in
Figure 6, while Table 3 summarizes the statistical results for both environments. The
results show that the RE (mean = 36.8, SD = 14.8) was significantly different from the
DE (mean = 49.5, SD = 14.8). That is, the TMD was significantly decreased (t(1,19) = 1.9,
p < 0.05, d = 0.86) in the RE compared to the DE, where a high TMD score indicates a good
emotional condition.
Table 3. The statistical results of TMD score for the RE and DE.
VR
RE
DE
*: p < 0.05.
Mean
36.8
49.5
Two-Sample t-Test
SD
t-Value
p-Value
Cohen’s D
14.8
14.8
1.9
0.035 *
0.86
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(a)
( b)
Figure 5. Average values of (a) HR and (b) for pre- and post-test of (left) RE and (right) DE. The
error bars indicate the SD, and the red stars indicate significant differences (* p < 0.05, ** p < 0.01, and
*** p < 0.001).
Figure 6. The total mood disturbance (TMD) for the RE and DE. Interpretation: red (*) indicates
p < 0.05.
In addition, a plot was created for the RE and DE of POMS, as shown in Figure 7. The
one-way ANOVA test demonstrated significant differences in the total POMS values and
its subscale (refer to Table 4). The POMS scores of all subscales were more decreased in the
RE compared to the DE. For example, the depression and confusion decreased by 3.3 and
4.4, respectively, and showed significant differences (D, F(1,18) = 5.2, p < 0.05, ηp2 = 0.22; C,
F(1,18) = 11.7, p < 0.01, ηp2 = 0.39). In contrast, tension, anger, fatigue, and vigor decreased
by 2.5, 1.8, 1.4, and 0.7 points, respectively, showing no significant differences.
Int. J. Environ. Res. Public Health 2021, 18, 11420
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η
8 of 12
Figure 7. Comparison of POMS subscales for the RE and DE. Interpretation: red (*) and (**) indicate
p < 0.05 and p < 0.01, respectively. The error bars represent the SD.
Table 4. Statistics for the POMS subscale comparison between the RE and DE.
POMS
Subscale
RE
Mean
SD
DE
Mean
SD
One-Way ANOVA
F-Value p-Value
ηηp2
Tension
13.0
3.3
15.5
3.7
2.6
0.126
0.13
Anger
8.9
3.6
10.7
2.4
1.8
0.200
0.09
Fatigue
10.4
3.8
11.8
4.41
0.6
0.455
0.03
Depression 9.3
3.3
12.6
3.1
5.2
0.035 *
0.22
Vigor
14.6
3.6
15.3
3.6
0.2
0.671
0.01
Confusion 9.8
3.0
14.2
2.7
11.7
0.003 **
0.39
RE: realistic environment, DE: dreamlike environment, SD: standard deviation, *: p < 0.05, **: p < 0.01.
4. Discussion
The authors of this study evaluated the restorative states of participants’ psychological
and physiological stress before and after viewing realistic and dreamlike environments
with VR devices. The results indicated that the use of VR-based forest environments could
be useful in aiding mental well-being. Importantly, we found that the use of VR led to
significant decreases in participants’ psychological and physiological stress levels.
4.1. The Impact of Virtual Forest Walk on Physiological Responses
One of the most remarkable outcomes in this study was the significant association
between virtual forest environments and positive psychological responses. The physio-
logical measurements (HR and SCL) demonstrated that participants in the virtual forest
environments reported more significant positive psychological impacts. For example, upon
exposure to realistic and dreamlike virtual environments, the mean values of HR decreased
by approximately 14.76% and 8.70%, respectively, and the SCL decreased by 57.14% and
24.66%, respectively. The participants in the virtual forest environments with dreamlike
scenes showed significant positive effects to a certain extent (HR: p < 0.01; SCL: p < 0.05),
though not as significant as with realistic scenes (HR: p < 0.01; SCL: p < 0.001).
The results showed that a realistic environment could substantially positively impact
sympathetic activity, resulting in a quicker recovery from stressful situations. These
findings were generally consistent with past research that discussed physiological response
when exposed to forest environments [24] and the positive effect of rural landscapes on
stress [40]. However, the reported high significance in the realistic environment might have
been more related to the greenery of scenes compared to the dreamlike environment, which
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was consistent with previous research findings on the use of green environments to mitigate
stress [40,41]. This potential of VR has been validated by other studies that have reported its
capability to reduce pain, fear, and anxiety associated with needle-related procedures [42]
and others that have revealed its positive impact on psychiatric disorders [23].
4.2. The Impact of Virtual Forest Walk on Psychological Responses
From the standpoint of psychological response, this study also showed the impact
of realistic and dreamlike forest environments on stress recovery. The measured TMD
data were analyzed with the appropriate two-sample t-test, which proved that the realistic
and dreamlike environments had statistically significant different effects on psychological
stress levels. The TMD values were significantly decreased (p < 0.05) when participants
were exposed to the realistic environment compared to the dreamlike environment. This
suggested that the realistic environment could relieve stress levels to a better extent than
the dreamlike environment, supporting the results of the physiological measures.
Further analysis based on one-way ANOVA showed the differences between the real-
istic and dreamlike environments were significant in two subscales (depression: p < 0.05;
confusion: p < 0.01) of the POMS. This variation could have been due to a variety of natural
factors in the VR of the two environments. This result is compatible with our physio-
logical results and those of several studies related to the effects of forest environments
on, e.g., stress relief, emotional situation adaptation, the positive association between
health parameters and natural environments, and the positive impact of the forest on the
activity of the nervous system (such as autonomic activity) [33,40,41,43,44]. Generally,
walking is connected with therapeutic effects, and most people consider it a beneficial
activity [45]. Past research studies have specifically looked at the impact of VR walking on
well-being outcomes, and evidence suggests that even small amounts of outdoor exercise
could improve self-esteem and mood [46]. The results of our study imply that VR nature
experiences may be an adequate substitute for individuals who cannot visit natural areas
for any reason.
4.3. Limitations and Directions for Future Research
This study had some limitations that could be addressed in future research. First, the
authors of this study only investigated the stress-relieving impact of two forest environ-
ments. A greater variety of real forest environments could be considered in future research.
Researchers should explore the interaction of environmental characteristics such as climate
and lighting with psychophysiological effects. Second, to achieve consistency in the data,
future research should consider the participants’ prior experience with VR. Third, the au-
thors of this study observed that different forest environments had various stress recovery
effects. However, the underlying causes of the variations, potentially including beauty,
naturalness, and peace of mind, were not discovered. That is, the internal mechanism
responsible for the various stress recovery effects was not identified. Fourth, in addition to
the relatively small sample size used in the study, the target population was undergraduate
students, so our results cannot be generalized to the general public who may participate
in forest therapy. Fifth, more physiological measures such as salivary alpha-amylase and
cortisol levels could be considered in future studies to validate the HR and SCL measures.
In the future, heart rate variability (HRV) and neuroimaging techniques such as EEG,
fNIRS, and fMRI should be added to improve the objectivity of research results.
5. Conclusions
The authors of this study evaluated the impacts of two virtual forest environments on
participants’ moods and psychophysiological responses by providing objective evidence
through HR, SCL, and POMS measures. The findings demonstrated that the forest envi-
ronment is one of the contributing factors to the psychophysiological impacts in forest
therapy. However, diverse types of forest environments may have varying impacts on
stress reduction. The forest environments used in this study had the effect of relieving
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stress, especially the realistic forest environment, which played a more significant role in
relieving physiological stress (HR: p < 0.01; SCL: p < 0.001) than the dreamlike environment
(HR: p < 0.01; SCL: p < 0.05). In this context, the realistic forest environment was also more
effective at rapidly alleviating psychological stress (POMS: p < 0.05) than the dreamlike
environment. These findings may pave the way for future research into forest therapy.
Modern life is becoming increasingly stressful, so understanding how to maximize the
benefits of virtual forest environments is essential.
Author Contributions: Conceptualization, E.A., T.C., D.R.A.R. and S.S.; methodology, E.A., D.R.A.R.,
S.S. and F.M.; validation, D.R.A.R., S.S., E.A. and N.D.; investigation, T.C., D.R.A.R. and S.S.; resources,
D.R.A.R., S.S. and F.M.; writing—original draft preparation, E.A.; writing—review and editing,
D.R.A.R., S.S. and N.D.; supervision, D.R.A.R. and S.S.; project administration, D.R.A.R. and S.S.;
funding acquisition, D.R.A.R. and S.S. All authors have read and agreed to the published version of
the manuscript.
Funding: This research is supported by Yayasan Universiti Teknologi PETRONAS through YUTP
Fundamental Research Grant No. 015LC0-001.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available on request from the
corresponding author.
Conflicts of Interest: The authors declare no conflict of interest.
References
1. Evans, G.; Cohen, S.; Stokols, D.; Altman, I. Handbook of Environmental Psychology; Wiley: Hoboken, NJ, USA, 1987.
2. Lovallo, W.R.; Buchanan, T.W. Stress hormones in psychophysiological research: Emotional, behavioral, and cognitive implica-
tions. In Handbook of Psychophysiology; Cambridge University Press: Cambridge, UK, 2017.
3. Van Dalfsen, J.H.; Markus, C.R. The influence of sleep on human hypothalamic–pituitary–adrenal (HPA) axis reactivity: A
systematic review. Sleep Med. Rev. 2018, 39, 187–194. [CrossRef]
4. Ushakov, V.A.; Ivanchenko, S.V.; Gagarina, A.A. Psychological stress in pathogenesis of essential hypertension. Curr. Hypertens.
Rev. 2016, 12, 203–214. [CrossRef]
5. Berto, R. The role of nature in coping with psycho-physiological stress: A literature review on restorativeness. Behav. Sci. 2014, 4,
394–409. [CrossRef] [PubMed]
6. Alyan, E.; Saad, N.M.; Kamel, N.; Rahman, M.A. Workplace design-related stress effects on prefrontal cortex connectivity and
neurovascular coupling. Appl. Ergon. 2021, 96, 103497. [CrossRef]
7. Alyan, E.; Saad, N.M.; Kamel, N. Effects of Workstation Type on Mental Stress: fNIRS Study. Hum. Factors 2020, 0018720820913173.
[CrossRef] [PubMed]
8. White, H.; Shah, P. Attention in Urban and Natural Environments. Yale J. Biol. Med. 2019, 92, 115–120. [PubMed]
9. Ulrich, R.S.; Simons, R.F.; Losito, B.D.; Fiorito, E.; Miles, M.A.; Zelson, M. Stress recovery during exposure to natural and urban
environments. J. Environ. Psychol. 1991, 11, 201–230. [CrossRef]
10. Bielinis, E.; Takayama, N.; Boiko, S.; Omelan, A.; Bielinis, L. The effect of winter forest bathing on psychological relaxation of
young Polish adults. Urban For. Urban Green. 2018, 29, 276–283. [CrossRef]
11. Yu, C.-P.; Lee, H.-Y.; Luo, X.-Y. The effect of virtual reality forest and urban environments on physiological and psychological
responses. Urban For. Urban Green. 2018, 35, 106–114. [CrossRef]
12. Song, C.; Ikei, H.; Kobayashi, M.; Miura, T.; Li, Q.; Kagawa, T.; Kumeda, S.; Imai, M.; Miyazaki, Y. Effects of viewing forest
landscape on middle-aged hypertensive men. Urban For. Urban Green. 2017, 21, 247–252. [CrossRef]
13. Ochiai, H.; Ikei, H.; Song, C.; Kobayashi, M.; Takamatsu, A.; Miura, T.; Kagawa, T.; Li, Q.; Kumeda, S.; Imai, M. Physiological and
psychological effects of forest therapy on middle-aged males with high-normal blood pressure. Int. J. Environ. Res. Public Health
2015, 12, 2532–2542. [CrossRef]
14. Song, C.; Ikei, H.; Miyazaki, Y. Physiological effects of nature therapy: A review of the research in Japan. Int. J. Environ. Res.
Public Health 2016, 13, 781. [CrossRef] [PubMed]
15. Stigsdotter, U.K.; Corazon, S.S.; Sidenius, U.; Kristiansen, J.; Grahn, P. It is not all bad for the grey city–A crossover study on
physiological and psychological restoration in a forest and an urban environment. Health Place 2017, 46, 145–154. [CrossRef]
16. Annerstedt, M.; Jönsson, P.; Wallergård, M.; Johansson, G.; Karlson, B.; Grahn, P.; Hansen, Å.M.; Währborg, P. Inducing
physiological stress recovery with sounds of nature in a virtual reality forest—Results from a pilot study. Physiol. Behav. 2013, 118,
240–250. [CrossRef]
Int. J. Environ. Res. Public Health 2021, 18, 11420
11 of 12
17. Tomao, A.; Secondi, L.; Carrus, G.; Corona, P.; Portoghesi, L.; Agrimi, M. Restorative urban forests: Exploring the relationships
between forest stand structure, perceived restorativeness and benefits gained by visitors to coastal Pinus pinea forests. Ecol. Indic.
2018, 90, 594–605. [CrossRef]
18. Korpela, K.; Savonen, E.-M.; Anttila, S.; Pasanen, T.; Ratcliffe, E. Enhancing wellbeing with psychological tasks along forest trails.
Urban For. Urban Green. 2017, 26, 25–30. [CrossRef]
19. Tsunetsugu, Y.; Lee, J.; Park, B.-J.; Tyrväinen, L.; Kagawa, T.; Miyazaki, Y. Physiological and psychological effects of viewing
urban forest landscapes assessed by multiple measurements. Landsc. Urban Plan. 2013, 113, 90–93. [CrossRef]
20. Hansen, M.M.; Jones, R.; Tocchini, K. Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review. Int. J.
Environ. Res. Public Health 2017, 14, 851. [CrossRef]
21. Chae, Y.; Lee, S.; Jo, Y.; Kang, S.; Park, S.; Kang, H. The Effects of Forest Therapy on Immune Function. Int. J. Environ. Res. Public
Health 2021, 18, 8440. [CrossRef] [PubMed]
22. Smith, J.W. Immersive virtual environment technology to supplement environmental perception, preference and behavior
research: A review with applications. Int. J. Environ. Res. Public Health 2015, 12, 11486–11505. [CrossRef]
23. Cies´lik, B.; Mazurek, J.; Rutkowski, S.; Kiper, P.; Turolla, A.; Szczepan´ ska-Gieracha, J. Virtual reality in psychiatric disorders: A
systematic review of reviews. Complement. Ther. Med. 2020, 52, 102480. [CrossRef] [PubMed]
24. Wang, X.; Shi, Y.; Zhang, B.; Chiang, Y. The Influence of Forest Resting Environments on Stress Using Virtual Reality. Int. J.
Environ. Res. Public Health 2019, 16, 3263. [CrossRef]
25. Ahmadpour, N.; Keep, M.; Janssen, A.; Rouf, A.S.; Marthick, M. Design strategies for virtual reality interventions for managing
pain and anxiety in children and adolescents: Scoping review. JMIR Serious Games 2020, 8, e14565. [CrossRef]
26. Wechsler, T.F.; Kümpers, F.; Mühlberger, A. Inferiority or even superiority of virtual reality exposure therapy in phobias?—A
systematic review and quantitative meta-analysis on randomized controlled trials specifically comparing the efficacy of virtual
reality exposure to gold standard in vivo exposure in agoraphobia, specific phobia, and social phobia. Front. Psychol. 2019,
10, 1758.
27. Park, M.J.; Kim, D.J.; Lee, U.; Na, E.J.; Jeon, H.J. A literature overview of virtual reality (VR) in treatment of psychiatric disorders:
Recent advances and limitations. Front. Psychiatry 2019, 10, 505. [CrossRef]
28. Reese, G.; Kohler, E.; Menzel, C. Restore or get restored: The effect of control on stress reduction and restoration in virtual nature
settings. Sustainability 2021, 13, 1995. [CrossRef]
29. Huang, Q.; Yang, M.; Jane, H.A.; Li, S.; Bauer, N. Trees, grass, or concrete? The effects of different types of environments on stress
reduction. Landsc. Urban Plan. 2020, 193, 103654. [CrossRef]
30. Van ’t Wout, M.; Spofford, C.M.; Unger, W.S.; Sevin, E.B.; Shea, M.T. Skin Conductance Reactivity to Standardized Virtual Reality
Combat Scenes in Veterans with PTSD. Appl. Psychophysiol. Biofeedback 2017, 42, 209–221. [CrossRef] [PubMed]
31. Bari, D.S.; Aldosky, H.Y.Y.; Tronstad, C.; Martinsen, Ø.G. The correlations among the skin conductance features responding to
physiological stress stimuli. Skin Res. Technol. 2021, 27, 582–588. [CrossRef] [PubMed]
32. Lee, J.; Park, B.J.; Tsunetsugu, Y.; Ohira, T.; Kagawa, T.; Miyazaki, Y. Effect of forest bathing on physiological and psychological
responses in young Japanese male subjects. Public Health 2011, 125, 93–100. [CrossRef]
33. Gao, T.; Zhang, T.; Zhu, L.; Gao, Y.; Qiu, L. Exploring Psychophysiological Restoration and Individual Preference in the Different
Environments Based on Virtual Reality. Int. J. Environ. Res. Public Health 2019, 16, 3102. [CrossRef]
34. Hodapp, V.; Heiligtag, U.; Störmer, S.W. Cardiovascular reactivity, anxiety and anger during perceived controllability. Biol.
Psychol. 1990, 30, 161–170. [CrossRef]
35. Stemmler, G. Physiological processes during emotion. In The Regulation of Emotion; Psychology Press: Mahwah, NJ, USA, 2004;
pp. 33–70.
36. Yin, J.; Zhu, S.; MacNaughton, P.; Allen, J.G.; Spengler, J.D. Physiological and cognitive performance of exposure to biophilic
indoor environment. Build. Environ. 2018, 132, 255–262. [CrossRef]
37. Alvarsson, J.J.; Wiens, S.; Nilsson, M.E. Stress recovery during exposure to nature sound and environmental noise. Int. J. Environ.
Res. Public Health 2010, 7, 1036–1046. [CrossRef]
38. McNair, D.; Lorr, M.; Droppleman, L. Revised manual for the profile of mood states. S. Diego Educ. Ind. Test. Serv. 1992, 7, 732–733.
39. Zhang, X.; Lian, Z.; Ding, Q. Investigation variance in human psychological responses to wooden indoor environments. Build.
Environ. 2016, 109, 58–67. [CrossRef]
40. Wang, X.; Zhu, H.; Shang, Z.; Chiang, Y. The influence of viewing photos of different types of rural landscapes on stress in Beijing.
Sustainability 2019, 11, 2537. [CrossRef]
41. Mitchell, R.; Popham, F. Effect of exposure to natural environment on health inequalities: An observational population study.
Lancet 2008, 372, 1655–1660. [CrossRef]
42. Czech, O.; Wrzeciono, A.; Rutkowska, A.; Guzik, A.; Kiper, P.; Rutkowski, S. Virtual Reality Interventions for Needle-Related
Procedural Pain, Fear and Anxiety—A Systematic Review and Meta-Analysis. J. Clin. Med. 2021, 10, 3248. [CrossRef] [PubMed]
43. Joung, D.; Kim, G.; Choi, Y.; Lim, H.; Park, S.; Woo, J.-M.; Park, B.-J. The prefrontal cortex activity and psychological effects of
viewing forest landscapes in autumn season. Int. J. Environ. Res. Public Health 2015, 12, 7235–7243. [CrossRef]
44. Herzog, T.R.; Black, A.M.; Fountaine, K.A.; Knotts, D.J. Reflection and attentional recovery as distinctive benefits of restorative
environments. J. Environ. Psychol. 1997, 17, 165–170. [CrossRef]
Int. J. Environ. Res. Public Health 2021, 18, 11420
12 of 12
45. Rybråten, S.; Skår, M.; Nordh, H. The phenomenon of walking: Diverse and dynamic. Landsc. Res. 2019, 44, 62–74. [CrossRef]
46. Barton, J.; Pretty, J. What is the best dose of nature and green exercise for improving mental health? A multi-study analysis.
Environ. Sci. Technol. 2010, 44, 3947–3955. [CrossRef] [PubMed]