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Systematic Review

Urban Green Spaces and Mental Well-Being: A Systematic Review of Studies Comparing Virtual Reality versus Real Nature

by
Liyuan Liang
1,
Like Gobeawan
2,
Siu-Kit Lau
3,
Ervine Shengwei Lin
3 and
Kai Keng Ang
1,4,*
1
Institute for Infocomm Research, Agency for Science, Technology and Research (A*STAR), 1 Fusionopolis Way, Singapore 138632, Singapore
2
Institute of High Performance Computing, Agency for Science, Technology and Research (A*STAR), 1 Fusionopolis Way, Singapore 138632, Singapore
3
Department of Architecture, College of Design and Engineering, National University of Singapore, Singapore 117575, Singapore
4
College of Computing and Data Science, Nanyang Technological University, 50 Nanyang Ave., Singapore 639798, Singapore
*
Author to whom correspondence should be addressed.
Future Internet 2024, 16(6), 182; https://doi.org/10.3390/fi16060182
Submission received: 5 April 2024 / Revised: 9 May 2024 / Accepted: 14 May 2024 / Published: 21 May 2024
(This article belongs to the Special Issue Advances in Extended Reality for Smart Cities)
Browse Figures
Versions Notes

Abstract

:
Increasingly, urban planners are adopting virtual reality (VR) in designing urban green spaces (UGS) to visualize landscape designs in immersive 3D. However, the psychological effect of green spaces from the experience in VR may differ from the actual experience in the real world. In this paper, we systematically reviewed studies in the literature that conducted experiments to investigate the psychological benefits of nature in both VR and the real world to study nature in VR anchored to nature in the real world. We separated these studies based on the type of VR setup used, specifically, 360-degree video or 3D virtual environment, and established a framework of commonly used standard questionnaires used to measure the perceived mental states. The most common questionnaires include Positive and Negative Affect Schedule (PANAS), Perceived Restorativeness Scale (PRS), and Restoration Outcome Scale (ROS). Although the results from studies that used 360-degree video were less clear, results from studies that used 3D virtual environments provided evidence that virtual nature is comparable to real-world nature and thus showed promise that UGS designs in VR can transfer into real-world designs to yield similar physiological effects.

1. Introduction

Virtual reality (VR) is increasingly adopted by architects as it allows a design to be visualized in immersive 3D and experienced better than 2D drawings and even miniature models [1]. In the design of landscapes such as urban green spaces (UGS), VR has the potential to improve designs and maximize mental well-being benefits [2]. However, UGS designs in VR may not be valid, as the psychological effects of nature in VR may not be transferable into the real world [3,4]. For instance, Gao et al. compared participants’ preferences for different UGS through either on-site, VR (panorama of landscape viewed through a head-mounted display (HMD)) or photos and found that participants’ preference for different types of UGS differed between the on-site and VR conditions [3]. Herman and Sherman [4] found that while exposure to virtual nature reduced anxiety, it did not improve directed attention as predicted by the attention restoration theory and as reported in other studies [5,6,7]. Thus, the effects of nature and green elements in VR may be different from reality and UGS designs in VR may be sub-optimal when transferred into the real world. Thus, it is important to establish the validity of the mental well-being or psychological benefits of nature in VR.
While many studies have established the effectiveness of nature in VR to elicit positive psychological benefits [8,9,10,11,12,13,14,15], these studies have different premises. These studies are based on the premise of knowing whether experiencing nature through VR can be used as a replacement for physically experiencing nature, for scenarios where physical nature is inaccessible due to distance or due to school or work commitments [12,16]. Thus, these studies are concerned only with whether experiencing nature through VR can have positive psychological benefits but not whether the experience of nature through VR produces the same psychological benefit as the same nature in the real world, which is the concern when designing nature environments and UGS through VR.
The ecological validity of nature in VR can be addressed by studies comparing the psychological effects of nature in VR with the same nature in the real world. While there have been reviews about the psychological benefits of virtual nature [17,18,19] and physical nature [20,21,22], there is, to our knowledge, no review of studies that explicitly compare virtual nature to real-world nature to establish the ecological validity of virtual nature.
Several review articles review the psychological benefits of nature through virtual reality. Frost et al. [17] conducted a systematic review of the psychological benefits of immersion in nature through VR, identifying 21 studies, with some evidence for a decreased negative affect. Brambilla et al. systematically reviewed the effect of nature in VR on nature connectedness in non-clinical populations. Lee et al. [18] systematically reviewed a range of mental health effects of green experiences through VR and synthesized results from 21 studies. Gentile et al. [19] systematically reviewed the stress reduction effects of nature exposure through VR. However, these systematic reviews were concerned with the psychological benefits of nature in VR but not with whether they are valid and correspond with real-world nature.
Other reviews have looked at the psychological benefits of physical or real-world nature. For example, Bolouki [20] reviewed studies that used EEG, fMRI, and fNIRS to measure neurophysiological differences between experiencing urban and natural environments. Grilli and Sacchelli [21] reviewed studies of stress relief and relaxation from forests. Tillmann et al. [22] reviewed studies of the mental health benefits of nature for children and teenagers (0–18 years old).
Thus, while there is an abundance of reviews (and studies) establishing the psychological benefits of physical nature and nature through VR, there has been no review that explicitly compares virtual nature to real-world nature to establish the ecological validity of virtual nature. Thus, we seek to fill the gap with a review of studies explicitly comparing virtual nature to real-world nature to establish whether they have the same positive psychological effects.
To do so, we develop a search strategy to explicitly include articles that involve both a virtual reality study and a real-world study.
We analyze the studies found from the search by classifying them according to the type of VR setup used, more specifically, into 360-degree video through HMD and the 3D virtual environment experienced through HMD as these are the two main types of VR setups used in the studies.
We extract details about methods and the experimental setup of studies to analyze the heterogeneity of the methods and devices between studies, which may cause variation in results. We also identify standard questionnaires for mental states that are common among studies. This helps to establish a common standard for comparison among studies and serves as a guideline for inclusion in future studies.
Finally, we synthesize the results across the 360-degree video studies and the 3D virtual environment studies for the ecological validity of nature experienced through VR. We show that nature experienced through 360-degree videos has more mixed results, while evidence suggests that nature experienced in VR through a 3D virtual environment is ecologically valid and produces the same psychological benefits as nature in the real world. As landscape and UGS design involve building 3D virtual models just as in the 3D virtual environment studies, this suggests the ecological validity of designs in VR and that landscape or UGS designs in VR can be transferred into real-world designs.

2. Methods

2.1. Background: Types of VR Setups and Level of Immersion

We provide a general scale ranking different VR setups on the level of immersion (Figure 1). However, the immersiveness still depends on the physical conditions of the setup. For example, if the setup causes perceptual incongruencies, it can still cause a less immersive experience [23].
We rank the setups such that HMD are more immersive than CAVE [24], which is in turn more immersive than modalities that are presented through a flat-screen [25]. For content presented through a flat-screen, 360-degree panorama is more immersive than 2D pictures [26]. Similarly, for content presented through HMD, virtual 3D space is more immersive than 360-degree video [27].
Head-mounted displays are in general more immersive than flat-screen displays because of stereoscopic vision and the responsiveness of the field of view to head movements [28]. In HMD, the field of view changes in response to head movements, just like in natural visual perception, helping to create a sense of immersion [29].
We rank the CAVE as lower than HMD setups because the CAVE is still projected onto flat-screens [24]. The CAVE is ranked higher than 2D pictures and 360-degree panorama on flat-screens because it allows greater free movement [24].
In 360-degree videos, specialized 360-degree cameras are used to capture a spherical panorama of a real-world scene [30] (Figure 2, top). Users watching the video through HMD can look around in every direction as if they were physically present at the location [30]. These videos capture the entirety of the surrounding environment, providing a passive panoramic experience [30].
Virtual 3D spaces (Figure 2, bottom), on the other hand, are created as 3D-modelled environments that the user can move around in [31]. As they move to different positions and move their head to look in a different direction, a view is rendered to be displayed through the HMD based on their position and viewing angle and the 3D virtual model [31]. The objects in the modeled environment may also be developed with natural movements and behaviors and respond with natural behavior when touched [31]. Thus, unlike 360-degree videos, these environments support a higher level of interaction, allowing users to engage with the virtual world in a more dynamic and responsive manner.
While each of the five types of VR setups detailed above and other types of setups are used in different studies, this review only includes studies using HMD as these are the most common and most canonical types of VR. One study that used CAVE is also included.

2.2. Search Strategy

We identified that articles needed to include three key concepts.
Firstly, they need to include the concept of nature. Secondly, they need to include the concept of the mental or psychological effect of the study. Thirdly, they need to simultaneously involve studies of both the virtual and real world. For an article to include both VR and the real world, we needed to specify that the terms occur in close proximity, for example, in the phrase “virtual and real nature”, as the terms may be non-specific and used in other contexts. If we searched for these separately, for example, with “virtual” and “real”, studies including “virtual” only may be included, as “real” may appear in another context that is not about real-world studies.
Thus, the keywords for each concept are detailed in Table 1. Each concept must be present in the article to be included. Hence, the keywords for each concept are combined with an AND operator. As the proximity operator differs for different databases, we used the respective proximity operator when searching the third concept, maintaining a maximum separation of 5 words.

2.3. Screening

We conducted the review according to guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement for screening articles during the systematic review process (Figure 3).
Two researchers independently screened articles for relevance and subsequently assessed the quality and relevance of the articles for inclusion in this review. Any conflicting decisions were resolved by discussion.
We first searched for records on three databases: PubMed, Web of Science, and Scopus. This yielded 123, 360, and 297 articles, respectively, for a total of 780. From these 780 articles, we removed 210 duplicate records, resulting in 570 articles. We screened these 570 articles by examining their title and abstracts to determine whether they fit the topic of our review. To determine that the article fits the topic, we determined if the article was on the topic of environmental psychology in VR or, in other words, that it involved each of the three key concepts: (1) VR, (2) nature, and (3) psychological effects. Thus, we excluded 45 articles that are reviews and 513 articles that are on unrelated topics. Many of these articles used the keywords “nature” and “real” in other contexts.
For all articles with relevant topics, we retrieved the full text for screening. We screened the full text to determine that the study involved both a VR experiment and a real-world experiment. We excluded three articles that used only a VR experiment but had no physical real-world experiment.
One study [32] used images of nature displayed on a computer in the VR condition. As it was the only study to use 2D images, we excluded it as it was in a less immersive mode than either the 360-degree video or 3D virtual environment, which was what most other studies used.
One article [33] only involved the virtual experiment. However, they modeled the virtual environment based on the physical environment of a previous study and compared the effects of both virtual and physical environments, which fit the other studies being reviewed and we chose to include it.

3. Analysis of Study Methods

3.1. Type of VR

Among the 12 papers reviewed, there were two primary modes of VR used: 360-degree videos of nature viewed through HMD and experience of nature in a fully immersive virtual world.
Five studies used 360-degree videos as a virtual reality method, while five studies used a virtual world model as a virtual reality method. One study [34] used both 360-degree videos and a virtual world model as a VR method. They found that a virtual environment was more effective than 360-degree videos. One study [35] used a Cave Automatic Virtual Environment (CAVE), which is a VR setup where the environment is projected onto the walls and floor and the subject can rotate the view and move around. As it allows movement and is more interactive, it is similar to a virtual environment, so we group it together with studies using virtual environments.
Even though both virtual environment and 360-degree video are experienced through HMD, they differ in the amount of interactivity allowed. In a virtual environment, participants have greater interactivity as they can move in the environment and interact with the objects, which produces a response. The ability to interact with the environment creates a greater sense of immersion. On the other hand, with 360-degree videos, participants can look in different directions, just as in the virtual environment, but they have less ability to interact. Thus, the virtual environment may be more immersive than the 360-degree video and consequently have greater psychological benefits. Thus, we separate the studies according to the type of VR they used and whether they used 360-degree videos or virtual environments so that fair comparisons and trends can emerge.

3.2. VR Devices

In studies that use 360-degree video for VR, three studies used the Samsung Gear VR device with a smartphone, one study used an Oculus Rift headset, and one study used an HMD but did not specify the model of the headset. Thus, there is a variety of VR devices with the most common being the Samsung Gear VR.
In studies that use virtual environments for VR, three studies used the HTC Vive, two studies used the Oculus Rift headset, and one study used the CAVE VR setup. Thus, there is a variety of VR devices used, with HTC Vive being slightly more popular than the Oculus Rift headset.

3.3. Physical Environment

In terms of the physical environment involved, there was a mix of different types of nature environments but the forest environment was the most common. In all studies combined, 6 out of 12 studies used a forest or forested environment as the physical and virtual nature environment. Others used natural environments such as panoramic lake views [36] and river paths [9]. In the virtual environment group, 4 out of 6 studies used a forest as the nature environment.

3.4. Within Subject Design

There was a roughly even split of studies using the within-subject design and not using within subject design. Five out of 12 studies used the within-subject design. A within-subject design means that each participant experiences both the virtual nature condition and real-world nature condition, which allows their mental states to be compared between virtual and real-world conditions. Without a within-subject design, the mental states must be averaged within each condition and compared.

3.5. Mental States

In this section, we tabulate and analyze the common standard questionnaires used in studies (Figure 4). The acronyms and full names of common standard questionaires are tabulated in Table 2. As the mental state measurement is a common goal regardless of whether the VR mode is 360-degree video or 3D virtual environment, we combine analysis across both types of VR mode.
From a tabulation and analysis of the questionnaires employed by these studies, we find that PANAS is the most common standard questionnaire used with 7 out of 12 studies using PANAS. Following this, PRS and ROS are used in three studies, both of which measure restoration. Restoration is a common prediction due to the attention restoration theory, a main theory behind the positive beneficial effect of nature. Finally, SVS is used in 2 studies. Besides psychological surveys, physiological measurements like ECG and skin conductance are also used in 2 studies.
The infrequent use of physiological measurements such as ECG and EEG suggests an area of future research. Physiological measurements may serve as more objective measurements unlike psychological questionnaires, which can be biased by location and intervention methods and expectations.

4. Synthesis of Studies across the 360-Degree Video and 3D Virtual Environment

4.1. Studies Using the 360-Degree Video

Studies using 360-degree video as VR mode is tabulated in Table 3. In the 360-degree video group, 2 out of 5 studies reported that virtual nature produces similar psychological benefits as nature in the real world. In the study by Chirico and Gaggioli [36], participants experienced similar emotions when exposed to a contemplative natural scene in both real life and virtual reality, with the exception of higher levels of anger in the real-life condition and higher amusement in VR. The sense of presence reported was also similar in both scenarios, suggesting that VR can closely mimic real life in terms of emotional response and presence.
Browning et al. [42] found that 6 min of outdoor exposure to nature (sitting in a foldable chair in an outdoor nature environment) had a greater effect on improving positive mood, while 6 min of virtual exposure to nature via 360-degree videos of the same environment with recorded soundscape only maintained positive mood before and after using VR to expose to nature.
In the Calogiuri et al. [43] study, they found that while participants reported similar restorativeness between the real-world condition and virtual condition, actual enjoyment of a walk and change in effect were higher in the real-world condition than in the virtual condition. However, they attribute a cause to cybersickness from using the HMD. Such a problem can be overcome by user self-selection or improvement in HMD technology to alleviate cybersickness.
Palanica et al. [44] found that while there was a difference in encouraging creativity in participants in a VR condition when comparing nature vs. urban stimuli, that difference vanished when switching to a real-world condition where participants sat on a chair in an outdoor scene. However, in the second study where they reported that virtual and real conditions had different results, Palanica et al. [44] actually compared 2D videos shown on iPad flat-screens with the real environment and not the videos experienced through HMD devices, which may account for the discrepant results. An HMD may be a better comparison and be more similar.
Thus, there is mixed evidence of whether virtual nature through 360-degree videos can have the same psychological benefit as nature in the real world. However, it may be partly attributed to practical details with the VR setup, like cybersickness.

4.2. Studies Using the 3D Virtual Environment Group

Studies using 3D virtual environment as VR mode is tabulated in Table 4. In the 3D virtual environment group, the results in 4 out of 6 studies showed that exposure to virtual nature had comparable effects with exposure to nature in the real world. One study [45] found no change in affect in both the VR condition and the real-world condition but a mild to moderate change in relaxation scores. Given the negative result even in the real-world exposure, we omitted the result instead of treating it as comparable.
In this study, Hejtmánek et al. [45] described a method for creating a digital twin of a physical forest from a LIDAR scan of the physical forest. They recruited 25 participants, of which 10 participants participated in both the VR forest condition and the real-world forest condition. They found no change in affect in both the VR condition and the real-world condition but a statistically significant but mild to moderate change in relaxation scores. Thus, even though they found no change in effect, the results did not differ between the VR forest and the real-world forest conditions.
In another study, Mattila et al. [33] compared the restorative effects of a VR forest environment with the restorative effect of real forests. It was found that a short exposure to this environment resulted in significant improvements in mood, vitality, and perceived restoration outcomes. Additionally, the VR environment was generally perceived as restorative as physical forests, indicating that VR could be an effective restorative tool during a typical work or school day.
Ünal et al. [35] showed that a virtual natural environment of a butterfly garden produced greater restoration than a virtual urban environment and was similar to the physical butterfly garden, which the virtual butterfly garden was modeled after, complete with soundscape and motion of the butterflies.
Mihara et al. [46] produced one of the few studies that employed physiological measurements, which include ECG and EEG. They compared the full-scale window with blinds open and the full-scale window with blinds closed in an office setting and found comparable evidence based on physiological measurements for virtual and real conditions.
Nukarinen et al. [34] conducted an experiment with two virtual conditions: a 3D forest environment and a 360-degree video of the forest, both experienced through HMD and measured both psychological and physiological restoration. They found that in terms of physiological measurements like HR and HRV, real forests were more restorative than virtual forests, even though results were more comparable when using psychological measurements. They also concluded that 3D forests were more restorative than 360-degree videos of the same forests, even though both are experienced through HMD.
Reese et al. [47] compared forest bathing both physically and through VR and found that there was no significant difference between the two interventions. Before and after measurements show that in both conditions, the positive and negative affect, subjective vitality, and stress improved.
Thus, compared to studies using 360-degree videos for nature exposure, there appears to be a greater consensus among studies using 3D virtual environments that nature exposure in VR has the same efficacy as nature in the real world.
Table 3. Studies that use 360-degree video for experience of virtual nature.
Table 3. Studies that use 360-degree video for experience of virtual nature.
StudyYearPopulationDuration Within-Subject DesignVR Mode VR DevicePhysical EnvironmentMental State MeasuresVR Same as Real?
Browning et al. [42]201989 subjects from
University		6 min No360-degree videoSamsung Gear VR with Galaxy Note 5 smartphone insertedNearby ForestMood (PANAS)
restorativeness (PRS),
physiological arousal (skin conductance)
disgust (Disgust Sensitivity Scale)
beauty (Natural Beauty Subscale of the Engagement with Beauty Scale)
VR experience		N
Calogiuri et al. [43]201826 healthy adults aged 20–4510 minYes360-degree videoSamsung Gear VR mask paired with a Samsung S7 smartphone displayOutdoor walk by riverRestorativeness (PRS),
Presence [Nichols et al., 2000]
Heart rate
Enjoyment
Affect (Physical Activity Affect Scale [lox 2000])		N
Chirico and Gaggioli [36]201950 young adults5 minNo360-degree videoGear VR with smartphone display (Galaxy Note 4)panoramic view of Lake Iseo and Isola mountainEmotions,
positive and negative affect (PANAS),
relaxation,
and presence (ITC-Sense of Presence Inventory)		Y
Palanica et al. [44]201989 and 97 for 2 studies4 minvaried360-degree videoOculus Rift headset Forested park or street intersectionCreativity (Alternative Use Test)N
Sarcinella et al. [48]202316 young adults5–10 minYes360-degree videoHead Mounted Display (HMD) using mobile phonesNature Reserve of Verbania in Piedmontpositive emotions, and
general aesthetic interest (DFAS)
Connectedness to Nature, Relatedness to Nature,
engagement with natural, artistic, and moral beauty,
emotions, and
Mood (PANAS)		Y
Table 4. Studies that use fully immersive 3D-modelled virtual environments for experience of virtual nature.
Table 4. Studies that use fully immersive 3D-modelled virtual environments for experience of virtual nature.
StudyYearPopulationDuration Within-Subject DesignVR Mode VR DevicePhysical Environment Modeling SoftwareMental State MeasuresVR Same as Real?
Hejtmánek et al. [45]202225 (mean age = 30)30 minYes3D virtual environmentHTC Vive Pro Eyeforest near Czech University of Life SciencesUnreal Engine, LIDAR scan of physical environmentPANAS
Restoration Outcome Scale (ROS)
Simulator Sickness Questionnaire (SSQ)		Excluded (Affect did not improve in both conditions)
Mattila et al. [33]2020100 (ages 2/3 <35, 1/3 > 35)5 minNo3D virtual environmentHTC Vive with headphonesforests in Helsinki, Finlandunreal engineSubjective Vitality Scale (SVS)
PANAS
ROS		Y
Mihara et al. [46]202226 healthy office workers (age = 25–59)5 minYes3D virtual environmentOculus Rift Soffice meeting room with full scale windowsNot statedSkin temperature and conductance
HRV
EEG
indoor environmental satisfaction, mood, self-reported performance, and simulator sickness
Simulator Sickness Questionnaire		Y
Nukarinen et al. [34]202024 University staff and students10 minNo3D virtual environment
and 360-degree video		HTC Vive headsetforest near University of Applied Sciences in TampereUnityHR, HRV,
electrodermal activity,
working memory capacity, and positive and negative affect		N
Reese et al. [47]202150 subjects around university (mean age = 24.2)Self-paced, 3–9.5 min avg 5.7No3D virtual environmentOculus rift + controllersnearby forestWorld Editor of Skyrim (Elder Scrolls V: Skyrim)positive affect, negative affect (PANAS),
stress (Standard Stress Scale),
subjective vitality (SVS), restoration outcome, perceived restoration, and previous VR experience		Y
Ünal et al. [35]202223 and 26 students (mean age = 20.4 and 19.5)20 minYes3D virtual environmentCave Automatic Virtual Environmentbutterfly garden in a zoo and shopping center3dsmax and inhouse software based on OpenScenegraphPerceived Restorative Characteristics Questionnaire (PRCQ)
preference, pleasure, and restoration		Y

5. Discussion

This systematic review critically evaluates the psychological benefits of experiencing nature through real-world and virtual urban green spaces (UGS). Our analysis underscores established benefits of real-world nature, such as relaxation and stress reduction, which align with previous findings in environmental psychology [49]. Similarly, emerging studies indicate that virtual reality (VR) representations of nature can also offer these psychological benefits [16,50], suggesting their potential utility in areas where access to natural environments is limited, which is increasingly common in urban settings and with the rise of remote work after COVID-19 [51]. While previous reviews have established the psychological benefits of experiencing nature in the physical world [8,17,18,19,52,53,54] and through VR [20,21,22,55,56] separately, to our knowledge, there has been no review that explicitly reviews the psychological benefits of directly comparable real-world and VR nature. Thus, our systematic review fills the gap establishing that nature experienced through VR can have the same effect as nature experienced in the real world.
A key focus of our review was to examine studies that explicitly compared the psychological impacts of real-world and virtual nature. While the therapeutic benefits of both modalities are well-documented, our review reveals nuances in their effectiveness. Studies employing immersive 3D virtual environments often reported outcomes that closely mirrored the experiences of real-world nature. In contrast, those utilizing less immersive 360-degree videos frequently reported less significant psychological benefits. This disparity underscores the importance of the level of immersion in virtual environments—fully immersive 3D settings appear to be more effective at replicating the sensory and emotional engagement typically facilitated by direct interaction with real nature.
The findings from our review have significant implications for landscape architecture and urban planning. They support the use of immersive VR technologies in the design and planning phases of urban green spaces. For landscape architects, integrating VR could enhance design processes by allowing for the simulation and testing of environmental impacts before physical spaces are constructed. This is particularly relevant for urban areas where space is at a premium and the integration of effective green spaces requires meticulous planning to maximize their psychological benefits.
Our review faced several methodological challenges. One limitation of our systematic review is the difficulty of developing precise search terms.
In this review, we sought to narrow the scope of the review to studies that examine both virtual and real-world nature and ask whether the psychological benefits of nature in VR were comparable to those of the same nature in the real world. To do that, we used the criteria that articles must contain the keywords “virtual” and “real” in close proximity. This strategy will capture explicit comparisons like “virtual and real nature” or “virtual forest and real forest” and thus likely include articles with a virtual and real-world study and exclude studies that only involve a virtual study or a physical real-world study.
If we did not impose a constraint that both virtual and real keywords must occur and must occur in close proximity, there would be an excessive number of results, most of which are likely in unrelated topics due to the multiple meanings of the keyword “real”.
Similarly, searching with only the “virtual” and related keywords without the “real” and related keywords produces an excessive number of results and many studies involving only the virtual condition but no real condition.
Thus, due to the general meaning of the search terms, it is difficult to develop a precise search strategy. A more general search strategy not imposing a proximity requirement or not requiring the “real” keyword may be used but will likely result in a much larger initial number of articles and a greater proportion of irrelevant articles during screening.
The limited number of studies that directly compare the effects of virtual and real nature suggests that this area is relatively understudied. This gap in research is further complicated by the heterogeneity of methods used across different studies, which produces varied results. This variability underscores the urgent need for the development of standardized methods, such as the adoption of common mental state questionnaires, which would allow for more consistent and comparable results across different studies. Establishing such standards could greatly facilitate the synthesis of findings and enable more definitive conclusions about the relative benefits of real versus virtual natural environments.
In the studies reviewed, few studies used physiological measurements to compare the effects of real and virtual environments and most only measured changes in mental states with self-report questionnaires. In this review, only 2 of the 12 studies reviewed used physiological measurements to compare between real and virtual environments. Physiological measurements from ECG and EEG have been used extensively to quantify relaxation [57,58,59], stress [14,60,61], and other psychological benefits [43,44] in both virtual and real-world studies of nature. Physiological measurements may be more objective and unbiased compared to self-report questionnaires [62,63,64]. Given the objectivity and reduced bias of physiological measurements compared to self-report questionnaires, they provide a valuable tool in assessing and comparing the effects of environmental setups and can allow for a controlled comparison between different setups and locations within the same subjects, enhancing the reliability of conclusions drawn from such studies.

6. Conclusions

We systematically reviewed the scientific literature to address whether VR is able to elicit psychological benefits that are comparable to nature in the real world. We found that the VR used in these studies can be broadly classified into two groups: 360-degree videos and 3D virtual environments. Results were more consistent in the 3D virtual environment group, suggesting that virtual nature produces similar psychological benefits compared to nature in the real world. However, the results in the 360-degree video group were mixed, probably due to lower immersion compared to the 3D virtual environment group. Hence, the immersiveness of the VR environment may be a contributing factor but is often not measured and reported directly by studies. While studies described the methods for creating the VR environment, details on the realism and hence immersion of the 3D environments are not extensively reported.
We also reviewed the standard questionnaires used to measure the mental state of participants of the studies reviewed. This may serve as guidance for designing future studies to include these questionnaires so that results can be compared with previous studies, which can be important due to the heterogeneity of methods and choice of study locations.
Finally, using VR to visualize landscape designs involved building a 3D virtual model. We found evidence in the reviewed literature that the results using an immersive 3D virtual environment are similar to nature in the real world. This shows that UGS designs in VR can transfer into real-world designs to yield similar physiological effects.

Author Contributions

Conceptualization, L.L, L.G., S.-K.L., E.S.L. and K.K.A.; methodology, L.L.; formal analysis, L.L.; investigation, L.L.; resources, L.L.; data curation, L.L.; writing—original draft preparation, L.L.; writing—review and editing, L.L, L.G., S.-K.L., E.S.L. and K.K.A.; visualization, L.L.; supervision, K.K.A.; project administration, K.K.A.; funding acquisition, K.K.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Agency for Science, Technology and Research (A*STAR) Brain-Body Initiative grant, project number C211817001.

Data Availability Statement

The data presented in this study are available in this article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Different types of virtual reality setups are used to simulate the experience of nature through VR ordered on a scale of level of immersion. At the top, three modes of presentation are shown: a flat-screen such as a computer monitor, a CAVE VR setup where the user is placed in a room and the environment is projected onto each of the three walls and onto the floor, and a head-mounted display device. In the second row, examples of stimuli presented are shown for each of the five setups ranked.
Figure 1. Different types of virtual reality setups are used to simulate the experience of nature through VR ordered on a scale of level of immersion. At the top, three modes of presentation are shown: a flat-screen such as a computer monitor, a CAVE VR setup where the user is placed in a room and the environment is projected onto each of the three walls and onto the floor, and a head-mounted display device. In the second row, examples of stimuli presented are shown for each of the five setups ranked.
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Figure 2. Top: An example of a 360-degree landscape panorama that can be used to simulate a virtual experience of nature. Bottom: A 3D virtual environment filled with natural elements (trees) in the Unity game engine.
Figure 2. Top: An example of a 360-degree landscape panorama that can be used to simulate a virtual experience of nature. Bottom: A 3D virtual environment filled with natural elements (trees) in the Unity game engine.
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Figure 3. Flow chart of screening and selection process. We retrieved articles from PubMed, Web of Science, and Scopus. Duplicates were removed and the remaining articles were screened for relevance to environmental psychology and virtual reality (VR). Finally, the full texts of relevant articles are retrieved and screened, resulting in 12 articles for review.
Figure 3. Flow chart of screening and selection process. We retrieved articles from PubMed, Web of Science, and Scopus. Duplicates were removed and the remaining articles were screened for relevance to environmental psychology and virtual reality (VR). Finally, the full texts of relevant articles are retrieved and screened, resulting in 12 articles for review.
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Figure 4. Tabulation of common standard questionnaires and physiological measurements used in 12 studies. ECG includes measurements derived from ECG such as heart rate and heart rate variability.
Figure 4. Tabulation of common standard questionnaires and physiological measurements used in 12 studies. ECG includes measurements derived from ECG such as heart rate and heart rate variability.
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Table 1. Keywords used to represent each of the concept for database search.
Table 1. Keywords used to represent each of the concept for database search.
ConceptKeywords
Nature(nature OR forest OR park OR “natural environment” OR “urban green space” OR green)
Mental mental OR psycho * OR mood OR restoration OR recovery OR stress OR attention
Real and virtual(virtual NEAR/5 real) OR (virtual NEAR/5 physical)
Table 2. Common standard questionnaires used in studies. Acronyms and the expanded name of the standard questionnaires are shown.
Table 2. Common standard questionnaires used in studies. Acronyms and the expanded name of the standard questionnaires are shown.
AcronymExpanded
PANAS [37]Positive And Negative Affect Scale
ROS [38]Restoration Outcome Scale
PRS [39]Perceived Restorativeness Scale
SVS [40]Subjective Vitality Scale
SSQ [41]Simulator Sickness Questionnaire
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Liang, L.; Gobeawan, L.; Lau, S.-K.; Lin, E.S.; Ang, K.K. Urban Green Spaces and Mental Well-Being: A Systematic Review of Studies Comparing Virtual Reality versus Real Nature. Future Internet 2024, 16, 182. https://doi.org/10.3390/fi16060182

AMA Style

Liang L, Gobeawan L, Lau S-K, Lin ES, Ang KK. Urban Green Spaces and Mental Well-Being: A Systematic Review of Studies Comparing Virtual Reality versus Real Nature. Future Internet. 2024; 16(6):182. https://doi.org/10.3390/fi16060182

Chicago/Turabian Style

Liang, Liyuan, Like Gobeawan, Siu-Kit Lau, Ervine Shengwei Lin, and Kai Keng Ang. 2024. "Urban Green Spaces and Mental Well-Being: A Systematic Review of Studies Comparing Virtual Reality versus Real Nature" Future Internet 16, no. 6: 182. https://doi.org/10.3390/fi16060182

APA Style

Liang, L., Gobeawan, L., Lau, S. -K., Lin, E. S., & Ang, K. K. (2024). Urban Green Spaces and Mental Well-Being: A Systematic Review of Studies Comparing Virtual Reality versus Real Nature. Future Internet, 16(6), 182. https://doi.org/10.3390/fi16060182

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