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Don’t Worry be Happy - Using virtual environments to induce emotional states measured by subjective scales and heart rate parameters Jan-Niklas Voigt-Antons * TU Berlin & DFKI Robert Spang TU Berlin Tanja Koji´ c TU Berlin Luis Meier § TU Berlin Maurizio Vergari TU Berlin Sebastian M ¨ oller || TU Berlin & DFKI ABSTRACT Advancing technology and higher availability of Virtual Reality (VR) devices sparked its application in various research fields. For instance, health-related research showed that simulated nature en- vironments in VR could reduce arousal and increase valence levels. This study investigates how the amount of possible interactivity influences the presence in nature environments and consequences on arousal and valence. After inducing fear (high arousal and low valence) through a VR-horror game, it was tested how participants recovered if they played a VR-nature game with either no, limited, or extensive interaction. The horror game proved to be a valid stim- ulus for inducing high arousal and low valence with a successful manipulation check. Igroup presence questionnaire (IPQ) scores showed that more interaction with the virtual environment increases spatial presence. A beneficial effect of experiencing nature can also be concluded. Results from the Self-Assessment Manikin question- naire (SAM) scores for valence indicate a significant increase in the conditions with extensive and limited interaction compared to the control group. The VR Nature experience did significantly decrease arousal and increase valence compared to the post-horror game rat- ings. The physiological responses support this finding. These results can increase the effectiveness of health-related VR-applications to elevate mood levels by either implementing plenty of interactions and consequently increasing spatial presence or doing the opposite and leaving out any interactions at all. Keywords: Virtual Reality, green environment, inducing fear, VR relaxation, emotional response Index Terms: Human-centered computing—Human computer interaction (HCI)—Interaction paradigms—Virtual reality; Human- centered computing—Human computer interaction (HCI)—HCI the- ory, concepts and models; Human-centered computing—Interaction design; 1 INTRODUCTION In past years, virtual reality (VR) technology has developed exten- sively [5]. VR goggles of different complexity are produced for the mass market and used far beyond entertainment games: education, astronauts training, museums, military simulators and a wide range of health care issues are now partly covered by VR applications [4]. One of the fast-developing topics in the VR is its application on health-related topics. Experiencing nature has plenty of positive * e-mail: [email protected] e-mail: [email protected] e-mail: [email protected] § e-mail: [email protected] e-mail: [email protected] || e-mail: [email protected] effects on individuals as the World Health Organisation reports [24]. For example, nature helps people to relax and to increase mood states. In times where people seem to be always stressed and busy, these findings become particularly important. Unfortunately, ur- ban life leads to nature experiences less and less, and consequently, people are deterred from natures beneficial effects [34]. Reasons for this development can be found in increasing distances to parks and forests and a change of lifestyle which is especially affecting younger generations. A solution to this problem might be providing a simulated nature environment in VR which people can visit from their homes. While Head-Mounted Displays (HMD) were a niche product which was almost exclusively used by researchers and spe- cialized companies, the newest generation of VR-devices like the Oculus Go and its latest successor Oculus Quest, became affordable and easy to use all-in-one solutions for the broad market. Hence more devices are being sold, which leads to increased availability of VR-devices. With this development in mind, a scenario where people come home from their stressful work and relax in a virtual forest environment seems less like science fiction. One question remains: could a simulation have similar beneficial effects as real nature experiences? Research has shown that experiencing simu- lated nature can evoke some of the benefits seen from real nature like, as mentioned, improving relaxation and enhancing mood states. Although research could show beneficial effects of simulated nature experiences, results are limited on comparisons between nature and urban environments. Figure 1: Screenshots from the environments of the used VR games: left is ”Nature Treks VR” and right is ”Dreadhalls” in other to simulate different emotional states. More research is needed in order to understand how these simula- tions influence emotional states and how the user experience could be improved. In order to gain knowledge about how to design a more relaxing and more mood-enhancing VR-application, this study wants not only to replicate natures beneficial effects on the specta- tor’s psyche, but also to examine different levels of engagement with the surrounding which might increase those effects. The level of interaction might influence the perceived realism of the experience. The presented work aims to answer the following questions: 670 2021 IEEE Virtual Reality and 3D User Interfaces (VR) 2642-5254/21/$31.00 ©2021 IEEE DOI 10.1109/VR50410.2021.00094

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Don't Worry be Happy - Using Virtual Environments to Induce Emotional States Measured by Subjective Scales and Heart Rate ParametersDon’t Worry be Happy - Using virtual environments to induce emotional states measured by subjective scales and heart rate parameters Jan-Niklas Voigt-Antons*
TU Berlin & DFKI Robert Spang†
TU Berlin Tanja Kojic‡
TU Berlin Luis Meier§
TU Berlin Maurizio Vergari¶
ABSTRACT
Advancing technology and higher availability of Virtual Reality (VR) devices sparked its application in various research fields. For instance, health-related research showed that simulated nature en- vironments in VR could reduce arousal and increase valence levels. This study investigates how the amount of possible interactivity influences the presence in nature environments and consequences on arousal and valence. After inducing fear (high arousal and low valence) through a VR-horror game, it was tested how participants recovered if they played a VR-nature game with either no, limited, or extensive interaction. The horror game proved to be a valid stim- ulus for inducing high arousal and low valence with a successful manipulation check. Igroup presence questionnaire (IPQ) scores showed that more interaction with the virtual environment increases spatial presence. A beneficial effect of experiencing nature can also be concluded. Results from the Self-Assessment Manikin question- naire (SAM) scores for valence indicate a significant increase in the conditions with extensive and limited interaction compared to the control group. The VR Nature experience did significantly decrease arousal and increase valence compared to the post-horror game rat- ings. The physiological responses support this finding. These results can increase the effectiveness of health-related VR-applications to elevate mood levels by either implementing plenty of interactions and consequently increasing spatial presence or doing the opposite and leaving out any interactions at all.
Keywords: Virtual Reality, green environment, inducing fear, VR relaxation, emotional response
Index Terms: Human-centered computing—Human computer interaction (HCI)—Interaction paradigms—Virtual reality; Human- centered computing—Human computer interaction (HCI)—HCI the- ory, concepts and models; Human-centered computing—Interaction design;
1 INTRODUCTION
In past years, virtual reality (VR) technology has developed exten- sively [5]. VR goggles of different complexity are produced for the mass market and used far beyond entertainment games: education, astronauts training, museums, military simulators and a wide range of health care issues are now partly covered by VR applications [4]. One of the fast-developing topics in the VR is its application on health-related topics. Experiencing nature has plenty of positive
*e-mail: [email protected] †e-mail: [email protected] ‡e-mail: [email protected] §e-mail: [email protected] ¶e-mail: [email protected] ||e-mail: [email protected]
effects on individuals as the World Health Organisation reports [24]. For example, nature helps people to relax and to increase mood states. In times where people seem to be always stressed and busy, these findings become particularly important. Unfortunately, ur- ban life leads to nature experiences less and less, and consequently, people are deterred from natures beneficial effects [34]. Reasons for this development can be found in increasing distances to parks and forests and a change of lifestyle which is especially affecting younger generations. A solution to this problem might be providing a simulated nature environment in VR which people can visit from their homes. While Head-Mounted Displays (HMD) were a niche product which was almost exclusively used by researchers and spe- cialized companies, the newest generation of VR-devices like the Oculus Go and its latest successor Oculus Quest, became affordable and easy to use all-in-one solutions for the broad market. Hence more devices are being sold, which leads to increased availability of VR-devices. With this development in mind, a scenario where people come home from their stressful work and relax in a virtual forest environment seems less like science fiction. One question remains: could a simulation have similar beneficial effects as real nature experiences? Research has shown that experiencing simu- lated nature can evoke some of the benefits seen from real nature like, as mentioned, improving relaxation and enhancing mood states. Although research could show beneficial effects of simulated nature experiences, results are limited on comparisons between nature and urban environments.
Figure 1: Screenshots from the environments of the used VR games: left is ”Nature Treks VR” and right is ”Dreadhalls” in other to simulate different emotional states.
More research is needed in order to understand how these simula- tions influence emotional states and how the user experience could be improved. In order to gain knowledge about how to design a more relaxing and more mood-enhancing VR-application, this study wants not only to replicate natures beneficial effects on the specta- tor’s psyche, but also to examine different levels of engagement with the surrounding which might increase those effects. The level of interaction might influence the perceived realism of the experience.
The presented work aims to answer the following questions:
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2642-5254/21/$31.00 ©2021 IEEE DOI 10.1109/VR50410.2021.00094
• Can a VR-horror game be a suitable stimulus for inducing high arousal and low valence?
• Can the already known relaxing and mood-enhancing effect of nature experiences be replicated through a nature-simulation experienced in VR?
• Can more interaction with the virtual environment make the user feel more present?
• How does interaction influence emotional change, as a change in the subjective experience emotion, regarding arousal and valence?
The remainder of this paper is organized as follows. The next section gives an overview of related work. In Section 3, the method- ology and details about the test design are described. The results of the conducted experiment are summarized in Section 4. Section 5 provides a discussion of the findings, its limitations and possible future work. Section 6 ends this work with a conclusion of the findings.
2 RELATED WORK The beginning of user research in VR was focusing mainly on evalu- ating its immersive features. With a growing interest in applying VR technology on health-related topics [28], such as treating psycho- logical illnesses, considerable research has grown around the theme of the influence of VR on emotional states [27] [31]. Many com- parative studies between VR and 2D Screen conditions have been conducted to see which medium has the biggest impact on emotional change. For those comparisons, researchers looked at a variety of different stimulus material. From pictures [12] and movies [11] to games [26], results showed that VR elicits a more intense emotional response, compared to 2D screen conditions.
These results can be explained with the features which distinguish VR from other media. Since users are not required to use a controller, they can freely look around in a 360-degree surrounding by just rotating their head or moving around in a defined space. Unlike looking at a 2D screen, users cannot look away and lose contact with the visual experience. Hence possible visual distractions are isolated [27], which leads to a higher level of focus [12] and consequently to a more intense experience. Another difference is that movement tracking gives the user the possibility to use his or her body to directly interact with the virtual environment [9], which allows a more realistic experience. In conclusion, VR is providing a more immersive experience with content appearing more realistic and users feeling a sense of really being in the virtual world [26], which is also described as presence [36].
The possibilities which VR provides are not limited to comparing existing content like affective pictures [18] and affective movies [19]. Chirico & Gaggioli [10] compared the emotional responses from real-world experience with those experienced through replications in VR, and found that they were mostly comparable. For this reason, recent studies focus on finding tools which can use the full possi- bilities of VR-environments. Instead of using an affective picture or affective movie, whole affective virtual environments were cre- ated [21] [20] [31]. For example, Riva et al. [31] used simulated park environments which had the same structure but differed in sound, lighting and textures in order to present either a relaxing, an anxious or neutral experience (control). Since all the affective environments elicited the expected emotional change and the neu- tral environment did not, VR environments might be used as an effective way to induce emotional states. [20] used affective virtual environments representing either a peaceful, a sad, a happy, a fearful or a distasteful experience and compared the emotional response from users exploring those environments in VR versus exploring it via a screen. They showed that only in a fearful condition, arousal
increased significantly higher in VR, compared to a 2D-screen in- crease for arousal. The authors stated that increasing the interactivity of the other virtual environments might improve emotional response in VR.
As described in the introduction, such affective VR environments could be used in order to replicate nature beneficial effect of increas- ing valence and decreasing arousal [40]. Anderson et al. [1] showed that participants that viewed 360-degree nature scenes showing the countryside of Ireland or a beach scene relaxed better compared to those who viewed indoor scenes. [35] found that already 90 seconds of looking at a screen displaying nature had a relaxing effect com- pared to looking at a screen displaying an urban city. As stated by [2] this could have implications for health-related usage like improving mental conditions of bed-bound patients, immobile older people or as a treatment for the reduction of depressive symptoms.Another possible application is people who are working in isolation, con- fined environments like submarines and space stations [1] or, as the most recent example, people who are at home isolated from the outside during lockdown or self-quarantine [22]. With the Atten- tion Restoration Theory (ART) Kaplan [16] created a theoretical framework explaining natures relaxing effect. ART differentiates two types of attention: directed attention describes a voluntary de- cision to focus on a stimulus while indirect attention describes an involuntary, effortless way to perceive our surrounding [17]. ART proclaims that modern urban life with all tasks and stimuli seeking for attention, people are overwhelmed by deciding where to direct their attention [16]. Nature, on the other hand, can restore attention capacities since, in this environment, people rather absorb their sur- rounding without the need for directed attention. Nature provides people with the possibility to escape everyday stress and experience softly fascinating environments which allow them to reflect and sort their thoughts [17]. While ART is a popular theory with diverse evidence, it is still not clear which aspects of attention exactly are influenced by natural experience [23].
3 METHODS
The experiment was conducted in a laboratory using the Oculus Quest all-in-one HMD. For a soothing nature experience, the relax- ation game ”Nature Treks VR” 1 was used. The game was developed for clinical use to help patients relax when they are afraid or are in pain. In the game, the player can walk around and discover their surroundings. For this experiment, the level ”green meadow” was selected, which is shown on Figure 2. It contains an environment with trees, green grass, butterflies, rabbits, deer and mountains on the horizon. In opposite to the calming environment of nature, the VR game ”Dreadhalls” is shown with Figure 3. This VR game was used for inducing the high arousal and low valence in experimental conditions due to it’s design of the virtual environment.
3.1 Measurement
Self-assessment Manekin (SAM) [7] with nine points was used to measure valence and arousal values. SAM is widely used for emo- tional measures and has been proven as a valid subjective measure. In order to measure presence, the Igroup Presence Questionnaire (IPQ) [32] [33] was used. It consists of 14 items and the three scales spatial presence, involvement and sense of realness. It is assumed that this three-part scale provides a better and distinct measure, com- pared to other questionnaires. As an objective measure for arousal, the heart rate was measured via the Polar H10 chest belt. The belt has been used as a test measure in previous research, and has shown to provide valid results while being easy to use [13]. The extracted parameter from the recordings was the heart rate variability mea- sured as Root Mean Square of the Successive Differences (RMSSD).
1https://greenergames.net/nature-treks-vr
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Figure 2: Scene from VR game used in this experiment ”Nature Treks VR” which was used for nature conditions.
Figure 3: Scene from VR game ”Dreadhalls” which was used as stimulus material for inducing high arousal and low valence.
It is a marker of alterations in the autonomic tone that are predomi- nantly vagally mediated ( [37]) and is associated with mental stress ( [6]).
In order to test how well participants can relax and lift their mood in different conditions, they first have to be in a stressful and unease state. Following the widely used circumplex model of affect [30], for this purpose participants should reach a high level of arousal and a low level of valence which represent the emotional state of fear, disgust and anger. In the past, such stimulus induction happened via pretested picture inventories like the International affective picture system [18]. For VR purposes a pretested inventory for 360-degree movie clips exists but material for high arousal, and low valence induction is missing [19]. Moreover, most of the videos used are story-driven, which might not be usable for a within test design, due to multiple usages. In order to keep the excitement high for each round, stimulus material which can be used more than once is needed. In this experiment, the horror game ”Dreadhalls” 2 was used since it allows playing automatically generated maps which can be used multiple times and [42] showed that horror environments could be used as a fearful stimulus for inducing low valence and high arousal. Although auto-generated maps were used, the fear- inducing concept was always the same. The player is informed that they might encounter a scary monster while navigating through the level knowing that they are missing any weapons to defend themselves with the only option to run away in order to survive. The experimenter instructed the participants to explore as much of the level as possible until they either find the exit, the time limit of 5 minutes runs out or they get killed by one of the monsters hiding
2http://www.dreadhalls.com/
in the level. If players died within the first minute, they were asked to try one more time in order to keep them longer in the stimulus condition.
Figure 4: Overview of the the experimental procedure. At first, baseline measurements from SAM questionnaire are recorded (1). Then, the participant iterates over the (2-3-4-5) flow for four times. At the beginning of each iterative cycle, the participant is exposed to the horror game stimulus (2). After the horror game new SAM measurements are done (3) before starting one of four randomised experimental conditions (4): C = control, NI = no interaction, LI = low interaction, EI = extensive interaction. The last step before starting a new cycle is to take the after-condition SAM measurements (5).
3.2 Test Setup With the aim to investigate the influence of interaction on Valence and Arousal, the experiment was conducted as a within-subject design with four factors, as seen in Figure 2:
• 1) No interaction (NI): participants were not able to move and were asked to look straight.
• 2) Limited Interaction (LI): participants were asked to explore the nature world. The one interaction participant were able to do is to navigate inside of the virtual world, but had no other task or interaction with gestures. The navigation inside of vitual world was possible by using controller buttons to walk around.
• 3) Extensive Interaction (EI): participants were asked to search and find a particular tree and collect as many branches as possible. With this task, additionally to walking for exploring the virtual world, participants had a reason to perform an interaction with body, particularly with hands. They had to perform gesture moves with their hands and controller, by pressing the back button on controller while performing the movement with hands to collect the branches.
• 4) Control (C): participants were asked to focus on a white cross in a greyscale virtual environment. This is used as an absolute baseline.
3.3 Procedure When the participants arrived, they first filled out a consent form and installed the Polar H10 chest belt in order to measure their heart rate. Then they were given a pre-questionnaire asking about demograph- ics, sight impairing, experience with VR-devices and experience with video games. Next, the first SAM questionnaire was filled out, which serves as a baseline measure. Then the experimenter explained the controls and how to set up the HMD. Next followed a sequence of steps which started with playing the horror game (stimulus) and then playing either the nature game (experimental conditions) or a greyscale application (control condition) for five
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minutes. Before and after each condition participants filled out SAM questionnaires. After each condition also the IPQ questionnaire was filled out. Each participant repeated the procedure 4 times and in the end, participants were rewarded with 12 Euros, once for each condition as shown on figure 4. All the games were played while seated. As for the testing the horror game and experiencing the high arousal and extreme fear induced by the game, we decided to have the participants seated for security reasons. In those extreme situations participants potentially could have tried to run away and bumped against the wall, or fallen to the ground. The experimen- tal condition was then conducted seated as well in order to have comparable situations.
3.4 Participants In total, 27 participants took part in the experiment, but one par- ticipant had to quit due to simulator sickness. After excluding this data that leaves 26 participants (13 female / 13 male). The average age was 29,38 ranging from 18 to 55 years (SD=9,078). Regard- ing prior experiences, participants reported, on a scale from one (no experience at all) to five (high experience) an average of 2,00 for VR-Devices (SD=0,938) and 3,42 for video games (SD=1,270). 19,2 percent of the participants reported wearing glasses, and 15,4 percent reported to wear contact lenses while the majority of 65,4 percent reported not to wear any visual aid.
3.5 Ethics This study was approved by the ethics committee of the faculty via a short track procedure.
Figure 5: Mean ratings for arousal and valence, averaged per partici- pant and per condition type. The changes between baseline and the horror game condition, as well as between the horror game and the subsequent VR Nature condition are strongest. Whiskers denote the standard error.
4 RESULTS The following results are grouped to present outcomes to each re- search question independently.
4.1 Influence of a VR-horror on experienced valence and arousal
We compared baseline ratings of the SAM’s valence and arousal scales against the ratings obtained after the participants played the horror game. Because the horror game was played multiple times, we averaged the horror game ratings per participant. This way, we obtained two score per scale per participant (see Figure 5). Non- parametric Wilcoxon signed-rank tests were used to analyze the ordinal scaled questionnaire data.
The valence ratings of the baseline (M = 7.039,SD= 1.562,SE = .306) were compared to the average valence ratings obtained after participants played the horror game (M = 4.99,SD = 2.415,SE = .474). A Shapiro-Wilk test showed a significant departure from normality. The signed-rank test showed a significant difference between baseline and post-horror game ratings of the valence scale (W = 17.5, p < .001,d f = 25), the effect is very strong (r > 1.0, according to [25]).
Likewise, the arousal ratings of the baseline (M = 4.115,SD = 1.946,SE = .382) were compared to the average arousal ratings obtained after participants played the horror game (M = 6.48,SD = 1.71,SE = .335). A Shapiro-Wilk test did not provide evidence for a departure from normality of the ratings. The signed-rank test showed a significant difference between baseline and post-horror game ratings of the arousal scale (W = 15, p < .001,d f = 25), the effect is very strong (dCohen <−1.0).
Given these results, the horror game did significantly increase arousal and decrease valence compared to baseline.
4.2 Influence of a VR Nature experience on experienced valence and arousal
Like the first research question, we compare valence and arousal rat- ings obtained immediately after the horror game with those recorded after the VR Nature experience. For comparison, we also compare the rating with the control condition (fixation cross). This way, we demonstrate a difference between the settings and quantify and test if the VR Nature game reduces arousal and increases the partici- pants’ valence (see Figure 5).As before, non-parametric Wilcoxon signed-rank tests were used to analyze ordinal scaled questionnaire data.
The averaged valence ratings obtained after playing the hor- ror game (as mentioned above) were compared to the average va- lence ratings obtained after experiencing the VR Nature conditions (M = 7.192,SD = 1.273,SE = .25). A Shapiro-Wilk test did not show evidence for normality violation; the signed-rank test showed a significant difference between post-horror game and post-VR na- ture ratings of the valence scale (W = 3, p < .001,d f = 25), the effect is very strong (dCohen <−1.0). The valence ratings from after the control condition (M = 5.807,SD = 1.96,SE = .384) were com- pared to the post-horror game ratings as well, showing no significant difference (W = 80.5, p = .223,d f = 25) with only a small effect (dCohen =−.371).
The averaged arousal ratings obtained after playing the horror game (as mentioned above) were compared to the average arousal ratings obtained after experiencing the VR Nature conditions (M = 2.949,SD = 1.316,SE = .258). A Shapiro-Wilk test did not show evidence for normality violation; the signed-rank test showed a significant difference between post-horror game and post-VR nature ratings of the arousal scale (W = 2.0, p< .001,d f = 25), the effect is very strong (dCohen > 1.0). The arousal ratings from after the control condition (M = 3.462,SD = 2.044,SE = .401) were compared to the post-horror game ratings as well, showing a significant difference between the two groups (W = 8.0, p =< .001,d f = 25) with a very strong effect (dCohen > 1.0).
Regarding the physiological measures, we compared the aver- age BPM recorded throughout the last minute of playing the horror game (M = 79.624,SD = 12.862,SE = 1.267) with the average of the last minute of the VR Nature experience (M = 77.614,SD = 11.637,SE = 1.147). A Shapiro-Wilk test did not indicate any de- viation from normality, so a paired t-test was employed, provid- ing a significant difference between the horror game and the VR Nature (t = 2.184, p = .031,d f = 25) with a minimal effect size (dCohen = .164). Similarly, the RMSSD values of playing the horror game (M = 59.848,SD= 86.108,SE = 8.526) were compared to the VR Nature experience (M = 187.66,SD = 663.121,SE = 65.339). As these values were not normally distributed, a Wilcoxon signed-
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Figure 6: Differences of SAM scale ratings between post-horror game and post-VR Nature experience per condition. Whiskers denote the standard error.
Figure 7: Mean values for spatial presence (SP), involvement (INV), and sense of realness (REAL) derived from IPQ over all conditions. Whiskers denote the standard error.
rank test was employed to test differences between the paired sam- ples of the RMSSD values. The test did indicate a tendency to- wards a difference between horror game and VR Nature recordings (W = 2065.0, p = .061,d f = 25); however, the effect is very strong (r > 1.0, according to [25]).
Given these results, the VR Nature experience did significantly decrease arousal and increase valence compared to the post-horror game ratings (see Figure 5). The physiological responses support this finding. Note that all reported p-values were adjusted for multiple comparisons.
4.3 Influence of interaction possibility in VR Nature ex- perience on experienced presence
A repeated measure Analysis of Variance (RM-ANOVA) was per- formed to investigate the effects among conditions with different interaction levels. The independent variable was the condition (C, NI, LI, EI), and the dependent variables were valence, arousal, spa- tial presence, involvement, and sense of realness, as well as heart rate (bpm) and heart rate variability (RMSSD).
Both groups were not normally distributed, as assessed by the Shapiro-Wilk test (p < .001). Assumptions like the normal dis- tribution, homogeneity of variances, and covariance matrices are violated. However, the RM-ANOVA procedure is conducted as it
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is considered to be robust against violations of the assumption of normal distribution according to Bray & Maxwell [8] and Wein- furt [41] as well as the violation of the assumption of homogeneity of covariance matrices as long as the sample size in each cell is similar [38], which is the case in this dataset. Table 1 provides an overview of the statistically significant results of the RM-ANOVA tests. Effects of arousal, heart rate, and heart rate variability are not further mentioned as only significant effects are reported.
Table 1: Significant effects of all four conditions tested using valence (SAM), spatial presence (SP), involvement (INV), and sense of realism (REAL), as obtained using a RM-ANOVA.
Effect d fn d fd F p η2 G
SP 1.91 47.82 37.51 0.001 0.60 INV 1.95 48.83 27.16 0.001 0.52 REAL 2.05 51.15 27.36 0.001 0.52 Valence 2.60 65.03 4.252 0.11 0.15
As shown in Figure 7, increasing interaction led to increased IPQ ratings for spatial presence, involvement, and sense of real- ism. RM-ANOVAs with Greenhouse-Geisser corrections showed statistically significant differences for all IPQ scales. For spatial presence, NI (M=4.439, SE=0.845), LI (M=4.723, SE=0.933) and EI (M=4.992, SE=0.899) were significantly higher compared to C (M=2.823, SE=1.094). For involvement, NI (M=4.519, SE=1.012), LI (M=4.701, SE=1.015), and EI (M=4.760, SE=1.019) were signif- icantly higher compared to C (M=2.663, SE=1.107).
For a sense of realism, NI (M=3.394, SE=1.094), LI (M=3.471, SE=1.182), and EI (M=3.548, SE=1.237) were significantly higher compared to C (M=1.750, SE=0.998). Sidak-adjusted post-hoc anal- ysis revealed a significant difference (p < .05) for spatial presence values between EI and LI (0.55, 95%-CI[0.10, 1.00]).
4.4 Influence of interaction possibility in VR Nature ex- perience on experienced arousal and valence
A RM-ANOVA with a Huynh-Feldt correction [14] determined that before- and after condition difference values for valence showed a statistically significant difference between measurements. Sidak- adjusted post-hoc analysis revealed a significant difference (p < .05) in valence ratings of no interaction group (M=2.539, SE=2.746) and extensive interaction group (M=2.269, SE=1.237) compared to the control group (M=1.000, SE=2.325).
A RM-ANOVA determined that before-after difference values for arousal showed no statistically significant difference for the different conditions, F(3, 75) = 1.93, p = .131. Although there were no significant differences between the groups for arousal values, descriptive statistics, depicted in Figure 6, show similar tendencies as the statistical results for valence.
Regarding the HR / HRV analysis, differences of mean values of the last minute of the horror game and the last minute of the corresponding experimental condition were computed (see Figure 8). A Shapiro-Wilk test revealed non-normality of the data (p < .001), hence a Friedman rank-sum test was conducted over the four condi- tions. We found a statistically significant difference regarding the heart rate between the four conditions (χ2(3) = 43.265, p = .013) with a very strong effect (WKendall > 1.0). For a post-hoc compari- son, independent pair-wise Wilcoxon signed-rank tests were carried out. Here, the comparison between NI and EI (p < .001), between LI and EI (p < .001), and between EI and C (p = .001) showed statistically significant differences.
Similarly, the Friedman rank-sum test was conducted to identify differences regarding the HRV over the four conditions. We found a statistically significant difference regarding the RMSSD between
Figure 8: Differences of BPM and RMSSD means between playing the horror game and experiencing VR Nature. While only the EI condition increases the heart rate compared to the horror game, the HRV indicates a more relaxed state throughout the VR Nature conditions. Whiskers denote the standard error.
the four conditions (χ2(3) = 38.641, p = .04) with a very strong effect (WKendall > 1.0). For a post-hoc comparison, independent pair-wise Wilcoxon signed-rank tests were carried out. Here, only the comparison between EI and C (p = .043) showed a statistically significant difference.
5 DISCUSSION
Interaction levels: One of the objectives of this study was to find out how different interaction strategies affect the emotional response in VR nature environments for arousal and valence. Results have shown that either extensive interaction or no interaction is enhancing mood (increase in valence) compared to the control group. On the contrary, no significant results could be found regarding influence on the arousal values and heart rate measurements. Nevertheless, there was still a tendency of nature conditions to provide a relaxing effect. Altogether, these results match to the ones from other research on the beneficial effects received from experiencing nature, and can partly be seen as a replication for nature restorative effects in a simulated nature VR environment. The findings are in line with ART ( [16]), which also corroborates mood increasing effect in the NI condition. In that experimental condition, the participants did not receive any task to do but looking straight at the nature environment. Hence, they were required no effort at focusing attention to any specific point of their surrounding. This way, they could have had better relaxation, facilitating attention capacities restoration. An interesting result was that participants in the EI condition were also able to enhance their mood while performing a precise task (collecting sticks from a special tree). According to ART, a precise task requires focus, so it should have not facilitated attention capacities restoration. Notwithstanding, results revealed that NI values for valence are higher than the EI ones. Moreover, the higher spatial presence score for the EI condition gives reasons to argue that the participants by performing a task, felt present enough in the virtual world to be, to some extent, diverted from their worries. In the LI condition, the participants had to navigate the level and explore the nature environment. Therefore the interaction level for LI condition is ranging in between NI and EI condition. The results suggested that the task of navigating and exploring might have provided a sufficiently strong interactivity component to hinder relaxation mood enhancement without having been able to reach the threshold to provide that sense of spatial presence measured in EI.
Horror game as stimulus material: From the statistical analysis of the differences between before- and after measure for arousal and valence SAM-values, it has been shown that stimulus induction
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was achieved, having the horror game led to an emotional change in the form of increasing arousal and decreasing valence. This result indicates that automatically generated levels of the horror games might be used as a valid stimulus induction tool for emotional change in VR experiments. Especially for within-subject designs, since stimulus material is used several times for the same participant, the previous result might be interesting. Moreover, it seems difficult to find material in the quadrant for low valence and high arousal [19]. While it remains possible that repetitive exposure to the horror game might have resulted in some ”extinction” of the effect on the participants, the unique randomly and automatically created levels appeared fresh and exciting enough to prevent a significant decrease of objective and subjective measures for arousal in the later rounds for the horror game, suggesting that the participants didn’t know what to expect.
5.1 Limitations & future directions Although there are findings which state that already short nature experiences might have a beneficial effect on emotions [3] [39], recent research showed that a nature experience of 20 to 30 minutes is the most efficient [15]. Thus it might be argued that the five- minute time span, participants spent in each condition, was too short for showing clearer results concerning arousal values and heart rate measures. Moreover, it stays unclear if nature was the relaxing factor of this study or if any other soothing game would have similar effects. This study focused on researching the influence of different interaction levels, so the control condition was designed not to contain any interactions at all. Nevertheless, having different levels of interaction also for the control condition could have allowed discerning the nature effects from the interaction ones. In fact, the interactivity of a task could have an influence itself since users’ attention might be diverted from their emotional state perception.
Implementing a control condition with a non-nature setting like an office or a city environment could be an interesting addition to the existing study design. As a control condition, we use a plain grayscale image, not a real environment. A more realistic environ- ment might provoke memories and feelings towards it, thus induce unwanted arousal and affect responses. For our research questions, the most neutral ground is preferable. However, we are aware that the chosen grayscale is rather a research artifact than a suggestion for real-world applications - and that users probably won’t actively spend time in such a scene. The design and test of calming, neu- tral, but realistic virtual environments, which even can be used as baseline conditions, is a question left open for subsequent research. For future research, it could also be interesting to test the influence of interaction in other affective settings like, for example, anxious environments. Another interesting approach for emotional change research, which could be integrated, is personalized VR. Here par- ticipants are first asked about objects which are personally relaxing for them and then exactly those items are integrated into a virtual environment from a data bank [29]. With extensive interaction be- ing an influencing factor for relaxation, it would be interesting for the future to research the influence of gesture control. Without the need for controllers, interacting with the virtual environment could be even more intuitive and thus lead to an even more immersive experience and a more relaxing and mood-lifting nature experience.
6 CONCLUSION Results indicate that for designing a high emotional experience in VR, it should be either optimized for extensive interaction possibili- ties in order to increase presence or be designed without interactions, giving users the possibility to perceive their surrounding inactively. A solution in-between those conditions can not be recommended. Automatically generated levels of a horror game were found to be a valid stimulus inducing high arousal and low valence. This could be helpful for researchers looking for a reusable stimulus material
and might find use in within study designs. The relaxing and mood- enhancing effect of nature experiences in VR could only be partly replicated.
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