Don’t Worry be Happy - Using virtual environments to induce emotionalstates measured by subjective scales and heart rate parametersJan-Niklas Voigt-Antons*

TU Berlin & DFKIRobert Spang†

TU BerlinTanja Kojic‡

TU BerlinLuis Meier§

TU BerlinMaurizio Vergari¶

TU Berlin

Sebastian Moller||

TU Berlin & DFKI

ABSTRACT

Advancing technology and higher availability of Virtual Reality(VR) devices sparked its application in various research fields. Forinstance, 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 interactivityinfluences the presence in nature environments and consequenceson arousal and valence. After inducing fear (high arousal and lowvalence) through a VR-horror game, it was tested how participantsrecovered 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 successfulmanipulation check. Igroup presence questionnaire (IPQ) scoresshowed that more interaction with the virtual environment increasesspatial presence. A beneficial effect of experiencing nature can alsobe concluded. Results from the Self-Assessment Manikin question-naire (SAM) scores for valence indicate a significant increase in theconditions with extensive and limited interaction compared to thecontrol group. The VR Nature experience did significantly decreasearousal and increase valence compared to the post-horror game rat-ings. The physiological responses support this finding. These resultscan increase the effectiveness of health-related VR-applications toelevate mood levels by either implementing plenty of interactionsand consequently increasing spatial presence or doing the oppositeand leaving out any interactions at all.

Keywords: Virtual Reality, green environment, inducing fear, VRrelaxation, emotional response

Index Terms: Human-centered computing—Human computerinteraction (HCI)—Interaction paradigms—Virtual reality; Human-centered computing—Human computer interaction (HCI)—HCI the-ory, concepts and models; Human-centered computing—Interactiondesign;

1 INTRODUCTION

In past years, virtual reality (VR) technology has developed exten-sively [5]. VR goggles of different complexity are produced for themass market and used far beyond entertainment games: education,astronauts training, museums, military simulators and a wide rangeof health care issues are now partly covered by VR applications [4].One of the fast-developing topics in the VR is its application onhealth-related topics. Experiencing nature has plenty of positive

*e-mail: jan-niklas.voigt-antons@tu-berlin.de†e-mail: spang@tu-berlin.de‡e-mail: tanja.kojic@tu-berlin.de§e-mail: meier@tu-berlin.de¶e-mail: maurizio.vergari@tu-berlin.de||e-mail: sebastian.moeller@tu-berlin.de

effects on individuals as the World Health Organisation reports [24].For example, nature helps people to relax and to increase moodstates. 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]. Reasonsfor this development can be found in increasing distances to parksand forests and a change of lifestyle which is especially affectingyounger generations. A solution to this problem might be providinga simulated nature environment in VR which people can visit fromtheir homes. While Head-Mounted Displays (HMD) were a nicheproduct which was almost exclusively used by researchers and spe-cialized companies, the newest generation of VR-devices like theOculus Go and its latest successor Oculus Quest, became affordableand easy to use all-in-one solutions for the broad market. Hencemore devices are being sold, which leads to increased availabilityof VR-devices. With this development in mind, a scenario wherepeople come home from their stressful work and relax in a virtualforest environment seems less like science fiction. One questionremains: could a simulation have similar beneficial effects as realnature experiences? Research has shown that experiencing simu-lated nature can evoke some of the benefits seen from real naturelike, as mentioned, improving relaxation and enhancing mood states.Although research could show beneficial effects of simulated natureexperiences, results are limited on comparisons between nature andurban environments.

Figure 1: Screenshots from the environments of the used VR games:left is ”Nature Treks VR” and right is ”Dreadhalls” in other tosimulate different emotional states.

More research is needed in order to understand how these simula-tions influence emotional states and how the user experience couldbe improved. In order to gain knowledge about how to design amore relaxing and more mood-enhancing VR-application, this studywants not only to replicate natures beneficial effects on the specta-tor’s psyche, but also to examine different levels of engagement withthe surrounding which might increase those effects. The level ofinteraction might influence the perceived realism of the experience.

The presented work aims to answer the following questions:

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2021 IEEE Virtual Reality and 3D User Interfaces (VR)

2642-5254/21/$31.00 ©2021 IEEEDOI 10.1109/VR50410.2021.00094

• Can a VR-horror game be a suitable stimulus for inducing higharousal and low valence?

• Can the already known relaxing and mood-enhancing effect ofnature experiences be replicated through a nature-simulationexperienced in VR?

• Can more interaction with the virtual environment make theuser feel more present?

• How does interaction influence emotional change, as a changein the subjective experience emotion, regarding arousal andvalence?

The remainder of this paper is organized as follows. The nextsection gives an overview of related work. In Section 3, the method-ology and details about the test design are described. The resultsof the conducted experiment are summarized in Section 4. Section5 provides a discussion of the findings, its limitations and possiblefuture work. Section 6 ends this work with a conclusion of thefindings.

2 RELATED WORKThe beginning of user research in VR was focusing mainly on evalu-ating its immersive features. With a growing interest in applying VRtechnology on health-related topics [28], such as treating psycho-logical illnesses, considerable research has grown around the themeof the influence of VR on emotional states [27] [31]. Many com-parative studies between VR and 2D Screen conditions have beenconducted to see which medium has the biggest impact on emotionalchange. For those comparisons, researchers looked at a variety ofdifferent stimulus material. From pictures [12] and movies [11] togames [26], results showed that VR elicits a more intense emotionalresponse, compared to 2D screen conditions.

These results can be explained with the features which distinguishVR from other media. Since users are not required to use a controller,they can freely look around in a 360-degree surrounding by justrotating their head or moving around in a defined space. Unlikelooking at a 2D screen, users cannot look away and lose contact withthe visual experience. Hence possible visual distractions are isolated[27], which leads to a higher level of focus [12] and consequentlyto a more intense experience. Another difference is that movementtracking gives the user the possibility to use his or her body todirectly interact with the virtual environment [9], which allows amore realistic experience. In conclusion, VR is providing a moreimmersive experience with content appearing more realistic andusers feeling a sense of really being in the virtual world [26], whichis also described as presence [36].

The possibilities which VR provides are not limited to comparingexisting content like affective pictures [18] and affective movies [19].Chirico & Gaggioli [10] compared the emotional responses fromreal-world experience with those experienced through replicationsin 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 pictureor affective movie, whole affective virtual environments were cre-ated [21] [20] [31]. For example, Riva et al. [31] used simulatedpark environments which had the same structure but differed insound, lighting and textures in order to present either a relaxing,an anxious or neutral experience (control). Since all the affectiveenvironments elicited the expected emotional change and the neu-tral environment did not, VR environments might be used as aneffective way to induce emotional states. [20] used affective virtualenvironments representing either a peaceful, a sad, a happy, a fearfulor a distasteful experience and compared the emotional responsefrom users exploring those environments in VR versus exploring itvia 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 interactivityof the other virtual environments might improve emotional responsein VR.

As described in the introduction, such affective VR environmentscould be used in order to replicate nature beneficial effect of increas-ing valence and decreasing arousal [40]. Anderson et al. [1] showedthat participants that viewed 360-degree nature scenes showing thecountryside of Ireland or a beach scene relaxed better compared tothose who viewed indoor scenes. [35] found that already 90 secondsof 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 improvingmental conditions of bed-bound patients, immobile older people oras a treatment for the reduction of depressive symptoms.Anotherpossible application is people who are working in isolation, con-fined environments like submarines and space stations [1] or, asthe most recent example, people who are at home isolated from theoutside during lockdown or self-quarantine [22]. With the Atten-tion Restoration Theory (ART) Kaplan [16] created a theoreticalframework explaining natures relaxing effect. ART differentiatestwo types of attention: directed attention describes a voluntary de-cision to focus on a stimulus while indirect attention describes aninvoluntary, effortless way to perceive our surrounding [17]. ARTproclaims that modern urban life with all tasks and stimuli seekingfor attention, people are overwhelmed by deciding where to directtheir attention [16]. Nature, on the other hand, can restore attentioncapacities since, in this environment, people rather absorb their sur-rounding without the need for directed attention. Nature providespeople with the possibility to escape everyday stress and experiencesoftly fascinating environments which allow them to reflect and sorttheir thoughts [17]. While ART is a popular theory with diverseevidence, it is still not clear which aspects of attention exactly areinfluenced by natural experience [23].

3 METHODS

The experiment was conducted in a laboratory using the OculusQuest all-in-one HMD. For a soothing nature experience, the relax-ation game ”Nature Treks VR” 1 was used. The game was developedfor clinical use to help patients relax when they are afraid or are inpain. In the game, the player can walk around and discover theirsurroundings. For this experiment, the level ”green meadow” wasselected, which is shown on Figure 2. It contains an environmentwith trees, green grass, butterflies, rabbits, deer and mountains onthe horizon. In opposite to the calming environment of nature, theVR game ”Dreadhalls” is shown with Figure 3. This VR game wasused for inducing the high arousal and low valence in experimentalconditions due to it’s design of the virtual environment.

3.1 Measurement

Self-assessment Manekin (SAM) [7] with nine points was used tomeasure 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 scalesspatial presence, involvement and sense of realness. It is assumedthat 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 belthas been used as a test measure in previous research, and has shownto provide valid results while being easy to use [13]. The extractedparameter 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 ”NatureTreks VR” which was used for nature conditions.

Figure 3: Scene from VR game ”Dreadhalls” which was used asstimulus 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 moodin different conditions, they first have to be in a stressful and uneasestate. Following the widely used circumplex model of affect [30],for this purpose participants should reach a high level of arousal anda low level of valence which represent the emotional state of fear,disgust and anger. In the past, such stimulus induction happened viapretested picture inventories like the International affective picturesystem [18]. For VR purposes a pretested inventory for 360-degreemovie clips exists but material for high arousal, and low valenceinduction is missing [19]. Moreover, most of the videos used arestory-driven, which might not be usable for a within test design,due to multiple usages. In order to keep the excitement high foreach round, stimulus material which can be used more than onceis needed. In this experiment, the horror game ”Dreadhalls” 2 wasused since it allows playing automatically generated maps which canbe used multiple times and [42] showed that horror environmentscould be used as a fearful stimulus for inducing low valence andhigh arousal. Although auto-generated maps were used, the fear-inducing concept was always the same. The player is informedthat they might encounter a scary monster while navigating throughthe level knowing that they are missing any weapons to defendthemselves with the only option to run away in order to survive. Theexperimenter instructed the participants to explore as much of thelevel as possible until they either find the exit, the time limit of 5minutes 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 askedto try one more time in order to keep them longer in the stimuluscondition.

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 exposedto the horror game stimulus (2). After the horror game new SAMmeasurements are done (3) before starting one of four randomisedexperimental conditions (4): C = control, NI = no interaction, LI= low interaction, EI = extensive interaction. The last step beforestarting a new cycle is to take the after-condition SAM measurements(5).

3.2 Test SetupWith the aim to investigate the influence of interaction on Valenceand Arousal, the experiment was conducted as a within-subjectdesign with four factors, as seen in Figure 2:

• 1) No interaction (NI): participants were not able to move andwere asked to look straight.

• 2) Limited Interaction (LI): participants were asked to explorethe nature world. The one interaction participant were able todo is to navigate inside of the virtual world, but had no othertask or interaction with gestures. The navigation inside ofvitual world was possible by using controller buttons to walkaround.

• 3) Extensive Interaction (EI): participants were asked to searchand find a particular tree and collect as many branches aspossible. With this task, additionally to walking for exploringthe virtual world, participants had a reason to perform aninteraction with body, particularly with hands. They had toperform gesture moves with their hands and controller, bypressing the back button on controller while performing themovement with hands to collect the branches.

• 4) Control (C): participants were asked to focus on a whitecross in a greyscale virtual environment. This is used as anabsolute baseline.

3.3 ProcedureWhen the participants arrived, they first filled out a consent form andinstalled 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 experiencewith video games. Next, the first SAM questionnaire was filledout, which serves as a baseline measure. Then the experimenterexplained the controls and how to set up the HMD. Next followeda sequence of steps which started with playing the horror game(stimulus) and then playing either the nature game (experimentalconditions) or a greyscale application (control condition) for five

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minutes. Before and after each condition participants filled out SAMquestionnaires. After each condition also the IPQ questionnaire wasfilled out. Each participant repeated the procedure 4 times and inthe end, participants were rewarded with 12 Euros, once for eachcondition as shown on figure 4. All the games were played whileseated. As for the testing the horror game and experiencing thehigh arousal and extreme fear induced by the game, we decided tohave the participants seated for security reasons. In those extremesituations participants potentially could have tried to run away andbumped against the wall, or fallen to the ground. The experimen-tal condition was then conducted seated as well in order to havecomparable situations.

3.4 ParticipantsIn total, 27 participants took part in the experiment, but one par-ticipant had to quit due to simulator sickness. After excluding thisdata that leaves 26 participants (13 female / 13 male). The averageage 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 2,00for VR-Devices (SD=0,938) and 3,42 for video games (SD=1,270).19,2 percent of the participants reported wearing glasses, and 15,4percent reported to wear contact lenses while the majority of 65,4percent reported not to wear any visual aid.

3.5 EthicsThis study was approved by the ethics committee of the faculty viaa short track procedure.

Figure 5: Mean ratings for arousal and valence, averaged per partici-pant and per condition type. The changes between baseline and thehorror game condition, as well as between the horror game and thesubsequent VR Nature condition are strongest. Whiskers denote thestandard error.

4 RESULTSThe following results are grouped to present outcomes to each re-search question independently.

4.1 Influence of a VR-horror on experienced valenceand arousal

We compared baseline ratings of the SAM’s valence and arousalscales against the ratings obtained after the participants played thehorror game. Because the horror game was played multiple times,we averaged the horror game ratings per participant. This way, weobtained two score per scale per participant (see Figure 5). Non-parametric Wilcoxon signed-rank tests were used to analyze theordinal 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 afterparticipants played the horror game (M = 4.99,SD = 2.415,SE =.474). A Shapiro-Wilk test showed a significant departure fromnormality. The signed-rank test showed a significant differencebetween 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 ratingsobtained after participants played the horror game (M = 6.48,SD =1.71,SE = .335). A Shapiro-Wilk test did not provide evidencefor a departure from normality of the ratings. The signed-rank testshowed a significant difference between baseline and post-horrorgame ratings of the arousal scale (W = 15, p < .001,d f = 25), theeffect is very strong (dCohen <−1.0).

Given these results, the horror game did significantly increasearousal and decrease valence compared to baseline.

4.2 Influence of a VR Nature experience on experiencedvalence and arousal

Like the first research question, we compare valence and arousal rat-ings obtained immediately after the horror game with those recordedafter the VR Nature experience. For comparison, we also comparethe rating with the control condition (fixation cross). This way, wedemonstrate a difference between the settings and quantify and testif the VR Nature game reduces arousal and increases the partici-pants’ valence (see Figure 5).As before, non-parametric Wilcoxonsigned-rank tests were used to analyze ordinal scaled questionnairedata.

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 notshow evidence for normality violation; the signed-rank test showeda significant difference between post-horror game and post-VR na-ture ratings of the valence scale (W = 3, p < .001,d f = 25), theeffect is very strong (dCohen <−1.0). The valence ratings from afterthe control condition (M = 5.807,SD = 1.96,SE = .384) were com-pared to the post-horror game ratings as well, showing no significantdifference (W = 80.5, p = .223,d f = 25) with only a small effect(dCohen =−.371).

The averaged arousal ratings obtained after playing the horrorgame (as mentioned above) were compared to the average arousalratings obtained after experiencing the VR Nature conditions (M =2.949,SD = 1.316,SE = .258). A Shapiro-Wilk test did not showevidence for normality violation; the signed-rank test showed asignificant difference between post-horror game and post-VR natureratings of the arousal scale (W = 2.0, p< .001,d f = 25), the effect isvery strong (dCohen > 1.0). The arousal ratings from after the controlcondition (M = 3.462,SD = 2.044,SE = .401) were compared tothe post-horror game ratings as well, showing a significant differencebetween the two groups (W = 8.0, p =< .001,d f = 25) with a verystrong effect (dCohen > 1.0).

Regarding the physiological measures, we compared the aver-age BPM recorded throughout the last minute of playing the horrorgame (M = 79.624,SD = 12.862,SE = 1.267) with the average ofthe 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 VRNature (t = 2.184, p = .031,d f = 25) with a minimal effect size(dCohen = .164). Similarly, the RMSSD values of playing the horrorgame (M = 59.848,SD= 86.108,SE = 8.526) were compared to theVR 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 thestandard 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 significantlydecrease arousal and increase valence compared to the post-horrorgame ratings (see Figure 5). The physiological responses support thisfinding. Note that all reported p-values were adjusted for multiplecomparisons.

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 differentinteraction 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 heartrate (bpm) and heart rate variability (RMSSD).

Both groups were not normally distributed, as assessed by theShapiro-Wilk test (p < .001). Assumptions like the normal dis-tribution, homogeneity of variances, and covariance matrices areviolated. However, the RM-ANOVA procedure is conducted as it

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is considered to be robust against violations of the assumption ofnormal distribution according to Bray & Maxwell [8] and Wein-furt [41] as well as the violation of the assumption of homogeneityof covariance matrices as long as the sample size in each cell issimilar [38], which is the case in this dataset. Table 1 provides anoverview of the statistically significant results of the RM-ANOVAtests. Effects of arousal, heart rate, and heart rate variability are notfurther 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 ofrealism (REAL), as obtained using a RM-ANOVA.

Effect d fn d fd F p η2G

SP 1.91 47.82 37.51 0.001 0.60INV 1.95 48.83 27.16 0.001 0.52REAL 2.05 51.15 27.36 0.001 0.52Valence 2.60 65.03 4.252 0.11 0.15

As shown in Figure 7, increasing interaction led to increasedIPQ ratings for spatial presence, involvement, and sense of real-ism. RM-ANOVAs with Greenhouse-Geisser corrections showedstatistically significant differences for all IPQ scales. For spatialpresence, NI (M=4.439, SE=0.845), LI (M=4.723, SE=0.933) andEI (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 highercompared to C (M=1.750, SE=0.998). Sidak-adjusted post-hoc anal-ysis revealed a significant difference (p < .05) for spatial presencevalues 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 thatbefore- and after condition difference values for valence showed astatistically 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) andextensive interaction group (M=2.269, SE=1.237) compared to thecontrol group (M=1.000, SE=2.325).

A RM-ANOVA determined that before-after difference valuesfor arousal showed no statistically significant difference for thedifferent conditions, F(3, 75) = 1.93, p = .131. Although there wereno significant differences between the groups for arousal values,descriptive statistics, depicted in Figure 6, show similar tendenciesas the statistical results for valence.

Regarding the HR / HRV analysis, differences of mean valuesof the last minute of the horror game and the last minute of thecorresponding 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 theheart 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 carriedout. Here, the comparison between NI and EI (p < .001), betweenLI and EI (p < .001), and between EI and C (p = .001) showedstatistically significant differences.

Similarly, the Friedman rank-sum test was conducted to identifydifferences regarding the HRV over the four conditions. We founda statistically significant difference regarding the RMSSD between

Figure 8: Differences of BPM and RMSSD means between playingthe horror game and experiencing VR Nature. While only the EIcondition increases the heart rate compared to the horror game,the HRV indicates a more relaxed state throughout the VR Natureconditions. Whiskers denote the standard error.

the four conditions (χ2(3) = 38.641, p = .04) with a very strongeffect (WKendall > 1.0). For a post-hoc comparison, independentpair-wise Wilcoxon signed-rank tests were carried out. Here, onlythe comparison between EI and C (p = .043) showed a statisticallysignificant difference.

5 DISCUSSION

Interaction levels: One of the objectives of this study was to findout how different interaction strategies affect the emotional responsein VR nature environments for arousal and valence. Results haveshown that either extensive interaction or no interaction is enhancingmood (increase in valence) compared to the control group. On thecontrary, no significant results could be found regarding influence onthe arousal values and heart rate measurements. Nevertheless, therewas still a tendency of nature conditions to provide a relaxing effect.Altogether, these results match to the ones from other research on thebeneficial effects received from experiencing nature, and can partlybe seen as a replication for nature restorative effects in a simulatednature 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 anytask to do but looking straight at the nature environment. Hence,they were required no effort at focusing attention to any specificpoint of their surrounding. This way, they could have had betterrelaxation, facilitating attention capacities restoration. An interestingresult was that participants in the EI condition were also able toenhance their mood while performing a precise task (collectingsticks from a special tree). According to ART, a precise task requiresfocus, so it should have not facilitated attention capacities restoration.Notwithstanding, results revealed that NI values for valence arehigher than the EI ones. Moreover, the higher spatial presence scorefor the EI condition gives reasons to argue that the participants byperforming 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 natureenvironment. Therefore the interaction level for LI condition isranging in between NI and EI condition. The results suggestedthat the task of navigating and exploring might have provided asufficiently strong interactivity component to hinder relaxation moodenhancement without having been able to reach the threshold toprovide that sense of spatial presence measured in EI.

Horror game as stimulus material: From the statistical analysisof the differences between before- and after measure for arousal andvalence SAM-values, it has been shown that stimulus induction

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was achieved, having the horror game led to an emotional changein the form of increasing arousal and decreasing valence. Thisresult indicates that automatically generated levels of the horrorgames might be used as a valid stimulus induction tool for emotionalchange 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 difficultto find material in the quadrant for low valence and high arousal[19]. While it remains possible that repetitive exposure to the horrorgame might have resulted in some ”extinction” of the effect on theparticipants, the unique randomly and automatically created levelsappeared fresh and exciting enough to prevent a significant decreaseof objective and subjective measures for arousal in the later roundsfor the horror game, suggesting that the participants didn’t knowwhat to expect.

5.1 Limitations & future directionsAlthough there are findings which state that already short natureexperiences might have a beneficial effect on emotions [3] [39],recent research showed that a nature experience of 20 to 30 minutesis the most efficient [15]. Thus it might be argued that the five-minute time span, participants spent in each condition, was tooshort for showing clearer results concerning arousal values andheart rate measures. Moreover, it stays unclear if nature was therelaxing factor of this study or if any other soothing game wouldhave similar effects. This study focused on researching the influenceof different interaction levels, so the control condition was designednot to contain any interactions at all. Nevertheless, having differentlevels of interaction also for the control condition could have alloweddiscerning the nature effects from the interaction ones. In fact, theinteractivity 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 likean office or a city environment could be an interesting addition tothe existing study design. As a control condition, we use a plaingrayscale image, not a real environment. A more realistic environ-ment might provoke memories and feelings towards it, thus induceunwanted arousal and affect responses. For our research questions,the most neutral ground is preferable. However, we are aware thatthe chosen grayscale is rather a research artifact than a suggestionfor real-world applications - and that users probably won’t activelyspend time in such a scene. The design and test of calming, neu-tral, but realistic virtual environments, which even can be used asbaseline conditions, is a question left open for subsequent research.For future research, it could also be interesting to test the influenceof interaction in other affective settings like, for example, anxiousenvironments. Another interesting approach for emotional changeresearch, which could be integrated, is personalized VR. Here par-ticipants are first asked about objects which are personally relaxingfor them and then exactly those items are integrated into a virtualenvironment from a data bank [29]. With extensive interaction be-ing an influencing factor for relaxation, it would be interesting forthe future to research the influence of gesture control. Without theneed for controllers, interacting with the virtual environment couldbe even more intuitive and thus lead to an even more immersiveexperience and a more relaxing and mood-lifting nature experience.

6 CONCLUSIONResults indicate that for designing a high emotional experience inVR, 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 bea valid stimulus inducing high arousal and low valence. This couldbe 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 partlyreplicated.

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