Bachelorproject EffortBased Decision Making in Virtual Reality S. van Dam Studentnummer: 10529691 Begeleider: Jasper Winkel Datum: juni, 2016
Index Abstract p.2 Introduction p.3 Method p.8 Results p.14 Discussion p.17 References p.20
Abstract This study addresses how presence affects two aspects of effortbased decision making (EBDM), namely effort and rewardvaluations. To get a clear picture of how presence specifically affects EBDM, sensitivity to reward (SR) (affecting rewardvaluations) will also be taken into account. 51 participants completed a task in virtual reality (VR). This consisted of a baseline (2Deffort, 2Dreward), reward (2Deffort, VRreward) and effort condition (VReffort, 2Dreward). Using this task the participant’s reward per unit effort was calculated. While presence was enhanced in the reward and effort condition, compared to the baseline condition, there was no effect of presence on the reward per unit effort. When SR was controlled for there was, again, no effect and SR itself had no effect on the reward per unit effort. Based on the current study we cannot conclude that presence affects EBDM.
Introduction Decision making is an important part of our daily lives. These can be ‘big decisions’ like buying a house, or deciding to start a family. For the most part however, the decisions we are faced with in our daytoday live have a much smaller impact (e.g. “what do I want to eat for dinner tonight? “). For each decision we make, a basic valuation can be made: the amount of effort that has to be spent to get a certain outcome, and the value of that outcome. We often experience effort as a burden, but most are willing to expend effort to reach a desired outcome (reward) (Kurniawan, GuitartMasip & Dolan, 2011). The valuation of effort and the valuation of reward are not fixed, and differ between individuals. For example, some will put in a considerable amount of time and energy to prepare a delicious meal for dinner, while others will opt for easy (and less palatable) instant food. This difference in effort and reward valuation between individuals is a common aspect of human economic behavior (Treadway et al. 2012). The integration of effort and reward valuations, and the choices one can make based on these valuations, are addressed in effort based decision making (EBDM). Consequently the valuation of effort and reward are the two core aspects of EBDM. Most organisms (including humans) will expend effort to obtain a reward. As the amount of required effort for a certain choice increases however, the preference for that choice will decrease if the reward does not increase as well (Kurniawan et al. 2011). EBDM entails how the amount of effort relates to the magnitude of the reward. In other words, EBDM involves how effort and reward relate to each other, and how this affects the decision making process (Treadway et al. 2012).
An important aspect that might play a role in the effort and reward valuations, is how ‘real’ one perceives the effort to be spend and the reward to be gained. For instance, intuitively one might say that ‘realistic effort’ feels more burdensome than ‘less realistic effort’. How real one perceives the task or decision at hand (e.g. how immersed a person is in making a decision and how real this person perceives the effort and reward of that decision) can be enhanced using different media. One medium that sets itself apart from other
technologies by immersing the participant’s senses, is virtual reality (VR). By immersing the senses and providing interaction with one’s (virtual) environment (Schuemie et al. 2001), one presumably feels more in touch with their surroundings, compared to the simple computer tasks commonly used in psychological research. This ‘sense of realism’ goes handinhand with a term coined by scientific literature as ‘presence’. Here, presence is defined as ‘the sense of being part of the (virtual) environment’. This ‘being part of a virtual environment’ enhances how ‘real’ one perceives the environment and his or her surroundings (Schuemie et al. 2001). Tasks in psychological research often consist of questionnaires and computer tasks. Arguably, these types of tasks do not elicit a strong ‘sense of being part of the enviroment’ (the enviroment being the task itself). An altered sense of presence might influence how one perceives and valuates (components of) a task or decision. Thus, task performance and/or decision making could be affected by one’s sense of presence. Since presence might affect perception and thereby one’s (effort and reward) valuations, the amount of effort one is willing to expand (for a certain reward) might be affected as well. In earlier scientific research covering this subject however, the evidence seemed to be mixed. The notion of presence being related to task performance was very popular, yet there was no evidence to
back up this claim (Welch, 1999). Consequently, there was much uncertainty whether presence actually affected task performance. (Schuemie et al, 2001). However, most scientific studies concerning presence that were conducted in the late nineties and beginning of the twenty first century, simply did not have the means to elicit a sense of presence in participants (Turner & Casey, 2014). For example, Kim and Biocca (1997) attempted to enhance presence in participants by showing them a TV infomercial. Since watching a TVinfomercial presumably does not elicit a sense of being part of the VE, this is not an ideal way to enhance presence in participants. Fortunately in modern day and age, incredible technological advancement has been made. These technological advances have made it possible to create a realistic virtual environment (VE) that is able to enhance one’s sense of presence (Fox, Arena & Bailenson, 2009; Turner & Casey, 2014). Moreover, according to Slater (2009), when faced with events within a VRenvironment, participants will respond and behave more realistically. In other words, participants act and react more realistically when their sense of presence is enhanced. In this manner, VR allows realistic and interactive behaviours to take place (Bohil, Alicea & Biocca, 2012). Despite the fact that there seems to be empirical evidence supporting the claim that presence enhances one’s sense of realism and thereby influencing one’s behavior, it is still unclear how presence affects decisionmaking behavior. For instance, individual differences play a role in both presence (Ling et al. 2013) and the valuations of effort and reward (Treadway et al. 2012). How presence relates to the valuation of effort and reward (and thereby, how presence affects decision making) remains to be determined. The main focus of this article is how presence affects EBDM. Specifically, this study will address how presence affects both effort and reward valuations. We hypothesize that presence will influence reward and effort valuations in two different ways. First, when a
decision is framed in such a way that the effort elicits a higher sense of presence than the reward, effort will be perceived as more realistic, and therefore more burdensome. When faced with a choice between high effort (HE) or low effort (LE) we expect that, in this case the LEoption will be more enticing when participants experience a high sense of presence (e.g. in a VRenvironment), compared to a situation in which participants experience a low sense of presence. Second, when a decision is framed in such a way that the reward elicits a higher sense of presence than the effort, the reward will be perceived as more realistic, and therefore more appealing. We expect that, when faced with a choice between a high reward (HR) or low reward (LR), in this case participants are willing to expend more effort for HR when experiencing a high sense of presence, compared to a situation in which participants experience a low sense of presence. Another aspect that might influence the valuation of effort and reward besides realism, is sensitivity to reward (SR). Here, SR is defined as a personalitytrait that is entrenched in the availability of dopamine in the mesocorticolimbic pathways. These are generally known as common ‘reward pathways’ (Davis et al. 2007). In other words, SR is a trait that differs among individuals and is rooted within neurological reward pathways. SR might influence how one valuates reward. For instance, if one is highly sensitive to reward, one is willing to expend more effort for a HR. In this manner, the proportion between effortand reward valuation is different from individuals with a low SR. This way, SR presumably affects reward valuations. Although SR presumably influences one aspect of EBDM it is yet to be decided whether or not SR influences EBDMbehavior. However, there seems empirical evidence suggesting that decisionmaking behavior is affected by SR (Davis et al. 2007; Van Leijenhorst et al. 2010). Consequently, there are two factors that might influence
EBDMbehavior (presence affecting effort and reward valuation, and SR affecting reward valuation). To get a clear picture of how presence specifically affects EBDM, it would be wise to take SR into account. We expect that SR will affect EBDM in two ways. First, when SR is controlled for, the effortvaluation will will be weighed more heavily, compared to the reward valuation. This effect is present in both high and low SR individuals. Second, when presence is higher for reward and SR will be controlled for, rewardvaluations will drop dramatically for high SRindividuals, compared to low presence for reward. This is due to the fact that individuals with high SR would be willing to expend more effort when the reward is more realistic, compared to low SR individuals. When SR is controlled for, this effect will be nullified. This is not the case for low SR individuals, since they already are less enticed by the reward. When SR is taken into account, one would opt less for high effort/high reward (HE/HR)options. This effect is likely most prominent when a decision is framed in such a way that the reward appears to be more realistic. When effort elicits a higher sense of presence than the reward, it is expected that one would already be less inclined to opt for a HR (since the reward already is less appealing, compared to the more realistic effort), thus here we expect that taking SR into account would have little effect. This study will first address how presence affects EBDM and how presence affects both effort and rewardvaluations. Second, SR is another factor that influences rewardvaluation. To get a clear picture of how presence specifically affects EBDM, SR will be controlled for.
Method Participants Fiftyone participants took part in the experiment. 44.12 percent was female, 85.29 percent was student and mean age was about 22 years old (M = 22.41, sd = 3.30). Participants were not paid for their attendance, but could win payment of the mean amount of coins over conditions, with each virtual coin representing 10 eurocents. One participant was awarded this reward. Task The experiment consisted of three conditions: a baseline condition (2D effort – 2D reward), an effort condition (VR effort – 2D reward condition) and a reward condition (2D effort – VR reward). Here, a low sense of realism (and thereby a low sense of presence) is obtained in the 2Dversion, while a high sense of realism (and thereby a high sense of presence) is obtained by VR. For this experiment, we used an Oculus Rift DK2 (Oculus VR, 2014). The 2Dversion of the task was also displayed within VR, on a virtual 2Dscreen. Participants completed the conditions in counterbalanced order, with conditions consisting of 13 trials each, all implemented in virtual reality. Participants were instructed to power a mine cart over a track by making pumping motions with a bicycle pump. At the beginning of each trial, participants were given a choice between a HE/HRroute or a loweffort/lowreward (LE/LR)route. Colorcoding in presentation of the tracks informed participants of the amount of effort a route would require; green sections of the track required no pumping input, orange sections of the track required medium effort and red sections of the track required high effort pumping. In the baseline condition (Figure 1a), the different route options and coin rewards were displayed on two different computer screens, one on the left side of the virtual room and one on the right. The coins were displayed abstractly on these screens as
stacked orange bars. After choosing a route with a mouse click, a third display in the middle of the room showed a power bar and progress within the chosen track. Participants were only able to track their progress on this screen: no visible cart was moving. In the reward condition (Figure 1b), participants were in the same virtual environment. Choices were again represented on two different screens, but now rewards were realistically represented as stacks of golden coins on the left and right side of a desk in front of the participant and no longer on the computer screens. After the decision is made, the coins of the chosen route would fly into a chest in front of the participant. Then participants drove the cart the same way as in the baseline condition, and saw their progress in the middle screen. In the effort condition (Figure 1c and 1d), participants found themselves in a minecart inside a room with two screens displaying the different route options and abstract coins as orange bars. After selecting a route, a large door would open and they drove themselves into an outside natural environment, using the same bicycle pump that they now saw integrated into their cart. Some sections of the outside tracks were overgrown with either grass (medium effort) or shrubs (large effort). Before the start of the experiment, participants completed one testtrial in every environment, to make sure they understood how the task worked and what each element (the representation of reward and effort, the progressbar, etc.) Figure 1a: Baseline condition Figure 1b: Reward condition
Figure 1c: Effort condition Figure 1d: Effort condition ‘outside’
A shortened version of the Igroup Presence Questionnaire (IPQ) (Schubert,
Friedmann & Regenbrecht, 2001) was adapted for this experiment specifically. The IPQ was used to measure the amount of presence participants experienced during the different conditions. The items were scored using a Likertscale (1 through 5). A higher score indicates a higher sense of presence. Furthermore, SR was measured in participants. To measure SR, participants completed a subscale of The Sensitivity to Punishment and Sensitivity to Reward
Questionnaire (SPSRQ) (Torrubia et al. 2001). The participants completed the Sensitivity to Reward (SR)subscale, which contained 24 yes/no items. For every item, one point can be obtained, with a minimum of zero points and a maximum of 24 points in total. A higher score on the SRsubscale indicates a higher sensitivity to reward. The SRsubscale is positively related to Eysenck’s Impulsiveness Scale and the Zuckerman’s Sensation Seeking Scales (Zuckerman & Cloninger, 1996; Torrubia et al. 2001).
For this experiment we created a custommade input device. The goal of this input device is to make participants expend considerable effort and to enhance one’s immersion by mimicking the VE. In the VE, participants are driving a minecart, similar to a human powered handcar. To mimic the motion made operating such a cart, we chose a bicycle pump as the base of our input device. Operating a bicycle pump (‘pumping’) resembles the motion one would make operating a handcar. Furthermore, the (air) resistance felt while operating the bicycle pump, makes its usage an effortful activity. In order to make this bicycle pump an appropriate input device for a computer, we attached a strip of aluminium to the handle of the pump. This strip of aluminium covers the entire length of the pump. Since this strip is only attached to the handle, it goes up and down, along with the pumping motion. Over the aluminium strip, a computer mouse (Logitech G300) was fixed. Consequently, when moving the bicycle pumphandle up and down, the aluminium strips moves similarly along the fixed computer mouse. In this manner, the computer mouse can register the motions of the pump. To keep the pump in its place while it was being used, we fixed the underside of the pump to a MDF board. This way, potential differences in tilting of the pump and participanttopump distance between participants are minimized. Point of Indifference As a measure of the relationship between reward and effort valuation, the point of indifference (POI) for each subject was determined per condition. Assigning POI values has demonstrated to be a reliable method for measuring individual differences in subjective effort (Westbrook, Kester, & Braver, 2013) The POI is reached when the subject no longer
expresses a preference for the options. At this point the subject will choose the HE/HR just as much as the LE/LR. The POI can take on a value between 0 and 1.25. To determine the POI value for each condition, the average of the values of ‘reward per unit effort’ modifier of the last four trials is calculated. When the POI is low, the subject needs less reward to choose the HE/HR option. A higher POI means that the subject needs a higher reward to choose the HE/HR option. When the POI is equal to zero the subject chooses the HE/HR option, regardless of effort. The differences in POI values represent the differences in effort valuation. The representation of the effort and reward could account for these differences. When reward representation is constant, differences in the POI values are due to effort valuation. When effort valuation is held constant, differences in the POI values can be attributed to reward valuation. Reward Modifier The rewardmodifier decreases the difference in reward between tracks with each HE choice, while the difference between trackrewards increases for each LE choice. For each trial the reward for both tracks is calculated by subtracting the total effort values from both tracks (zero for green, two for orange and four for red) and multiplying this value with the rewardmodifier. The outcome is then added to ten for the HEtrack and subtracted from ten for the LEtrack. The value of the rewardmodifier ranges between 0, which means no difference between rewards, and 1.25, which is the maximum possible reward (20 coins) divided by the maximum possible difference between tracks (16). Each trial starts with a rewardmodifier
value of 0.625, which is the maximum rewardmodifier value divided by two. For each HEchoice, a value is subtracted from the rewardmodifier value and for each LEchoice a value is added to the rewardmodifier. The added or subtracted value grows for each consecutive choice of the same effort type. This value is 0.02 for the first choice, 0.05 for the second, 0.1 for the third and 0.2 for the fourth (or a higher) consecutive choice of the same type of effort. With each switch in effort type (from HE to LE or vice versa) this value drops back to 0.02. The minimum value of the reward modifier has been set to 0 to avoid that the LE choice pertains a higher reward than the HE choice. The maximum value of the rewardmodifier has been set to 1.25 to avoid scores that are higher than 20 coins . Analysis The data will be analyzed using a oneway repeated measures ANOVA (with presence as predictor variable with three levels). First, we expect a main effect of presence. Second, we expect that POI’s will be higher in the reward condition, and POI’s will be lower in the effort condition, compared to the baseline condition. For our manipulationcheck (the IPQ) the same analysis will be used. To take SR into account, the SRscores (using a median split) will be used as a betweensubjects factor in a factorial mixed ANOVA. When SR is controlled for, we expect the POI’s to be lower in all conditions. Furthermore, when SR is taken into account we expect both POI’s in the baseline and effort to be lower, while we expect POI’s in the reward condition to be dramatically lower. Figure 2 shows a simplified visualisation of these expectations: using a median split, SR is divided into two groups (high and lowSR individuals). For lowSR individuals POI’s will be (slightly) lower in all conditions. For highSR individuals POI’s would be lower in the baseline and effort condition. POI’s in the
reward condition however, would be dramatically lower. Figure 2. Mean POI’s in the Baseline, Reward and Effort condition for High and Low SR individuals (simplified visualisation of expectations). Results Thirty four participants were included in the analysis. Sixteen participants were excluded from analysis due to ceiling effects in measurements. One participant did not partake in all three of the conditions due to nausea, and was excluded. Three participants did not fill in the IPQ. First, IPQdata were analysed using a oneway repeated measures ANOVA. Mean IPQscores and standard deviations are displayed in table 1a. Figure 3a shows the mean IPQscore of each condition with corresponding 95% confidence intervals. Mauchly’s W indicated that the assumption of sphericity was not violated (χ2= 1.608, p = 0.447). There
was a main effect of presence (F(2,60) = 64,674, p <0.01). Planned contrasts revealed that presence was significantly higher in both the reward condition (F(1,30) = 9.384, p = 0.05) and the effort condition (F(1,30) = 42.766 , p < 0.01.) compared to the baseline condition. Table 1a. Mean IPQscore and Standard Deviation (between Brackets) for the Baseline, Reward and Effort Condition Figure 3a. Mean IPQscore in the Baseline, Reward and Effort condition with corresponding 95% confidence intervals, adjusted for a withinsubjects design.
The POIdata were analysed using a one way repeated measures ANOVA. Mean POI’s and standard deviations are displayed in table 1b. Figure 3b shows the mean POI of the three conditions with corresponding 95% confidence intervals. Mauchly’s W indicates that the assumption of sphericity is not violated (χ2 = 3.512, p = 0.173). There was no main effect of presence on POI (F(2,66) = 1.448, p = 0.242). Planned contrasts revealed that there was no significant difference in POI between the reward and baseline condition (F(1,33) = 0.318, p = 0.577). Furthermore, there was no difference in POI between the effort and baseline condition, but a trend was showing, however: F(1,33) = 3.680, p = 0.064. Table 1b Mean POI and Standard Deviation (between Brackets) for the Baseline, Reward and Effort Condition Figure 3b. Mean POI in the Baseline, Reward and Effort condition with corresponding 95%
confidence intervals, adjusted for a withinsubjects design. The POIdata were also analysed with SRscores as a between subjects factor, using a factorial mixed ANOVA. Mauchly’s W indicates that the assumption of sphericity was not violated (χ2 = 3.631, p = 0.163). Also the assumption of equality of variance was not violated for all measurements (p < 0.05). There were no differences in POI between high and low SR F(1,32) = .667, p = 0.420. Furthermore, SR had no main effect on POI (F (2,64)= 0.279, p = 0.757). Planned contrast revealed that was no difference in POI between the reward (F(1,32) = 0.180, p = 0.675) and baseline condition. Compared to the baseline condition, the effort condition had no effect (F(1,32) = 0.746, p = 0.394). Mean POIscores for low and high SR are displayed in figure 4. Figure 4. Mean POI for High and Low SR (median split) for the Baseline Reward and Effort condition, with correspoding 95% confidence intervals, adjusted for a withinsubjects design. Discussion
In the current study, we assessed if presence affects two components of EBDM (effort and reward valuation). To get a clear picture of how presence specifically affects EBDM, we also took SR, another factor affecting EBDM (specifically: reward valuation), into account. Our expectations were not met; there was no effect of presence on EBDM. When SR was taken into account there was, again, no effect. Presence however, was higher in the reward and effort condition, compared to the baseline condition, as expected. While presence was enhanced, this had no effect on EBDM. This might imply that there simply is no effect of presence on EBDM. However, this study has some technical flaws which might have contributed to this noneffect. For instance, VR is a relatively new technology, and there is still much to learn about its characteristics (Fox, 2009). Another technical flaw is that a large portion of the participants were excluded from analysis due to ceilingeffects. The POI was not reached, because the POI was ‘out of range’ for our measurements. This can have a number of causes. One possible cause for this ceilingeffect, may be due to participants making their decision regardless of effort. This can happen because the required effort simply isn’t effortful enough. When there is no effort to be considered, one would naturally opt for the HR. In this experiment, we used physical activity as effort. Making physical activity more effortful might not be a solution, however. Again, participants are prone to fatigue. When the required effort is too high, participants will not have the strength and endurance to complete the task. However, physical activity does not necessarily have to be ‘heavy’ to require effort. Heavy physical effort is wearisome, but wearisome activity does not have to be physically heavy. For instance, threading a needle is considered to be tedious and effortrequiring, but not a physical burden. Finding a way to elicit effort in participants, without being (too) physically heavy, might reduce the ceilingeffect.
Furthermore, in psychological research, VR is a relatively new technology. Therefore, it is still unclear what the specific characteristics of VR are and how this relates to and affects psychological research (Fox, 2009; Turner & Casey, 2014). For instance, while using VR in psychological research, VR itself might affect participants, and thereby VR might be a confounding variable (like invoking high arousal or symptoms of motion sickness) (Bruck & Waters, 2009). However, there are multiple examples of VR being an effective tool in (neuro) psychological research, like using VR as an effective tool for psychological interventions (Turner & Casey, 2014). Another example is VR’s compatibility with neuroimaging techniques, where a VRsystem can immerse the senses and thereby successfully eliciting psychological construct of interest (Bohil et al. 2012). Since VR can be an effective tool in (neuro)psychological research, VR may give new insights to EBDM as well. Based on the current study, we cannot conclude that presence affects EBDM. However, this study was prone to multiple technical flaws. Therefore, our current goal should be to identify and solve these technical problems. When this study (and the experiment) is free of technical limitations, we may (finally) get a decisive answer whether presence affects EBDM. Not only might this give more insight into EBDM, but this may also give more insight in VR in psychological research as well. Thus, this study may contribute to a growing body of knowledge regarding VR in psychological research.
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