Bachelorthesis
Effort-Based Decision Making in Virtual Reality R Huetink
University of Amsterdam 01-07-2015
10319050 Jasper Winkel
Abstract
In this paper I examined whether Virtual Reality is a suitable technique to make psychological tests more realistic. Furthermore, I examined whether the participants’ effort-based decision making behaviour differs between various digital environments: 2D, 3D and VR. At last, I examined whether Gaming Experience had an effect on the results that were found. Forty-nine participants took part in this study. The participants completed two hours of filling in questionnaires and finishing tests. I found that sense of presence was higher in VR compared to the 3D environment, which supports the idea that VR is experienced as more realistic. The Point of Indifference, an indication of effort-based decision making behaviour, did not differ between conditions. Gaming Experience turned out not to be of influence on the Point of Indifference and sense of presence. These findings suggest that VR is a good candidate for psychological research. More research is needed to examine whether certain effects weren’t found due to flaws in the manipulation or simply because they don’t exist.
Introduction
Decision making is a cognitive process that has great influence on both present-day issues, and on an individual level as a social level. People constantly have to evaluate their options and make decisions about all kinds of issues, such as ‘Which socks am I going to wear today?’ or ‘Am I going to commit a crime?’. Decision making has great influence on many social problems in different scientific fields. A few of those fields are the clinical field, the business field and the advertisement field. For example, in the clinical field it is interesting to examine decision making because it can influence the tendency of people to attempt suicide (Jollant et al., 2014). In the business field, decision making is important for leadership (Westaby, Probst & Lee, 2010) and in the field of advertisement decision making is important because it influences buying behaviour in consumers (Kim, Ferrin & Rao, 2008). For this reason, decision making has been of great interest in scientific research.
In decision making research in humans, various types of decisions are
distinguished. Examples of these types of decisions are risk-based decisions, perception-based decisions and effort-perception-based decisions. To investigate the decision making
behaviour of people, several tasks have been developed in the past. For example, a commonly used task in risk-based decision making research is the IOWA Gambling Task
(Bechara et al., 1994), and in perception-based decision making research the moving dot task is commonly used (Britten et al., 1992). For effort-based decision making, a
commonly used task is the Effort Expenditure for Reward Task (Treadway et al., 2012). Effort-based decision making is a type of decision making in which participants are presented different kinds of options to choose from. Those different options vary in reward that can be obtained and the amount of effort participants have to invest. The choice of the participants will depend on how much effort they are willing to put in for a certain reward.
The tasks used in psychological research like decision making studies mean to reflect a real-life situation in which people have to make a certain kind of decision, as pointed out above. These tasks are pretty basic: although their purpose is to reflect a real-life situation, most of the time these computer tasks do not seem realistic. For example, as described in a recent study (Treadway et al., 2009) the Effort Expenditure for Reward Task (EEfRT) is a 2D computer task in which participants can choose between two different task levels (the hard level and the easy level) in order to obtain secondary rewards. The two task levels require different amounts of effort, and the more effort a participant invests the higher the secondary reward will be. The hard level requires a lot of button presses in order to obtain the reward compared to the amount of button presses required in the easy level. A point of discussion that often is expressed about tasks like the EEfRT is that they aren’t realistic enough, which possibly distorts the data (Burgess et al., 2006). In other words, researchers wonder if the conclusions of these studies can be generalized to real life situations. This is an important point of criticism, because it questions the ecological validity of many psychological studies. The ecological validity reflects how approximate the method of a study is to the real-world situation that is being examined (Araújo, Davids & Passos, 2007). Improving the ecological validity of psychological experiments will have a positive effect on the
generalizability of psychological studies. In order to make psychological tests such as the EEfRT more realistic, I will introduce an alternate method of presenting experiments: through Virtual Reality.
A new, promising technique is Virtual Reality (VR). VR is already being used in the gaming industry, and has also proved its use in clinical practice. VR is for example applied in therapies for several phobias such as social phobia (Klinger, Bouchard, Légeron, Lauer, Chemin & Nugues, 2005) and arachnophobia (Bouchard, Côte,
St-Jacques, Robillard & Renaud, 2006). VR has also proved its usefulness in treating Post Traumatic Stress Disorder (Difede, Cukor, Patt, Giosan & Hoffman, 2006). VR is an attractive alternative to in vivo exposure and basic 2D computer tasks because it offers both a controlled experimental setting and a realistic experience, thus high ecological validity. VR creates an immersive 3D digital environment, and the participants
experience this environment both visually and auditorily. The experience is realised through a Head-Mounted Display (HMD), which is a stereoscopic display that provides depth perception and is able to track the position of the participant. Because the HMD tracks all head movements of the participant, the participant is able to look around in the VR. The goal of this study is to validate the use of VR in psychological experiments. In order to measure how realistic a task is experienced by the participants, I will introduce the construct Presence.
Presence is a psychological construct that has been of interest in the gaming industry because of its influence on gaming experience (Takatalo, Häkkinen,
Komulainen, Särkelä & Nyman, 2006). Sense of presence is an indication of the relation between psychological awareness and the current time and place in which somebody is located (Waterworth, Waterworth, Mantovani & Riva, 2013). Based on previous
definitions (Wissmath, Weibel & Groner, 2009) presence is defined in this paper as the sense that a person feels spatially present in the current environment or the current digital environment, such as VR or a 2D computer environment. In other words,
presence is the indicator of how realistic a task experience feels to a participant, thus it reflects the ecological validity of a task. Presence will be quantified in this study using the Igroup Presence Questionnaire (Schubert, Friedmann & Regenbrecht, 2001). An interesting theory that has been developed about presence is the spatial presence theory (Wirth et al., 2007). This theory states that sense of spatial presence arises based on two steps: the construction of a mental model of the environment, including space-related information, and confirmation of perceived self-location in this environment. Experiencing a digital environment as being your physical environment depends on various characteristics of this environment such as being able to undertake actions within this environment.
Research has shown that sense of presence is higher in a 3D gaming experience compared to a 2D gaming experience (Rajae-Joordens, 2008). Rajae-Joordens examined a 2D experience compared to 3D graphics on a flat screen: note that a flat 3D experience
is not the same as an HMD experience. Presence was higher in a 3D gaming experience compared to the 2D experience, which leads to the conclusion that the 3D experience felt more real to the user than the 2D experience. Kober, Kurzmann and Neuper (2012) found that presence was higher in an immersive 3D experience using a 3D projection on a single wall, compared to a 2D experience. However, these results indicate that
presence was higher in immersive 3D and flat 3D compared to 2D experiences, but research hasn’t examined yet whether an HMD experience will create a higher sense of presence compared to 2D or an experience using 3D graphics on a flat screen. Based on these results, it is expected that a task using an HMD will be experienced as even more realistic than a 2D experience or a flat 3D experience.
The goal of this study is to investigate whether sense of presence is higher in a VR experience compared to 2D and flat 3D experience in a psychological
experiment. Based on the spatial presence theory, the first hypothesis predicts that condition (2D, 3D or VR) will have an effect on sense of presence. The second hypothesis states that in an HMD experience, sense of presence will be higher than in the 3D
experience. Furthermore, the third hypothesis predicts that in a flat 3D experience sense of presence will be higher compared to 2D experience. If presence is higher in an HMD experience, this way of testing is experienced as more real than a 2D experience or a flat 3D experience. This means that the generalizability of the results of studies using VR will be higher compared to the results of studies using 2D or 3D tasks, which is positive for the ecological validity of these studies. This study will also examine the effect of
different digital environments on effort-based decision making. I hypothesize that when an experience evokes higher levels of presence, the amount of effort a participant has to invest in an effort-based decision task will be perceived as higher while the reward representation stays fairly the same. Because the amount of effort is perceived as higher, I expect that participants would invest less effort in a more realistic experience. On each trial in the experimental task (in 2D, 3D and VR) the difference in reward between the two options is based on the amount of effort the participant has to invest, multiplied by a valuation function. This valuation function updates dynamically, increasing when the low effort alternative is selected, and decreasing when the high effort alternative is selected via a staircasing procedure (Tversky & Kahneman, 1992). This function was built to find each participant’s individual shifting point: the Point of Indifference (PoI). The PoI represents the amount of effort a participant is willing to invest for a certain
reward. Because the time needed to complete a track is identical in both choices, the PoI should only represent a trade-off between the amount of effort invested and the reward obtained. Thus, based on the decisions participants make, their personal PoI will be calculated that reflects their effort-based decision making behaviour in a certain digital environment. I expect that when a task is experienced as more realistic the PoI will differ from the PoI of a task that is experienced as less realistic. Therefore, the fourth hypothesis states that condition will have an effect on the PoI. The fifth hypothesis states that there is a correlation between the differences in sense of presence between
conditions and the differences in the PoI between conditions.
A possible confounding factor for sense of presence is gaming experience. Huh & Bowman (2008) found that addiction to gaming is associated with the personality traits neuroticism and extraversion. Furthermore, the personality trait extraversion enhances sense of presence (Alsina-Jurnet, Gutiérrez-Maldonado, 2010). It follows that gaming experience could be a confounding factor because subjects with a lot of gaming experience possibly have higher sense of presence due to their extravert personality. Since there wasn’t a questionnaire available that would be suitable for this experiment, I designed and validated a questionnaire myself. Details of this validation process are provided in the Methods section. This Game Experience Questionnaire (GEQ) will be taken in order to examine the sixth and seventh hypotheses. The sixth hypothesis states that gaming experience has an effect on sense of presence, and the seventh hypothesis states that gaming experience has an effect on the PoI.
Methods and Materials Participants
Forty-nine participants were included in this study. All participants completed a screening to examine whether they were suitable for this study. Participants were recruited through the website of the University of Amsterdam, verbal advertisements and posters. Subjects participated either voluntarily, or they received 20 euro or 3 points Psychology Research Credit. Subjects were between 18 and 28 years old, from which 17 were male and 32 were female. Mean age was 23 years old. After the
participants read the form with information about the study, written consent was obtained. The Department of Psychology Ethics Review Board approved this study.
Materials
All experimental tasks in this study, including the VR, were created using a software tool: the Unreal Engine 4 (Epic Games, 2012). The Head Mounted Display that displayed the VR was the Oculus Rift DK2 (Oculus VR, 2014). The participants navigated in the environment using an xbox one game controller (Microsoft, 2013). Participants performed the task in the 2D environment, the flat 3D environment, and in VR. The order in which the participants performed these tasks was counterbalanced. During this task, participants navigated a little cart across a track. This track split up each trial in two different directions, and the participants had to choose between those two directions. These directions differed in levels of effort and corresponding levels of
reward. The rewards were shown as a number representing a monetary reward, and the effort was shown schematically prior to the choice. The participants were instructed to use the analog sticks on the game controller in an alternative way: they had to move the analog sticks with their fists (instead of with their thumbs), which made setting the cart in motion harder, so that the high effort tracks would actually perceived as requiring higher effort.
b
c
Figure 1.
Illustrations of the task.
a. Screenshot taken from the 2D task, in which effort is represented as the bar. Green parts of the bar reflected low effort, orange parts of the bar reflected medium effort and red parts of the bar reflected high effort. The monetary reward that would be obtained after completing the trial was shown as the number above the bars. b. Screenshot taken from the 3D task. The representations of effort and reward remained the same as in the 2D task. c. Screenshot taken from the VR task. The screenshot is taken from the
Presence was measured using the Igroup Presence Questionnaire (IPQ), developed and validated by Schubert, Friedmann and Regenbrecht (2001). This questionnaire consists of 14 items, which were answered on a 5-points Likert scale, varying from 0 (strongly disagree) to 5 (strongly agree). This questionnaire was
translated to Dutch. For example, items in this questionnaire were: ‘I felt present in the Virtual Reality’ and ‘I was paying attention to the real environment’. Where appropriate, items were reverse-scored. The highest obtainable score was 70 and represented an extremely high sense of presence. The lowest obtainable score was 0 and represented an extremely low sense of presence.
To measure Gaming Experience, I conducted a pilot study to test the reliability of this new questionnaire. This questionnaire consists of six items, from which some were answered on a 4-point Likert scale and the rest had 4 different possible answers. For example, questions in this questionnaire were ‘For how long have you been playing video games regularly?’ and ’Do you have experience with Virtual Reality?’. The highest obtainable score was 24, which represented extremely high Gaming Experience. The lowest obtainable score was 0, which represented extremely low Gaming Experience. The questionnaire was designed in Dutch, since the participants’ first language is Dutch. One sample of 106 Dutch participants, who would not be taking part in the actual study, was recruited via the social network Facebook (https://www.facebook.com/). The participants filled in the questionnaire online via Google Forms
(https://www.google.nl/intl/nl/forms/about/). I tested the reliability of the questionnaire on this sample of 106 participants. Crohnbach’s reliability estimate resulted in an α of .74, surpassing the .7 treshold for a reliable test (Kline, 1999). This led to the conclusion that the questionnaire was reliable and suited to be used in this study.
During this experiment, several other questionnaires have been taken. These will not be addressed in this paper, since I did not use that data. More information is
Procedure
Data collection took part in the Brain & Cognition lab at the University of Amsterdam. The participants were explained that they could earn extra monetary reward, depending on how they performed in the computer tasks. All participants received 50 cents extra after completing the tasks. Participants completed a one-hour assessment consisting of the different computer tasks, and completed one hour of filling in questionnaires. The order in which the participants had to do this was counterbalanced (either starting with the questionnaires, or starting with the computer tasks). The order in which the
participants completed the computer tasks (2D, flat 3D & VR) was also counterbalanced. I assisted the participants at the beginning of each computer task and at the beginning of filling out the questionnaires.
Data analyses
Means and standard deviations were calculated for all continuous variables. I tested whether sense of presence differs between the three conditions (VR, 2D & 3D) with a one-way repeated measures ANOVA. I used a repeated contrast. To check whether Gaming Experience had an effect on sense of presence, the scores on the Gaming Experience Questionnaire were used as a covariate in the statistical analyses. To see whether the Point of Indifference differs between the 3 conditions, also one-way repeated measures ANOVA was conducted with the same contrast. Gaming experience was used as a covariate again. To see whether there was a correlation between sense of presence and PoI, the difference in scores in sense of presence were calculated
(difference between 2D scores and 3D scores, and the difference between 3D and VR scores) and the difference in PoI scores were calculated, in the same manner. I tested whether these differential scores (2D-3D & 3D-VR) correlated.
Results Table 1
Descriptive Statistics.
Means and Standard Deviations of Sense of Presence and Point of Indifference over Different Conditions.
Sense of Presence Point of Indifference
Mean SD Mean SD
2D 21.91 4.97 18.32 16.85
3D 34.68 7.80 17.00 17.87
VR 49.50 5.32 17.50 21.24
Nine subjects were excluded from analyses, because they weren’t instructed to move the analog sticks with their fists and did it with their fingers instead, which is experienced as lower effort so the manipulation did not succeed in these subjects. Furthermore, the subjects with a PoI score below 3 were excluded from analyses. A negative PoI score represented overall choice for high effort regardless of the amount of reward. A PoI score between 0 and 3 represented overall choice for high reward, regardless of the amount of effort the participant had to invest. Since the goal of this study was to
examine effort-based decision making, the participants were meant to make their choice based on the amount of effort compared to the amount of reward. When participants ignored the amount of reward, or the amount of effort, I concluded that the
manipulation failed and excluded those participants from analyses. This concerned 17 participants. An extremely high PoI score (>50) represented overall choice for low effort, regardless of the amount of reward, but since I haven’t noted any participants with an extremely high PoI score no subjects were excluded from analyses based on this criterion. Also, there weren’t any participants consistently choosing low reward
regardless of the amount of effort, so no participants were excluded based on this criterion either. Participant 48 was excluded because the computer failed to save this person’s questionnaires. Twenty-two participants remained of the original sample of 49
participants. Mean age of the remaining participants was 23 years old, and from the remaining participants 6 were male and 16 were female.
The effect of the conditions (2D, 3D & VR) on sense of presence was tested with repeated measures ANOVA.
↑ Scores on the IPQ → condition Figure 2.
Graph that displays differences in sense of presence over the three conditions with within-subject error bars representing the standard error of the mean.
As predicted in hypothesis 1, I found a main effect of condition on sense of presence, F(2,40) = 10.889, p<.001. The second hypothesis is also supported: sense of presence was higher in VR compared to 3D, F(1,20) = 19.863, p<.001. The third hypothesis was not supported, sense of presence was not higher in 3D compared to 2D, F(1,20) = .387,
p=.541. The fourth hypothesis stated that there is a main effect of condition on PoI. To test whether this hypothesis is supported another repeated measures ANOVA is conducted. I did not find a main effect found for condition on PoI, F(2,40) = 2.286, p=.115. There wasn’t a difference in PoI between 2D and 3D F(1,20) = .089, p=.768, but there was a difference found in PoI between 3D and VR, F(1,20) = 5.586, p=.028.
↑ Point of Indiff- erence → condition Figure 3.
Graph that displays differences in the Point of Indifference over the three conditions with within-subject error bars. The error bars represent the standard error of the mean.
The fifth hypothesis stated that the differences in scores between conditions in sense of presence should correlate with the differences in scores between conditions of the PoI. Firstly I tested whether the differences in scores between the 2D and 3D conditions correlated. I did not find a significant correlation, r=.201, p=.370. Secondly I tested
whether the differences in scores between the 3D and VR conditions correlated, I did not find a significant correlation r=.125, p=.579. The sixth hypothesis that stated that
gaming experience has an effect on sense of presence is not supported, F(2,40) = 1.553, p=.224. This value was found when using Gaming Experience as a covariate in the
repeated measures ANOVA testing the main effect of condition on sense of presence. The seventh hypothesis that stated that gaming experience has an effect on PoI was also not supported, but I did find a trend, F(2,40) = 2.553, p=.090. I found this value when using Gaming Experience as a covariate in the repeated measures ANOVA testing the main effect of condition on PoI.
Discussion
The goal of this research was to examine whether VR could contribute to making
psychological tests more realistic, and thus more ecologically valid. I hypothesized based on the spatial presence theory that VR should raise higher sense of presence compared to the other conditions. A main effect of condition on sense of presence has been found. Since sense of presence was higher in VR compared to the 3D experience, VR could possibly be a suitable candidate to become a new technique used in psychological experiments. The finding of the main effect of condition on sense of presence is in line with the spatial presence theory. Since the hypothesized main effect of condition on PoI has not been found in this experiment, more research is needed to examine whether the use of VR actually leads to more reliable results. I hypothesized that the 3D experience should raise higher sense of presence compared to the 2D experience, but this effect has not been found. This finding was not in line with the spatial presence theory. In this paper I also examined whether immersion made effort seem higher. I hypothesized that that the point of indifference should differ between conditions, but I haven’t found this effect. The last hypotheses stated that Gaming Experience could be a confounding factor in sense of presence and PoI, but I haven’t found these effects. I expect that Gaming Experience simply does not have a big influence on these variables. However, it is possible that several of the other effects that haven’t been found weren’t found due to flaws in the manipulation, and this remains to be examined.
Many participants were excluded from analyses because the manipulation failed; this was due to the way I set up the manipulation. In this experiment, during the high
effort trials the participants had to move the analog sticks more often than in the low effort trials. I noted that in 10 participants, the high effort trials weren’t experienced as a lot higher effort than the low effort trials, because people tended to consistently choose for high reward trials regardless of the effort. In an attempt to make the high effort trials be experienced as actually costing more effort, I instructed the rest of the participants to move the analog sticks with their fists. Even after this adjustment the manipulation failed in 17 other participants. To prevent this from happening again, in a new
experiment the high effort trials should cost the participants significantly more effort to complete compared to how much effort the high effort trials cost in this experiment. A suggestion to realise this is to use joysticks instead of xbox controllers, and then putting weights on the participants’ wrists. Moving joysticks is a bigger movement than using navigation keys, and with weights on your wrists this will cost even more effort. Since people barely have to move the joysticks in the low effort trials, and in the high effort they do, the contrast in perceived effort between the trials will hopefully be bigger when using joysticks and weights.
In summary, this paper shows that different digital environments lead to different experiences in terms of sense of presence. In three different conditions participants had to complete the same psychological task, and the VR experience was accompanied by the highest sense of presence compared to the other digital
environments. I did not find a main effect of condition on PoI, but more research is needed to determine whether this was due to flaws in the manipulation or not. Further research is needed to investigate whether the use of VR in psychological research could contribute to higher ecological validity and more reliable results.
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Appendix A
Questionnaire Gaming Experience (Game ervaring vragenlijst)
Speel je vaak computergames (PC of console games; playstation, XBOX etc)? - Zelden/Nooit
- Weinig - Regelmatig - Vaak
Hoeveel uur per week schat je dat je gemiddeld computer games speelt, genomen over het afgelopen jaar?
0-2 uur 2-6 uur 6-14 uur 14+ uur
Hoe lang speel je al regelmatig computergames? 0-3 jaar
3-6 jaar 6-9 jaar 9+ jaar
Speel je vaak 2D games (bijvoorbeeld Candycrush, Flappy bird etc)? - Zelden/Nooit
- Weinig - Regelmatig - Vaak
Speel je vaak first-person games met 3D graphics (Battlefield, Portal etc)? - Zelden/Nooit
- Weinig - Regelmatig - Vaak
Heb je ervaring met Virtual Reality? - Geen ervaring
- Wel eens geprobeerd - Regelmatig gedaan - Vaak gedaan
Appendix B Additional questionnaires
QUESTIONNAIRE REFERENCE
Locus of Control Questionnaire Rotter, J. B. (1966). Generalized
expectancies for internal versus external control of reinforcement. Psychological monographs: General and applied, 80, 1-28. Temporal Experience of Pleasure
Questionnaire
Gard, D. E., Gard, M. G., Kring, A. M., & John, O. P. (2006). Anticipatory and
consummatory components of the experience of pleasure: a scale
development study. Journal of Research in Personality, 40, 1086-1102.
Sociaal-Economische Status Questionnaire (Social-Economic Status Questionnaire)
Students designed this questionnaire, no citation.
Short Questionnaire to Assess Health-Enhancing Physical Activity
Wendel-Vos, G. W., Schuit, A. J., Saris, W. H., & Kromhout, D. (2003). Reproducibility and relative validity of the short
questionnaire to assess health-enhancing physical activity. Journal of clinical
epidemiology, 56, 1163-1169.
Immersive Tendencies Questionnaire Witmer, B. G., & Singer, M. J. (1998). Measuring presence in virtual environments: A presence
questionnaire. Presence: Teleoperators and virtual environments, 7, 225-240.
Listening Span Test Vos, S. H., Gunter, T. C., Kolk, H. H., & Mulder, G. (2001). Working memory constraints on syntactic processing: An electrophysiological investigation. Psychophysiology, 38, 41-63.
