New perspectives on ego-depletion

New perspectives on ego-depletion

The effects of long-term strain and various levels of short-term strain on self-control. The robustness of a concept tested.

Master thesis University of Groningen Faculty of Economics and Business

Msc Business Administration Marketing Management

New perspectives on ego-depletion

The effects of long-term strain and various levels of short-term strain on self-control. The robustness of a concept tested.

University of Groningen Faculty of Economics and Business

ABSTRACT

PREFACE

This master thesis is the closing chapter of my study. It is based on research done between May and December 2012 at the Faculty of Economics and Business at the University of Groningen.

It was not easy to find a topic that was both daring and interesting enough to engage in for this period of time. After having rejected two previous ideas, I turned to prof. dr. B. M. Fennis. After the first meeting, the road of writing this thesis was pretty smooth, with only a few bumps along the way. I would like to thank him as my first examiner for helping me to get started and for motivating me by commenting the submitted chapters and providing the much needed deadlines.

Secondly, I would like to thank Reinder Dallinga for pointing out matters that had not even crossed my mind, and helping me to get them out of my mind again. The self-evident way he arranged all sorts of practical things made the data-collection period of this thesis so much less stressful.

Another word of thank goes to dr. M. C. Leliveld, for responding to my call for help even when having a jetlag, a crowded agenda and a cold. If it wasn’t for her attentive eye, I wouldn’t have been able to start the data collection process. I would also like to thank Roy Sijbom. His last adjustments completed my work in Authorware.

Furthermore, I would like to thank all 294 participants who took the time to complete the

questionnaires or participated in the experiment. They were crucial in the completion of my studies. I would not be able to finish my thesis, or my studies at all, if it wasn’t for the help of my friends and family, who were always willing to complete yet another questionnaire for me. This was the last one, guys! At least for now.

Lastly, I would like to thank my parents for being there. And for not giving to many faces when my planning skills were once again not optimal. Their support, in many ways, means a lot to me and has helped me to come to this point.

Ryanne Smit

MANAGEMENT SUMMARY Theory

Self-control is the ability to attain control over temptations, enabling one to potentially accomplish a different deliberate response. This control is used to override impulses, immediate desires and habitual responses in favor of those that are more beneficial in the long-term (Baumeister & Heatherton, 1996). The strength model explains that usage of the self-control resource leads to a reduction in the capacity to exert further self-control, which is termed ego-depletion. We focused on the robustness of the ego-depletion effect, in which we identified two unexplored issues. The first issue we discussed was the robustness of the ego-depletion effect on the long-term, explaining how we expect that many daily strains combined with too little replenishment of the self-control resource leads to chronic depletion. The second issue we discussed is that contradicting findings about the direction of the self-control performance after self-control strain, make the assumption of the assumed linearity of the effect not unequivocal.

Studies

In the first study, we compared students’ self-control, buying impulsiveness and expenses at the beginning and end of the college year. We hypothesized that students’ self-control would be higher and the buying impulsiveness and expenses higher at the beginning of the year, compared to the end of the year.

In the second study, muscle contraction was used as strain while participants’ self-control was tested. We hypothesized that light contraction would lead to enhanced self-control; moderate contraction would lead to either enhanced or reduced self-control, and heavy contraction would lead to reduced self-control, compared to the control group.

Results

Results in the first study show that students’ expenses were higher at the end of the year, compared to the beginning of the year, for purchases in supermarkets and on food. An interaction effect between students’ expenses and the presence of exams was found. Only a the beginning of the year, students’ expenses were higher for the students who did not have exams in the previous four weeks, compared to those without exams. This difference was not found at the end of the year. There were no significant differences found in self-control and buying impulsiveness.

There were no significant results in the second study. Self-control and reported self-control was equal for the three contraction conditions and the self-control condition.

Conclusion

the lack of results on the other two measures (i.e. self-control and impulsive buying) we cannot accept our hypothesis for a certainty.

In the second study, we could not confirm out hypothesis, due to a lack of results on all measures.

Discussion

The results in the first study are the first indication that the limited resource of self-control changes and actually decreases over a time period of as long as a year. This idea would extent the metaphor of self-control as a muscle; shortage of recovery of self-control can lead to long-term depletion effects, like a muscle that incurs a long-term injury when it has a continuous lack of rest and recovery. Practical implications for marketers of the finding that students become more lenient with money at the end of the year, is that extra impulse buying incentives at this moment of the year can increase students’ purchases. Also, when finding more evidence for the chronic depletion effect, heuristics cues in marketing techniques would be most effective.

Both studies are susceptible to some limitations, which could have been the reason for the lack of results. In the first study, the research method (i.e. online questionnaire) allows limited exclusion of other influential factors. Also, the convenience sample we used can lead to misrepresentation. For example, due to the sampling method, the age difference between the two groups is larger than its standard deviation. However, the correlation between timing in the college year and expenses are remarkable, and give input for further research.

For the lack of results in the second study, causes are mostly sought in the manipulation of the independent variable of muscle contraction. We have opted that the amount of muscle contraction and the type of muscle contracted may have differed from the research of Hung and Labroo (2009). Secondly, muscles were contracted during the self-control demanding activities, which may result in different performance. Thirdly, muscle contraction may not be a depleting activity. Another justification for the lack of results is that the Stroop task used to measure self-control may not be a proper measure. The reasoning in this research that the ego-depletion effect might be curvilinear may still hold.

INTRODUCTION

In daily life, people are tempted to “do” things that are pleasant at that particular moment, however these are not necessarily the most beneficial for goals on the long-term. Students prefer to browse on Facebook instead of studying for their exams, even though the last option may well serve their best interest for the future. Many people feel like time flies in the evening hours and stay up late even though it would be more sensible to go to bed early and start the next day fresh. Likewise people are tempted to overeat, overspend, say things that come up in mind immediately, procrastinate work, drink too much alcohol or give in to other impulses or immediate desires. In all these examples, a potential conflict arises between the long-term goals and immediate desires.

Self-control1 _{is the ability to attain control over these temptations, enabling one to potentially} accomplish a deliberate different response. This control is used to override impulses, immediate desires and habitual responses in favor of those that are more beneficial in the long-term (Baumeister & Heatherton, 1996).

There is a large body of work on self-control and consequences of self-control failure in marketing and consumer science (e.g. Vohs & Faber, 2007; Hofmann, Strack & Deutsch, 2008; Fennis, Janssen & Vohs, 2009; Baumeister, Sparks, Stillman & Vohs, 2008). This stream in psychology became popular after Baumeister, Bratislavsky, Munraven and Tice (1998) discovered in a series of experiments that choice, active response, self-regulation and other volitional acts are all drawn from a common “inner resource”. Using this resource effectively leads to a reduction in subsequent capacity or willingness to engage in volitional action (Baumeister et al., 1998). In the last two decades, many researchers conducted experiments to determine which specific activities cause ego-depletion and to what extend.

The present research is concerned with the robustness of the theory on self-control effects in two different ways. Our goals in this study were (1) to investigate the long-term effect of strain on self-control in real-life, and (2) to test whether various levels of strain on self-control result in a linear effect or whether another (e.g. curvilinear) effect can be detected.

The strength model of self-control

The conflicts between impulses or immediate desires and long-term goals as described in the introduction rely on self-control. Similarly, all acts that involve the regulation of thoughts, emotion or moods and performance put strain on the mechanism of self-control as well (Baumeister, 2012). In this research, we define strain as ’conditions that place a demand on the self-control resource’.

So what is this self-control resource and how does it work? Baumeister and colleagues developed the strength model, in which the mechanism of self-control is dependent on a resource,

providing a limited amount of strength or energy (Baumeister, Vohs & Tice, 2007). All acts that involve controlling or altering the self put a strain on this same limited resource. After this resource is used, the capacity for further exertion of self-control is reduced. The reduction in self-control after strain is termed ego-depletion (Baumeister, Heatherton & Tice, 1994). In the strength model, the self-control resource can be compared to a muscle. Just like a muscle that loses strength after a period of exertion, self-control performance decreases after previous exertion; the resource is depleted.

The analogy with a muscle stretches further than the finiteness of the resource. Firstly, it appears that exercises can improve the self-control resource in the same way that a muscle strengthens after training (Baumeister, Gailliot, DeWall & Oaten, 2006; Baumeister et al., 2007; Munraven, Baumeister & Tice, 1999). Students who participated in a study intervention program, as a form of repeated exercise, improved their self-control capacity whereas students who not participate in such program displayed lower self-control due to exam stress. The improved self-control had effect in non-related domains as well, such as eating, drinking and smoking (Oaten & Cheng, 2006).

Secondly, self-control capacity can be ‘saved’ when future self-control demands are expected, like muscle strength is preserved when there is an important match in prospect. Munraven, Shmueli and Burkley (2006) took 4 experiments in which two subsequent self-control demanding activities were to be completed. Depleted participants who were informed about the second task performed better on this task than those who were not informed (Munraven et al., 2006).

Thirdly, the depleting effect of previously exerted self-control is moderated by motivation. When depleted individuals are motivated by the idea that performance on the second task helps themselves (or others), they perform better at this second task compared to individuals not motivated by this idea (Munraven & Slessareva, 2003). Similarly, runners can use muscle strength that not seemed to be present before, when they approached the finish. These characteristics form the basis of the strength model.

Sequential-task paradigm

B). Subsequently, all participants were asked to complete as much anagrams as possible in 6 minutes (depleting activity C). Participants who engaged in activity B before solving the anagrams solved significantly more anagrams than the participants who engaged in activity A (Baumeister et al., 1998).

The sequential-task paradigm has been successful in demonstrating the strength model of self-control in more than 100 studies (for a meta-analysis, see Hagger, Wood, Stiff & Chatzisarantis,

2010). However, the procedure of this paradigm is limited in testing the robustness of the mechanism of self-control.

One issue is that it measures self-control on the short-term. Time spans of these experiments are about half an hour to one hour. How long ego-depletion persists, and what the long-term effects of self-control exertion are remains unclear.

A second issue is that the sequential-task paradigm experiments so far indicate a linear effect of self-control exertion on subsequent self-control performance. The actual working of the self-control resource might well be more complex.

Extending the strength model

The first issue identified in the previous paragraph concerns the robustness of the strength model over time. Baumeister et al. (2007) put forward that “how far the muscle analogy can be pushed remains an open question” (p.353). They propose that it might be possible that the self-control mechanism resembles a strained or injured muscle, resulting in continuous impaired performance on the long-term. Burnout has been suggested as a consequence of the self-control resource being used beyond its capacity (Baumeister et al., 1998; Baumeister et al., 2007). There are several indications for the statement that ego depletion is not only a short-term deficiency in self-control, but there might exist something like ‘chronic depletion’ as well.

As stated, most experiments use the sequential-task paradigm, and test the effect of a previous self-control demanding activity on another in isolation of other self-control acts. Hofmann, Baumeister, Förster and Vohs (2012) were the first to look at self-control in real-life setting. In their research, 205 adults wore a beeper for a week, and were asked to report their desires, its strength and whether they resisted or enacted upon it every time the beeper went off. A total of 10.558 responses resulted in 7.827 declarations of desire in one of the 15 categories, e.g. sleeping, eating, leisure, sex, alcohol etc. (Hofmann, Vohs & Baumeister, 2012). All humans are confronted with multiple desires and temptations during a day, both succeeding and overlapping each other. These immediate desires

can possibly conflict with long-term goals, which puts a strain on self-control throughout the day. For example, the desire to sleep might conflict with educational, sports and work achievement goals. Next to these urges, humans are confronted with other depleting activities, such as making difficult decisions (Baumeister et al., 1998), coping with stress (Munraven & Baumeister, 2000; Oaten & Cheng, 2005), taking someone else’s perspective when socializing (Fennis, 2011), controlling one’s emotions (Baumeister et al., 1998; Vohs & Heatherton, 2000) or concentrating on a task (Baumeister, 2002a). All these successive and overlapping self-control activities deplete its inner resource throughout the day.

Replenishment. In order to perform self-control acts at full strength after being consumed, its resource needs to be replenished. We can use the analogy of the self-control resource with a muscle again. Just as a muscle needs to recover from exertion, rest is needed in order for the self-control resource to re-strengthen (Baumeister, 2003; Munraven & Baumeister, 2000; Baumeister, Faber & Wallace, 1999). Tyler and Burns (2008) found evidence for this replenishing effect, using the sequential-task paradigm; when individuals receive a 10-minute period of rest or relaxation after the first depleting task, their performance on the second task equaled those of non-depleted individuals. The replenishment of the self-control resource is proportional to the duration of the relaxation period, meaning that a shorter period of rest leads to lesser improvements in performance of self-control. This is referred to as a dose-effect (Tyler & Burns, 2008; Hagger et al., 2010).

Effects of sleep. Against a day of making choices, resisting desires and other volition, the proportion of replenishment can be found in night of sleep (Baumeister, 2003; Tyler & Burns, 2008; Hagger, 2010; Barber, Munz, Bagsby & Powell, 2010; Baumeister et al., 2009). Without sleep, self-control performance suffers: individuals engage in impulsive behavior, find it harder to concentrate, have difficulty controlling their emotions and perform less at work tasks (Baumeister et al., 1994; Baumeister et al., 2009). For optimal replenishment of self-control resources, both sleep duration and consistency in sleep duration are important (Barber et al., 2009). Even when an individual makes sure he/she gets enough sleep, this effect is negated when the hours of sleep are inconsistently spread over the week. Sufficient hours of rest, acquired through a consistent sleep schedule are thus important in the replenishment of the self-control resource and its executive functions. When we assume that humans are indeed depleted throughout the day and replenished by means of sufficient and consistent sleep practices, it is logical to argue how one becomes chronically depleted. Many people do not sleep enough to compensate for the depleting activities during the day. Even though the actual number of hours needed to recover differs per individual (e.g. age, activeness, quality of sleep of the individual), the average need for sleep for (young) adult is 8,5 hours per night (Wehr et al., 1993). However, the average hours of sleep among adults is 7.2-7.4 hours per night, indicating a shortage of about one hour every night (Bonnet & Arand, 1995).

the duration of the recovery (or sleep). Multiple consecutive nights of mild or moderate shortage of sleep, initially performance decreases, however performance stabilizes on a below-baseline performance level after a few days, whereas severe deprivation of sleep leads to continuous decline in performance (Belenky et al., 2003). The authors of the present research paper expect that many people actually perform at below-baseline level, due to weeks or months of accumulated small shortages of sleep, for which the term ‘chronic depletion’ will be used (Hagger, 2010). This below-baseline performance becomes the new standard of performance for the chronic depleted individuals, which will temporarily decrease after engaging in a depleting activity (e.g. coping with emotions or performing work tasks) and temporarily increase after a good night sleep, similarly to non-depleted individuals.

Recovery from chronic depletion. Considering the dose-effect of rest to replenish the self-control resource, it takes a longer period to recover from chronic depletion. We can make the analogy with a muscle again. A severely injured muscle cannot recover from ordinary rest after exertion; the chronically depleted self-control resource needs longer and more intense period of rest. The muscle needs ‘a break’ from exertion and physical effort for several weeks to months. Likewise, the self-control resource needs a period in which little demands on the resource are made, such as a vacation. This is reflected in the annual cycle of many people’s life’s; they work or study throughout the year, and then take one or multiple weeks of vacation to recharge. Previous research has shown how an annual vacation indeed has recovering effects; it increases well-being and lowers job stress, exhaustion and signs of burnout (Westman & Eden, 1997; Etzion, 2003; Fritz & Sonnentag, 2006). This present research has a focus on self-control changes during this annual cycle.

The relation between various strain levels and self-control

The second unresolved issue is the robustness of the exact effect of self-control and subsequent depletion. The strength model explains that control diminishes after previous self-control exertion. However, more recent studies have shown that certain activities actually enhance self-control. We will discuss these contradicting findings and propose how they can be reconciled.

making difficult or multiple choices (Baumeister et al., 1998; Vohs et al., 2008), taking the perspective of someone else (Fennis, 2011) and concentrating on a task (Baumeister, 2002a) have a depleting effect on self-control in a subsequent activity.

Self-control enhancement. Although the extant literature provides strong evidence for the negative linear effect of self-control demanding activities on succeeding self-control activities, recent studies have demonstrated there might be a positive linear effect. Where we previously discussed how dieters fail to keep themselves to their diet after engaging in a self-control demanding activity, Trudel and Murray (2013) found that this is not the case when the dieters are provided with information about the ‘costs’ of eating. In their experiments, participants were given either information about the nutritional contents of food, the pleasure of eating or no information at all. Participants with information about the nutritional values in the food present, not only equaled the control group, but even increased their self-control compared to the participants in the other two conditions. Furthermore, Dewitte, Bruyneel and Geykens (2009) showed that in situation where two similar self-control conflicts succeed each other, self-control increases in the second task. Using the sequential task paradigm, participants who completed two succeeding response reversal tasks, two succeeding food resistance tasks and two succeeding choice tasks performed better at the second task than the participants who previously engaged in a dissimilar self-control tasks, and better than the participants who previously participated in a task which did not require self-control (Dewitte, Bruyneel & Geyskens, 2009). Tuk, Trampe & Warlop (2012) found this enhancing effect of self-control in unrelated domains as well. When participants were required to exert control over their bladder after drinking a large amount of water, which requires self-control, their performance in subsequent impulse control tasks was higher than participants who had no bladder pressure. Together, these researches indicate that self-control can be enhanced after initial self-control exertion in both related and unrelated domains.

pressure, and thus self-control exertion, might lead to reduced self-control. In this case, demanding too much exertion can absorb all self-control energy, making it impossible to exert further self-control in other tasks. The exact mechanism of a possible curvilinear function should be determined.

The present research

STUDY 1

The intent of this study is to commence research in the field of chronic depletion. To our knowledge, no study has evaluated self-control in the light of the annual cycle. Most previous experiments have focused on determining which activities cause ego-depletion and what its short-term effects are. Hoffman et al. (2012) extended this view by examining self-control in daily life, over the course of a week. When people engaged in prior self-control activities, they were inclined to concede to subsequent desires on the same day (Hoffman et al., 2012). Similarly, ego-depletion was found when examining self-control during a college semester. Oaten and Cheng (2005) found that students lost self-control under academic-examination-stress at the end of the semester, even though it was already present at the beginning of the semester. While the objective of this study was to test students’ self-control under situations that involve stress, their study gives rise to the question whether the time span of their experiment has influence on the results. Students might not only be depleted from stress but also because they have studied, resisted the desire to engage in activities that are more enjoyable than studying, and a range of acts that require control without being able to replenish the self-control resource. This effect would hypothetically be even stronger after the full academic year, where students have participated in all kinds of activities that involve self-control for almost a year.

As discussed, research on recovery has shown that a period of rest or relaxation after a demanding task leads to a reduction or even elimination of the ego depletion effect (Tyler & Burns, 2008; Munraven & Baumeister, 2000). However, these experiments are typically conducted within a short time span. It is likely that students, who engage in many academic and non-academic activities during the year, do not take the rest required to fully recover, leading to a chronic depletion effect. Activities such as dealing with exam stress (Munraven & Baumeister, 2000), controlling emotions act tough (Baumeister et al., 1998), studying the course material (Baumeister et al, 1994), taking the perspective of fellow students when socializing (Fennis, 2011), making important choices in life (Baumeister et al., 1998) and resisting temptations (Hofmann et al., 2012) lead to ego-depletion. Students often lack a regular sleep program, missing out on both sleep duration and sleep duration consistency, needed to replenish the self-control resource (Barber et al., 2009). If people are unable to replenish their self-control resource, this results in a net loss of available resources (Munraven & Baumeister; 2000). Therefore we hypothesize that students have more self-control and perform better at the beginning than at the end of the academic year.

The lack of self-control among students at the end of the academic year can reflect itself in buying behavior. Impulse buying involves ‘spontaneous and unreflective desires to buy, without thoughtful consideration of why and for what reason a person should have the product’ (Vohs & Faber, 2007, p. 537). This is often the result of under-regulation, caused by ego-depletion (Faber & Vohs, 2004). When people are depleted, they feel stronger urges to buy and are willing to spend more money (Vohs & Faber, 2007). Therefore, we hypothesize that students at the end of the year, when students are more depleted, engage in more impulse buying behavior and spent more money than at the beginning of the year, when students have used little of the self-control resource.

Design and procedure

One hundred thirty nine Dutch students (36 male, 103 female; Mage = 21.09, SD = 2.50) participated in an on-line questionnaire. Students were recruited through the social network of the researcher, and were approached either at the beginning or the end of the year to avoid double completion. The end-of-the-year group included 68 participants (22 male, 46 female; Mage = 22.32 years, SD = 2.36). The beginning-of-the-year group included 71 participants (14 male, 57 female; Mage = 19.76, SD = 1.88). Participants who were not a student or did not complete the whole questionnaire were deleted from the study. The study used a 2 (college year: beginning vs. end) x 2 (exams vs. no exams) between-subjects factorial design.

Students were explained that they would take part in a study on student buying behavior and it would take them about 10 minutes to complete the questions. For complete questionnaire, see appendix 1.

Independent measures

Time in college year. Time of questionnaire completion determined group allocation. Participants who completed the questionnaire between July 4th and July 22nd in 2012 entered the end-of-the-year group. Participants who completed the questionnaire between September 12th _{and October} 20th _{in 2012 entered the beginning-of-the-year group. Both groups completed the same questionnaire.} Time periods were deliberately set between payment-dates of student grants and loans on the 24th of the month, to take away the ‘immediate-spending-effect’.

Dependent measures

Self-control. The 13-item brief Self-Control Scale measured students’ self-control (SCS; Tangney, Baumeister & Boone, 2004). This scale contains general self-control statements such as ‘I am good at resisting temptation’ and reversed statements such as ‘I wish I had more self-discipline’ (1 = not at all, 5 = very much). This scale is a widely used self-report measure for self-control at different point in time (Sultan, Joiremann & Sprott, 2012; Duckworth & Seligman, 2005)

Buying impulsiveness. The Buying Impulsiveness Scale (BIS), developed by Rook and Fisher (1995), was used to measure students’ buying impulsiveness. The BIS is normally used to measure generalized urges to measure impulsiveness to buy (Sultan et al., 2012; Vohs & Faber, 2007). The BIS scale contains statements such as ‘I often buy things spontaneously’ and ‘”just do it”, describes the way I buy things’ (1 = not at all, 5 = very much).

We used the SCS and BIS as trait measures because we are aware of no widely accepted self-report state measures of self-control and buying impulsiveness. Furthermore, trait-level measures appear to be good predictors of behavioral self-control (Schmeichel & Zell, 2007). Statements in both scales were translated to Dutch for better understanding.

Participants’ expenses. Participants were asked to estimate their last month’s expenses in number of purchases (clothing, internet purchases) and amount of money spent (groceries, social evenings and restaurant/cafeteria). These questions served a dual cause. Firstly, participants were provoked to think about the way they purchased in the last month before completing the BIS. Secondly, the questions itself served a dependent measure for spending patterns across the year. Results and discussion

Furthermore, a 2 (college year: beginning vs. end) x 2 (exams vs. no exams) ANOVA on ‘the money spent on food, besides the money spent in the supermarket’ yielded a significant main effect of time in the college year, F(1,138) = 9.370, p < 0.005, η2 _{= 0.065. Participants who completed the} questionnaire at the end of the year estimated that they had spent more money on food (in Euros), besides the money spent in the supermarket (MEuros = 59.81, SDEuros = 50.15) than the people who completed the questionnaire at the beginning of the year (MEuros = 38.55, SDEuros = 33.12). However not fully significant, an interaction is found again between the time in the college year and whether students had exams or not, F(1,138) = 2.665, p = 0.105, η2 _{= 0.019). Participants with exams in the} previous 4 weeks spent less money (MEuros = 24.30, SDEuros = 24.50) than participants who do not (MEuros = 47.30, SDEuros = 34.89), in the beginning of the year. In the end of the year, there is no difference between the participants who had exams (MEuros = 60.16, SDEuros = 45.46) and those who did not (MEuros = 59.20, SDEuros = 58.34).

No significant results were found for the time in the college year or the presence of exams on the BIS or the SCS.

STUDY 2

The second study in this paper is concerned with the contradicting findings in literature about the effect of reduced self-control on a subsequent self-control demanding task. We have discussed that literature on self-control provides both enhancing and reducing effects of self-control strain on subsequent self-control exertion. As a possible explanation for these contradicting results, we have put forward that the effect of self-control strain on subsequent self-control does not have the presumed linear effect, but might be non-linear (i.e. curvilinear).

To investigate whether a curvilinear effect can be determined, we focused on the relation between muscle contraction and self-control. Hung and Labroo (2011) have showed in a series of experiments that when participants clenched their fists, tightly clasped a pen, stretched their calf muscles, stretched their fingers or contracted their biceps, they enhanced their performance on measures of self-control and self-reported self-control. Similar effects have been found for chewing gum, which leads to higher alertness and concentration, and less time to encode information and to react (Smith, 2010). Even in the use of visceral muscles, of which the exertion is non-conscious, results in enhanced self-control (Tuk et al., 2012). Participants in this experiment performed better on self-control related tasks, namely a Stroop task and ‘making intertemporal choices’, when they drank five cups of water, as compared to those who drank only one cup.

These articles seem to provide evidence that the contraction of muscles has an enhancing effect on self-control. Contradictory, however, Glass and Singer (1972) reported that that the exposure to an unpleasant electric shock leads to subsequent poorer performance on a Stroop task. Since an electric shock occurs when an electric current contracts the muscles, this research provides evidence for the idea that muscles contraction does not always lead to improved performance.

These inconsistent findings give rise to the idea of en curvilinear effect of muscle contraction on self-control. Comparing the studies by Hung and Labroo (2011), where muscle were slightly tightened, and Glass and Singer (1972), where muscles were fiercely tightened, the current research hypothesizes that, compared to no muscles exertion, slight muscle contraction leads to improved self-control performance, moderate muscle contraction leads to either improved or reduced performance, and firm muscle contraction will lead to reduced performance.

Design and procedure

Participants were explained that they were participating in study how students’ muscle strength and exercise schedule influences performance on different tasks. They were asked to take place in a cubicle with a computer and to follow the instructions on screen. For instructions and questions, see appendix 3.

Independent measures

Muscle condition. To determine the state of the participants’ muscles, we asked ‘how many hours per week do you do exercises, in which your arms are trained?’, ‘To what extent do you consider your biceps well-trained?’ (1 = not at all, 7 = very much), and ‘Did you exercise today, in which the training of your arm was involved?’.

Muscle contraction. Before the experiment, we conducted a pretest (N=24) to find what weights bring about light, moderate and heavy muscle contraction. Participants were given dumbbells with different weights (0.5 kg, 1 kg, 1.5 kg, 2 kg, 2.5 kg and 3 kg), and asked to hold these weights for 8 minutes (the approximated time to finish at the Stroop task, intertemporal choices and questions on self-reported self-control) in their non-dominant hand, defined as ‘the hand they do not write with’. The participants in this pre-test answered three questions of a new measure we developed to determine muscle contraction (see appendix 2). These questions were combined into a contraction perception scale (α = 0.725). No difference was found between the weight groups (F(1,23) = 0.800, p = 0.560, η2 = 0.250) or gender (F(1,23) = 0.360, p = 0.571, η2 _{= 0.029). However, it has been shown that} perception of muscle contraction and actual muscle contraction are often dissimilar (Bannister, 1979). Since we were interested in actual muscle contraction we used the dumbbell weights that differ mostly, namely 0.5 kg for the light-weight condition, 1.5 kg for the moderate-weight condition and 3 kg for the heavy-weight condition. In the experiment, participants in the three contraction conditions were instructed to hold a dumbbell with corresponding weight, in the hand they do not use to write with. Their arm was to be stretched alongside their body, without their arm or the dumbbell touching anything. Holding the dumbbell should result in a light, moderate or heavy muscle contraction. Participants in the control condition were asked to place their hands on their lap.

Table 1

Average rating on contraction perception scale as a function of dumbbell weight and gender

Gender 0,5 kg 1,0 kg 1,5 kg 2,0 kg 2,5 kg 3,0 kg

Male 4,25 4,75 4,00 3,75 4,50 3,88

Dependent Measures

Self-control. The effect of muscle contraction on self-control was measured with a Stroop task (Stroop, 1935). Participants were shown a word representing a color (blue, red, yellow or green), but which is written in another font color. All four colors were given as answer option. They had to check the box with the color ink that each word is written in and refrain from checking the box with the word itself. Because it requires the participant to override an initial response to click on the font color instead of the color in which the word is printed, it requires self-control (Gailliot et al. 2007). The Stroop task consisted of 32 trials, of which two measures were registered, namely (1) the time it took the participants to finish the Stroop task, and (2) the number of mistakes the participant made. According to earlier research, previous self-control use result in lower (Job, Dweck & Walton, 2010; Fennis et al., 2009) or higher performance on the incongruent Stroop task (Tuk et al., 2012; Glass & Singer, 1972).

Self-reported self-control. Participants were asked to indicate how much self-control they could summon while performing the Stroop task (1 = very little, 7 = very much), how much they needed to control their mind (1 = very much, 7 = not at all) and how mentally strong they felt (1 = not strong at all, 7 = very strong) to measure self-reported self-control (adopted from Hung & Labroo, 2011).

Intertemporal choices. As a second measure of self-control, participants were exposed to 7 different choice sets (similar to Li, 2008). Each set consisted of an option of a smaller reward that they would receive the next day and an option for a larger reward that they would receive later in time. To place the choices in context, instructions were given about new payment possibilities of the FEB lab of the University of Groningen: automatic payment possibilities would inhibit immediate payment, but could be enlarged due to lower administration costs. Participants were asked which payment method they preferred (for example, receiving 15 Euros the next day or receiving 35 Euros, 10 days later). The ability to inhibit the urge to choose more immediate but smaller rewards and to choose more often for rewards that are beneficial in the long-term are seen as an act of self-control (Tuk et al., 2011). Results and discussion

1.153) do not significantly differ, as do the participants in the moderate-weight and heavy-weight condition.

Stroop Task. Incorrect responses and response times more than 2.5 standard deviations below or above the average in the Stroop task were excluded from the analysis, which left a sample of 125 participants2_{. However, an ANOVA on the number of correct answers in the color-naming Stroop task} did not yield in a significant difference between the conditions, F(3,124) = 1.47, p = 0.225. Likewise, there was no significant difference in the response time between the conditions. The mean values of the conditions are reported in table 1. Standard deviations are displayed between parentheses.

Table 2 Results Stroop Task

Self-reported self-control. An ANOVA on the self-reported self-control shows a upward tendency in the participants’ declared extent (on a scale from 1 to 7) to which they deliberately used their mental capacity when making the color-naming task, F(3,130) = 20.856, p < 0.001. However, Post-hoc Tukey tests indicate that only the control condition (M = 5.12, SD = 1.166) differs significantly from the heavy-weight condition (M = 6.04, SD = 0.647, p < 0,005). Self-reported self-control of the participants in the light-weight condition (M = 5.30, SD = 1.159) does not differ significantly from the participants in the moderate-weight condition (M = 5.67, SD = 1.051) or the weight condition, as do the participants from the moderate-weight condition and the heavy-weight condition.

Intertemporal Choices. An ANOVA on the intertemporal choices, whereby the participants are asked for their preference between a smaller reward that is received the next day or a bigger reward that is received in a future point in time, did not yield in a significant difference between the conditions (F(3,127) = 0.115, p = 0.951). Table 2 shows the percentage of participants per condition who chose the smaller reward to be received the next day, over the bigger reward to be received in the future.

Other effects. The participants’ muscle condition at the time of the experiment and the instructional manipulation check had no influence on any of the results above.

2

_{No significant effect of weight conditions on average number of correct answers (F(3,130) = 1.17, p = 0,325) /average}

Strooptask Control group Light-weight Moderate-weight Heavy-weight

These results indicate that the degree of muscle contraction has no influence on self-control, when measured by a Stroop task or making intertemporal choices. There is no evidence for a curvilinear effect of muscle contraction and self-control.

Table 3

Percentage of respondents choosing smaller-sooner rewards

Choice Control group Light-weight Moderate-weight Heavy-weight

GENERAL DISCUSSION

This paper was aimed at expanding the knowledge in the robustness of self-control theory. Self-control is “the capacity to alter, modify, change or override ones’ impulses, desires and habitual responses” (Baumeister & Heatherton, 1996). Two important issues concerning the robustness of the depletion effect in self-control were presented, for which previous research has found no evidence or justification. Specifically, our goals in this study were (1) to investigate the long-term effect of strain on self-control in real-life, and (2) to test whether various levels of strain on self-control result in a linear effect or whether another (e.g. curvilinear) effect can be detected.

Study 1 focused on students’ self-control at different moments in the college year. We expected students to have more self-control at the beginning of the year compared to the end of the year, as students may not take enough time to recover throughout the year. The self-control resource is not replenished enough, which leads to chronic depletion at end of the college year. Since impulsive behavior results from ego-depletion, we hypothesized that students concede less in impulsive buying and spend less money at the beginning of the year than at the end of the year. These hypotheses were tested with an on-line questionnaire, distributed to students at the beginning and the end of the college year. Responding students indicate to spent more money in the supermarket and on food at the end of the year, than at the beginning of the year. Furthermore, students who had exams in the previous 4 weeks spent more money at the beginning of the year than those without exams. This effect disappears at the end of the year, when both groups indicate to spend more money with approximately equal amounts.

These results are the first indication that the limited resource of self-control changes and actually decreases over a time period of as long as a year. The study shows that students become more lenient with spending money at the end of the year. Baumeister (2002b) explains how a depleted self-control resource leads to more impulsive behavior. People who report being under stress or coping with problems end up spending more money and doing so more impulsively. Romal and Kaplan (1995) also provide evidence that people with high self-control save more money and spend less. The present study shows that students spend more money at the end of the year compared to the beginning, which indicates that students have less self-control at the end of the year.

is striking that these findings are opposing the findings of Oaten and Cheng (2009). All these issues give rise to new questions. Future research should provide more understanding on this topic.

The results of this study should be interpreted with a certain degree of reservation. The research method in this study allows for limited exclusion of other influences. This makes it difficult to ascertain that ego-depletion was the factor leading to the differences in estimated spending patterns. This study can only establish a correlation between the amount of money spent and the moment in the college year. Further research needs to be done in order to rule out other possible influences.

We used a convenience sample in this study, which may lead to a misrepresentation of the derived data. For example, it is not inconceivable that students who were under too much exam stress or those who were highly depleted did not react to the appeal to fill in the questionnaire, which diminishes the effects reflected in this study. Also, most students in this study are within the social network of the author, which can cause the sample to have limited diversity. Another important weakness of this sample is that the age difference between the two time groups is larger than the standard deviation of the beginning-of-the-year group, causing another discrepancy besides time difference.

Moreover, it is important to note that the scores on the Buying Impulsiveness Scale and the Self-Control Scale were not significantly different for the beginning and the end of the year. A possible explanation for this result is that these measures were not suitable to establish long-term ego-depletion. The two measures are designed to determine a person’s traits, or permanent individual characteristics. However, ego-depletion caused by a shortage of recovery is a state, or a temporary change in someone’s personality. Another possible problem with the BIS and SCS in this study is that participants were required to answer on a 5-point scale, which might be insufficient to detect subtle differences between the moments in time.

Even though the results of this study are not unambiguous, the differences in spending patterns give an indication that the effects of ego-depletion can span a long period of time. This idea would extent the metaphor of self-control as a muscle. The strength model of self-control is explained as a muscle, from which energy is used when performing acts that require self-control (Baumeister, et al., 1998; Baumeister & Heatherton, 1996; Baumeister, et al., 2007; Muraven & Baumeister, 2000). After a period of exertion, this ‘muscle’ becomes fatigued and has a reduced capacity to exert further strength. Like a muscle that becomes stronger after training, practicing in tasks that require self-control can attenuate the ego-depletion effect (Hagger et al., 2010). Furthermore, rest and recovery can regenerate self-control, similar to a muscle that recovers after a period of rest (Munraven & Baumeister, 2000). The present study indicates that a shortage of recovery of self-control can lead to long-term depletion effects, like a muscle that incurs a long-term injury when it has a continuous lack of rest and recovery.

increase students’ purchases. When students’ indeed have lower self-control at the end of the year, marketing techniques such as advertisements should primarily rely on heuristic cues at this moment, since decisions are based on simple heuristics when people are depleted (Fennis et al., 2009). Further research should provide more evidence for the chronic depletion effect to make such statement.

Study 2 focused on the effects of various levels of strain on self-control. We discussed how contradictory findings in literature about the effect of initial control exertion on subsequent self-control exertion (i.e. reducing or enhancing) leads to the idea that linearity of this effect is not unequivocally supported. We hypothesized that different levels of self-control strain might cause those different effects, forming a curvilinear function. To test this idea, we conducted an experiment in which we used muscle contraction as strain. We expected that little muscle contraction would improve self-control, whereas (too) much contraction leads to ego-depletion. The degree of muscle contraction was manipulated by giving the participants a dumbbell with different weights. While holding this weight, the participants were asked to answer several questions, complete a Stroop task and make a decision in seven intertemporal choices, adapted from Li (2008). The results show that there is no difference in the scores on the Stroop task for the different conditions. Also, the conditions do not differ in choosing for smaller-sooner or larger-later rewards. In both components of the study, the control condition did not differ from one of the contraction-conditions either. The control condition does differ from the other conditions in self-reported willpower, however the contraction conditions do not significantly differ from each other.

There are two other explanations for the lack of effect concerning the independent variable of muscle contraction. Firstly, the strain of muscle contraction was applied during the completion of the self-control tasks. Most research on self-control use the sequential-task paradigm, in which one activity is succeeded by another activity. Restraining the self-control muscle simultaneously to the execution of a self-control activity may differ from restraining it in the first activity of succeeding activities. Secondly, muscle contraction may not be a depleting activity at all. The straining effect on self-control in the experiment of Glass & Singer (1972) may be caused by something else than muscle contraction, for example the physical impact of an electric shock. The enhancing effect of muscle contraction on self-control (Hung & Labroo, 2011; Smith, 2010; Tuk et at al., 2012) is convincing but does not establish the self-control demanding effect of muscle contraction.

Wertenbroch, Vosgerau, & Bruyneel (2008) offer another possible explanation for the lack of results on the Stroop task. According to this study, the Stroop task is not suitable to measure self-control and ego-depletion because it is not a self-self-control problem as it does not involve a moral conflict and it does not affect a person’s self-interest in any way. According to Wertenbroch et al. (2008), self-control should be measured by conflicts that involve an intertemporal or moral conflict and that consumers would invariably resolve in favor of their short-term impulses in the absence of self-control. The second measure, the intertemporal choices adapted from Li (2008) seem to satisfy these requirements. However, no significant differences were found between the conditions.

Even though the second study provided no significant results, there is still reason to assume that there might be a curvilinear relation between initial control exertion and subsequent self-control performance. The findings in literature on this effect are not consistent, for which no other justification has been found yet. Converse and DeShon (2009) offer the initial notion for this idea. In their research, self-control was higher after 3 self-control demanding activities (or more self-control exertion) than after 2 self-control demanding activities (or less self-control exertion). Future research should take the explanations for the lack of results in the present study described above into account. A better manipulation of the conditions and possibly the use of other dependent measures can still provide the expected outcomes.

Together, both studies support the supposition that the ego-depletion effect is not as robust as previously stated by Baumeister and his colleagues. It is well possible that the robustness of the ego-depletion effect over time and different strain levels can further be determined by other methods and manipulations. The present research and suggestions for future research can be used in order to further examine the robustness of the ego-depletion effect.

REFERENCES

Banister, E. W. (1979). The perception of effort: An inductive approach. European Journal of Applied Physiology and Occupational Physiology, 41, 141-150.

Barber, L. K., Munz, D. C., Bagsby, P. G., & Powell, E. D. (2009). Sleep consistency and sufficiency: Are both necessary for less psychological strain? Stress and Health, 26, 186-193.

Baumeister, R. F. (2002a). Yielding to temptation: Self-control failure, impulsive purchasing, and consumer behavior. Journal of Consumer Research, 28, 670-676.

Baumeister, R. F. (2002b). Ego depletion and self-control failure: An energy model of the self ’s executive function. Self and Identity, 1, 129-136.

Baumeister, R. F. (2003). Ego depletion and self-regulation failure: A resource model of self-control. Alcoholism: Clinical and Experimental Research, 27, 281-284.

Baumeister, R. F. (2012). Self-control: The moral muscle. The Psychologist, 25, 112-115.

Baumeister, R. F., Bratslavsky, E., Muraven, M., & Tice, D. M. (1998). Ego depletion: Is the active self a limited resource? Journal of Personality and Social PsychoIogv, 74, 1252-1265.

Baumeister, R. F., Faber, J. E., & Wallace, H. M. (1999). Coping and ego-depletion: Recovery after the coping process. In C. R. Snyder (Eds.), Coping: The psychology of what works. (pp. 50-69). New York, NY: Oxford University Press.

Baumeister, R. F., Sparks, E. A., Stillman, T. F., & Vohs, K. D. (2008). Free will in consumer behavior: self-control, ego depletion and choice. Journal of Consumer Psychology, 18, 4-13.

Baumeister, R. F., Gailliot, M. T., DeWall, C. N., & Oaten, M. (2006). Self-regulation and personality: How interventions increase regulatory success, and how depletion moderates the effects of traits on behavior. Journal of Personality, 74, 1773-1801.

Baumeister, R. F., & Heatherton, T. F. (1996). Self-regulation failure: An overview. Psychological Inquiry, 7, 1-15.

Baumeister, R. F., Heaherton, T. F., & Tice, D. M. (1994). Losing control: how and why people fail at self-regulation. San Diego, CA: Academic Press.

Baumeister, R. F., Vohs, K. D., & Tice, D. M. (2007). The strength model of self-control. Current Directions in Psychological Science, 16, 351-355.

Belenky, G., Wesensten, N. J., Thorne, D. R., Thomas, M. L., Sing, H. C., Redmond, D. P., Russo, M. B., & Balkin, T. J. (2003). Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: A sleep dose-response study. Journal of Sleep Research, 12, 1-12.

Bonnet, M. H., & Arand, D. L. (1995). We are chronically sleep deprived. Sleep, 18, 908-911.

Converse, P. D., & DeShon, R. P. (2009). A tale of two tasks: Reversing the self-regulatory resource depletion effect. Journal of Applied Psychology, 94, 1318-1324.

Dewitte, S., Bruyneel, S., & Geykens, K. (2009). Self-regulating enhances self-regulation in subsequent consumer decisions involving similar response conflicts. Journal of Consumer Research, 36, 394-405.

Duckworth, A. L., & Seligman, M. E. P. (2005). Self-discipline outdoes IQ in predicting academic performance of adolescents. Psychological Science, 16, 939-944.

Etzion, D. (2003). Annual vacation: Duration and relief from job stress and burnout. Anxiety, Stress and Coping: An International Journal, 16, 213-226.

Faber, R. J., & Vohs, K. D. (2004). To buy or not to buy? Self-control and self-regulatory failure in purchase behavior. In Baumeister, R. F. & Vohs, K D (Eds.), Handbook of Self-Regulation: Research, Theory and Applications, (pp. 509-524) New York, NY: Guilford.

Fennis, B.M. (2010). Can’t get over me: Ego depletion attenuates prosocial effects of perspective taking. European Journal of Social Psychology, 41, 580-585.

Fennis, B. M., Janssen, L., & Vohs, K. D. (2009). Acts of benevolence: a limited-resource account of compliance with charitable requests. Journal of Consumer Research, 35, 906-924.

Fritz, C., & Sonnentag, S. (2006). Recovery, well-being, and performance-related outcomes: The role of workload and vacation experiences. Journal of Applied Psychology, 4, 936-945.

Gailliot, M.T., Baumeister, R.F., DeWall, C.N., Maner, J.K., Plant, E.A., Tice, D.M., Brewer, L. E., & Schmeichel, B. J. (2007). Self-control relies on glucose as a limited energy source: Willpower is more than a metaphor. Journal of Personality and Social Psychology, 92, 325-336.

Glass, D. C., & Singer, J. E. (1972). Urban stress: Experiments on noise and social stressors. New York, NY: Academic Press.

Hagger, M. S. (2010). Sleep, self-regulation, self-control and health. Stress and Health, 26, 181-185. Hagger, M.S., Wood, C., Stiff, C., & Chatzisarantis, N.L.D. (2010). Ego depletion and the strength model of self-control: A meta- analysis. Psychological Bulletin, 136, 495-525.

Hoffman, W., Baumeister, R. F., Förster, G., & Vohs, K. D. (2012). Everyday temptations: An experience sampling study of desire, conflict, and self-control. Journal of Personality and Social Psychology, 102, 1318-1335.

Hofmann, W., Strack, F., & Deutsch, R. (2008). Free to buy? Explaining self-control and impulse in consumer behavior. Journal of Consumer Psychology, 18, 22-26.

Hoffman, W., Vohs, K. D., & Baumeister, R. F. (2012). What people desire, feel conflicted about and try to resist in everyday life. Psychological science, 23, 582-588.

Hung, I.W., & Labroo, A. A. (2011). From firm muscles to firm willpower: Understanding the role of embodied cognition in self- regulation. Journal of Consumer Research, 37, 1046-1064.

Inzlicht, M., & Schmeichel, B. J. (2012). What is ego depletion? Toward a mechanistic revision of the resource model of self-control. Perspectives on Psychological Science, 7, 450-463.

Li, X.P. (2008). The effects of appetitive stimuli on out-of-domain consumption impatience. Journal of Consumer Research, 34, 649-656.

Muraven, M., & Baumeister, R. F. (2000). Self-regulation and depletion of limited resources: Does self-control resemble a muscle? Psychological Bulletin, 126, 247-259.

Muraven, M., Baumeister, R. F., & Tice, D. M. (1999). Longitudinal improvement of self-regulation through practice: Building self-control strength through repeated exercise. Journal of Social Psychology, 139, 446-457.

Muraven, M., Collins, R. L., & Nienhaus, K. (2002). Self-control and alcohol restraint: An initial application of the self-control strength model. Psychology of Addictive Behaviors, 16, 113-120.

Muraven, M., Shmueli, D., & Burkley, E. (2006). Conserving self-control strength. Journal of Personality and Social Psychology, 91, 524-537.

Muraven, M., & Slessareva, E. (2003). Mechanisms of self-control failure: Motivation and limited resources. Personality and Social Psychology Bulletin, 29, 894-906.

Oaten, M., & Cheng, K. (2005). Academic Examination Stress Impairs Self–Control. Journal of Social and Clinical Psychology, 24, 254-279.

Oaten, M., & Cheng, K. (2006). Improved self-control: The benefits of a regular program of academic study. Basic and Applied Social Psychology, 28, 1-16.

Peck, J., & Childers, T. L. (2006). If I touch it I have to have it: Individual and environmental influences on impulse purchasing. Journal of Business Research, 59, 765-769.

Romal, J. B., & Kaplan, B. J. (1995). Difference in self-control among spenders and savers, Psychology: A Quarterly Journal of Human Behavior, 32, 8-17.

Rook, D. W., & Fisher, R. J. (1995). Normative influences on impulsive buying behavior. Journal of Consumer Research, 22, 305-313.

Schmeichel, B. J., & Zell, A. (2007). Trait self-control predicts performance on behavioral tests of self-control. Journal of Personality, 75, 743-756.

Scholey, A., Harper, S., & Kennedy, D.O. (2001). Cognitive demand and blood glucose. Physiology & Behavior, 73, 585-592.

Smith, A. (2010). Effects of chewing gum on cognitive function, mood and physiology in stressed and non-stressed volunteers. Nutritional Neuroscience, 37, 7-16.

Stroop, J. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643-662.

Sultan, A. J., Joiremann, J., & Sprott, D. E. (2012). Building consumer control: The effect of self-control exercises on impulse buying urges. Marketing Letters, 23, 61-72.

Tangney, J. P., Baumeister, R. F., & Boone, A. L. (2004). High self-control predicts good adjustment, less pathgology, better grades, and interpersonal success. Journal of Personality, 72, 271-324.

Tuk, M. A., Trampe, D., & Warlop, L. (2011). Inhibitory spillover: Increased urination urgency facilitates impulse control in unrelated domains. Psychological Science, 22, 627-633.

Tyler, J. M., & Burns, K. C. (2008). After depletion: The replenishment of the self’s regulatory resources. Self and Identity, 7, 305-321.

Tyler, J. M., & Burns, K. C. (2009). Triggering conservation of the self’s regulatory resources. Basic and Applied Social Psychology, 31, 255-266.

Vohs, K. D., Baumeister, R. F., Schmeichel, B. J., Twenge, J. M., Nelson, N. M., & Tice, D. M. (2008). Making choices impairs subsequent self-control: A limited-resource account of decision making, self- regulation, and active initiative. Journal of Personality and Social Psychology, 94, 883-898.

Vohs, K. D., & Faber, R. J. (2007). Spent resources: Self-regulatory resource availability affects impulse buying. Journal of Consumer Research, 33, 537-547.

Vohs, K. D., & Heatherton, T. F. (2000). Self-regulatory failure: A resource-depletion approach. Psychological Science, 11, 249-254.

Wehr T. A., Moul, D. E., Barbato, G., Giesen, H. A., Seidel, J. A., Barker, C., & Bender, C. (1993). Conservation of photoperiod-responsive mechanisms in humans. American Journal of Physiology, 265, 846-57.

Wertenbroch, K., Vosgerau, J., & Bruyneel, S. B. (2008) Free will, temptation, and self-control: We must believe in free will, we have no choice (Isaac B. Singer). Journal of Consumer Psychology, 18, 27-33.

APPENDICES

Appendix A. Questionnaire study 1

Bedankt voor het aanklikken van de link naar deze vragenlijst. Het invullen van de vragen zal ongeveer 5 minuten duren. Succes!

Wat is je geslacht? (man/vrouw) Wat is je leeftijd? (Open question)

Welke studie heb je het afgelopen jaar gevolgd?/Welke studie ga je dit jaar volgen? (Open question) Hoeveel jaren heb je tot nu toe gestudeerd? (gerekend vanaf het eerste jaar dat je ging studeren, ongeacht of dit dezelfde studie was als hiervoor ingevuld) (Open question)

De volgende vragen zullen gaan over je persoonlijkheid. Probeer bij iedere stelling aan te geven in hoeverre deze op jou van toepassing is.

Geef met gebruik van de gegevens schaal aan in hoeverre de onderstaande stellingen op jou van toepassing zijn. (Absoluut niet van toepassing 1 – 2 – 3 – 4 – 5 Heel erg van toepassing)

- Ik ben goed in het weerstaan van verleiding

- Ik vind het moeilijk om slechte gewoonten te doorbreken

- Ik ben lui

- Ik zeg ongepaste dingen

- Ik doe bepaalde dingen die slecht voor me zijn, maar wel leuk zijn

- Ik weiger dingen die slecht voor me zijn

- Ik zou willen dat ik meer zelfdiscipline had

- Mensen zouden zeggen dat ik een ijzeren zelfdiscipline heb

- Plezier en lol weerhouden me er soms van om werk gedaan te krijgen

- Ik heb moeite me te concentreren

- Ik ben in staat om effectief naar lange-termijn doelen te werken

- Soms kan ik mezelf er niet van weerhouden om iets te doen, ook al weet ik dat het fout is

- Ik doe vaak dingen zonder alle alternatieven af te gaan

De volgende vragen zullen gaan over de aankopen die je in de afgelopen periode hebt gedaan. Het begrip ‘aankopen’ kan ruim worden toegepast; het gaat om alle uitgaven die je in de afgelopen 5 weken hebt gedaan, ongeacht het bedrag. Neem de tijd om te bedenken hoe veel en wat voor soort aankopen je de afgelopen 5 weken hebt gedaan.

Hoeveel kledingstukken heb je de afgelopen 5 weken gekocht? (antwoord in totaal aantal kledingstukken, ongeacht het bedrag) (Open question)

Hoe vaak heb je een bestelling gedaan via internet in de afgelopen 5 weken? (antwoord in totaal aantal bestellingen, ongeacht het bedrag) (Open question)

Maak een schatting van het bedrag in euro's dat je in de afgelopen 5 weken hebt uitgegeven in de supermarkt. (Open question)

Maak een schatting van het bedrag in euro's dat je in de afgelopen 5 weken hebt uitgegeven op uitgaansavonden. (Open question)

Maak een schatting van het bedrag in euro's dat je in de afgelopen 5 weken hebt uitgegeven aan

etenswaren die je hebt gekocht, buiten de aankopen in de supermarkt om. Hieronder vallen onder andere etenswaren en dranken in restaurants, cafe's, kantines en uit snack-automaten, buiten uitgaansavonden om. (Open question)

Geef aan in welke mate de onderstaande stellingen typisch op jou van toepassing zijn. (Absoluut niet van toepassing 1 – 2 – 3 – 4 – 5 Heel erg van toepassing)

- ‘Gewoon doen’ beschrijft de manier waarop ik dingen koop

- Ik koop vaak dingen zonder er over na te denken

- ‘Ik zie het, ik koop het’ omschrijft mij

- ‘Eerst kopen, dan nadenken’ is wat mij omschrijft

- Soms heb ik zin om dingen te kopen in een opwelling

- Ik koop dingen naar hoe ik me op dat moment voel

- Ik plan de meeste van mijn aankopen zorgvuldig

- Soms ben ik een beetje roekeloos in wat ik koop

Heb je in de afgelopen 4 weken een of meerdere tentamens gehad? (Ja/Nee) Heb je ergens in de komende 2 weken een of meerdere tentamens? (Ja/Nee)

Appendix B. Pretest study 2 Instructions

Participants were given a dumbbell that weights 0.5 kg, 1 kg, 1.5 kg, 2 kg, 2.5 kg or 3 kg. For each category, 2 female and 2 male participants were recruited. They were asked to hold the dumbbell for 8 minutes, which is the approximated time to finish the Stroop task and the intertemporal choices . After holding the dumbbell for 8 minutes, participants were asked to fill in the form below.

Questionnaire

Dear reader,

Thank you for participating in this study. Your input is of great use to my master thesis. I asked you to hold a dumbbell for a while. Now, I would like you to answer the questions below.

What is you age? ….

What is your gender? Male/Female

How much did you contract you muscles to hold this weight?

Not at all 1 2 3 4 5 6 7 Very much

How tight do your muscles feel?

Not tight at all 1 2 3 4 5 6 7 Very tight

To what extent did you feel you could not hold a heavier weight?

Not at all 1 2 3 4 5 6 7 Very much

To what extent do you feel you used all the strength in your muscles?

Not at all 1 2 3 4 5 6 7 Very much

Thank you again for participating. If you are interested in the purpose of this research, please write down your email address below, so I can debrief you afterwards.