Improving Self-control by Practicing Logical Reasoning

Self and Identity, 2014 Vol. 13, No. 4, 419–431, http://dx.doi.org/10.1080/15298868.2013.836562

Improving Self-control by Practicing Logical Reasoning Alex Bertrams1 and Brandon J. Schmeichel2 1 2

Department of Psychology, University of Mannheim, Mannheim, Germany Department of Psychology, Texas A&M University, College Station, USA

We tested the hypothesis that practicing logical reasoning can improve self-control. In an experimental training study (N ¼ 49 undergraduates), for one week participants engaged in daily mental exercises with or without the requirement to practice logical reasoning. Participants in the logic group showed improvements in self-control, as revealed by anagram performance after a depleting self-control task. The benefits of the intervention were short-lived; participants in the two groups performed similarly just one week after the intervention had ended. We discuss the findings with respect to the strength model of self-control and consider possible benefits of regular cognitive challenges in education. Keywords: Ego depletion; Intervention; Reasoning; Self-control; Self-regulation.

Self-control is vital for reaching one’s goals. Research suggests that good self-control is beneficial in several life domains, including educational attainment, mental and physical health, and social relationships. For instance, good self-control is associated with academic success and psychological adjustment (Bertrams, 2012; Duckworth & Seligman, 2005; Tangney, Baumeister, & Boone, 2004). Conversely, poor self-control has been linked with undesirable behaviors, such as unhealthy eating, inappropriate selfpresentation, and aggression (Finkel, DeWall, Slotter, Oaten, & Foshee, 2009; Hofmann, Rauch, & Gawronski, 2007; Vohs, Baumeister, & Ciarocco, 2005). In the present investigation, we tested the hypothesis that practicing intelligent thought — specifically, logical reasoning — can improve self-control.

Self-control and the Strength Model Self-control can be described as the exertion of control by the self over its own processes and responses (Muraven & Baumeister, 2000). More precisely, self-control has been defined as the capacity persons have to override or alter their predominant response tendencies (Baumeister, Heatherton, & Tice, 1994; Schmeichel & Vohs, 2009). Selfcontrol entails, for example, resisting the impulse to consume a tasty but unhealthy dessert, suppressing an inappropriate emotional expression, refraining from task-irrelevant mindwandering, and forcing oneself to begin and stick with an unpleasant chore. Received 27 March 2013; accepted 15 August 2013; first published online 24 September 2013. Correspondence should be addressed to: Alex Bertrams, School of Social Sciences, Department of Psychology, University of Mannheim, A5, 6, 68131 Mannheim, Germany. Email: alex.bertrams@uni-mannheim. de q 2013 Taylor & Francis

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When and why do people fail in self-control? Several answers have been offered (see Vohs & Baumeister, 2011). The current investigation focused on the strength model of self-control and its proposal that self-control operates on the basis of a limited inner resource or strength (Baumeister, Vohs, & Tice, 2007; Muraven & Baumeister, 2000). According to the strength model, exerting self-control and other acts of volition consume and temporarily deplete this strength (i.e., the ego depletion effect), leaving less available for subsequent efforts. Therefore, self-control is temporarily more likely to fail following an exertion of self-control. Over one hundred experiments have lent support to the strength model by finding that initial efforts at self-control undermine subsequent efforts (for a meta-analysis, see Hagger, Wood, Stiff, & Chatzisarantis, 2010). These findings also reveal that different kinds of self-control rely on the same underlying resource or strength (executive capacity; Schmeichel, 2007). For example, controlling one’s thoughts can impair subsequent efforts to control one’s emotional expressions (e.g., Muraven, Tice, & Baumeister, 1998), and making many choices can undermine subsequent efforts to solve anagrams or persist at other difficult challenges (e.g., Vohs et al., 2008). Extensions of the Strength Model In recent years, researchers expanded the strength model by relating self-control to complex cognitive processes, particularly the executive functions (see Hofmann, Schmeichel, & Baddeley, 2012). Research has observed that initial exertions of selfcontrol temporarily undermine executive functions. For example, Schmeichel, Vohs, and Baumeister (2003) found that logical reasoning and high-level reading comprehension depend on the same limited capacity as does suppressing forbidden thoughts and stifling emotional expressions. Other complex thought processes also have been found to vary as a function of executive capacity, including choice-making, cognitive estimation, updating working memory, and other forms of thought that typically reflect fluid intelligence (e.g., Pohl, Erdfelder, Hilbig, Liebke, & Stahlberg, 2013; Vohs et al., 2008). Crystallized intelligence and more basic, nonexecutive cognitive processes (e.g., short-term memory, simple mathematical calculations) do not appear to rely on executive capacity. Research has also found that performing cognitive tasks that require executive functions can undermine subsequent efforts at self-control. For example, one study found that completing a test of working memory capacity undermines subsequent efforts to control one’s emotional expressions (Schmeichel, 2007). In further support of the strength metaphor for self-control, evidence has suggested that regular exercises in self-control (e.g., over the course of a week or two) can make executive capacity more resistant to the typical depletion effect. For example, in one study, individuals practiced self-control by using their non-dominant hand in mundane tasks (e.g., brushing their teeth) for two weeks. Before and after this self-control intervention, subsequent to a potentially depleting self-control task, the likelihood of being physically aggressive after provocation was assessed. Participants who had been practicing selfcontrol became less likely to respond aggressively from before to after the intervention. In contrast, individuals in a control group who had not practiced self-control did not change in this regard (Finkel et al., 2009; see also Denson, Capper, Oaten, Friese, & Schofield, 2011; Gailliot, Plant, Butz, & Baumeister, 2007; Muraven, 2010; Muraven, Baumeister, & Tice, 1999; Oaten & Cheng, 2006; Wright et al., 2007). Thus, much like physical exercise promotes increased stamina and strength despite short-term muscle fatigue, the self apparently can increase its stamina and executive capacity with regular efforts at self-control. The evidence for training-related improvements

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in self-control also supports the view that executive capacity is not specific to a particular domain of control, as improvements have been found to extend even to acts of self-control that were not practiced. As Baumeister, Gailliot, DeWall, and Oaten (2006) wrote, “ . . . improving self-regulation operates by increasing a general core capacity” (p. 1786). The Present Research The present work combined the aforementioned extensions of the strength model. Specifically, based on the evidence that logical reasoning relies on executive capacity (e.g., Schmeichel et al., 2003), we hypothesized that regular exercises of logical reasoning can make executive capacity more resistant to depletion, meaning sustained or potentially enhanced self-control. Our central prediction was that regularly engaging in logical reasoning leads to increased resistance to the ego depletion effect. We chose logical reasoning to form the core of the training regimen because, unlike previously-used regimens (e.g., repeated use of the non-dominant hand), logical reasoning is a common feature of educational settings, and the strength model of self-control suggests previously unrecognized benefits of regular reasoning practice for self-control stamina. We used an experimental design to test whether a one-week intervention that required (versus did not require) regular practice at logical reasoning causes executive capacity to become more resistant to depletion. One group of participants was instructed to engage in logical reasoning during a daily task for one week. Another group worked on the same task materials but without the requirement to practice logical reasoning. We assumed that the logical reasoning group would outperform the control group on a post-intervention measure of self-control. We also had participants perform a simpler cognitive task (i.e., solving math problems), so that we could assess the possibility that the intervention boosts cognitive performance generally. Given our rationale, the intervention should improve performance only on tasks that draw on executive capacity. Solving simple math problems appears not to rely on executive capacity (e.g., Muraven, 2010), so no post-intervention differences in math performance were expected. Another novel aim of our study was to examine for the first time whether the effect of the intervention vanishes after the intervention has finished. In line with the muscle or strength metaphor (Muraven & Baumeister, 2000), the benefits of regularly engaging in logical reasoning should wear off after the exercise has been discontinued. Presumably, the principle of “use it or lose it” applies to psychological as well as physical strength. Beyond a mere metaphor, then, we think that it may generally be functional for the organism to regularly exercise its executive capacity. If usage patterns return to baseline levels, then executive capacity should decline. Based on these considerations, we assumed the proposed effect of the logical reasoning intervention would be in evidence immediately after the intervention period but would be weaker or perhaps nonexistent by one week after the end of the intervention.

Method Participants Forty-nine undergraduate students (38 female; age M ¼ 22.49, SD ¼ 3.50) enrolled in a German university were recruited via public notices on campus. They participated in return for e50 (at that time approximately US$70). Participants were randomly assigned either to the condition requiring regular logical reasoning (logic condition; n ¼ 25) or to the condition without the requirement to engage in regular logical reasoning (no logic

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condition; n ¼ 24). One additional participant had to be excluded from analyses because she missed the appointment for the post- and follow-up tests. Procedure and Materials At a preliminary meeting participants answered the 16-item short version of the Need for Cognition Scale (Bless, Wa¨nke, Bohner, Fellhauer, & Schwarz, 1994). We used this measure to control for interindividual differences in the general motivation to engage in cognitive effort (Cacioppo, Petty, Feinstein, & Jarvis, 1996). Cronbach’s alpha in the present sample was .88. On a different occasion, participants completed a pre-test behavioral measure of selfcontrol, adapted from previous research (Gailliot et al., 2007). The measure proceeded as follows. First, participants unscrambled as many anagrams (e.g., KTAES; solution: SKATE) as possible within six minutes. This served as a baseline measure of anagram ability. Afterwards, participants attempted to solve as many math problems (e.g., [9 £ 3] 23) as possible within two minutes. This served as a baseline measure of mathematical ability. Next was an effortful typing task that required the exertion of self-control (see Muraven, Gagne´, & Rosman, 2008). Participants were instructed to transcribe a paragraph on the computer without using the letter e and without hitting the space bar. (Participants could not see the consequences of their keystrokes on the screen.) Then, participants again attempted to solve as many anagrams as they could in six minutes. Last, they tried again to solve as many math problems as possible within two minutes. Solving anagrams required self-control because participants had to keep breaking and altering the tentative combinations of letters they had formed and keep trying despite initial failures (Baumeister, Bratslavsky, Muraven, & Tice, 1998). The typing task involved self-control because typing is a highly automatic task for students, and changing habitual ways of typing demands a good deal of self-stopping (Muraven et al., 2008). Performance on the second anagram task, completed after the typing task and adjusted for initial anagram ability, may be taken as an indicator of interindividual differences in selfcontrol, as the typing task depletes executive capacity prior to the second attempt at solving anagrams (Gailliot et al., 2007). Solving math problems does not draw on executive capacity (e.g., Schmeichel, 2007) and was included to assess the discriminant validity of the intervention effect.1 On the next day, the intervention phase started. Participants received take-home workbooks containing the material for each of seven days. They were asked to complete the materials for Day 1 that day, and to go on working on the day-specific materials for each of the next six days. The materials, except for the instructions, were identical for both the logic condition and the no logic condition. Each day participants read 10 controversial statements (e.g., “Physician-assisted suicide should be permitted;” “Video games with aggressive content should generally be prohibited”). They viewed different statements every day, making a total of 70 different statements during the whole intervention. The participants were told to write down their opinions on these statements on empty pages in the workbook for 45 minutes each day. Participants in the logic condition received the instruction to avoid writing spontaneously, to reason and pay attention to logical consistency throughout their writing, and to consider counter-arguments. In contrast, participants in the no logic condition were instructed to write spontaneously whatever comes to mind and not to care about logical consistency. Each day, participants noted the time of day they started and stopped working. In addition, after each daily task they answered two questions pertaining to the task

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(“I experienced working on the task as effortful today;” “During working on the task, I would have liked to stop and do something different”) using seven-point scales from 1 (not true at all) to 7 (very true). Responses to these questions were considered as approximations of the amount of self-control participants exerted during the task, so that we could control for potential differences in the exertion of self-control (as we were interested in the effect of logical reasoning per se). The two questions formed reliable measures across the seven days of intervention. Cronbach’s alphas were .79 for effort experienced while working on the tasks and .84 for the wish to stop the tasks and do something different. We averaged participants’ responses from each of the seven days on each item for further analyses. After the seven days of the intervention, participants returned to the laboratory, handed in their completed workbooks, and then attempted the post-test measure of selfcontrol. One week after the post-test, participants returned again for a follow-up measure of self-control. The procedure for the post-test and follow-up measures was identical to the pre-test measure (i.e., assessing anagram and math performance before and after a self-controlled typing task) except that different sets of anagrams and math problems were used. Between the post-test and the follow-up, no intervention took place. As a manipulation check, an education graduate with experience in evaluating student work evaluated each participant’s writing with regard to the degree of logical reasoning invested. She was unaware of the participants’ experimental condition. She rated the participants’ writings on three items (e.g., “How much effort had the person made to substantiate his/her opinion with rational logic?”) applying seven-point scales from 1 (not at all) to 7 (very much). The responses to the three items were averaged prior to analyses (a ¼ .97).

Results Analysis Strategy Table 1 provides all means and standard deviations for anagram and math performances. Following Gailliot et al. (2007), we built standardized residuals of the number of anagrams solved correctly at the end of each session (pre-test, post-test, follow-up), controlling for the number of anagrams solved at the beginning of the respective session. Thus, the

TABLE 1

Means and Standard Deviations (in Parentheses) of Anagram and Math Performances Logic condition Time during session

Performance Anagrams Pre-test Post-test Follow-up Math problems Pre-test Post-test Follow-up

Before depletion

After depletion

No logic condition Time during session Before depletion

After depletion

15.32 (7.87) 11.92 (6.49) 13.12 (5.45)

10.56 (6.03) 13.92 (5.22) 13.32 (5.02)

14.21 (6.65) 14.13 (5.11) 13.71 (5.03)

11.42 (4.35) 13.88 (5.46) 12.67 (5.04)

26.96 (12.45) 32.52 (8.98) 34.92 (10.85)

30.00 (9.47) 33.24 (10.07) 34.68 (10.05)

25.04 (9.58) 33.58 (9.29) 33.79 (11.29)

27.63 (9.95) 31.13 (10.70) 31.88 (10.49)

Note: n ¼ 25 in the logic condition, n ¼ 24 in the no logic condition. Depicted are original values without square root transformations.

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residual scores represent anagram performances adjusted for individual differences in baseline abilities at each session. By adjusting for baseline abilities, we aimed to minimize error variance and to increase statistical power. The residual scores were computed via regressing the post-test on the pre-test anagram performance of the same session. Analogously, we built standardized residuals of math problems solved correctly.2 To analyze the effect of practicing logical reasoning on self-control, we used analyses of covariance (ANCOVA). In a first ANCOVA we tested whether the logic versus no logic conditions differed in terms of change in residual scores of anagram performance (i.e., the target measure of self-control), controlling for the respective pre-test measure. In a second ANCOVA, we examined whether the two conditions differed in the followup measure of self-control, holding constant the respective pre-test measure. Differences between the conditions with pre-test performance included as covariate would indicate an effect of the intervention (see Van Breukelen, 2006). Analogous analyses were conducted on math performance. In these group comparisons we included as covariates the need for cognition, averaged ratings of effort while working on the tasks, and averaged ratings on the wish to stop the tasks and do something different. This was done in order to hold constant individual differences in self-control exerted during the tasks. By this means, we aimed to get a clearer impression of the effect of logical reasoning itself. Manipulation Check Participants’ writings were rated as being more strongly based on logical reasoning in the logic condition (M ¼ 5.63, SD ¼ 1.51) than in the no logic condition (M ¼ 3.28, SD ¼ 1.70), t(46) ¼ 5.07, p , .001, d ¼ 1.47. Thus, the experimental manipulation of engagement in logical reasoning was successful. Intervention Effect on Self-control First, we checked for potential group differences on the pre-test measure (i.e., prior to the logical thinking intervention) and found no statistically significant difference in selfcontrol (i.e., the standardized residual number of anagrams solved at the end of the session) between the logic (Madjusted ¼ 2 .23, SEadjusted ¼ .20) and no logic conditions (Madjusted ¼ .24, SEadjusted ¼ .20), p ¼ .10. (Only need for cognition was a covariate in this analysis.) Next, we tested the effect of the intervention on self-control. The ANCOVA revealed a statistically significant difference between the logic condition and the no logic condition on the post-test measure of self-control, F(1, 43) ¼ 5.05, p ¼ .03, h2partial ¼ .11, indicating that the intervention of practicing logical reasoning had a positive effect on executive capacity (see Figure 1a). In a further analysis, we tested whether the intervention effect could be detected one week after the intervention had ended. The intervention effect was no longer statistically significant for the follow-up assessment of self-control, p ¼ .22, indicating that the intervention effect had vanished (see Figure 1a). In none of the previous analyses did need for cognition, experienced effort, or the wish to stop the tasks and do something different predict anagram performance, ps . .31. Therefore, we repeated the analyses without controlling for these covariates. The observed effects were slightly weaker, but the logic condition still outperformed the no logic condition on the post-test measure of self-control, p ¼ .049, h2partial ¼ .08. Again, this difference was no longer detectable at the follow-up assessment, p ¼ .21.3

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FIGURE 1 Effect of intervention on (a) self-control and (b) math ability on post-test (immediately after the intervention period) and follow-up (one week after the intervention). Displayed are adjusted means and standard errors (i.e., controlling for respective pre-test measures and covariates). n ¼ 25 in the logic condition, n ¼ 24 in the no logic condition.

Supplementary Analyses We repeated the previous analyses with math performances as independent variables. The two intervention conditions did not differ in pre-test math performance. Moreover, the conditions did not differ in post-test and follow-up math performance, controlling for pretest math performance. The null-results emerged with and without controlling for need for cognition, experienced effort, and the wish to stop the tasks and do something different, all ps . .11 (see Figure 1b). These findings indicate that, as expected, the intervention had no effect on participants’ ability to solve math problems.

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However, visual inspection of the results indicated that the condition-related patterns of self-control and math performance were similar (see panel a and panel b of Figure 1). These patterns suggest that the intervention may have influenced some unspecified cognitive ability that contributes to both anagram and math performance (e.g., processing speed). This alternative explanation of a shared cognitive ability appears unlikely, however, given that the post-test measures of self-control and math performance were uncorrelated, r ¼ 2 .06, p ¼ .67. Moreover, the intervention effect on post-test selfcontrol remained significant when math performance on the post-test was controlled as a statistical covariate, F(1, 42) ¼ 5.54, p ¼ .02, h2partial ¼ .12 (without controlling for need for cognition, effort, and wish to stop: p ¼ .04, h2partial ¼ .09). The covariate (math performance) was not a significant predictor of self-control, p ¼ .43.

Discussion Interpretation of Results Our study supported the hypothesis that practicing logical reasoning can enhance selfcontrol. Participants who engaged in daily logic exercises exhibited better self-control (i.e., better anagram performance) after a depleting typing task compared to participants in a control group. Thus, executive capacity can apparently be trained by regular exertion of logical reasoning—a seemingly very different act than the traditional acts of self-control used in previous research (e.g., Muraven, 2010). As numerous previous experiments have observed, acts of self-control as well as tasks that entail high-level cognitive processing can cause a temporary depletion of executive capacity, much like exercise can fatigue physical muscles (Hagger et al., 2010). The current research adds to a growing body of research suggesting that repeated practice can, over time, increase resistance to depletion, as though the practice boosts executive capacity much like repeated exercise strengthens muscles. However, the results indicated also that the self-control benefits of practicing logical reasoning were fairly short-lived. Just one week after the logical reasoning intervention had ended, participants who had, versus had not, been assigned to practice logical reasoning exhibited roughly equivalent levels of self-control. Hence, the benefits of practicing logical reasoning were apparent immediately after the intervention but had disappeared within a week. This pattern suggests that to sustain the self-control benefits of practicing logical reasoning, one must continue to practice. These self-control patterns again harken back to the muscle metaphor, as muscular strength and endurance also begin to fade in the absence of regular exercise or use. We do not mean to suggest that executive capacity would disappear altogether without practice. Rather, it seems likely that persons who do not regularly exercise executive capacity would exhibit their trait levels of self-control, as executive functioning (and self-control) appears to have a heritable component (e.g., Miyake & Friedman, 2012). The current results suggest that, in addition to any heritable component of executive capacity, practice and use can enhance self-control. For unknown reasons baseline anagram performance fluctuated over time such that performances at the beginning of the post-test sessions were generally less impressive relative to the earlier pre-test sessions (see Table 1). We measured and adjusted for baseline anagram performance, but the pattern of means suggests that participants did not experience an absolute improvement in self-control. Corresponding to previous research (e.g., Oaten & Cheng, 2006), practicing logical reasoning apparently decreased participants’ proneness to suffering depleted executive capacity.

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As depicted in Table 1, after one week of practicing logical reasoning, participants’ anagram performance improved from before to after the depleting typing task. This pattern may be easily explained by a spontaneous learning effect during the session that took place in parallel to the depletion effect (cf. Stern, 1938). As participants’ executive stamina improved, the depletion effect declined and therefore the learning effect became more visible in their anagram performance. Among participants who did not practice logical reasoning, the depletion effect appeared to be stronger than the learning effect, as anagram performance was higher at the beginning compared to the end of the sessions. Alternative Explanations The present results suggested that the effect of practicing logical reasoning was specific to improvements in self-control. There was no significant effect on participants’ ability to solve math problems. The null effect on math performance was expected, as previous research has found that solving simple math problems does not rely on executive capacity (e.g., Muraven, 2010). Thus, the logic intervention appeared to train executive capacity specifically rather than cognitive capacity more generally. This view is also supported by the fact that post-test (post-intervention) measures of self-control and math performance were unrelated in the present sample. If the intervention had influenced a general cognitive ability underlying both tasks, then they should have shared some variance. Moreover, the intervention effect on post-test self-control did not change when post-test math performance was statistically controlled. Another alternative explanation of the present finding could be that self-control during the daily tasks was confounded with practice at logical reasoning, and was actually responsible for the improvement in self-control. Repeated exercises in self-control have reliably been demonstrated to have a positive effect on self-control (e.g., Finkel et al., 2009; Gailliot et al., 2007). Thus, if participants in the logic condition had to engage more strongly in self-control than participants in the no logic condition, regular self-control rather than regular logical reasoning might have been responsible for the observed results. To address this alternative explanation, we assessed and controlled for individual differences in two indicators of self-control exertion during the daily tasks. First, we asked how effortful the participants perceived the daily tasks to be. Even though effort often indicates the exertion of self-control, it seems to be principally independent from the consumption of executive capacity (Schmeichel, 2007); this means that we held constant self-control exertion but not necessarily the regular use of executive capacity. Second, we asked participants how much they wished to stop and do something different during the daily tasks. Overriding this wish might have demanded a great deal of self-control. Over and above these self-report measures of self-control exertion, we found an effect of the logical reasoning intervention. This pattern suggests that practicing logical reasoning itself (i.e., independent of potential self-control ingredients of the daily tasks) drove the effect of the intervention. Implications and Future Research It is widely acknowledged that self-control improves with age, likely in conjunction with brain maturation of the frontal cortex (Romer, Duckworth, Sznitman, & Park, 2010; Steinberg, 2008). The current results suggest that experience may also play a role for individuals’ capacity to exert self-control (see also Romer et al., 2010). A hopeful implication of the present work is therefore that frequent tasks and assignments involving logical reasoning can benefit not just learning but also self-discipline and self-control.

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Perhaps parents could foster their children’s self-control by enriching every-day life with opportunities to engage in cognitive challenges (e.g., providing them with age-appropriate brain games and thought-provoking literature). Teachers can attach importance to regular reasoning exercises in classes and in homework assignments (e.g., obligatory rational discussions of controversial topics as in the logic condition of the present study). Being practiced in both logical reasoning and self-control may substantially increase individuals’ success in life: Whereas logical reasoning is required for making intelligent plans (e.g., scheduling the way to graduation), self-control is vital for realizing these plans (e.g., persistently pursuing the scheduled way to graduation). The abovementioned practical implications of the present findings point to one future direction: Does integrating frequent logical reasoning into mundane activities in applied settings really show the expected effect on self-control? For examining this question, schools may be an appropriate place. The school context allows implementing regular logical reasoning within a structured schedule, and also implies demands on self-control (e.g., focused learning instead of doing something perceived as more attractive). In addition, it may be interesting to examine whether practicing logical reasoning has desirable effects on further variables, mediated via increased executive capacity. For instance, in a recent study, primary-school students who participated in an intervention of philosophical inquiry involving critical thinking improved relative to a control group in socio-emotional variables (e.g., their self-esteem went up and their anxiety decreased; Trickey & Topping, 2006). According to the present research, by practicing critical thinking, these students may also have experienced an increase in the executive capacity that enables self-control. Given the role of self-control for psychological adjustment and emotion regulation (Bertrams, Englert, & Dickha¨user, 2010; Tangney et al., 2004), the assumed improvement in self-control may have been a mediating mechanism underlying the observed positive effect of the thinking program on socio-emotional variables. As a theoretically relevant question, future research may also address the nature of executive capacity to explain the effect of logical reasoning on self-control in more depth. The present study was based on previous findings that various executive acts such as logical reasoning and self-control share a common resource (e.g., Schmeichel et al., 2003). Our results support this view. There is some reason to assume that working memory capacity may be this basic resource (Hofmann, Friese, Schmeichel, & Baddeley, 2011). Both logical reasoning and self-control have been found to be dependent on working memory capacity (Fry & Hale, 1996; Hofmann, Gschwendner, Friese, Wiers, & Schmitt, 2008), and working memory capacity also appears to be improvable by training (Klingberg, 2010; Melby-Lervag & Hulme, 2013). Thus, a deeper explanation for the present findings may be that working memory capacity improved by its regular use through logical reasoning, leading to improvements in self-control, an executive act also based on this capacity. Given that working memory capacity is of relevance for a variety of outcomes of executive processes (Engle, 2002; Furley & Memmert, 2010; Hofmann et al., 2011), the working memory capacity explanation would be in line with theory and findings that executive capacity is not domain-specific (Baumeister et al., 2006). In coming studies, it may be fruitful to assess the extent to which increases in working memory capacity mediate the effect of regular logical reasoning on self-control or other executive acts. Such research may also extend the present work by including outcome measures that are not primarily cognitive in nature (e.g., resisting eating impulses; Hofmann et al., 2008). In the past, some authors have questioned the usefulness of conscious in contrast to automatic thinking, whereas others have defended it (see Baumeister & Masicampo, 2010; DeWall, Baumeister, & Masicampo, 2008). The present research may add novel insight to the debate. Logical reasoning as in our study is based on conscious rather than automatic

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thinking (DeWall et al., 2008), and it improved self-control. The observed effect of regular logic thinking suggests that one benefit of conscious thinking lies in its potential to improve a basic ability that is required for pursuing long-term goals and is positively associated with achievement, health, and well-being.

Notes 1. The pre-test, post-test, and follow-up sessions also included self-report measures on mood and motivation. These measures did not reveal significant differences between the intervention conditions. 2. We corrected for skewness in all anagram performance measures by applying square root transformations (Tabachnick & Fidell, 2007). For the math performance measures no adjustments to normal distribution were required. Decisions for correction were based on Q-Q plots and histograms. 3. Van Breukelen (2006) demonstrated that ANCOVA and ANOVA of change from baseline are unbiased in terms of detecting treatment effects; however, ANCOVA has more statistical power in randomized samples. Therefore, we made the a priori decision to apply ANCOVA to test the effect of practicing logical reasoning. When repeating the analysis with ANOVA of change, we found a pattern of results widely in line with the ANCOVA results. Most important, the interaction between treatment (logic condition versus no logic condition) and time of measure (pre-test versus post-test versus follow-up) predicted anagram performance, p ¼ .02, but did not predict math performance, p ¼ .71.

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