Psychology of Sport and Exercise 15 (2014) 521e527 Contents lists available at ScienceDirect Psychology of Sport and Exercise journal homepage: www.elsevier.com/locate/psychsport Athletics and executive functioning: How athletic participation and sport type correlate with cognitive performance Jed Jacobson*, Leland Matthaeus 1 Whitman College, 345Boyer Ave, Walla Walla, WA 99362, USA a r t i c l e i n f o a b s t r a c t Article history: Received 23 June 2013 Received in revised form 18 April 2014 Accepted 21 May 2014 Available online 2 June 2014 Objectives: This study aims to further the knowledge regarding the documented link between physical exercise and cognitive function. Specifically, we examined the relationship between the type and level of sports in which college students participate and their executive functioning (EF). Design: We utilized a 3-way quasi-experimental design, and grouped participants by athletic status (athlete or non-athlete), sport type (self-paced, externally paced, or non-athlete; see Singer, 2000), and level (high-skilled or recreational). Methods: We evaluated EF by administering a battery of validated tests of decision making, problem solving, and inhibition. Results: We found that athletes scored higher on some of the EF measures than non-athletes. Furthermore, we observed that scores varied by sport type according to which subset of EF each test measured. Self-paced athletes scored highest on an inhibition task, and externally paced athletes scored highest on a problem-solving task. Conclusions: Our results suggest that athletes outperform non-athletes on tests of such EF domains as inhibition and problem solving, and that different types of athletic experience may correlate with higher levels of particular EF domains. © 2014 Elsevier Ltd. All rights reserved. Keywords: Executive functioning Problem solving Inhibition Self-paced sports Externally paced sports Many researchers have sought to explore the ways the body and mind influence one another. Recent studies (e.g., Keating, Castelli, & Ayers, 2013) have established a link between exercise and cognitive proficiency. After sessions of acute physical exercise, people tend to score higher on cognitive tests than when they have not exercised (Etnier & Chang, 2009). Of more significance to our study, elite athletes appear to perform with higher proficiency on tasks testing executive functioning (EF), a subcategory of cognitive functioning (Vestberg, Gustafson, Maurex, Ingvar, & Petrovic, 2012). Situations that require EF include activities that involve effortful problem solving, inhibition, planning, or vigilance (Diamond, 2006). Executive functions are highly utilized both in goal-oriented action under distraction and in novel response production when habitual dominant responses are apparent (Unsworth et al., 2009). Abbreviations: EF, executive functioning; CST, cognitive skill transfer; DM, decision making; DMA, decision-making accuracy; DMS, decision-making speed; PS, problem solving; MPS, mental processing apeed; SP, self-paced; EP, externally paced. * Corresponding author. Present address: 4840 86th Ave SE, Mercer Island, WA 98040, USA. Tel.: þ1 (206) 375 3401. E-mail addresses: jedediah.jacobson@gmail.com (J. Jacobson), matthalp@ whitman.edu (L. Matthaeus). 1 Tel.: þ1 (425) 445 4369. http://dx.doi.org/10.1016/j.psychsport.2014.05.005 1469-0292/© 2014 Elsevier Ltd. All rights reserved. Researchers break EF into more specific mental capacities such as problem solving, planning, inhibition, and decision making, in order to operationally measure it (Diamond, 2006; Spreen & Strauss, 1998). Researchers have been assessing both the relationship between exercise and EF, and the relationship between sport training and cognition, and many researchers are working to unite these two related lines of research (Pesce, 2012). To our knowledge, no previous researchers have tested hypotheses regarding the relationship between EF and specific types of sports; we aim to examine this relationship in our study. We seek to illuminate the relationship between sports and cognitive performance, which may have implications for athletic programs and physical education. If certain sports correlate with higher cognitive ability more than others, then physical educators, coaches, and policy-makers may seek to emphasize certain activities in athletics and throughout development. The documented differences in EF performance between elite athletes and non-athletes (e.g., Vestberg et al., 2012) may be attributed to cognitive skill transfer (CST), the process by which training in a cognitive task may improve performance on related untrained cognitive tasks. Various models for how CST works have been proposed, and, although they differ, most theorists agree that every task consists of many skills and/or pieces of knowledge, and 522 J. Jacobson, L. Matthaeus / Psychology of Sport and Exercise 15 (2014) 521e527 that tasks that share more skills and knowledge will have the strongest transfer effects in both the short and longterm (Taatgen, 2013). Researchers disagree on how “far” these skills can transfer; that is, the degree of difference between two given tasks for which transfer effects may be present. For example, chess players appear to have improved working memory capacity with regard to arrangements of chess pieces, but their overall working memory is normal (Chase & Simon, 1973). This finding supports the “narrow transfer” hypothesis: the idea that individuals with expertise in a particular field may have superior cognitive processes within that field, but not necessarily outside of it (Furley & Memmert, 2011). Contradictorily, video game training appears to cause improvements in scores on laboratory reaction time tests (Green, Pouget, & Bavelier, 2010). This finding supports the “broad transfer” hypothesis: the theory that extensive practice of context-specific skills improves individual components of cognition, and that these improvements are present regardless of context (Furley & Memmert, 2011). With regard specifically to sports, a parallel debate is ongoing. Voss, Kramer, Basak, Prakash, and Roberts (2010) made a distinction between two paradigms for analyzing improved cognition in athletes. Researchers using the “expert performance” approach have investigated the idea that athletes have improved cognition within their sport (e.g., Mann, Williams, Ward, & Janelle, 2007; Singer, Cauraugh, Chen, Steinberg, & Frehlich, 1996). On the other hand, proponents of the “cognitive component skills” approach assert that athletes improve in specific cognitive skills, which are present in non-sport contexts and can be measured in the laboratory (Voss et al., 2010). Although much research has supported this idea with respect to skills like attention (Anzeneder & Bosel, 1998; Pesce, Cereatti, Casella, Baldari, & Capranica, 2007), many studies have found no benefits for athletes on related cognitive skills (e.g., Lum, Enns, & Pratt, 2002). Research on the transfer of EF skills from athletics is sparse (Voss et al., 2010); we propose that differences in EF may be present between athletes and non-athletes, and that CST may play a role in this. Researchers have employed various methods in the pursuit of improving EF (e.g., Diamond & Lee, 2011; Kesler et al., 2013). In a study of disabled athletes (Di Russo et al., 2010), the researchers suggested that overall EF was lower in physically disabled populations, and that playing certain sports such as basketball, in which the athlete interacts with his/her environment on a constantly changing basis, may reduce this deficit by promoting response flexibility. On the other hand, sports like swimming, where athletes are not thinking creatively or reacting to timepressured stimuli, did not seem to benefit participants in this manner (Di Russo et al., 2010). These results indicate that different types of sports may differentially facilitate EF improvements. Contrastingly, in a meta-analysis of fitness training and cognitive function (Colcombe & Kramer, 2003), the authors suggested that particularly aerobic fitness training is likely to have positive effects on EF. In our study, we aim to address not only the effects of mere aerobic exercise on cognition, but also the sport-specific mental skills that may be related to differences in particular aspects of EF. In a literature review of sports psychology (Singer, 2000), focused on improving performance, the researcher asserted that sports could be classified into two categories: self-paced (SP) and externally paced (EP). Sports like bowling, golf, and running, as well as aspects of sports like baseball pitches and tennis serves, were classified as SP because they allow time for the athletes to prepare themselves for critical actions and perform at a pace they control. Sports like soccer, basketball, and volleyball require adaptability and quick decision making in response to external cues, and are labeled as EP. Two sub-categories of EP sports are interceptive sports, such as racquet sports, and strategic sports, or sports which involve multiple teammates and opponents and tactical formations (Mann et al., 2007). The EP vs. SP sport distinctions were based partly upon Singer's (1988) experiment, geared towards understanding how to improve performance in self-paced athletics. Later, Singer (2000) developed a strategy to improve performance in EP sports, highlighting attention and decision making. EP athletes, especially those playing at a high level, may have faster and more accurate decisionmaking processes (Singer et al., 1996; Zoudji, Thon, & Debû, 2010). We theorized that the categorical distinction between self- and externally paced athletes would correspond to differential performances on EF tasks testing skills like inhibition and decision making. Furthering the notion of athletics correlating with higher levels of cognitive performance, Vestberg et al. (2012) evaluated the relationship between EF and athletic ability in a healthy population of elite athletes (Swedish professional soccer players) and nonathletes. They compared the participants' scores on tasks measuring creativity, inhibition, and cognitive flexibility, finding significant variation between two levels of athletes and a control group of non-athletes (Vestberg et al., 2012). These results indicate a positive correlation between EF and athletic ability. Based on this finding, we drew a distinction in our study between high-skilled and recreational athletes; we expected that athletes with more expertise would score higher on EF tests. In the Swedish study, the researchers later tracked the athletes through two seasons and analyzed their goal and assist statistics (the most objective measure of soccer success). They found that players who had scored higher on the EF tasks scored and assisted more goals than those who had not performed as well on the tasks (Vestberg et al., 2012). Therefore, high EF may predict athletic success in EP sports like soccer. Below, we elaborate on the facets of executive functioning that we expected to correlate most strongly with each of the classifications of athletics. These constructs include decision making (DM), problem solving (PS), and inhibition. Decision making is “the cognitive process of choosing between two or more alternatives, ranging from the relatively clear cut … to the complex” (VandenBos, 2006, p. 259). It utilizes the executive functions of shifting, planning, and categorization (Brand et al., 2005). Adaptive decision making has been closely linked with higher-level EF in military leaders (Hannah, Balthazard, Waldman, Jennings, & Thatcher, 2013). Because EF has such a strong association with DM, we predicted that the higher EF seen in athletes (Vestberg et al., 2012) would correlate with improvements in their DM abilities. Problem solving is “the process by which individuals attempt to overcome difficulties, achieve plans that move them from a starting situation to a desired goal, or reach conclusions through the use of higher mental functions, such as reasoning and creative thinking” (VandenBos, 2006, p. 735). The relationship between EF and PS is well documented (e.g., Harris, 2001; Kotsopoulos & Lee, 2012). PS highly utilizes shifting and updating, two widely accepted foundational executive functions (Diamond, 2013; Kotsopoulos & Lee, 2012). Improvements in EF appear to correlate with improved PS abilities in healthy college students (Wen, Butler, & Koutstaal, 2012). Because of this direct link to EF we predicted that, as with DM, the documented EF proficiency seen in EP athletes (Vestberg et al., 2012) would correlate with higher PS abilities. Inhibition is “the suppression of covert responses in order to prevent incorrect responses” (VandenBos, 2006, p. 481). Inhibition is a stand-alone executive function according to a number of theorists (e.g., Diamond, 2006; Kotsopoulos & Lee, 2012). Multiple types and definitions of inhibition exist (Miyake, Friedman, Emerson, Witzki, & Howerter, 2000); in this study we focus on the suppression of dominant or prepotent responses. Inhibition correlates moderately with other executive functions like shifting and updating, but the functions are separable and differentially contribute to performance on complex executive tasks (Miyake et al., 2000). Inhibition can be bettered through practice; in a J. Jacobson, L. Matthaeus / Psychology of Sport and Exercise 15 (2014) 521e527 sample of children with developmental coordination disorder, a 10week soccer training intervention improved performance on an inhibition task (Tsai, Wang, & Tseng, 2012). We hypothesized that athletes would outperform non-athletes on all EF tasks. We further hypothesized that EP athletes would score highest on the DMA, DMS, and PS tasks, followed by their SP and non-athlete counterparts, because EP sports require the athletes to constantly be adapting to the conditions of the contest and to act quickly and strategically to outperform the opposing side. Because of the inhibition required in the highly-regimented practice of tasks requiring intense focus despite internal distractors such as fatigue and external distractors such as cheering spectators, we hypothesized that SP athletes would score highest on the inhibition task, followed by EP athletes and non-athletes. Lastly, we hypothesized that high-skilled athletes would score higher on all EF tasks than recreational athletes because they practice more often and perform at a higher level. We did not expect significant inter-group variation on the vocabulary task because we recruited students from one school with constant admission standards, although admissions standards may be more lenient for incoming varsity athletes. Methods 523 Design We utilized a between-groups 3-way quasi-experimental design. Participants completed four psychometric tests and one self-report questionnaire. We chose the two EF tests based on their demonstrated close correspondence to EF, the MPS test because of its influence on our measures of EF, and the vocabulary test because vocabulary correlates strongly with overall intelligence. We chose a quasi-experimental design in which we did not assign participants to groups, but rather grouped them by preexisting characteristics. We tested hypotheses regarding differences between athletes and non-athletes, between self-paced athletes, externally paced athletes, and non-athletes, and between high-skilled and recreational athletes, in their scores on the EF tasks, the MPS task, and the vocabulary task. We grouped participants as athletes or non-athletes based on their self-reported sports participation, where participating in sports once or more per week qualified an individual as an athlete. We grouped participants by sport type (EP or SP) based upon Singer's (2000) article, and we grouped participants by sport level (high-skilled or recreational). The high-skilled athlete group included college varsity, semi-professional, and professional athletes. The statistical calculations in this study were performed in SPSS. Participants Measures We sampled from a population of students at a small undergraduate college in the western United States. There were 54 participants in total, with ages ranging from 18 to 24 (M ¼ 20.13; SD ¼ 1.30); participants were predominantly female (57.41%), and predominantly White (81.48%). Further participant demographics are given in Table 1. Participants were recruited via the college's email listservs. Potential participants received an email inviting them to participate in a study on extracurricular activities and cognitive skills. The sampling method was quick, convenient, and permitted us to reach a large number of possible participants. Exclusion criteria included: a) Self-reported diagnosis of an attention disorder by a psychologist or psychiatrist; b) Head injury that caused a loss of consciousness lasting more than one to 2 min; and c) Being under the influence of a mind-altering substance at the time of testing. Portions of a few participants' data were excluded because of either misunderstanding of the instructions or experimenter error (e.g., Tower Test scores when the experimenter mistakenly omitted an item; Coding Test scores when the participant ignored the instructions to complete all items in order). This may have led to some type of immeasurable selection bias, but if so, it was likely not significant. In adherence to ethical guidelines, participants were informed that they could choose not to complete any part of the study and that individuals' data would be kept confidential. The Whitman College Institutional Review Board approved this study. Participants were asked not to share information from debriefing. Table 1 Demographic statistics of the sample. Athletes (N ¼ 39) Age Sex Race GPA M SD Male Female Caucasian Latino Asian M SD Externally paced (N ¼ 22) Self-paced (N ¼ 17) 20.05 1.17 14 8 19 1 2 3.46 .34 20.18 1.51 3 14 15 0 2 3.64 .24 Non-athletes (N ¼ 15) To measure EF, we used two validated psychological tests: namely the DeliseKaplan Executive Function System (D-KEFS) Tower Test and ColoreWord Interference Test (Delis, Kaplan, & Kramer, 2001a). To evaluate discriminant validity we administered a vocabulary test in order to establish a baseline of intelligence, and a coding exercise to measure MPS. Lastly we administered a questionnaire designed to measure participant demographics as well as place participants into groups. To control for potential differences between researchers, we ran inter-rater reliability analyses for each of the tests (see Table 2). Due to time and equipment constraints, we were only able to analyze interrater reliability for 10 participants' data. Despite the small sample, the analyses indicated very strong inter-rater reliability for each test, and we have no concerns about scores being influenced by the experimenters. For the D-KEFS tests, we videotaped the first ten participants as they performed the tests and the second scorer scored the tests independently while watching the video. For the vocabulary test and the coding test, we simply scored each test separately and compared scores afterward for the first ten participants. D-KEFS tower The D-KEFS Tower Test (Delis et al., 2001a) consists of nine items that require the participant to move circular disks on and off pegs to create a tower that matches a given model. The disks differ in size; the participant must avoid placing larger disks on top of smaller ones, and he/she may only touch one disk at a time. The participant Total (N ¼ 54) Table 2 Inter-rater reliability analysis. 20.20 1.27 6 9 10 1 4 3.51 .32 20.13 1.30 23 31 44 2 8 3.53 .31 Inhibition Decision Making Accuracy Decision Making Speed Mental Processing Speed Vocabulary k Std. Error t p 1.000 .674 .158 .888 .887 .000 .148 .114 .104 .111 6.58 7.50 2.36 8.23 6.09 <.001** <.001** .018* <.001** <.001** *Significant at a ¼ .05, **Significant at a ¼ .009 (Sidak correction for multiple testing), df ¼ 9. 524 J. Jacobson, L. Matthaeus / Psychology of Sport and Exercise 15 (2014) 521e527 is instructed to construct the tower in the fewest moves possible. Later items feature more disks and tend to be more challenging. We obtained three scores from this test: the Total Achievement Score, the Time-per-Move Ratio, and the Move Accuracy Ratio. The Total Achievement Score measures overall performance in terms of building the correct tower in the fewest possible moves, and demonstrates participants' spatial planning, rule learning, and set creation and shifting (Delis et al., 2001a, p. 195). Because this task required the participants to use these skills to solve a complex puzzle, we employed the age-scaled Total Achievement Score as our measure of problem solving (PS). For the purposes of our study, we divided the concept of DM into two domains: Decision-Making Accuracy (DMA; one's ability to make desirable decisions among alternatives during goal-oriented activity) and Decision-Making Speed (DMS; one's ability to quickly make goal-oriented choices, regardless of accuracy). The Move Accuracy Ratio provides a measure of how often participants are able to make correct decisions among alternatives during goaloriented activity. Age-scaled Move Accuracy Ratio scores provided us with our measure of decision-making accuracy (DMA). The Time-per-Move Ratio measures how quickly the participant arrives at a decision for his/her next move; these ratios provided our decision-making speed (DMS) scores. The D-KEFS Tower Test has demonstrated strong internal consistency, construct validity, and testeretest reliability, as well as moderate correlations between the sub-scores of the test (Delis, Kaplan, & Kramer, 2001b, p. 40). Inter-rater reliability scores (given by Cohen's Kappa; see Table 2) in our study were as follows: k ¼ .767, t ¼ 6.25, p < .001 (Total Achievement Score); k ¼ .674, t ¼ 7.50, p < .001 (Move Accuracy Ratio); and k ¼ .158 t ¼ 2.36 p < .018 (Time-per-move Ratio). The D-KEFS Tower is a modified version of a long-standing Tower of Hanoi test, also known as the Tower of London. It has demonstrated construct validity in the detection of brain damage (particularly frontal lobe dysfunction) as well as measuring important areas of higher-level executive functions (Delis et al., 2001b). D-KEFS ColoreWord Interference The D-KEFS Color-Word Interference Test (Delis et al., 2001a), a modified Stroop Test, consists of four items (participants were only asked to complete three), which require the participant to name ink colors and read color names. The first condition, color naming, contains 50 colored boxes (some red, some green, and some blue). The participants named the colors one by one as fast as possible. The second condition, word reading, has 50 names of the same three colors all written in black ink, and the participant must read these. The third condition, inhibition, contains 50 color names written in different colored ink, and requires the participant to inhibit the more salient response of reading the word, and instead name the dissonant ink color. From this test we obtained the inhibition score by subtracting the scaled scores from the first condition from the scaled scores on the third. This score shows verbal inhibition controlling for color naming speed and participant age (Delis et al., 2001a). The authors reported high internal consistency and testeretest reliability scores on the ColoreWord Interference test (Delis et al., 2001b, p. 40). The inter-rater reliability statistics in our study were k ¼ 1.00, t ¼ 6.58, p < .001. The test's documented ability to detect brain damage and evaluate higher-level EF, much like the Tower, indicates strong construct validity (Delis et al., 2001b). Coding test We also measured a related construct that works in tandem with EF but is not considered a subcategory of EF: mental processing speed (MPS). MPS is the speed of cognitive functioning and is used as a measure of the efficiency of a variety of cognitive abilities, including EF (Baudouin, Clarys, Vanneste, & Isingrini, 2009). As such, it was a prime candidate for a covariate to partial out in our planned analyses. We controlled for MPS to ensure that our EF variables, not other mental factors, were accounting for potential observed EF differences. Researchers (e.g., Baudouin et al., 2009) frequently use coding exercises to measure MPS. In these exercises, the participant learns pairs of corresponding numbers and symbols and uses this information to fill in blanks. The coding test we used is an equivalent version of the Digit Symbol Substitution Test (DSST, Wechsler, 1997), a highly reliable and frequently used test of processing speed (Baudouin et al., 2009; Dickinson & Gold, 2008). Participants were shown a code table with pairs of digits (0e9) and symbols, and rows of empty boxes with a digit from 0 to 9 in the top corner of the box. The task requires the participant to use the code table to write the symbol associated with each digit in the box. The participants had two min to write as many symbols as possible in the empty boxes below each corresponding digit. The digits were randomized using an online random number generator to ensure that no patterns or redundancies could sway the results. The MPS score was given by the number of symbols correctly coded by a participant in this exercise. Our inter-rater reliability analysis showed k ¼ .888, t ¼ 8.23, p < .001. Vocabulary test Because EF measures correlate strongly with tests of overall intelligence, such as the WAIS-III (Davis, Pierson & Finch, 2011), we attempted to statistically control for overall intelligence while evaluating EF. We employed a vocabulary test as a brief intelligence measure because in recent studies (e.g., Smith, Smith, Taylor, & Hobby, 2005) researchers have found that vocabulary tests correlate strongly with every section of standardized intelligence tests. In a correlational analysis of 243 7e17 year old learning-disabled students' performances on standardized vocabulary tests and IQ tests (Smith et al., 2005), scores on the vocabulary test correlated highly with Full Scale IQ (r ¼ .74; p < .01). The vocabulary test consists of 15 items, each ranked equally on the scoring scale. The words were selected from a list Graduate Records Examinations (GRE) vocabulary words; selected to represent different parts of speech, different semantic categories and different affective valences (e.g., turbid, a goad, to preclude). The participants were not under time constraints and were asked to define every word to the best of their ability. We calculated the total score by adding together the fifteen item scores. Scoring criteria are based on the possible definitions listed in the American Heritage Dictionary (Morris, 1976). This test resembles those used in the WAIS-IV (Wechsler, 2008). Each word is scored on a two-point scale; a correct definition received two points, a partially correct definition received one point, and an incorrect definition received zero points. Participants' vocabulary scores were the total number of points scored. Our inter-rater reliability was k ¼ 887, t ¼ 6.09, p < .001. Demographic questionnaire The questionnaire was designed for the dual purposes of sorting the participants into groups depending on their athletic level/type and obtaining some basic demographic information regarding age, race, and sex. We also asked a number of questions to capture potential confounding variables such as time of day, the participants' sleep, and the participants' caffeine consumption. Procedure The participants were tested in a laboratory. They were informed that they would be performing cognitive tests for a study J. Jacobson, L. Matthaeus / Psychology of Sport and Exercise 15 (2014) 521e527 on extracurricular activities and EF, and that the study would take approximately 30 min. Tests were administered in the following order for all participants: 1) D-KEFS ColoreWord Interference; 2) coding exercise; 3) D-KEFS Tower; 4) vocabulary test; 5) demographic questionnaire. To mitigate potential fatigue/boredom effects, participants were given a 1-min break between the coding exercise and the Tower test. For the same reasons, the vocabulary test, which allows participants to relax and take their time, was administered last. After testing, the participants were offered an incentive (baked goods and/or fruit) and debriefed about the study. Results We removed two outliers from the data. Two non-athletes scored extremely high on inhibition, to the extent that their data were statistical outliers within their own group and within the entire sample. These participants may have misunderstood the instructions, and differentially weighted speed and accuracy on condition 1 vs. condition 3. This could cause a normal inhibition score to appear very high when compared with a very low word reading score. In our hypothesis testing, we set alpha levels at .05 for all tests. We used independent-samples t tests to test the hypothesis that athletes and non-athletes would differ on the EF tasks. Some of our hypotheses received support. As shown in Table 3, scores on the inhibition task show significant mean variation between athletes and non-athletes. Athletes also outscored non-athletes on our measure of PS, the Tower Test Total Achievement Score. Effect sizes of both the inhibition finding and the PS finding were large. Differences between the mean Time-per-move (DMS) and Move Accuracy ratios (DMA) for athletes and non-athletes were not statistically significant. Mean scores on the MPS and vocabulary tasks showed no significant intergroup variation. Table 4 shows between-subjects variation for all athletes according to sport level and sport type. We found no significant variation in EF scores, MPS scores, or vocabulary scores by sport level, sport type, or the interaction between these variables, in the absence of our control group of non-athletes. As shown in Table 5, hypotheses regarding intergroup differences on the inhibition and PS tasks between SP athletes, EP athletes, and non-athletes, received support. We ran planned contrast analyses for each EF variable. All contrast values are listed above the mean and standard deviation values of each variable and reflect our predictions expressed in the hypotheses. With contrasts included, mean scores on inhibition varied significantly and consistently with our hypotheses. As predicted, SP athletes scored the highest on Table 3 Independent samples t test analysis of athlete and non-athlete scores. Inhibition Problem Solving Decision Making Accuracy Decision Making Speed Mental Processing Speed Vocabulary M SD M SD M SD M SD M SD M SD Athletes Nonathletes t p d r 11.26 1.55 10.97 2.28 9.58 2.43 10.21 1.56 86.99 11.84 6.35 2.86 9.69 1.65 9.47 1.60 8.53 2.97 9.87 2.90 84.67 8.52 6.53 3.80 3.10 .002** .98 .44 2.33 .012** .76 .36 1.32 .096 .39 .19 .56 .290 .15 .07 .69 .490 .23 .11 .20 .845 .05 .03 Table 4 Between-subjects analysis of variance for sport level, sport type, and interaction therein for athlete participants. Independent variable Dependent variable F Sig. Partial s2 Problem Solving <.01 .951 <.01 Decision-Making Speed .49 .489 <.01 Decision-Making Accuracy .50 .486 .01 Inhibition .01 .923 .01 Mental Processing Speed .04 .834 <.01 Vocabulary 3.51 .067 .07 Sport Type (Self-Paced or Problem Solving 1.71 .200 .01 Externally Paced) Decision-Making Speed .05 .819 .04 Decision-Making Accuracy .53 .472 .01 Inhibition .28 .602 <.01 Mental Processing Speed 1.88 .177 .04 Vocabulary .79 .378 .02 Sport Level* Problem Solving .04 .837 <.01 Sport Type (Interaction) Decision-Making Speed <.01 .956 <.01 Decision-Making Accuracy 1.92 .175 .03 Inhibition .11 .743 <.01 Mental Processing Speed .11 .741 <.01 Vocabulary 2.04 .160 .04 Sport Level (High-Skilled or Recreational) df1 ¼ 1; df2 ¼ 38 (Inhibition, PS, DMA, and DMS analyses are one-tailed tests. MPS and vocabulary analyses are two-tailed tests). inhibition, followed by EP athletes and non-athletes, respectively, with a large effect size. On the PS task analysis with contrasts, EP athletes scored highest, followed by SP athletes and non-athletes respectively, again with a large effect size. We found no significant differences in DMA, DMS, vocabulary or MPS scores. In a study like this one with many test variables, multiplicity of tests inherently poses a threat to validity. However, we utilized the Sidak correction for multiple testing and adjusted our alpha levels to reduce the likelihood of false positives. Nearly all of our findings had p-values significant at Sidak-corrected alpha levels of .013 or .009, indicating that significant differences were present despite the potential for error. The majority of our findings also had large effect sizes. Discussion We found substantial support for many of our hypotheses. We predicted that athletes would outscore non-athletes on all EF measures. We expected SP athletes to outscore EP athletes and nonathletes on the inhibition task, and EP athletes to outscore SP athletes and non-athletes on the PS, DMS, and DMA tasks. All of these hypotheses received substantial support, except for those involving DMS and DMA scores. Potential reasons for this are Table 5 Planned contrast analysis of externally paced, self-paced, and non-athlete scores (one-tailed). Externally Self- Nont paced paced athletes Inhibition *Significant at a ¼ .05, **Significant at a ¼ .013 (Sidak correction for multiple testing), df ¼ 52 (Inhibition, PS, DMA, and DMS analyses are one-tailed tests. MPS and vocabulary analyses are two-tailed tests). 525 Contrast M SD Problem Solving Contrast M SD Decision Making Contrast Accuracy M SD Decision Contrast Making Speed M SD 0 11.14 1.61 1 11.43 2.27 1 10.05 2.54 1 10.29 1.27 1 11.41 1.50 0 10.41 2.24 0 9.00 2.24 0 10.12 1.90 1 9.69 1.65 1 9.47 1.60 1 8.53 2.97 1 9.87 2.90 p d r 2.94 .003** .80 .37 2.77 .004** .76 .35 1.51 .045* .41 .20 .61 .273 .17 .08 *Significant at a ¼ .05, **Significant at a ¼ .013 (Sidak correction for multiple testing), df ¼ 52. 526 J. Jacobson, L. Matthaeus / Psychology of Sport and Exercise 15 (2014) 521e527 discussed below. We also hypothesized that high-skilled athletes would outperform recreational athletes on all EF tests; these hypotheses did not receive support. Our findings suggest the presence of a substantial link between athletics and subcategories of executive functioning (EF). The first between-groups analysis (see Table 3) suggests that athletes outperformed non-athletes in the problem solving task as well as the inhibition task. There were not significant differences in vocabulary scores (a proxy for overall intelligence), or mental processing speed scores (a variable highly correlated with EF), between athletes and non-athletes. This suggests that the groups did not differ in overall intelligence or mental processing capacity. Although our results do not permit us to infer a causal relationship between the variables, we speculate that the observed differences in EF may result, at least in part, from athletic participation. The athletes in this study participated in sports that require the use of goal-oriented planning and suppression of inappropriate responses (Singer, 2000). Mere non-sport exercise has been shown to benefit EF throughout development (Davis et al., 2011) and in adult populations (Colcombe & Kramer, 2003). Therefore, the physical exercise in sports, plus habitual practice of EF skills in training and competition, may lead to even further improvements. The field is lacking in research on the effect of sport participation on EF throughout development (Diamond & Lee, 2011); further research should address this. It is also possible that individuals who naturally (without training) develop strong EF skills are more likely to become and remain athletes. The findings of Vestberg et al. (2012), suggest that EF competence predicts athletic success. People tend to get more enjoyment from activities at which they excel; this may serve to partially explain our findings. More likely still is an interaction between these two theoretical phenomena: high-EF individuals become athletes more often, and their EF subsequently further improves with training, in a reinforcing cycle. Our analysis of the relationship between sport type and EF performance provided further support for our hypotheses. We found that EP athletes scored higher on the PS task than SP athletes and non-athletes. In EP sports, like soccer and tennis, athletes make time-pressured decisions in response to external cues during goaloriented activity (Singer, 2001). In the Tower test, participants solved each individual problem by planning and shifting in response to the configuration of the pieces while maximizing efficiency (Delis et al., 2001a). We speculate that our findings can be explained in part by a broad transfer from sport-related EF training, similar to the way athletes have improved attention (Anzeneder & Bosel, 1998). For example, EP athletes have experience with quickly determining the positions of people and objects around them, and subsequently using their bodies to manipulate the movements of these people and objects. A parallel process occurs in the Tower Test, where the participants were under time pressure to alter the arrangement of the pieces to achieve the desired outcome. Assuming that broad transfer of EF skills is possible, these mental challenges appear similar enough that transfer effects could be present in our study. In our study, SP athletes scored highest on the inhibition task, compared to EP athletes and non-athletes. SP sports, such as running and swimming, allow the athlete time to plan each critical movement and require high levels of focus and discipline (Singer, 2001). The ColoreWord Interference Test requires the suppression of a dominant responsedreading the worddin favor of a more preferable response: naming the ink color (Delis et al., 2001a). An SP athlete trains and competes in activities where his primary mental challenge is to suppress external and internal distractors to maximize performance (Singer, 1988). For example, a cross-country runner must suppress his internal pain and exhaustion in order to remain focused and continue running efficiently. Although, to our knowledge, no evidence exists of an effect of sport practice on EF, we speculate that the mental aspects of athletic training, through cognitive skill transfer, may improve laboratory performance on EF tasks. Importantly, these skill-specific findings indicate that the positive effects of purely aerobic exercise (Colcombe & Kramer, 2003), do not account for the entirety of the EF improvements observed in athletes; some other mechanism appears to be contributing as well. Our hypotheses involving the EF performance of high-skilled and recreational athletes did not receive support. Inconsistent with findings by Vestberg et al. (2012), high-skilled athletes in our study did not score higher on any of the EF tasks than recreational athletes. This may be related to the possibility that in our study, the high-skilled and recreational athletes may not have differed substantially in expertise and time devoted to their sports. We grouped them according to varsity or non-varsity status, which is a fairly limited indicator of sport level. There is also evidence that athletes of different levels may not differ significantly in some aspects of non-sport-specific cognition (Memmert, Simons, & Grimme, 2009). Our study has a number of limitations. These limitations, listed below along with suggestions for how they may be avoided in further research, weaken the statistical power of our study to some extent. However, our most noteworthy findings, regarding the sport-type-based differences in EF scores, were significant with 99.5 percent confidence intervals and large effect sizes. First, two of the variables, decision-making speed and decision-making accuracy, did not yield any significant results. The measures for these variables were the Tower Time-per-move Ratio and Move Accuracy Ratio, respectively. These two scores may be misleading, because poor overall performance on the Tower test could actually lead to desirable scores on either of these measures. Participants who were wildly inaccurate with their moves sometimes had low Time-permove Ratios (indicating strong DMS), because they would attempt move after move with little planning. The more incorrect decisions they made, the faster they worked. On the other hand, many participants failed to complete items, but did not attempt many moves. This would lead to a strong Move Accuracy Ratio because despite not completing the items, their numbers of attempted moves were similar to or even less than the minimum number of moves required to complete the items. Future researchers should avoid using these scores when seeking to evaluate higher-level EF, as they are more useful in the detection of brain damage. Furthermore, the inexact understanding of cognitive skill transfer (CST) causes some ambiguity. Research is inconclusive on whether sport-related cognitive skills can transfer beyond the sport-specific context (Pesce, 2012). Although much research supports the existence of CST (e.g., Taatgen, 2013), it remains unclear exactly how and on what type of timeline this phenomenon operates. This causes multiple problems. First, in our study, we only counted as athletes those participants who currently participated in sports at the time of testing. This meant that former varsity, youth, or high school athletes who may have quit very recently were considered non-athletes, when they may have actually been more similar to the participants in the athlete group. On the other hand, out-of-season varsity athletes, who may have not played their sport for multiple months, were still counted as athletes. Additionally, one might argue that the apparent differences in EF between athletes and non-athletes may result from the likelihood that athletes are more likely to have recently exercised. As Etnier and Chang (2009) found, recent physical exercise improves laboratory EF performance. This effect may have been present in our results comparing athletes and non-athletes; however, it cannot account for our findings regarding the differences between athletes J. Jacobson, L. Matthaeus / Psychology of Sport and Exercise 15 (2014) 521e527 of different sport types. In our study, we found no significant relationship between time of day of testing and scores on any of the tests. Further research is necessary to specify the nature of CST as it applies to EF. A longitudinal study that tracks individuals' EF as they alter their athletic and exercise habits over time could likely provide useful information to clear up this uncertainty. Because executive functions are so highly utilized in various activities, potential confounds exist. Not only athletes, but also musicians, debaters, and even video gamers all utilize mental sets, inhibit distractions, and make rapid decisions in goal-oriented activity. According to our CST-based theory, participation in activities like these may similarly correlate with higher EF. We were unable to control for non-athletic extracurricular activities in our study, so some of the observed variation may have resulted from non-sports related transfer effects. Further research may focus on differences in EF between those who participate in these other activities and those who do not (perhaps controlling for athletic participation). Our study is somewhat limited in depth and scope. Although our sample size (N ¼ 54) was large enough to yield significant results and large effect sizes, a study with a larger N could have stronger statistical power. Furthermore, our sample was not representative of the population at large. We sampled from a small liberal arts college, which contains mostly affluent, Caucasian, highfunctioning young adults. In order to generalize these findings beyond this type of population, we would need to collect data from a less restricted sample. We suggest further research on different populations with a larger sample. Finally, because our study was quasi-experimental, we were unable to determine causality and could only speculate about the reasons for our results. We suggest a future pretesteposttest design study in which participants are randomly assigned to SP athlete, EP athlete, and non-athlete groups. If EF subcategories improve through athletic training and competition in a manner consistent with our findings, we would have strong evidence that certain types of athletics indeed differentially improve EF. References Anzeneder, C. P., & Bosel, R. (1998). Modulation of the spatial extent of the attentional focus in high-level volleyball players. 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