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The role of time on task performance in modifying the effects of gum chewing on attention
Appetite 56 (2011) 299–301
Contents lists available at ScienceDirect
Appetite journal homepage: www.elsevier.com/locate/appet
Short communication
The role of time on task performance in modifying the effects of gum chewing on attention Lara Tucha a,*, William Simpson b a
Department of Clinical and Developmental Neuropsychology, Faculty of Behavioural and Social Sciences, University of Groningen, Grote Kruisstraat 2/1, 9712 TS Groningen, The Netherlands b School of Psychology, University of Plymouth, United Kingdom
A R T I C L E I N F O
A B S T R A C T
Article history: Received 3 November 2010 Received in revised form 14 December 2010 Accepted 21 December 2010 Available online 28 December 2010
Recent research examined the effects of chewing gum on attention and reported a significant interaction of gum chewing with time. Using a crossover within-subject design, the present study examined the effect of gum chewing on sustained attention in healthy adults over a period of 30 min. The results revealed a significant main effect of time and a significant interaction between gum chewing and time. The findings suggest that gum chewing differentially affects attention performance. While gum chewing has detrimental effects on sustained attention in earlier stages of the task, beneficial effects on sustained attention were observed at later stages. ß 2010 Elsevier Ltd. All rights reserved.
Keywords: Chewing gum Vigilance Attention Time Cognition
Introduction It has been observed that the chewing of a piece of ordinary chewing gum can facilitate cognition (Baker, Bezance, Zellaby, & Aggleton, 2004; Houcan & Li, 2007; Johnson & Miles, 2008; Stephens & Tunney, 2004b; Wilkinson, Scholey, & Wesnes, 2002). With regard to attentional functioning, beneficial effects of gum chewing have been found on alertness, selective attention, language-based attention and sustained attention (Scholey et al., 2009; Smith, 2009b, 2010; Stephens & Tunney, 2004b; Tucha, Mecklinger, Maier, Hammerl, & Lange, 2004). This facilitation of cognitive functioning by gum chewing has been ascribed to a chewing-related increase of regional cerebral blood flow, in particular in fronto-temporal brain regions, and an enhanced release of insulin. However, several studies failed to replicate these findings or demonstrated that gum chewing may even adversely affect attentional functioning (Kohler, Pavy, & Van Den Heuvel, 2006; Rost, Wirthwein, Frey, & Becker, 2010; Smith, 2009a; Tucha, Mecklinger, Maier, et al., 2004; Wilkinson et al., 2002). The difficulties in replicating the results of studies have been attributed to methodological differences between studies. Comparisons between studies revealed that studies differed in regard to statistical power, the test procedures applied, the brands of chewing
* Corresponding author. E-mail address: [email protected] (L. Tucha). 0195-6663/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.appet.2010.12.021
gums used, the participants’ familiarity with chewing gum (because of their different nationalities), the experimental designs (withinversus between-subjects design, lack of baseline assessments), the statistical analyses performed (parametric versus non-parametric analysis) and possible changes in gum consistency and flavor during the course of the examination (Scholey, 2004a, 2004b; Stephens & Tunney, 2004a; Tucha, Mecklinger, Hammerl, & Lange, 2004). Although the studies differed in all of these aspects, it appears that no single factor or combination of factors can explain the disagreement of results of available studies. In a recent study a new idea was put forward that might explain why some studies found beneficial and others detrimental effects of gum chewing on cognition (Ta¨nzer, von Fintel, & Eikermann, 2009). This idea focuses on time as an important factor in the psychodynamics of gum chewing. In their study, Ta¨nzer et al. (2009) examined concentration performance in 8–9 year-old children by using a cancellation task for a period of 16 min. Children who chewed a piece of chewing gum throughout the test session performed more poorly than the children who did not chew gum. However, this difference was only present during the first part of the task. After the twelfth minute, children who chewed a piece of gum outperformed the children of the no-gumcondition. Statistical analysis revealed that the interaction between conditions (gum chewing versus no gum chewing) and test period (earlier parts versus later parts of the task) was significant. In their discussion, Ta¨nzer et al. (2009) mentioned that the poorer concentration performance of children chewing gum
L. Tucha, W. Simpson / Appetite 56 (2011) 299–301
might have resulted from a biased selection of children with regard to their concentration performance. However, since no baseline assessment of concentration performance of groups has been performed, this is only one possible speculation. On the basis of the available literature, one could also assume that gum chewing might have detrimental or no effects on performance at earlier stages of tasks and beneficial effects at later stages. This explanation receives some support by a closer inspection of the sequence and timing of tests as applied in available studies. While some studies reporting beneficial effects of gum chewing on cognition observed the effects in tests that were performed during later stages of assessment (e.g. Smith, 2009b, 2010; Tucha, Mecklinger, Maier, et al., 2004; Wilkinson et al., 2002), studies that failed to replicate these effects performed similar measures at the beginning of assessment (e.g. Johnson & Miles, 2007; Tucha, Mecklinger, Maier, et al., 2004). However, the evidence provided by an inspection of the test sequences as used in published studies is not clear-cut because there is a lack of detail in publications concerning the exact timing and duration of tasks. Furthermore, positive effects of gum chewing on cognition were also observed at early stages of assessment (Smith, 2009a; Wilkinson et al., 2002). Therefore, it remains unclear whether time represents a mediating factor in the effects of gum chewing on cognition. The aim of the present study was to examine the impact of gum chewing on cognitive performance over a prolonged period of time. Using a computerized task that has been shown to be sensitive to the effects of gum chewing (Tucha, Mecklinger, Maier, et al., 2004), attention performance of healthy adults was registered for a period of 30 min. Methods Forty-two healthy adults participated in the present study (21 female, 21 male; mean age = 22.2 years, SD = 2.4 years). The study used a crossover design in which participants were assessed both with chewing gum (gum-condition) and without chewing gum (no-gum-condition). In the gum-condition, participants were asked to chew naturally and constantly a piece of spearmint flavored sugar-free chewing gum throughout the whole test session. Half of the participants were tested first with chewing gum and then without chewing gum. The remaining participants were examined in the reverse order. Participants were randomly assigned to the starting condition. Participants were tested individually in two sessions on subsequent days. The study was approved by the ethics committee of the University of Plymouth, UK. Written informed consent was obtained from all participants. A computerized attention test was performed for the measurement of sustained attention (Zimmermann & Fimm, 1993). The test was presented on a computer screen. Instructions were given orally. Participants were instructed to perform the computerized test as quickly as possible but to maintain a high level of accuracy. A brief sequence of practice trials preceded the test in order to familiarize the participants with the task. In the attention test, a structure consisting of two squares was presented in the centre of the computer screen. One square was situated on top of the other. These squares were alternately filled with a pattern (stimulus) for 500 ms with an interstimulus interval of 1000 ms. The duration of the test was 30 min. The participants were requested to press a button when no change of the pattern location occurred. The target rate (i.e. no change of pattern location) was about one target stimulus per minute. The time intervals between target stimuli were irregular. Reaction time for correct responses was recorded. To measure the effect of time on task performance, the whole task was divided into six consecutive time blocks of 5 min (1st time block: 1st to 5th minute; 2nd time block: 6th to 10th minute; 3rd time block: 11th to 15th minute; 4th time block: 16th to 20th
minute; 5th time block: 21st to 25th minute; 6th time block: 26th to 30th minute). Statistical analysis was performed using a 2 6 MANOVA (condition by time block). Normal distribution of data was analyzed using Kolmogorov–Smirnov tests. For statistical analysis an alpha level of p < .05 was applied. All analyses were carried out using SPSS 16.0 for Windows. Furthermore, the index h2 (eta squared) was calculated. According to Cohen (1988) a small effect size corresponds to an h2 = .0099, a medium effect size to an h2 = .0588 and a large effect size to an h2 = .1379. Post hoc analysis was performed using paired t-tests. A determination of the required sample size in this type of studies with multiple within-subject factors is in general very complicated, in particular because available research did not provide sufficient information concerning the magnitude of the effects of gum chewing on cognition over a prolonged period of time. Ta¨nzer et al. (2009) who found that time is a mediating factor in the psychodynamics of gum chewing unfortunately reported only mean scores but not standard deviations. This makes an analysis of effect sizes impossible. Tucha, Mecklinger, Hammerl, et al. (2004) and Tucha, Mecklinger, Maier, et al. (2004) also considered the effect of time on attention performance in a previous study by calculating ipsative mean scores of participants’ performance. From these data a medium effect (i.e. effect sizes between .5 and .6 SD) can be estimated. Considering this range of effect sizes and setting power at .80 and the significance criterion at .05, sample sizes between 35 and 50 per cell appear to be sufficient (Cohen, 1988). With sample sizes of 42 per cell, this criterion was achieved in the present study. Results There was no evidence to reject the assumption of normal distribution of reaction time data. Because of a violation of the sphericity assumption, the Greenhouse–Geisser correction was employed. Multivariate analysis of variance (MANOVA) revealed a significant main effect of time block (F(4.06, 205) = 17.13, p < .001, Greenhouse–Geisser corrected). The effect size for this difference in reaction time was large (h2 = .295). Subsequent post hoc analysis [()TD$FIG] using paired t-tests (Bonferroni adjusted) indicated that the 750
700
Reaction time (in ms)
300
650
600
550
500 1st time 2nd time 3rd time 4th time 5th time 6th time block block block block block block gum condition
no-gum condition
Fig. 1. Reaction times (in ms) of participants in the two conditions across the six time blocks (means SE).
L. Tucha, W. Simpson / Appetite 56 (2011) 299–301
reaction times shown during the first two 5 min blocks (1st to 10th minute of task) differed significantly (p < .001) from the reaction times during the remaining 5 min blocks (11th to 30th minute). The remaining pairwise comparisons did not reach significance (p > .05). Furthermore, there was a significant condition by time block interaction (F(3.73, 205) = 5.22, p = .001, Greenhouse–Geisser corrected) indicating a medium effect (h2 = .113). The difference between conditions was not significant (F(1, 41) = .61, p = .439) and represented only a small effect (h2 = .015). Test performances of participants are presented in Fig. 1. An additional analysis in which the order of gum condition was included revealed no significant effect regarding the order of gum condition (results not shown). Discussion In the present study, the effect of gum chewing on attentional functioning over a prolonged period of time was examined. Attentional functioning was assessed by performing a computerized sustained attention task. Reaction time was measured for each of six consecutive time blocks of 5 min so that changes in test performance over time could be analyzed. An analysis of the number of omission and commission errors was not included in the present study, because errors in healthy participants have been found to be a rare phenomenon (Tucha et al., 2009) in particular when analyzing time periods of only 5 min (number of omission and commission errors < 1). Moreover, the reliability of examinations based on the observation of short test scales and rare events is usually very small (Kline, 2000). The present results suggest that there is a significant main effect of time denoting an increase of reaction times with task duration. This time-on-task effect is not surprising considering that the whole concept of sustained attention is based on the robust finding that human performance deteriorates over time (Cohen, 1993). The condition by time block interaction also reached significance. Similar to the findings of Ta¨nzer et al. (2009), the performance of participants in the gum-condition was poorer during the first part of the task (first 10 min) than in the no-gum-condition. One may argue that the findings of Ta¨nzer et al. (2009) might have resulted from a biased selection and group allocation of participants to conditions (as assumed by the authors themselves). The present study, however, applied a crossover within-subject design. Half of the participants were tested first with chewing gum and then without chewing gum. Furthermore, conditions of assessment were kept constant over the course of the study. Therefore, the present findings provide evidence that gum chewing can adversely affect attention performance during the early phases of an attention task. This result is also consistent with the findings of previous studies reporting detrimental effects of gum chewing on attentional performance (Kohler et al., 2006; Rost et al., 2010; Tucha, Mecklinger, Maier, et al., 2004; Tucha et al., 2010). Since different attention tests have been applied in these studies the deficits observed appear not to be task dependent. The present study also found a beneficial effect of gum chewing on performance at later stages of an attention task. In the gumcondition, participants’ reaction time increased less with task duration than in the no-gum-condition (in particular in the period from the 20th to the 30th minute). Therefore, time-on-task appears to be a crucial mediating factor in the effects of gum chewing on attention. This assumption is supported by studies measuring the effects of repetitive movements and exercise on cognition. Recent overviews and meta-analyses of this research (e.g. Brisswalter, Collardeau, & Arcelin, 2002; Lambourne & Tomporowski, 2010) revealed that cognitive performance is reduced during the earlier phases (initial 10–20 min) but facilitated during the later phases of exercise (after 20 min). Furthermore, it has been shown that these effects depend on the type of exercise and the type of cognitive task
301
performed. It is assumed that cognitive functioning is compromised in the initial phases by a dual-task interference (Lambourne & Tomporowski, 2010). The consideration of the interaction between time and effect of gum chewing might considerably contribute to the discussion why some groups found positive and other negative effects of gum chewing on cognition. It is difficult to explain why there are different time-dependent effects of gum chewing on cognition. One might speculate that participants might be distracted by gum chewing during early stages of cognitive tasks or that certain biological processes (e.g. increase of regional cerebral blood flow) have to add up or reach a certain threshold to facilitate cognitive processing. The examination of the underlying factors of the time course of effects and the exact time course for different cognitive tasks or functions could be the aim of future studies. The present findings confirm our previous conclusions (Tucha, Mecklinger, Maier, et al., 2004) that gum chewing differentially affects attention and that claims stating that gum chewing improves cognition should be viewed with caution. References Baker, J. R., Bezance, J. B., Zellaby, E., & Aggleton, J. P. (2004). Chewing gum can produce context-dependent effects upon memory. Appetite, 43, 207–210. Brisswalter, J., Collardeau, M., & Arcelin, R. (2002). Effects of acute physical exercise characteristics on cognitive performance. Sports Medicine, 32, 555–566. Cohen, J. (1988). Statistical power analysis for the behavioral sciences. Hillsdale: Erlbaum. Cohen, R. A. (1993). The neuropsychology of attention. New York: Plenum Press. Houcan, Z., & Li, W. (2007). Effects of chewing gum on learning and memory. China Journal of Health Psychology, 15, 518–520. Johnson, A. J., & Miles, C. (2007). Evidence against memorial facilitation and contextdependent memory effects through the chewing of gum. Appetite, 48, 394–396. Johnson, A. J., & Miles, C. (2008). Chewing gum and context-dependent memory. The independent roles of chewing gum and mint flavour. British Journal of Psychology, 99, 293–306. Kline, P. (2000). Handbook of psychological testing. London: Routledge. Kohler, M., Pavy, A., & Van Den Heuvel, C. (2006). The effects of chewing versus caffeine on alertness, cognitive performance and cardiac autonomic activity during sleep deprivation. Journal of Sleep Research, 15, 358–368. Lambourne, K, & Tomporowski, P. (2010). The effect of exercise-induced arousal on cognitive task performance. A meta-regression analysis. Brain Research, 1341, 12– 24. Rost, D. H., Wirthwein, L., Frey, K., & Becker, E. (2010). Steigert Kaugummikauen das kognitive Leistungsvermoegen? Zwei Experimente der besonderen Art [Does chewing gum enhance cognitive abilities? Two rather extraordinary experiments]. Zeitschrift Fur Padagogische Psychologie, 24, 39–49. Scholey, A. (2004a). Chewing gum and cognitive performance. A case of a functional food with function but no food? Appetite, 43, 215–216. Scholey, A. (2004b). Further issues regarding the possible modulation of cognitive function by the chewing of gum. Response to Stephens and Tunney (2004) and Tucha et al. (2004). Appetite, 43, 221–223. Scholey, A., Haskell, C., Robertson, B., Kennedy, D., Milner, A., & Wetherell, M. (2009). Chewing gum alleviates negative mood and reduces cortisol during acute laboratory psychological stress. Physiology & Behavior, 97, 304–312. Smith, A. (2009a). Effects of caffeine in chewing gum on mood and attention. Human Psychopharmacology: Clinical and Experimental, 24, 239–247. Smith, A. (2009b). Effects of chewing gum on mood, learning, memory and performance of an intelligence test. Nutritional Neuroscience, 12, 81–88. Smith, A. (2010). Effects of chewing gum on cognitive function, mood and physiology in stressed and non-stressed volunteers. Nutritional Neuroscience, 13, 7–16. Stephens, R., & Tunney, R. J. (2004a). How does chewing gum affect cognitive function? Reply to Scholey. Appetite, 43, 217–218. Stephens, R., & Tunney, R. J. (2004b). Role of glucose in chewing gum-related facilitation of cognitive function. Appetite, 43, 211–213. Ta¨nzer, U., von Fintel, A., & Eikermann, T. (2009). Chewing gum and concentration performance. Psychological Reports, 105, 372–374. Tucha, L., Tucha, O., Walitza, S., Sontag, T. A., Laufkoetter, R., Linder, M., et al. (2009). Vigilance and sustained attention in children and adults with ADHD. Journal of Attention Disorders, 12, 410–421. Tucha, O., Mecklinger, L., Hammerl, M., & Lange, K. W. (2004). Effects of gum chewing on memory and attention. Reply to Scholey (2004). Appetite, 43, 219–220. Tucha, O., Mecklinger, L., Maier, K., Hammerl, M., & Lange, K. W. (2004). Chewing gum differentially affects aspects of attention in healthy subjects. Appetite, 42, 327–329. Tucha, L., Simpson, W., Evans, L., Birrel, L., Sontag, T. A., Lange, K. W., et al. (2010). Detrimental effects of gum chewing on vigilance in children with attention deficit hyperactivity disorder. Appetite, 55, 679–684. Wilkinson, L., Scholey, A., & Wesnes, K. (2002). Chewing gum selectively improves aspects of memory in healthy volunteers. Appetite, 38, 235–236. Zimmermann, P., & Fimm, B. (1993). A computerized neuropsychological assessment of attention deficits. Herzogenrath, Germany: PsyTest.
Contents lists available at ScienceDirect
Appetite journal homepage: www.elsevier.com/locate/appet
Short communication
The role of time on task performance in modifying the effects of gum chewing on attention Lara Tucha a,*, William Simpson b a
Department of Clinical and Developmental Neuropsychology, Faculty of Behavioural and Social Sciences, University of Groningen, Grote Kruisstraat 2/1, 9712 TS Groningen, The Netherlands b School of Psychology, University of Plymouth, United Kingdom
A R T I C L E I N F O
A B S T R A C T
Article history: Received 3 November 2010 Received in revised form 14 December 2010 Accepted 21 December 2010 Available online 28 December 2010
Recent research examined the effects of chewing gum on attention and reported a significant interaction of gum chewing with time. Using a crossover within-subject design, the present study examined the effect of gum chewing on sustained attention in healthy adults over a period of 30 min. The results revealed a significant main effect of time and a significant interaction between gum chewing and time. The findings suggest that gum chewing differentially affects attention performance. While gum chewing has detrimental effects on sustained attention in earlier stages of the task, beneficial effects on sustained attention were observed at later stages. ß 2010 Elsevier Ltd. All rights reserved.
Keywords: Chewing gum Vigilance Attention Time Cognition
Introduction It has been observed that the chewing of a piece of ordinary chewing gum can facilitate cognition (Baker, Bezance, Zellaby, & Aggleton, 2004; Houcan & Li, 2007; Johnson & Miles, 2008; Stephens & Tunney, 2004b; Wilkinson, Scholey, & Wesnes, 2002). With regard to attentional functioning, beneficial effects of gum chewing have been found on alertness, selective attention, language-based attention and sustained attention (Scholey et al., 2009; Smith, 2009b, 2010; Stephens & Tunney, 2004b; Tucha, Mecklinger, Maier, Hammerl, & Lange, 2004). This facilitation of cognitive functioning by gum chewing has been ascribed to a chewing-related increase of regional cerebral blood flow, in particular in fronto-temporal brain regions, and an enhanced release of insulin. However, several studies failed to replicate these findings or demonstrated that gum chewing may even adversely affect attentional functioning (Kohler, Pavy, & Van Den Heuvel, 2006; Rost, Wirthwein, Frey, & Becker, 2010; Smith, 2009a; Tucha, Mecklinger, Maier, et al., 2004; Wilkinson et al., 2002). The difficulties in replicating the results of studies have been attributed to methodological differences between studies. Comparisons between studies revealed that studies differed in regard to statistical power, the test procedures applied, the brands of chewing
* Corresponding author. E-mail address: [email protected] (L. Tucha). 0195-6663/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.appet.2010.12.021
gums used, the participants’ familiarity with chewing gum (because of their different nationalities), the experimental designs (withinversus between-subjects design, lack of baseline assessments), the statistical analyses performed (parametric versus non-parametric analysis) and possible changes in gum consistency and flavor during the course of the examination (Scholey, 2004a, 2004b; Stephens & Tunney, 2004a; Tucha, Mecklinger, Hammerl, & Lange, 2004). Although the studies differed in all of these aspects, it appears that no single factor or combination of factors can explain the disagreement of results of available studies. In a recent study a new idea was put forward that might explain why some studies found beneficial and others detrimental effects of gum chewing on cognition (Ta¨nzer, von Fintel, & Eikermann, 2009). This idea focuses on time as an important factor in the psychodynamics of gum chewing. In their study, Ta¨nzer et al. (2009) examined concentration performance in 8–9 year-old children by using a cancellation task for a period of 16 min. Children who chewed a piece of chewing gum throughout the test session performed more poorly than the children who did not chew gum. However, this difference was only present during the first part of the task. After the twelfth minute, children who chewed a piece of gum outperformed the children of the no-gumcondition. Statistical analysis revealed that the interaction between conditions (gum chewing versus no gum chewing) and test period (earlier parts versus later parts of the task) was significant. In their discussion, Ta¨nzer et al. (2009) mentioned that the poorer concentration performance of children chewing gum
L. Tucha, W. Simpson / Appetite 56 (2011) 299–301
might have resulted from a biased selection of children with regard to their concentration performance. However, since no baseline assessment of concentration performance of groups has been performed, this is only one possible speculation. On the basis of the available literature, one could also assume that gum chewing might have detrimental or no effects on performance at earlier stages of tasks and beneficial effects at later stages. This explanation receives some support by a closer inspection of the sequence and timing of tests as applied in available studies. While some studies reporting beneficial effects of gum chewing on cognition observed the effects in tests that were performed during later stages of assessment (e.g. Smith, 2009b, 2010; Tucha, Mecklinger, Maier, et al., 2004; Wilkinson et al., 2002), studies that failed to replicate these effects performed similar measures at the beginning of assessment (e.g. Johnson & Miles, 2007; Tucha, Mecklinger, Maier, et al., 2004). However, the evidence provided by an inspection of the test sequences as used in published studies is not clear-cut because there is a lack of detail in publications concerning the exact timing and duration of tasks. Furthermore, positive effects of gum chewing on cognition were also observed at early stages of assessment (Smith, 2009a; Wilkinson et al., 2002). Therefore, it remains unclear whether time represents a mediating factor in the effects of gum chewing on cognition. The aim of the present study was to examine the impact of gum chewing on cognitive performance over a prolonged period of time. Using a computerized task that has been shown to be sensitive to the effects of gum chewing (Tucha, Mecklinger, Maier, et al., 2004), attention performance of healthy adults was registered for a period of 30 min. Methods Forty-two healthy adults participated in the present study (21 female, 21 male; mean age = 22.2 years, SD = 2.4 years). The study used a crossover design in which participants were assessed both with chewing gum (gum-condition) and without chewing gum (no-gum-condition). In the gum-condition, participants were asked to chew naturally and constantly a piece of spearmint flavored sugar-free chewing gum throughout the whole test session. Half of the participants were tested first with chewing gum and then without chewing gum. The remaining participants were examined in the reverse order. Participants were randomly assigned to the starting condition. Participants were tested individually in two sessions on subsequent days. The study was approved by the ethics committee of the University of Plymouth, UK. Written informed consent was obtained from all participants. A computerized attention test was performed for the measurement of sustained attention (Zimmermann & Fimm, 1993). The test was presented on a computer screen. Instructions were given orally. Participants were instructed to perform the computerized test as quickly as possible but to maintain a high level of accuracy. A brief sequence of practice trials preceded the test in order to familiarize the participants with the task. In the attention test, a structure consisting of two squares was presented in the centre of the computer screen. One square was situated on top of the other. These squares were alternately filled with a pattern (stimulus) for 500 ms with an interstimulus interval of 1000 ms. The duration of the test was 30 min. The participants were requested to press a button when no change of the pattern location occurred. The target rate (i.e. no change of pattern location) was about one target stimulus per minute. The time intervals between target stimuli were irregular. Reaction time for correct responses was recorded. To measure the effect of time on task performance, the whole task was divided into six consecutive time blocks of 5 min (1st time block: 1st to 5th minute; 2nd time block: 6th to 10th minute; 3rd time block: 11th to 15th minute; 4th time block: 16th to 20th
minute; 5th time block: 21st to 25th minute; 6th time block: 26th to 30th minute). Statistical analysis was performed using a 2 6 MANOVA (condition by time block). Normal distribution of data was analyzed using Kolmogorov–Smirnov tests. For statistical analysis an alpha level of p < .05 was applied. All analyses were carried out using SPSS 16.0 for Windows. Furthermore, the index h2 (eta squared) was calculated. According to Cohen (1988) a small effect size corresponds to an h2 = .0099, a medium effect size to an h2 = .0588 and a large effect size to an h2 = .1379. Post hoc analysis was performed using paired t-tests. A determination of the required sample size in this type of studies with multiple within-subject factors is in general very complicated, in particular because available research did not provide sufficient information concerning the magnitude of the effects of gum chewing on cognition over a prolonged period of time. Ta¨nzer et al. (2009) who found that time is a mediating factor in the psychodynamics of gum chewing unfortunately reported only mean scores but not standard deviations. This makes an analysis of effect sizes impossible. Tucha, Mecklinger, Hammerl, et al. (2004) and Tucha, Mecklinger, Maier, et al. (2004) also considered the effect of time on attention performance in a previous study by calculating ipsative mean scores of participants’ performance. From these data a medium effect (i.e. effect sizes between .5 and .6 SD) can be estimated. Considering this range of effect sizes and setting power at .80 and the significance criterion at .05, sample sizes between 35 and 50 per cell appear to be sufficient (Cohen, 1988). With sample sizes of 42 per cell, this criterion was achieved in the present study. Results There was no evidence to reject the assumption of normal distribution of reaction time data. Because of a violation of the sphericity assumption, the Greenhouse–Geisser correction was employed. Multivariate analysis of variance (MANOVA) revealed a significant main effect of time block (F(4.06, 205) = 17.13, p < .001, Greenhouse–Geisser corrected). The effect size for this difference in reaction time was large (h2 = .295). Subsequent post hoc analysis [()TD$FIG] using paired t-tests (Bonferroni adjusted) indicated that the 750
700
Reaction time (in ms)
300
650
600
550
500 1st time 2nd time 3rd time 4th time 5th time 6th time block block block block block block gum condition
no-gum condition
Fig. 1. Reaction times (in ms) of participants in the two conditions across the six time blocks (means SE).
L. Tucha, W. Simpson / Appetite 56 (2011) 299–301
reaction times shown during the first two 5 min blocks (1st to 10th minute of task) differed significantly (p < .001) from the reaction times during the remaining 5 min blocks (11th to 30th minute). The remaining pairwise comparisons did not reach significance (p > .05). Furthermore, there was a significant condition by time block interaction (F(3.73, 205) = 5.22, p = .001, Greenhouse–Geisser corrected) indicating a medium effect (h2 = .113). The difference between conditions was not significant (F(1, 41) = .61, p = .439) and represented only a small effect (h2 = .015). Test performances of participants are presented in Fig. 1. An additional analysis in which the order of gum condition was included revealed no significant effect regarding the order of gum condition (results not shown). Discussion In the present study, the effect of gum chewing on attentional functioning over a prolonged period of time was examined. Attentional functioning was assessed by performing a computerized sustained attention task. Reaction time was measured for each of six consecutive time blocks of 5 min so that changes in test performance over time could be analyzed. An analysis of the number of omission and commission errors was not included in the present study, because errors in healthy participants have been found to be a rare phenomenon (Tucha et al., 2009) in particular when analyzing time periods of only 5 min (number of omission and commission errors < 1). Moreover, the reliability of examinations based on the observation of short test scales and rare events is usually very small (Kline, 2000). The present results suggest that there is a significant main effect of time denoting an increase of reaction times with task duration. This time-on-task effect is not surprising considering that the whole concept of sustained attention is based on the robust finding that human performance deteriorates over time (Cohen, 1993). The condition by time block interaction also reached significance. Similar to the findings of Ta¨nzer et al. (2009), the performance of participants in the gum-condition was poorer during the first part of the task (first 10 min) than in the no-gum-condition. One may argue that the findings of Ta¨nzer et al. (2009) might have resulted from a biased selection and group allocation of participants to conditions (as assumed by the authors themselves). The present study, however, applied a crossover within-subject design. Half of the participants were tested first with chewing gum and then without chewing gum. Furthermore, conditions of assessment were kept constant over the course of the study. Therefore, the present findings provide evidence that gum chewing can adversely affect attention performance during the early phases of an attention task. This result is also consistent with the findings of previous studies reporting detrimental effects of gum chewing on attentional performance (Kohler et al., 2006; Rost et al., 2010; Tucha, Mecklinger, Maier, et al., 2004; Tucha et al., 2010). Since different attention tests have been applied in these studies the deficits observed appear not to be task dependent. The present study also found a beneficial effect of gum chewing on performance at later stages of an attention task. In the gumcondition, participants’ reaction time increased less with task duration than in the no-gum-condition (in particular in the period from the 20th to the 30th minute). Therefore, time-on-task appears to be a crucial mediating factor in the effects of gum chewing on attention. This assumption is supported by studies measuring the effects of repetitive movements and exercise on cognition. Recent overviews and meta-analyses of this research (e.g. Brisswalter, Collardeau, & Arcelin, 2002; Lambourne & Tomporowski, 2010) revealed that cognitive performance is reduced during the earlier phases (initial 10–20 min) but facilitated during the later phases of exercise (after 20 min). Furthermore, it has been shown that these effects depend on the type of exercise and the type of cognitive task
301
performed. It is assumed that cognitive functioning is compromised in the initial phases by a dual-task interference (Lambourne & Tomporowski, 2010). The consideration of the interaction between time and effect of gum chewing might considerably contribute to the discussion why some groups found positive and other negative effects of gum chewing on cognition. It is difficult to explain why there are different time-dependent effects of gum chewing on cognition. One might speculate that participants might be distracted by gum chewing during early stages of cognitive tasks or that certain biological processes (e.g. increase of regional cerebral blood flow) have to add up or reach a certain threshold to facilitate cognitive processing. The examination of the underlying factors of the time course of effects and the exact time course for different cognitive tasks or functions could be the aim of future studies. 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