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Influence of test tasks with different cognitive demands on salivary cortisol concentrations in school students
International Journal of Psychophysiology 86 (2012) 245–250
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International Journal of Psychophysiology journal homepage: www.elsevier.com/locate/ijpsycho
Influence of test tasks with different cognitive demands on salivary cortisol concentrations in school students N. Minkley ⁎, W.H. Kirchner Ruhr University Bochum, Faculty of Biology and Biotechnology, Behavioural Biology and Biology Education, Universitätsstr. 150, D-44801 Bochum, Germany
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Article history: Received 19 July 2012 Received in revised form 25 September 2012 Accepted 28 September 2012 Available online 5 October 2012 Keywords: Cortisol Saliva Realistic test situation School students Social-evaluative threat Examination
a b s t r a c t This study aimed to investigate the effects of test tasks with different cognitive demands on salivary cortisol concentrations in school students. The salivary cortisol levels of 93 students (56 males and 37 females, mean age 17.86 yrs.) were measured before and after 2 brief tests and 2 control situations, respectively. One of the tests comprised reproductive, the other transfer and problem-solving tasks. In the control groups, students were instructed to either write whatever they want, or to wait. Statistical analysis (ANOVA) indicated a significant main effect of the experimental treatment on the cortisol response. The cortisol increase was significantly higher following the reproduction tasks as compared to both control conditions. Although not significant the cortisol increase during reproduction tasks was over twice as much in males compared to females. In contrast the increase during transfer and problem solving tasks does not differ significantly from the control conditions under which the cortisol concentration remains nearly the same and decreases respectively. These findings indicate an influence of the task demand on the cortisol concentration. Furthermore, it can be assumed that reproduction tasks in particular have the potential to be a major stressor during school examinations. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The main aim of the current investigation was to investigate the extent to which tasks with differing cognitive demands can influence the cortisol concentration of school students, and whether their sex modulates this hormonal reaction. Previous investigations have already shown that examination situations, as well as examination periods are stressors for students (Allen et al., 1985; Jones et al., 1986; Malarkey et al., 1995; Lacey et al., 2000; Martinek et al., 2003; Gaab et al., 2006; Katsuura et al., 2010), which can lead to an increase in cortisol levels. However, some studies have described a decrease in cortisol concentrations between pre- and post-examination measurements (Vedhara et al., 2000; Ng et al., 2003; Martinek et al., 2003), and no effect of the examination period itself (Malarkey et al., 1995). It could not be ascertained, however, whether the test situation in itself leads to the cortisol increase, or whether specific single parameters (e.g., anticipation, social-evaluative threat, cognitive effort, and demand) are responsible. Some of these potentially stressful aspects have been previously investigated separately. Previous studies have revealed an anticipatory cortisol reaction prior to the examination (Lacey et al., 2000; Martinek et al., 2003; Verschoor and Markus, 2011). In these studies, the pre-examination cortisol level was found to be significantly higher when compared to both a control-day and a control-group. After a ⁎ Corresponding author. Tel.: +49 234 32 29020; fax: +49 234 32 14011. E-mail address: [email protected] (N. Minkley). 0167-8760/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijpsycho.2012.09.015
test situation, some authors observed a further cortisol increase (Allen et al., 1985), no cortisol increase (Johansson et al., 1983), or even a cortisol decrease (Martinek et al., 2003; Gaab et al., 2006; Pletzer et al., 2010) compared to measurements taken before the examination. Taken together, these findings indicate that the major stressor seems to be the anticipation of being tested, rather than the test situation itself. However, one possible reason for the limited increase in cortisol during the test itself could be the fact that cortisol activates a negative feedback loop (Rensing et al., 2006) that may lead to a decrease in cortisol levels following an initial peak. Such a negative feedback effect was previously observed in the laboratory study of McCann et al. (1993), in which cortisol concentrations showed an initial peak, and then decreased back to the baseline concentration after a 1-hour task. Thus, these participants may have reacted with a down regulation of cortisol to a long-term cognitively demanding situation, which is also likely to apply to examination situations. Additionally, social-evaluative threat can be an effective factor for raising cortisol concentrations (Dickerson and Kemeny, 2004). This effect was observed when cortisol levels were measured before and after exposure to psychosocial stress during the ‘Trier Social Stress Test’ (TSST) (Kirschbaum et al., 1993). After the TSST (which consists of a free speech concerning the subject's suitability for employment in a mock job interview in front of an evaluation panel), the cortisol concentration increased significantly above baseline in the majority of the participants (Kirschbaum et al., 1993; Schommer et al., 2004). In contrast, the cortisol concentration showed a decline following the placebo version of the TSST, where the participants were required
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to talk about a superficial (not self-relevant) topic, without an evaluation panel (Het et al., 2009). Thus, Het et al. concluded that the missing social-evaluative threat and uncontrollability prevented the cortisol reaction, which is consistent with the theory of Dickerson and Kemeny (2004). The social-evaluative threat could also play a key role in naturalistic test situations, where personal performance is measured by tasks imposing various degrees of cognitive demand. Another influencing parameter might be the cognitive effort involved in a task. However, several previous studies have shown that cognitive effort alone does not correspond to a strong cortisol increase. Frankenhaeuser (1982) distinguished between the effects of effort and distress on cortisol concentrations. She considered effort as being primarily related to catecholamine secretion, and distress to cortisol secretion. These conclusions were later confirmed by, for example, the laboratory study of Peters et al. (1998), where participants showed a cortisol decrease following tasks with high effort and controllability. In this study, only tasks with high effort and uncontrollability lead to a cortisol increase. Thus, Peters et al. concluded that it is the uncontrollability of a task that leads to a cortisol increase, not the cognitive effort required. However, it remains unclear to what extent the various cognitive efforts and demands of naturalistic tasks (e.g., in schools) influence cortisol secretion. According to the common classification of learning objectives by Bloom et al. (1956), and its revision by Anderson et al. (2000), tests and examinations in schools comprise several tasks which differ in their demand and thus examine the achievement of different learning objectives. Both authors pointed out that learning takes place at different levels, with the higher levels depending on previously acquired knowledge and skills. This means that one needs to be able to reproduce knowledge (and skills) before she/he is able to transfer it, or to use it to solve a problem. Although Marzano and Kendall (2007) designed a partially contradictory new taxonomy of educational objectives, they agree that the reproduction level builds the basis of this hierarchy. Therefore, in our study, we decided to use this school-specific distinction between reproduction and transfer or problem-solving tasks to investigate whether these different cognitive demands influence cortisol secretion to different degrees. Besides test specific aspects which may modulate the cortisol reaction, individual differences between students could also contribute to the cortisol change. For instance, in various studies male students display a greater increase in cortisol levels than their female counterparts (e.g., Frankenhaeuser et al., 1978; Kirschbaum et al., 1995; Kudielka and Kirschbaum, 2005; Schoofs and Wolf, 2011). In addition, several studies indicate a correlation between specific gene polymorphisms and cortisol reactivity (e.g., Wüst et al., 2004; Brummett et al., 2012). Furthermore, a study by Murphy et al. (2010) revealed that an individual's behavior during a stressful period could influence cortisol concentrations: students who spent more time studying during the examination week showed significantly lower cortisol concentrations. 2. Materials and methods 2.1. Participants All of the 93 participants were students of biology courses at secondary or comprehensive schools (n = 13) in Bochum or nearby cities. Students with the following attributes were excluded from this study because of possible confounding effects on cortisol levels: smoking, over or underweight (BMI above 25 kg/m 2 or below 18.5, respectively), use of any long-term medication or oral contraceptives, or presence of a medical condition (Foley and Kirschbaum, 2010). In addition, 4 students were excluded because of blood contamination or an insufficient amount of saliva for cortisol measurement. The experiment was conducted in accordance with the Declaration of Helsinki and was approved by the ethics commission for the medical
school of the University of Bochum. All participants provided written informed consent.
2.2. Experimental conditions In this study the participants were randomly assigned to one of the four different treatment groups: The first group was asked to deal with tasks associated with the reproduction of knowledge (hereafter referred to as “reproduction,” e.g., “describe the eight steps of our DNA-extraction protocol”), while students assigned to the second group were asked to deal with tasks associated with transfer and problem-solving (hereafter referred to as “transfer”, e.g., “present a possibility to shorten the DNA-extraction protocol”). All tasks dealt directly with processing the information that the students had recently learned during the previous 2 h at the laboratory, in order to prevent the effects of different previous knowledge. The third group served as the control for the writing activity (hereafter referred to as “control”). Students in this group were free to write anything (only 5 suggestions were given, for instance, they were asked to write about their hobbies), while their course mates took the tests. The fourth group also served as a control. In this group (“no test”) the students were required to sit quietly without anticipating a test situation. Thus, they were informed about their purpose before any of the participants know that the stressor will be a short written test. 2.3. Experimental time line The experimental procedure starts approximately 2 h after the commencement of the project (11 AM) with the briefing of the students (duration: 10 min). Thereafter (11.10 AM), the first saliva sample was taken (duration: 5 min) to identify the cortisol baseline. At 11.15 AM the “no test” group was informed that they just have to sit down and wait. Thereafter (11.20 AM), the remaining students prepared themselves for the test (duration: 5 min). Then (11.25 AM), the test (duration: 10 min) started by the distribution of three different task sheets. After the end of the test (11.35 AM), the students collected the second saliva sample at 11.40 AM. Thus, the experiment ended at about 11.45 AM. The timeframe for the collection of the saliva samples, as well as the collection of the samples in the morning, was based on logistics. The project ended at approximately 2.30 PM, with a lunch break between 12 and 1 PM. Thus, we were unable to collect the saliva sample in the afternoon due to possible contamination with food or drink. But, as the students had to travel to the students' laboratory before the project started (9 AM), we can be sure that we measured the hormonal reaction after the cortisol peak concentration (awakening response). Furthermore, we have assessed their average awakening time which was between 6 AM and 7 AM. Thus, they were awake for at least 4 h before we collected the saliva. Furthermore, we aimed to test the students in relatively standardized conditions (same location, time of the day, tutor, information, etc.). Therefore, we were dependent on students participating in the laboratory projects, and we had to conduct our tests in a time interval where no project experiments were taking place. This was between 11 and 11.30 AM, requiring collection of the second sample after 15 instead of 20 min, when we would expect the peak cortisol reaction to occur. 2.4. Experimental procedure Subjects participated in a 1-day project on molecular biology at the Alfried-Krupp student laboratory located at the Ruhr University in Bochum. The project encompassed receiving molecular biology instructions and performing hands-on experiments to identify the students own mitochondrial haplotype.
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One hour before the experiment started, the participants were instructed not to ingest any food or drink in order to eliminate possible contaminations of their saliva. At the beginning of the experiment a short introduction about the objectives and the procedure of the investigation was given. Then, the first saliva sample was collected in order to identify the cortisol baseline. Thereafter, the students of the “no test” group were randomly assigned and informed about their purpose, because these students should be tested without anticipating a test situation. Then, the remaining students were informed that they would be required to answer a short written test based on the facts they recently learned during the molecular biology project. The test started when three different task sheets (each including 5 questions) were distributed among the participants, and they were thus randomly assigned to 1 of the 3 remaining treatment groups. All students had to complete the test within a time frame of 10 min. The second saliva sample (post-test) was collected as soon as possible after the end of the test, resulting in a time interval of approximately 15 min between the onset of the stressor (reading the tasks which the students had to complete) and the start of the second saliva sampling. The relatively short time interval of 10 min for the test was chosen because preliminary investigations showed that most of the students stopped taking the tasks seriously if they were dealing with them for a longer period of time (15 min), indulging in conversation with their neighbors, etc. In order to enhance the stress during the test the remaining time was announced after 5 min and again after 8 min. 2.5. Assessment of performance For the rating of test performance, the suggested solutions were derived from the information which the students had received before the test started. For each correct answer or explanation, 1 point was given. Thereby, we were able to rate the performance of each student in comparison with the maximum possible number of points. The tasks were graded before the cortisol analysis started. 2.6. Cortisol assessment Saliva samples were collected by unstimulated passive drool through a shortened straw into polypropylene micro tubes (Sarstedt, Nürmbrecht, Germany). Immediately after collection, samples were stored at − 20 °C. On the following day, samples were thawed at room temperature, vortexed, and centrifuged at 2500 × g for 15 min. The supernatant was transferred to a new micro tube and frozen (− 20 °C) until assay. On the day of the assay (no later than 2 weeks after sampling), the samples were thawed, vortexed, and centrifuged again. Then, the supernatant of each probe was transferred in duplicate into a precoated micro-well plate. Cortisol levels were quantified using the cortisol saliva immunoassay kit from DRG (Marburg, Germany). Analyses were carried out using a 96-well ELISA reader (Thermo Fisher, Vantaa, Finland). Intra-assay coefficients of variance were below 7% and inter-assay coefficients were below 11%.
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analyzed by Hochberg's GT2 post hoc test, which controls for the type I error rate and is adapted for varying sample sizes (Field, 2009). The analyses include the partial η 2 as measure of effect size. Following the classification of Cohen (1973), partial η 2 = 0.01 is considered as a small, 0.06 as a medium-sized, and 0.14 as a large effect. Overall level of significance was defined as p b 0.05. Statistical analyses were performed using SPSS 20 (IBM).
3. Results The total sample consisted of 56 male and 37 female participants with a mean age of 17.86 yrs. (±0.096 S.E.M.) and a mean BMI of 22.17 kg/m 2 (± 0.35 S.E.M.). There was no significant intergroup difference in the distribution according to sex, age, or BMI (p > 0.05).
3.1. Influence of different cognitive demand tasks on salivary cortisol concentrations A clear increase in the salivary cortisol concentration was seen in the “reproduction” group. Cortisol elevation was also observed in the “transfer” group, but this increase was much smaller. In the control group (where the students wrote about their hobbies, etc.), the cortisol change between pre and post measurement was very small and in contrast to all other groups, the cortisol concentration decreased between the first and the second measurement in the group who did not write anything (“no test”; Table 1, Fig. 1). The repeated measurement ANOVA including the repeated measurement factor TIME (before test vs. after test) and the between group factors TREATMENT (reproduction, transfer, control and no test) and SEX (men vs. women) showed a significant main effect for TREATMENT (F(3, 85) = 6.173; p b 0.01, η 2 = 0.179) whereas the effects for TIME (F(1, 85) = 3.111; p > 0.05, η 2 = 0.035) and SEX (F(1, 85) = 0.705; p > 0.05, η 2 = 0.008) were not significant. Furthermore, a significant TIME ∗ TREATMENT (F(3, 85) = 8.483; p b 0.001, η 2 = 0.23) interaction was observed. The ANOVA yielded no significant results for the TIME ∗ SEX (F(1, 85) = 1.501; p > 0.05, η 2 = 0.017) and TIME ∗ TREATMENT ∗ SEX (F(3, 85) = 0.545; p > 0.05, η 2 = 0.019) interactions. The subsequent univariate analysis of variance revealed a significant main effect, with a large effect size, of the factor TREATMENT on the cortisol change (F(3, 85) = 5.130, p b 0.01, η 2 = 0.153). Post hoc Hochberg's GT2 test indicated that the cortisol increase was significantly higher during the test associated with reproduction tasks than under either control condition (p b 0.05). However, the cortisol increase occurring during transfer and problem-solving tasks was not significantly different compared to the control conditions (Fig. 1). The independent variable SEX had no significant effect on the cortisol change (F(1, 85) = 1.995, p > 0.05, η 2 = 0.023). However, male students showed a higher cortisol increase compared to female students when dealing with reproduction or transfer and problemsolving tasks (Fig. 2). There was also no significant interaction effect between TREATMENT∗ SEX (F(3, 85) = 0.592, p > 0.05, η 2 = 0.020).
2.7. Statistical analysis Demographic and descriptive variables were analyzed using Pearson's Chi-square-tests and Student's t-tests. Cortisol concentrations were first analyzed by a repeated measure ANOVA. Data were log-transformed when appropriate and Greenhouse–Geisser adjusted p values are reported in case of violated sphericity assumption. Thereafter, we calculated the cortisol response defined as the difference between pre and post measurement and subjected these values to a one-way ANOVA. Significant main effects were further
Table 1 Raw values of cortisol concentrations (nmol/L) under each test condition at the different collection times (mean ± S.E.M.) and their change. Treatment
n
Before test
After test
Δ [nmol/L]
Δ [%]
Reproduction Transfer Control No test
25 20 28 20
8.71 ± 1.17 11.98 ± 1.51 9.59 ± 0.97 6.45 ± 0.54
11.48 ± 1.57 13.26 ± 1.82 9.85 ± 1.06 5.50 ± 0.38
2.77 ± 0.81 1.28 ± 0.65 0.26 ± 0.33 −0.95 ± 0.44
33.89 ± 6.61 10.28 ± 4.53 4.35 ± 3.99 −7.75 ± 7.47
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Fig. 1. The increase in cortisol was significantly higher after the reproduction tasks (n = 25) compared to the cortisol change under both control conditions (“control” n = 28; “no test” n = 20) (**p b 0.001, *pb 0.05). Values are presented as mean ± S.E.M.
3.2. Test performance The students' test performance was distributed normally (Kolmogorov–Smirnov, p > 0.05). Only 12% (reproduction) or 15% (transfer and problem-solving) of the students achieved more than half of the possible points. However, test performance in both kinds of tasks does not correlate significantly with the height of the cortisol change (p > 0.12, Pearson). 4. Discussion Examination situations such as oral and written examinations are widely known as stressors that raise the cortisol concentration in most participants (Martinek et al., 2003). In particular, test situations that have a strong social-evaluative component (e.g., oral examinations) are likely to be powerful stressors and, thus, cause a large cortisol
5 Female Male
Cortisol Change [nmo1/L]
4
3
2
1
0 Reproduction
Transfer
Treatment Group Fig. 2. Male students (n = 18) showed a higher cortisol increase compared to female students (n = 7) when dealing with reproduction tasks; the difference was, however, not significant (p > 0.10). This difference was much smaller between male (n = 9) and female students (n = 11) dealing with transfer and problem-solving tasks. Values are presented as mean ± S.E.M.
increase (Martinek et al., 2003; Dickerson and Kemeny, 2004; Schoofs et al., 2007). As mentioned above, other aspects of examination situations (e.g., anticipation) have been investigated for their potential to raise cortisol concentrations, but the extent to which realistic test tasks with a variety of cognitive demands influence the cortisol response remains unclear. To provide a stressor that is as naturalistic as possible within an experimental laboratory design, we used a brief test (a frequent situation in schools) with questions typical of different cognitive demands in a completely anonymous situation. In this testing situation we were able to investigate the hormonal stress reaction in the context of realistic (school) tasks under standardized conditions. Furthermore, the test performance should not have a strong social-evaluative component for the participants. Nevertheless, cortisol levels increased during the test as compared to baseline concentrations. Therefore, in our study, confrontation with the test tasks themselves was responsible for raising cortisol concentrations — the response was not dependent on whether the test has real life consequences. Unexpectedly, cortisol increase was greatest when test tasks were associated with simple knowledge reproduction. In the tests comprising the more complex tasks (transfer and problem-solving), the cortisol concentration was also increased, but without statistical significance. Thus, for the present study, the demand of the task was correlated with the extent of the cortisol reaction independently of the task's relative complexity. A possible explanation for this finding lies in the fact that in the reproduction tasks, participants had to answer questions that tested their knowledge retrieval (e.g., “describe the eight steps of the DNA-extraction protocol”); thus, they would immediately know whether they are capable of describing the steps easily, or whether they would have difficulties in their retrieval. Moreover, even if the students remembered most of the steps, they may feel that they are being imprecise using their own words, because none of them reproduced the exact wording that they have heard before. Therefore, they may perceive a degree of helplessness and distress, which are associated with increased cortisol secretion (Frankenhaeuser, 1982; Weiner, 1992). Concerning the transfer and problem-solving tasks in which students were asked, for example, to develop possibilities to shorten the DNA-extraction protocol, there was a little possibility of controlling their own performance. For instance, students could propose an unfeasible protocol, without knowing it. Furthermore, due to the task structure, they could not rely on any precise description they may have heard before. Thus, they may perceive effort without (a lot of) distress if they are able to write something down (regardless of whether it is right, wrong, or imprecise) instead of reproducing facts that could be right or wrong. As mentioned before, such a combination (effort without distress) leads to catecholamine secretion rather than cortisol secretion (Frankenhaeuser, 1982). Therefore, it would be interesting to measure the catecholamine secretion in combination with different demanding tasks in future studies, and also the students' subjective rating of task difficulty. Furthermore, performance on the test did not correlate with the cortisol change, which is in accordance with the findings of Schoofs et al. (2007). In their study, they did not detect an association between the cortisol concentrations and academic performance (received grade). Moreover, analysis of the independent variable, sex, showed no significant influence on cortisol concentrations. The hormonal increase was present in both sexes for the reproduction as well as the transfer and problem-solving tasks. However, a greater cortisol response occurred in boys than in girls, although this difference was not significant. This finding is consistent with many previous studies showing greater cortisol responses in males than in females in laboratory studies, as well as in studies using naturalistic stressors (e.g., Frankenhaeuser et al., 1978; Kirschbaum et al., 1995; Kudielka and Kirschbaum, 2005). In contrast to the participants who were dealing with the test tasks or the free writing task, those who did not have to write anything, but just sat down and waited for 10 min, showed a cortisol
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decrease. Besides the fact that they did not have to write anything, they also did not anticipate writing a test (they were directly informed that they just have to sit down and wait). Thus, they perceived neither the stressor “task” nor “anticipation”. However, their cortisol decrease was not significantly different to the increase in the other control group (who were anticipating writing a test for the few minutes until they received their task sheet). Therefore, the relatively short period of anticipation of being tested soon had no significant influence on cortisol concentrations, as expected. The cortisol decline of the “no test” group could be rather explained by the fact that the participants in this group had time to relax while they waited. In contrast to our results, prior studies with a longer anticipation period prior to naturalistic examination situations showed a clear cortisol increase directly before a written examination (Lacey et al., 2000; Martinek et al., 2003; Pletzer et al., 2010; Preuß et al., 2010). These authors concluded that the expectation of taking part in an examination leads to an increase in cortisol concentration. Some studies have even shown that the cortisol reaction in examination situations is mainly an anticipatory effect, as they observed no further elevations after the test (Johansson et al., 1983), or even a cortisol decrease (Martinek et al., 2003; Gaab et al., 2006; Preuß et al., 2010). Although this finding may be due to the negative feedback function of the hormonal system (as mentioned above), the anticipation effect of examination situations is undisputed. Additionally, some authors (Martinek et al., 2003; Schoofs et al., 2007; Preuß et al., 2010) have demonstrated that a high socialevaluative threat, such as that which occurs during oral presentations or examinations, leads to a significant cortisol increase from pre- to post-measurements. However, since the test situation in our study was anonymous, and thus without high social evaluation, we can (virtually) exclude a high influence of social-evaluative threat on the observed cortisol increase. However, the students might receive a kind of evaluation by the observer who was announcing the remaining time and monitoring their progress. Furthermore, they might feel evaluated as a group which might also cause a feeling of social-evaluation. But, as the cortisol increase was only significant during the reproduction tasks this social-evaluative treat could not be responsible for it solely. However, in contrast to our test situation, naturalistic tests, as well as tasks in school, can be a highly effective social-evaluative threat. As Dickerson and Kemeny (2004) pointed out, such a threat occurs when an important aspect of the self-identity could be negatively judged by teachers or course mates. Furthermore, they considered intelligence and competence, which are key abilities for solving tests and tasks, as core attributes of the self-identity. Therefore, it would be interesting to measure the cortisol concentration of students during reproductive as well as transfer and problem-solving tasks in a naturalistic and personally relevant school test or examination. It is noteworthy that in our experimental design, the high cortisol elevation during the reproduction tasks might well be independent of an anticipation effect and of a high social evaluative threat. On the contrary, the observed increase in cortisol levels might be a reaction to the confrontation with the specific demand of these tasks, and thus, the subjective difficulties/inability of answering them correctly. Albeit indicative, the separation of different cognitive demands in our study was relatively rough. It would therefore be informative to analyze hormonal reactions (cortisol and alpha-amylase) using finer graduations of cognitive demands. The results of these future studies (cortisol measurement during different tasks in school examinations and finer graduated demands) together with the present results could be used to provide possibilities to reduce the stress inducing aspects of test situations. One of this possibilities might be the focusing on transfer and problem solving tasks, where teachers can also assess the retrieval of knowledge but in a less obvious and stressful way.
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Acknowledgments Thanks to O. T. Wolf and C. Schulz for critically reading the manuscript and insightful comments. We also thank R. Evans for proofreading.
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International Journal of Psychophysiology journal homepage: www.elsevier.com/locate/ijpsycho
Influence of test tasks with different cognitive demands on salivary cortisol concentrations in school students N. Minkley ⁎, W.H. Kirchner Ruhr University Bochum, Faculty of Biology and Biotechnology, Behavioural Biology and Biology Education, Universitätsstr. 150, D-44801 Bochum, Germany
a r t i c l e
i n f o
Article history: Received 19 July 2012 Received in revised form 25 September 2012 Accepted 28 September 2012 Available online 5 October 2012 Keywords: Cortisol Saliva Realistic test situation School students Social-evaluative threat Examination
a b s t r a c t This study aimed to investigate the effects of test tasks with different cognitive demands on salivary cortisol concentrations in school students. The salivary cortisol levels of 93 students (56 males and 37 females, mean age 17.86 yrs.) were measured before and after 2 brief tests and 2 control situations, respectively. One of the tests comprised reproductive, the other transfer and problem-solving tasks. In the control groups, students were instructed to either write whatever they want, or to wait. Statistical analysis (ANOVA) indicated a significant main effect of the experimental treatment on the cortisol response. The cortisol increase was significantly higher following the reproduction tasks as compared to both control conditions. Although not significant the cortisol increase during reproduction tasks was over twice as much in males compared to females. In contrast the increase during transfer and problem solving tasks does not differ significantly from the control conditions under which the cortisol concentration remains nearly the same and decreases respectively. These findings indicate an influence of the task demand on the cortisol concentration. Furthermore, it can be assumed that reproduction tasks in particular have the potential to be a major stressor during school examinations. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The main aim of the current investigation was to investigate the extent to which tasks with differing cognitive demands can influence the cortisol concentration of school students, and whether their sex modulates this hormonal reaction. Previous investigations have already shown that examination situations, as well as examination periods are stressors for students (Allen et al., 1985; Jones et al., 1986; Malarkey et al., 1995; Lacey et al., 2000; Martinek et al., 2003; Gaab et al., 2006; Katsuura et al., 2010), which can lead to an increase in cortisol levels. However, some studies have described a decrease in cortisol concentrations between pre- and post-examination measurements (Vedhara et al., 2000; Ng et al., 2003; Martinek et al., 2003), and no effect of the examination period itself (Malarkey et al., 1995). It could not be ascertained, however, whether the test situation in itself leads to the cortisol increase, or whether specific single parameters (e.g., anticipation, social-evaluative threat, cognitive effort, and demand) are responsible. Some of these potentially stressful aspects have been previously investigated separately. Previous studies have revealed an anticipatory cortisol reaction prior to the examination (Lacey et al., 2000; Martinek et al., 2003; Verschoor and Markus, 2011). In these studies, the pre-examination cortisol level was found to be significantly higher when compared to both a control-day and a control-group. After a ⁎ Corresponding author. Tel.: +49 234 32 29020; fax: +49 234 32 14011. E-mail address: [email protected] (N. Minkley). 0167-8760/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijpsycho.2012.09.015
test situation, some authors observed a further cortisol increase (Allen et al., 1985), no cortisol increase (Johansson et al., 1983), or even a cortisol decrease (Martinek et al., 2003; Gaab et al., 2006; Pletzer et al., 2010) compared to measurements taken before the examination. Taken together, these findings indicate that the major stressor seems to be the anticipation of being tested, rather than the test situation itself. However, one possible reason for the limited increase in cortisol during the test itself could be the fact that cortisol activates a negative feedback loop (Rensing et al., 2006) that may lead to a decrease in cortisol levels following an initial peak. Such a negative feedback effect was previously observed in the laboratory study of McCann et al. (1993), in which cortisol concentrations showed an initial peak, and then decreased back to the baseline concentration after a 1-hour task. Thus, these participants may have reacted with a down regulation of cortisol to a long-term cognitively demanding situation, which is also likely to apply to examination situations. Additionally, social-evaluative threat can be an effective factor for raising cortisol concentrations (Dickerson and Kemeny, 2004). This effect was observed when cortisol levels were measured before and after exposure to psychosocial stress during the ‘Trier Social Stress Test’ (TSST) (Kirschbaum et al., 1993). After the TSST (which consists of a free speech concerning the subject's suitability for employment in a mock job interview in front of an evaluation panel), the cortisol concentration increased significantly above baseline in the majority of the participants (Kirschbaum et al., 1993; Schommer et al., 2004). In contrast, the cortisol concentration showed a decline following the placebo version of the TSST, where the participants were required
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to talk about a superficial (not self-relevant) topic, without an evaluation panel (Het et al., 2009). Thus, Het et al. concluded that the missing social-evaluative threat and uncontrollability prevented the cortisol reaction, which is consistent with the theory of Dickerson and Kemeny (2004). The social-evaluative threat could also play a key role in naturalistic test situations, where personal performance is measured by tasks imposing various degrees of cognitive demand. Another influencing parameter might be the cognitive effort involved in a task. However, several previous studies have shown that cognitive effort alone does not correspond to a strong cortisol increase. Frankenhaeuser (1982) distinguished between the effects of effort and distress on cortisol concentrations. She considered effort as being primarily related to catecholamine secretion, and distress to cortisol secretion. These conclusions were later confirmed by, for example, the laboratory study of Peters et al. (1998), where participants showed a cortisol decrease following tasks with high effort and controllability. In this study, only tasks with high effort and uncontrollability lead to a cortisol increase. Thus, Peters et al. concluded that it is the uncontrollability of a task that leads to a cortisol increase, not the cognitive effort required. However, it remains unclear to what extent the various cognitive efforts and demands of naturalistic tasks (e.g., in schools) influence cortisol secretion. According to the common classification of learning objectives by Bloom et al. (1956), and its revision by Anderson et al. (2000), tests and examinations in schools comprise several tasks which differ in their demand and thus examine the achievement of different learning objectives. Both authors pointed out that learning takes place at different levels, with the higher levels depending on previously acquired knowledge and skills. This means that one needs to be able to reproduce knowledge (and skills) before she/he is able to transfer it, or to use it to solve a problem. Although Marzano and Kendall (2007) designed a partially contradictory new taxonomy of educational objectives, they agree that the reproduction level builds the basis of this hierarchy. Therefore, in our study, we decided to use this school-specific distinction between reproduction and transfer or problem-solving tasks to investigate whether these different cognitive demands influence cortisol secretion to different degrees. Besides test specific aspects which may modulate the cortisol reaction, individual differences between students could also contribute to the cortisol change. For instance, in various studies male students display a greater increase in cortisol levels than their female counterparts (e.g., Frankenhaeuser et al., 1978; Kirschbaum et al., 1995; Kudielka and Kirschbaum, 2005; Schoofs and Wolf, 2011). In addition, several studies indicate a correlation between specific gene polymorphisms and cortisol reactivity (e.g., Wüst et al., 2004; Brummett et al., 2012). Furthermore, a study by Murphy et al. (2010) revealed that an individual's behavior during a stressful period could influence cortisol concentrations: students who spent more time studying during the examination week showed significantly lower cortisol concentrations. 2. Materials and methods 2.1. Participants All of the 93 participants were students of biology courses at secondary or comprehensive schools (n = 13) in Bochum or nearby cities. Students with the following attributes were excluded from this study because of possible confounding effects on cortisol levels: smoking, over or underweight (BMI above 25 kg/m 2 or below 18.5, respectively), use of any long-term medication or oral contraceptives, or presence of a medical condition (Foley and Kirschbaum, 2010). In addition, 4 students were excluded because of blood contamination or an insufficient amount of saliva for cortisol measurement. The experiment was conducted in accordance with the Declaration of Helsinki and was approved by the ethics commission for the medical
school of the University of Bochum. All participants provided written informed consent.
2.2. Experimental conditions In this study the participants were randomly assigned to one of the four different treatment groups: The first group was asked to deal with tasks associated with the reproduction of knowledge (hereafter referred to as “reproduction,” e.g., “describe the eight steps of our DNA-extraction protocol”), while students assigned to the second group were asked to deal with tasks associated with transfer and problem-solving (hereafter referred to as “transfer”, e.g., “present a possibility to shorten the DNA-extraction protocol”). All tasks dealt directly with processing the information that the students had recently learned during the previous 2 h at the laboratory, in order to prevent the effects of different previous knowledge. The third group served as the control for the writing activity (hereafter referred to as “control”). Students in this group were free to write anything (only 5 suggestions were given, for instance, they were asked to write about their hobbies), while their course mates took the tests. The fourth group also served as a control. In this group (“no test”) the students were required to sit quietly without anticipating a test situation. Thus, they were informed about their purpose before any of the participants know that the stressor will be a short written test. 2.3. Experimental time line The experimental procedure starts approximately 2 h after the commencement of the project (11 AM) with the briefing of the students (duration: 10 min). Thereafter (11.10 AM), the first saliva sample was taken (duration: 5 min) to identify the cortisol baseline. At 11.15 AM the “no test” group was informed that they just have to sit down and wait. Thereafter (11.20 AM), the remaining students prepared themselves for the test (duration: 5 min). Then (11.25 AM), the test (duration: 10 min) started by the distribution of three different task sheets. After the end of the test (11.35 AM), the students collected the second saliva sample at 11.40 AM. Thus, the experiment ended at about 11.45 AM. The timeframe for the collection of the saliva samples, as well as the collection of the samples in the morning, was based on logistics. The project ended at approximately 2.30 PM, with a lunch break between 12 and 1 PM. Thus, we were unable to collect the saliva sample in the afternoon due to possible contamination with food or drink. But, as the students had to travel to the students' laboratory before the project started (9 AM), we can be sure that we measured the hormonal reaction after the cortisol peak concentration (awakening response). Furthermore, we have assessed their average awakening time which was between 6 AM and 7 AM. Thus, they were awake for at least 4 h before we collected the saliva. Furthermore, we aimed to test the students in relatively standardized conditions (same location, time of the day, tutor, information, etc.). Therefore, we were dependent on students participating in the laboratory projects, and we had to conduct our tests in a time interval where no project experiments were taking place. This was between 11 and 11.30 AM, requiring collection of the second sample after 15 instead of 20 min, when we would expect the peak cortisol reaction to occur. 2.4. Experimental procedure Subjects participated in a 1-day project on molecular biology at the Alfried-Krupp student laboratory located at the Ruhr University in Bochum. The project encompassed receiving molecular biology instructions and performing hands-on experiments to identify the students own mitochondrial haplotype.
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One hour before the experiment started, the participants were instructed not to ingest any food or drink in order to eliminate possible contaminations of their saliva. At the beginning of the experiment a short introduction about the objectives and the procedure of the investigation was given. Then, the first saliva sample was collected in order to identify the cortisol baseline. Thereafter, the students of the “no test” group were randomly assigned and informed about their purpose, because these students should be tested without anticipating a test situation. Then, the remaining students were informed that they would be required to answer a short written test based on the facts they recently learned during the molecular biology project. The test started when three different task sheets (each including 5 questions) were distributed among the participants, and they were thus randomly assigned to 1 of the 3 remaining treatment groups. All students had to complete the test within a time frame of 10 min. The second saliva sample (post-test) was collected as soon as possible after the end of the test, resulting in a time interval of approximately 15 min between the onset of the stressor (reading the tasks which the students had to complete) and the start of the second saliva sampling. The relatively short time interval of 10 min for the test was chosen because preliminary investigations showed that most of the students stopped taking the tasks seriously if they were dealing with them for a longer period of time (15 min), indulging in conversation with their neighbors, etc. In order to enhance the stress during the test the remaining time was announced after 5 min and again after 8 min. 2.5. Assessment of performance For the rating of test performance, the suggested solutions were derived from the information which the students had received before the test started. For each correct answer or explanation, 1 point was given. Thereby, we were able to rate the performance of each student in comparison with the maximum possible number of points. The tasks were graded before the cortisol analysis started. 2.6. Cortisol assessment Saliva samples were collected by unstimulated passive drool through a shortened straw into polypropylene micro tubes (Sarstedt, Nürmbrecht, Germany). Immediately after collection, samples were stored at − 20 °C. On the following day, samples were thawed at room temperature, vortexed, and centrifuged at 2500 × g for 15 min. The supernatant was transferred to a new micro tube and frozen (− 20 °C) until assay. On the day of the assay (no later than 2 weeks after sampling), the samples were thawed, vortexed, and centrifuged again. Then, the supernatant of each probe was transferred in duplicate into a precoated micro-well plate. Cortisol levels were quantified using the cortisol saliva immunoassay kit from DRG (Marburg, Germany). Analyses were carried out using a 96-well ELISA reader (Thermo Fisher, Vantaa, Finland). Intra-assay coefficients of variance were below 7% and inter-assay coefficients were below 11%.
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analyzed by Hochberg's GT2 post hoc test, which controls for the type I error rate and is adapted for varying sample sizes (Field, 2009). The analyses include the partial η 2 as measure of effect size. Following the classification of Cohen (1973), partial η 2 = 0.01 is considered as a small, 0.06 as a medium-sized, and 0.14 as a large effect. Overall level of significance was defined as p b 0.05. Statistical analyses were performed using SPSS 20 (IBM).
3. Results The total sample consisted of 56 male and 37 female participants with a mean age of 17.86 yrs. (±0.096 S.E.M.) and a mean BMI of 22.17 kg/m 2 (± 0.35 S.E.M.). There was no significant intergroup difference in the distribution according to sex, age, or BMI (p > 0.05).
3.1. Influence of different cognitive demand tasks on salivary cortisol concentrations A clear increase in the salivary cortisol concentration was seen in the “reproduction” group. Cortisol elevation was also observed in the “transfer” group, but this increase was much smaller. In the control group (where the students wrote about their hobbies, etc.), the cortisol change between pre and post measurement was very small and in contrast to all other groups, the cortisol concentration decreased between the first and the second measurement in the group who did not write anything (“no test”; Table 1, Fig. 1). The repeated measurement ANOVA including the repeated measurement factor TIME (before test vs. after test) and the between group factors TREATMENT (reproduction, transfer, control and no test) and SEX (men vs. women) showed a significant main effect for TREATMENT (F(3, 85) = 6.173; p b 0.01, η 2 = 0.179) whereas the effects for TIME (F(1, 85) = 3.111; p > 0.05, η 2 = 0.035) and SEX (F(1, 85) = 0.705; p > 0.05, η 2 = 0.008) were not significant. Furthermore, a significant TIME ∗ TREATMENT (F(3, 85) = 8.483; p b 0.001, η 2 = 0.23) interaction was observed. The ANOVA yielded no significant results for the TIME ∗ SEX (F(1, 85) = 1.501; p > 0.05, η 2 = 0.017) and TIME ∗ TREATMENT ∗ SEX (F(3, 85) = 0.545; p > 0.05, η 2 = 0.019) interactions. The subsequent univariate analysis of variance revealed a significant main effect, with a large effect size, of the factor TREATMENT on the cortisol change (F(3, 85) = 5.130, p b 0.01, η 2 = 0.153). Post hoc Hochberg's GT2 test indicated that the cortisol increase was significantly higher during the test associated with reproduction tasks than under either control condition (p b 0.05). However, the cortisol increase occurring during transfer and problem-solving tasks was not significantly different compared to the control conditions (Fig. 1). The independent variable SEX had no significant effect on the cortisol change (F(1, 85) = 1.995, p > 0.05, η 2 = 0.023). However, male students showed a higher cortisol increase compared to female students when dealing with reproduction or transfer and problemsolving tasks (Fig. 2). There was also no significant interaction effect between TREATMENT∗ SEX (F(3, 85) = 0.592, p > 0.05, η 2 = 0.020).
2.7. Statistical analysis Demographic and descriptive variables were analyzed using Pearson's Chi-square-tests and Student's t-tests. Cortisol concentrations were first analyzed by a repeated measure ANOVA. Data were log-transformed when appropriate and Greenhouse–Geisser adjusted p values are reported in case of violated sphericity assumption. Thereafter, we calculated the cortisol response defined as the difference between pre and post measurement and subjected these values to a one-way ANOVA. Significant main effects were further
Table 1 Raw values of cortisol concentrations (nmol/L) under each test condition at the different collection times (mean ± S.E.M.) and their change. Treatment
n
Before test
After test
Δ [nmol/L]
Δ [%]
Reproduction Transfer Control No test
25 20 28 20
8.71 ± 1.17 11.98 ± 1.51 9.59 ± 0.97 6.45 ± 0.54
11.48 ± 1.57 13.26 ± 1.82 9.85 ± 1.06 5.50 ± 0.38
2.77 ± 0.81 1.28 ± 0.65 0.26 ± 0.33 −0.95 ± 0.44
33.89 ± 6.61 10.28 ± 4.53 4.35 ± 3.99 −7.75 ± 7.47
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Fig. 1. The increase in cortisol was significantly higher after the reproduction tasks (n = 25) compared to the cortisol change under both control conditions (“control” n = 28; “no test” n = 20) (**p b 0.001, *pb 0.05). Values are presented as mean ± S.E.M.
3.2. Test performance The students' test performance was distributed normally (Kolmogorov–Smirnov, p > 0.05). Only 12% (reproduction) or 15% (transfer and problem-solving) of the students achieved more than half of the possible points. However, test performance in both kinds of tasks does not correlate significantly with the height of the cortisol change (p > 0.12, Pearson). 4. Discussion Examination situations such as oral and written examinations are widely known as stressors that raise the cortisol concentration in most participants (Martinek et al., 2003). In particular, test situations that have a strong social-evaluative component (e.g., oral examinations) are likely to be powerful stressors and, thus, cause a large cortisol
5 Female Male
Cortisol Change [nmo1/L]
4
3
2
1
0 Reproduction
Transfer
Treatment Group Fig. 2. Male students (n = 18) showed a higher cortisol increase compared to female students (n = 7) when dealing with reproduction tasks; the difference was, however, not significant (p > 0.10). This difference was much smaller between male (n = 9) and female students (n = 11) dealing with transfer and problem-solving tasks. Values are presented as mean ± S.E.M.
increase (Martinek et al., 2003; Dickerson and Kemeny, 2004; Schoofs et al., 2007). As mentioned above, other aspects of examination situations (e.g., anticipation) have been investigated for their potential to raise cortisol concentrations, but the extent to which realistic test tasks with a variety of cognitive demands influence the cortisol response remains unclear. To provide a stressor that is as naturalistic as possible within an experimental laboratory design, we used a brief test (a frequent situation in schools) with questions typical of different cognitive demands in a completely anonymous situation. In this testing situation we were able to investigate the hormonal stress reaction in the context of realistic (school) tasks under standardized conditions. Furthermore, the test performance should not have a strong social-evaluative component for the participants. Nevertheless, cortisol levels increased during the test as compared to baseline concentrations. Therefore, in our study, confrontation with the test tasks themselves was responsible for raising cortisol concentrations — the response was not dependent on whether the test has real life consequences. Unexpectedly, cortisol increase was greatest when test tasks were associated with simple knowledge reproduction. In the tests comprising the more complex tasks (transfer and problem-solving), the cortisol concentration was also increased, but without statistical significance. Thus, for the present study, the demand of the task was correlated with the extent of the cortisol reaction independently of the task's relative complexity. A possible explanation for this finding lies in the fact that in the reproduction tasks, participants had to answer questions that tested their knowledge retrieval (e.g., “describe the eight steps of the DNA-extraction protocol”); thus, they would immediately know whether they are capable of describing the steps easily, or whether they would have difficulties in their retrieval. Moreover, even if the students remembered most of the steps, they may feel that they are being imprecise using their own words, because none of them reproduced the exact wording that they have heard before. Therefore, they may perceive a degree of helplessness and distress, which are associated with increased cortisol secretion (Frankenhaeuser, 1982; Weiner, 1992). Concerning the transfer and problem-solving tasks in which students were asked, for example, to develop possibilities to shorten the DNA-extraction protocol, there was a little possibility of controlling their own performance. For instance, students could propose an unfeasible protocol, without knowing it. Furthermore, due to the task structure, they could not rely on any precise description they may have heard before. Thus, they may perceive effort without (a lot of) distress if they are able to write something down (regardless of whether it is right, wrong, or imprecise) instead of reproducing facts that could be right or wrong. As mentioned before, such a combination (effort without distress) leads to catecholamine secretion rather than cortisol secretion (Frankenhaeuser, 1982). Therefore, it would be interesting to measure the catecholamine secretion in combination with different demanding tasks in future studies, and also the students' subjective rating of task difficulty. Furthermore, performance on the test did not correlate with the cortisol change, which is in accordance with the findings of Schoofs et al. (2007). In their study, they did not detect an association between the cortisol concentrations and academic performance (received grade). Moreover, analysis of the independent variable, sex, showed no significant influence on cortisol concentrations. The hormonal increase was present in both sexes for the reproduction as well as the transfer and problem-solving tasks. However, a greater cortisol response occurred in boys than in girls, although this difference was not significant. This finding is consistent with many previous studies showing greater cortisol responses in males than in females in laboratory studies, as well as in studies using naturalistic stressors (e.g., Frankenhaeuser et al., 1978; Kirschbaum et al., 1995; Kudielka and Kirschbaum, 2005). In contrast to the participants who were dealing with the test tasks or the free writing task, those who did not have to write anything, but just sat down and waited for 10 min, showed a cortisol
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decrease. Besides the fact that they did not have to write anything, they also did not anticipate writing a test (they were directly informed that they just have to sit down and wait). Thus, they perceived neither the stressor “task” nor “anticipation”. However, their cortisol decrease was not significantly different to the increase in the other control group (who were anticipating writing a test for the few minutes until they received their task sheet). Therefore, the relatively short period of anticipation of being tested soon had no significant influence on cortisol concentrations, as expected. The cortisol decline of the “no test” group could be rather explained by the fact that the participants in this group had time to relax while they waited. In contrast to our results, prior studies with a longer anticipation period prior to naturalistic examination situations showed a clear cortisol increase directly before a written examination (Lacey et al., 2000; Martinek et al., 2003; Pletzer et al., 2010; Preuß et al., 2010). These authors concluded that the expectation of taking part in an examination leads to an increase in cortisol concentration. Some studies have even shown that the cortisol reaction in examination situations is mainly an anticipatory effect, as they observed no further elevations after the test (Johansson et al., 1983), or even a cortisol decrease (Martinek et al., 2003; Gaab et al., 2006; Preuß et al., 2010). Although this finding may be due to the negative feedback function of the hormonal system (as mentioned above), the anticipation effect of examination situations is undisputed. Additionally, some authors (Martinek et al., 2003; Schoofs et al., 2007; Preuß et al., 2010) have demonstrated that a high socialevaluative threat, such as that which occurs during oral presentations or examinations, leads to a significant cortisol increase from pre- to post-measurements. However, since the test situation in our study was anonymous, and thus without high social evaluation, we can (virtually) exclude a high influence of social-evaluative threat on the observed cortisol increase. However, the students might receive a kind of evaluation by the observer who was announcing the remaining time and monitoring their progress. Furthermore, they might feel evaluated as a group which might also cause a feeling of social-evaluation. But, as the cortisol increase was only significant during the reproduction tasks this social-evaluative treat could not be responsible for it solely. However, in contrast to our test situation, naturalistic tests, as well as tasks in school, can be a highly effective social-evaluative threat. As Dickerson and Kemeny (2004) pointed out, such a threat occurs when an important aspect of the self-identity could be negatively judged by teachers or course mates. Furthermore, they considered intelligence and competence, which are key abilities for solving tests and tasks, as core attributes of the self-identity. Therefore, it would be interesting to measure the cortisol concentration of students during reproductive as well as transfer and problem-solving tasks in a naturalistic and personally relevant school test or examination. It is noteworthy that in our experimental design, the high cortisol elevation during the reproduction tasks might well be independent of an anticipation effect and of a high social evaluative threat. On the contrary, the observed increase in cortisol levels might be a reaction to the confrontation with the specific demand of these tasks, and thus, the subjective difficulties/inability of answering them correctly. Albeit indicative, the separation of different cognitive demands in our study was relatively rough. It would therefore be informative to analyze hormonal reactions (cortisol and alpha-amylase) using finer graduations of cognitive demands. The results of these future studies (cortisol measurement during different tasks in school examinations and finer graduated demands) together with the present results could be used to provide possibilities to reduce the stress inducing aspects of test situations. One of this possibilities might be the focusing on transfer and problem solving tasks, where teachers can also assess the retrieval of knowledge but in a less obvious and stressful way.
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Acknowledgments Thanks to O. T. Wolf and C. Schulz for critically reading the manuscript and insightful comments. We also thank R. Evans for proofreading.
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