Serial Subtraction Performance in the Cycling Study

Transcription

1 COLLEGE OF INFORMATION SCIENCES AND TECHNOLOGY THE PENNSYLVANIA STATE UNIVERSITY Serial Subtraction Performance in the Cycling Study Frank E. Ritter, Jeanette Bennett, and Laura Cousino Klein Technical Report No. ACS December 2006 Applied Cognitive Science Lab College of Information Sciences and Technology University Park, PA acs.ist.psu.edu Phone +1 (814) Fax +1 (814)

2 Serial Subtraction Performance in the Cycling Study Frank E. Ritter, Jeanette Bennett, and Laura Cousino Klein Applied Cognitive Science Lab College of Information Sciences and Technology University Park, PA acs.ist.psu.edu Phone +1 (814) Fax +1 (814) Technical Report No. ACS December 2006 Abstract Serial subtraction, repeatedly subtracting a 1- or 2-digit number from a 4-digit number, has been often used to study the physiological effects of stress as part of the Trier Social Stressor Task. We present here several details of how this task is performed in the Cycling study as an initial attempt to study how stress influences cognition. We included the range of subtraction rates, errors, and which half of the subtraction blocks the errors occurred in. While in most cases within-session performance decreases, most surprisingly, across session performance improves. These details describe how the task is performed and can serve as a benchmark to compare how the effects of stress on cognition can be mitigated. Acknowledgements This project was supported by the US Office of Navy Research, award number N (FER and LCK), the National Science Foundation (SBR ; LCK), PSU Internal Funds (LCK), and by the Director of Technology Development, Ministry of Defence, Metropole Building, Northumberland Ave, London WC2N 5BP and was carried out under the terms of Contract No RT/COM/2/007 (FER and SK). The services provided by the General Clinical Research Center of The Pennsylvania State University are appreciated (NIH Grant M01 RR 10732). We appreciate the dedicated assistance of Drs. E. Corwin and M. Stine in completing this project, as well as the research assistants in the Biobehavioral Health Studies Laboratory for participant recruitment, data entry, and data cleaning. Mike Schoelles provided useful comments; Sue Kase helped proofread and edit this version. i

3 Table of Contents 1.0 Introduction Method Participants Design and Procedure Data Analysis Results Discussion and Conclusions References...6 ii

4 1.0 Introduction Serial subtraction, repeatedly subtracting a 1- or 2-digit number from a 4-digit number is part of the Trier Social Stressor Task (Kirschbaum, Pirke, & Hellhammer, 1993). This task has been used extensively to examine the physiological effects of stress in a laboratory setting among children and adults (e.g., Kudlielka, Buske-Kirschbaum, Hellhammer, & Kirschbaum, 2004; Nater et al., 2006; Taylor et al., 2006; Tomaka, Blascovich, Kelsey, & Leitten, 1993). Typically, participants perform the serial subtraction task, and their stress response is measured using physiological measures, but their performance on the task itself is not recorded or analyzed. Thus, the details of participants performance of serial subtraction, and how performance and cognition change in this task over time and due to other factors are not well known. It would be useful to know the details of performance on this task. This would help us understand mental arithmetic in general, but it would also serve as a baseline for comparing how cognition and task performance changes under different amounts and kinds of stress, as well as helping to characterize different responses to stress. As part of a larger project to study the biobehavioral effects of stress in men and women, serial subtraction was administered as part of the Trier Social Stressor Task. Several aspects of serial subtraction performance also were recorded in this study, and we present them here as an initial summary of performance on serial subtraction. 2.0 Method 2.1 Participants Thirty-six healthy women and 20 men, years of age (mean age years), were recruited to participate in a study examining hormonal responses to challenge. Potential participants were recruited through advertisements in the local newspaper, and flyers posted in the local community and on Penn State s main campus. A telephone questionnaire was used to help determine eligibility for participation in the current study. Specifically, the telephone interviewer asked potential participants questions that documented significant health problems and the use of medications or drugs that may affect the interpretation of neuroendocrine or cardiovascular data collected as part of the larger experiment (e.g., a history of smoking, angina, arrhythmia, medications for blood pressure, diagnosed insulin-dependent diabetes). In addition, no women using birth control pills were included in the study. Women were randomly assigned to come to the laboratory during the late luteal or follicular phase of the menstrual cycle. Approximately 20% of all callers met these requirements. All but one participant were high school graduates; 78% had some college education, and 22% of the participants had more than a college education. 2.2 Design and Procedure Overview. The experimental design was a mixed model. The between-subjects factors were sex (male; female) and menstrual cycle phase (late luteal; follicular). The within-subjects factor was stress. Specifically, all participants participated in the same protocol, which consisted of a baseline rest period, a challenge period (13.5-minute speech challenge and 15-minute mental arithmetic task), and a recovery period. Laboratory Protocol. Eligible participants arrived at the General Clinical Research Center at 1:00 PM and were met by a trained research assistant who first obtained informed consent. Next, participants 1

5 briefly were interviewed by a certified nurse practitioner to confirm their health status and study eligibility. Body weight and height also were measured. Next, participants were asked to complete standardized mood measures (e.g., Speilberger State-Trait Anxiety Inventory, Symptoms Check List-90, Profile of Mood States). Following completion of the questionnaires, a standard blood pressure cuff was placed on the participant s dominant arm, and a trained nurse inserted an indwelling catheter in the non-dominant arm using standard antiseptic techniques. After a 10-minute acclimation period, participants were asked to sit quietly for 15 minutes while baseline blood pressure readings were taken automatically (Dinamap blood pressure monitor). The blood pressure cuff and catheter were used for biological samples that were part of the larger experiment. Following baseline, participants were exposed to the Trier Social Stressor Task (Kirschbaum, Kudielka, Gaab, Schommer, & Hellhammer, 1999). Specifically, they were asked to prepare a 3.5-minute speech, which they were told would be recorded on videotape for later observation by a panel of psychologists. In the speech, they discussed a personal failure that had a negative consequence on their life. Participants were given 10 minutes to prepare the speech, and then they took 3.5 minutes to deliver the speech in front of a video camera. No recording actually was made of the speech and participants were debriefed about this deception at the completion of the laboratory session. Following the speech, participants were asked to complete two blocks of serial subtraction across a 15-minute period of time. Subjects answers were corrected against a list of correct answers from the starting number. When an incorrect answer was given, the subject was told to Start over at <the last correct number>. At two minutes into each 4-minute session, subjects were told that 2-minutes remain, you need to hurry up. This served to increase stress. This stressor session took 30 minutes to complete. Performance on the first block of 7 s and first block of 13 s was recorded on the experimenter s scoring sheets. Part way through the study, a mark indicating where the 2-minute warning occurred was added to measure the pace of the subtractions. Participants also were asked to complete several post-task measures of mood at the end of the study and were paid $30 for their time. 2.3 Data Analysis In each experimental session the experimenter checked off the subject s subtractions on a sheet showing the correct subtractions for that block. The number of subtractions was taken from these sheets. The 2- minute warning mark was also transcribed into a spreadsheet, allowing performance before and after the 2-minute warning to be analyzed separately. Data from the first two 4-minute blocks (first 7 s and first 13 s) out of the four blocks could be retrieved from the running notes and are reported below. 3.0 Results All of the 56 subjects completed the task. While participants reported stress measures, these are not yet available for analyses. We report the performance data here. Table 1 shows the rate of subtractions for the two problem types. Participants performance overall was generally accurate. The proportion correct ranged from 0.43 to 1.00 on the 7 s, and from 0.31 to 1.00 on the 13 s, and individuals were not different across problem types (t(56)=1.7, n.s.). These results are fairly comparable to the Tomaka et al. s (1993) data of 61 attempts for challenge and 46 for threat. While we do not know the variance in Tomaka s data, we can compare it assuming that the variance in each case is equivalent. If we do so, for number of attempts and number correct there is not a reliable difference between this data and Tomaka et al. s (1994) threatened condition t(36)<1.0, and a reliable difference between this data and the challenged condition t(36) > 4, p<0.05. There is also a reliable difference for proportion correct, with Tomaka s subjects being correct more often. 2

6 Table 1. Performance on serial subtraction in the Cycling (N=56) on a 4-minute block of 7 s and 13 s, including SD and ranges. 7 s 13 s Attempts 47.0 (17.1) (8-106) 36.3 (15.1) (9-78) Correct 40.0 (18.7) (6-105) 29.6 (15.7) (3-78) %Correct 82% (14) (43-100) 78% (17) (31-100) When the individual performance is examined, a wide range is found. In the first block, the 7 s, the number of attempts ranged from 8 to 106 subtractions, and the number correct and error rates had similar variance. The range of performance is shown in Figure 1. In the second block, the 13 s, the variance was similar. The range of these scores suggests more individual variability than implied by Tomaka et al. s values or the means in Table 1. Figure 1. Histogram of attempts and number correct for the 7 s block. The plot of number of attempts vs. number of errors for 7 s in Figure 2 shows a reliable inverse correlation of -0.48, t(54) = 4.07, p< The distribution for 13 s is similar, but correlates less well, r= -0.29, t(54)=2.20, p< This has to be due in part to the time that errors take. With each error the experimenter provided instructions about where to start over. 3

7 Figure 2. Number of attempts vs. number of errors for all 7 s problems for all subjects. Error rates by sub-blocks were also computed for subjects where the scoring sheet was marked with the location of the 2-minute warning. These scores are shown in Table 2. Subjects made many more errors in the second half of the experiment than in the first half. This trend appeared to be a consistent trend across subjects. On the 7 s problems, 33 of the 34 subjects increased their errors in the second block; on the 13 s problems, 30 increased their errors. These errors could have occurred either because of fatigue, the cumulative effects of stress, memory effects such as proactive interference, or perhaps due to the interruption. Or, the errors could be due to a combination of these effects. This effect is not surprising, in that many theories of stress predict that you start out good and get worse as time progresses (Ritter, Reifers, Schoelles, & Klein, in press). More fine-grained data will be required to see where and how the increase in errors occurs. Table 2. Performance on serial subtraction in the Cycling (N=34) before and after the 2-minute warning. 7 s 13 s Pre-2-min. Post-2-min. Pre-2-min. Post-2-min. Errors 0.94 (1.32) 6.65 (3.69) 1.15 (1.92) 6.58 (4.07) Min/max 0/5 1/20 0/8 1/26 % of Errors 6% (12%) 94% 13% (21%) 87% Table 3 and Table 4 show how performance varied by sex. Overall, women made about 30% less attempts and were about 10% less correct. In Table 3, the differences in number of subtractions and number correct and percent correct between columns are all reliably different, (minimum t(54) > 4.7). As a group women had less variance in most measures than the men. The inferential results for the 13 s problems are similar. These results suggest that the distribution of men and women will influence the results on this task. 4

8 Table 3. Performance on serial subtraction in the Cycling study on a 4-minute block of 7 s (and standard deviations). Women (N=36) Men (N=20) Attempts 39.9 (13.9) 59.7 (14.8) Correct 31.9 (14.5) 54.7 (15.7) %Correct 77% (15%) 91% (7%) Min/max attempts 8/72 43/106 Table 4. Performance on serial subtraction in the Cycling (N=34) before and after the 2-minute warning. Men 7 s (N=10) 13 s (N=9) Pre-2-min. Post-2-min. Pre-2-min. Post-2-min. Errors 0.40 (0.97) 5.30 (3.40) 0.56 (0.53) 5.78 (2.59) Min/max 0/3 1/12 0/1 3/10 % of Errors 1% (2%) 99% 8% (8%) 92% Women 7 s (N=24) 13 s (N=24) Pre-2-min. Post-2-min. Pre-2-min. Post-2-min. Errors 1.17 (1.40) 7.21 (3.73) 1.38 (2.2) 6.88 (4.51) Min/max 0/5 2/20 0/8 1/26 % of Errors 8% (14%) 92% 15% (24%) 85% 4.0 Discussion and Conclusions The data from this study extend the details of what we know about how people perform serial subtraction, part of the Trier Social Stressor Task. We provide further details on this task, including means, standard deviations, and ranges on subtraction attempts, correct subtractions, and errors by subblock, and across sex. We also present the distribution for the number of attempts and number correct. This study also provided data on another problem size and more types of data. It provided the additional measures of performance on a slightly larger problem, the 13 s. The 13 s problems appear to be slightly more difficult than the 7 s, and this is not too surprising. The rate of 13 s subtractions appears to be slightly slower than 7 s, with a slightly higher error rate, which might be expected. The results confirm the rate of subtractions by 7 s for 4-minute blocks previously found, but the rates found here are slightly slower than Tomaka et al. (1993, exp. 2) found. There may be several reasons for the lower number of subtractions per 4-minute block here than in the Tomaka et al. study. The cycling participants were in a more threatening condition. While the Tomaka et al. s participants were connected to an EKG, the cycling study participants were connected to a blood pressure measurement machine, had an indwelling catheter in their arm, and their subtraction attempts were preceded by a talk to a video camera on an embarrassing incident. Tomaka s participants had a longer break between sessions than did the cycling study participants (5 min. vs. a set of word problems that took about 4 minutes). Tomaka et al. s participants were all male, whereas our subjects were both male and female. Table 3 suggests that the cycling male participants were more similar to Tomaka s participants in their performance. The results show a trend to increasing errors with time. Nearly all participants made most of their errors in the second half of the tasks. While we cannot see exactly where the errors occurred, it does appear that either the warning or the time on the task eventually leads to errors. 5

9 The results suggest that there is at least a typical range of performance on this task. The participants with the greatest and the least number of attempted subtractions were each 5.3 and 3.5 standard deviations away from the mean. There are a few further measures that would be useful for characterizing behavior on serial subtraction. It would be interesting to know how the pace of subtractions, not just errors, changes over time. Do subjects get faster or slower over time? The error rate could increase because they are performing more subtractions, or it could be that they are performing them more poorly over time. Similarly, it would be interesting to know what errors subjects are making. Are they misretrieving the sub-answers, or are they forgetting to borrow or to decrement? This study lacks full appraisal measures, and it does not yet provide very detailed descriptions of the timing of individual subtractions, nor does it provide what kinds of errors subjects made. Further studies will be needed to understand how subjects perform this task, and to understand how it is stressful, and how stress influences performance on this task. 5.0 References Kirschbaum, C., Kudielka, B. M., Gaab, J., Schommer, N. C., & Hellhammer, D. H. (1999). Impact of gender, menstrual cycle phase, and oral contraceptives on the activity of hypothalamus-pituitaryadrenal axis. Psychosomatic Medicine, 61, Kirschbaum, C., Pirke, K.-M., & Hellhammer, D. H. (1993). The Trier Social Stress Test A tool for investigating psychobiological stress responses in a laboratory setting. Neuropsychobiology, 28, Kudlielka, B. M., Buske-Kirschbaum, A., Hellhammer, O. H., & Kirschbaum, C. (2004). HPA axis responses to laboratory psychosocial stress in healthy elderly adults, younger adults, and children: Impact of age and gender. Psychoneuroendocrinology, 29, Nater, U. M., La Marca, R., Florin, L., Moses, A., Langhans, W., Koller, M. M., et al. (2006). Stressinduced changes in human salivary alpha-amylase activity -- associations with adrenergic activity. Psychoneuroendocrinology, 31(1), Ritter, F. E., Reifers, A. L., Schoelles, M., & Klein, L. C. (in press). Lessons from defining theories of stress for architectures. In W. Gray (Ed.), Integrated models of cognitive systems. New York, NY: Oxford University Press. Taylor, S. E., Gonzaga, G. C., Klein, L. C., Hu, P., Greendale, G. A., & Seeman, T. E. (2006). Relation of oxytocin to psychological stress responses and hypothalamic-pituitary-adrenocortical axis activity in older women. Psychosomatic Medicine, 68, Tomaka, J., Blascovich, J., Kelsey, R. M., & Leitten, C. L. (1993). Subjective, physiological, and behavioral effects of threat and challenge appraisal. Journal of Personality and Social Psychology, 65(2),