PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 45th ANNUAL MEETING- 2001 901 INFORMATION PROCESSING CHANGES FOLLOWING EXTENDED STRESS Peter A. Hancock, Wayne C. Harris, and Scot C. Harris University of Minnesota Extended periods of stress are associated with subjective fatigue and performance deterioration. Psychological state and cognitive performance were assessed before and after one week of field training at a Navy Survival, Evasion, Resistance and Escape School. Subjective discomfort increased, but average cognitive performance deterioration was limited to increased Simple Reaction Time. Considering that decrements in complex performance are commonly associated with fatigue, the stability or improvement of' the more complex cognitive tasks was unexpected. Given that increasing effort is required to maintain performance as time-on-task increases, performance changes within pre and post-training trials were compared. While performance was stable or improved in the pre-training session, complex task performance deteriorated during post-training trials. The results are consistent with the hypotheses that fatigued individuals maintain complex cognitive task performance by exerting increased effort, but that increasing effort becomes increasingly difficult even during brief assessments. Impaired decision making is expected during periods of high stress levels, but chronic stress can produce pervasive cognitive changes, judgement degradation, and decrease safety margins, Individuals who are capable of performing a task at one time, later become unable to perform the same task at an equivalent level. While avoiding extended periods of stress is ideal, operational activities often include sustained stress, a condition that impairs information processing (Wickens, 1996), the basis for judgement. The effect of fatigue on cognitive performance is becoming a more important issue with current efforts to simultaneously decrease manning and increasing the use of advanced technology to enhance warfighter capabilities (Orasanu, & Baker, 1996). However, attempts to detect cognitive changes that produce operational decrements have been less successful (Elsmore, Naitoh, & Linneville,1992; Callister, Percival & Retzlaff, 1999; Slaven & Windle,1999). However, the cognitive batteries have assessed a limited numbers of cognitive components, and have lacked experimental control during data collection that compromised the experimenter's ability to detect changes, The present study attempted to increases the likelihood of detecting information processing changes by examining cognitive changes in an environment with stress similar to levels present in operational settings that provide the opportunity to exert experimental control. Specific goals included; 1) assessment of the type and amount of cognitive changes that follow a period of sustained physical and psychological stress, 2) measurement of the subjective changes that occur during this period, and 3) determination of the relationship between subjective changes and cognitive performance changes. METHOD Participants Two groups of military personnel participated in the study. The first group was 35 active duty Navy and Marine Corps personnel enrolled in the Survival, Evasion, Resistance, and Escape (SERE) school at Brunswick, ME. The second group was 15 Army Reserve Office Training Corp (AROTC) cadets at Minnesota State University, Mankato who were not involved in demanding military training during the week that separated assessments. 902 PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS Assessment Cognitive performance was assessed with the Automated Neurological Assessment Metric (ANAM). The battery used in the present study included sub-tests that assessed attention, stimulus encoding, memory, and the manipulation of spatial and symbolic information. Subjective state was assessed with the Profile of Mood States (McNair, Lorr, & Droppleman, 1992),the Sustained Operations Assessment Profile (Retzlaff, King, Marsh, & French, 1997), and the Stanford Sleepiness Scale (SSS). Pracedures After signing the informed consent document, participants received instructions conceming the Automated Neuropsychological Assessment Metric (ANAM), the Profile of Mood States (POMS), and the Sustained Operations Assessment Profile (SOAP). Due to the procedural complexity of the ANAM, subjects completed a short version of the battery twice before proceeding to the pre-training ANAM assessment. Initial assessment was immediately before participants were transported to the field-training site. Training included survival training and simulated being isolated from friendly forces. Participants completed the ANAM battery, the POMS, and the SOAP seven days later, immediately after they retumed from the remote trainingfacility, To determine ANAM changes that occur during repeated assessment, identical procedures were followed with Minnesota State University, Mankato Army Reserve Officer Training Corp (AROTC) students during a period without demanding militarytraining, RESULTS Cognitive performance was assessed by a set of 7 tasks from the Automated Neuropsychological Assessment Metric (ANAM). Subjective state was assessed using the Profile of Mood States (POMS), the Sustained Operations Assessment Profile (SOAP), and the Stanford Sleepiness Scale (SSS). Multivariate analysis of variance (MANOVA) using SOCIETY 45th ANNUAL MEETING- 2001 theWilks' Lambdacriterionwasperformedinitially to determine the statistical significance of ANAM, POMS, and SOAP changes. When overall MANOVA significance was found, univariate analysis was used to examine individual sub-scales of these batteries. Army Reserve Officer Training Corp cadets To determine the stability of the ANAM battery under the conditions used with the SERE students, identical procedures were followed with a group of ROTC students during a one-week period during the school year. Cadets attended classes and theydidnotparticipatein militaryexercisesduring that week. Measures of subjective state and cognitive performance did not change in the sample of AROTC cadets during the week. MANOVA analysis indicated a trend in the SOAP profile (F (10, 5) - 3.5, p< .09), and examination of individual scales indicated decreased subjective discomfort on 9 of the l0 SOAP scales. The POMS was stable (F (6, 10) - 1.08, p< .44). Analysis indicated ANAM accuracy scores were stable (F (7, 8)= .47, p<. 84), but there was a trend toward more rapid responding, F (7, 8) = 2.18, p<. 15. SERE Students Average session cognitive accuracy and response time. MANOVA analysis of SERE student data indicatedthat averageaccuracyin thepre and post-training session differed, F (6, 24) - 5.56, p< .001. Univariate analysis of accuracy scores indicated that the accuracy of spatial processing and the continuous memory task improved significantly (P< .02 and .04). Analysis of average response time indicateda significantchangebetweenthepre and post-training cognitive assessment, MANOVA, F(7,23) = 6.6, p< .001. Univariate analysis of response time indicated significantly slower simple reaction time responding (p = .03) but faster responding on the spatial processing and 6-item memory response time (p< .01), and the continuous performance task (p< .04). Contrary to expectations, performance change did not reflect a consistent pattem of performance deterioration. 903 PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 45th ANNUAL MEETING- 2001 Within session cognitive accuracy and response time. One interpretation of the minimal deterioration in average post-training complex cognitive tasks is that performance had not stabilized during training and that pot-training improvement reflected learning and that fatigued participants maintained performance by increasing effort. Although cognitive tasks were relatively brief, maintaining performance by increasing effort is difficult. A second analysis was therefore initiated to determine whether fatigued participant sub-task performance deteriorated within trials. The analysis compared cognitive performance during the first and last portion of each sub-task during the pre and post-training sessions, Within trial performance was stable or improved during the pre-training session, but post-training trial complex cognitive task performance deteriorated when the beginning and end of the post-training session were compared (see Figure 1). Continuous Performance Task (CTP) contained a variety of disruptions including missed responses and responses with extremely short response tianes that suggest that participants were responding without examining the stimuli. SERE Student Subjective State. Three measures of subjective state were used. Analysis of POMS changes in the SERE students indicated that significant changes occurred during the week of survival training (MANOVA), F(6, 13)= 21.1, p< .0001. Univariate analysis indicated that fatigue and confusion scores increased and that the vigor score decreased (p< .0001, .007, and .001, respectively). A significant change occurred in the SOAP profiles (MANOVA), F (10, 9) = 13.2,p< .001. Scales exhibiting the largest increases were Poor Sleep, Physical Discomfort, and Work Frustration. SERE participants also reported increased sleepiness on the Stanford Sleepiness Scale. SRT Response Time Mood change 250 2O.OO "G 8, 15.oo p.. 230 _ 5.o0, = 240 • :. :: .. . _,:_. ... .. _. ,..._ m= "' 8 220 ,_................................... 210 ,..............._.................................. ,........................ Star Finish Pre-training Start Finish Post-training Figure 1. Within session Simple Response Time changes Simple Reaction Time and Code Substitution response time increased as the pot-training session progressed, and Spatial Processing exhibited decreased accuracy. Grammatical Reasoning response time increased and accuracy decreased when the beginning and end of post-training sessions were compared. A less consistent pattern of changes occurred in the memory tasks. In the post-training session, the Sternberg 2 and 6 (ST2 & ST6) tasks exhibited no evidence of deterioration, P.u)o.oo -5.0o -10.oo POMS Scale Figure 2. Mood change during training. The relationship between subjective mood and cognitive performance changes. A regression analysis was used to determine whether the subjective state and cognitive performance changes observed following extended periods of stress are related. Simple Reaction Time, the cognitive performance that deteriorated significantly following stress, was regressed upon the POMS scales that consistently changed during exposure to stress, fatigue, confusion and vigor. Analysis indicated a significant relationship between Simple 904 PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS Reaction Time and the three POMS sub-scales, F(3, 15) =4.41, p< .021, adjusted R square = .362. The standardized coefficients and significance of the three scales were Fatigue (Beta =- .866, p < .3004), Confusion (Beta =.627,p< .015) and Vigor (Beta = - .292, p< .203). It should be noted that the Betas found with vigor and confusion lie in the expected direction, increased confusion and decreased vigor are associated with increased reaction time. The negative Beta associated with fatigue indicates that as reported fatigue increases, simple reaction time decreases, however, the level of significance suggests that minimal confidence can be placed on this relationship, Although the level of accuracy changes did not reach traditional levels of significance, the 2-item memory task accuracy declined (p < .06) while moderate improvement would be expected between the third and fourth administration. The 2-item memory set task was therefore also regressed upon the three POMS scales that consistently changed in response to stress. Analysis indicated a significant relationship between the 2-item memory task (ST2) and the three POMS sub-scales, F(3, 15) =4.71, p< .016, adjusted R square = .382. The standardized coefficients and significance of the three scales were Fatigue (Beta = .355, p < .427), Confusion (Beta = 1.255, P< .060) and Vigor (Beta = 1.723, p< .007). The results suggest that decreased ST2 accuracy is primarily associated with decreased vigor, DISCUSSION During sustained and continuous operations, military personnel must complete missions while exposed to high levels of physical and psychological discomfort. With sufficient exposure, stress can completely incapacitate, but before that point is reached, people continue to perform at a diminished level. The present study examines the effects of exposure to an extended period of stress. During these conditions, skilled and motivated people are known to make uncharacteristic errors and exhibit poor judgement that suggests reduced processing information efficiently, SOCIETY 45th ANNUAL MEETING- 2001 The initial analysis of average complex tas_k performance was consistent with previous studies that failed to detect cognitive performance changes following stress (Elsmore, Naitoh, & Linnevill e, 1992; Callister, Percival & Retzlaff, 1999; Sla_een & Windle, 1999). However, the inclusion of less complex items in the battery provided evidence that the performance of simple tasks deteriorates following stress. Resource theories of informa_tion processing suggest that when resources become limited, individuals prioritize tasks and allocate available resources to high priority tasks (Hockey, Wastell, & Sauer, 1998). If allocating increased resources is limited to tasks that involve controlled processing (Heuer, Spijkers, Kiesswetter, & Schmidtke, 1998), performance stability should be limited to controlled processing tasks. Thus, the apparent stability of complex cognitive tasks may be because fatigued participants maintained performance by increasing effort. With this assumption, it would be predicted that highly motivated individuals should exhibit minimal performance change during brief assessments. However, maintaining performance with increased effort becomes more difficult with time, therefore, a second analysis was performed in which performance during the initial and final trials in each task were compared. The results of the within trial analysis suggest that complex cognitive performance is affected by stress, but that complex taskdeterioration canbetemporarily maskedby increased effort. The results indicate that cognitive performance deteriorates following stress and describe the relative decrements of information processing components. Furthermore, the analysis suggest that stress related cognitive performance changes can be detected in brief assessments by simple reaction time changes or by examining the pattem of within trial performance. As anticipated, subjective state changes indicated elevated levels of discomfort. All the SOAP scales with the exception of anxiety and depression changed in response to the experience. The ease of distorting subjective state makes self-reports questionable when individuals are motivated to distort their feelings. However, the association betweencognitivestateandperformance changes suggest that subjective state may be a useful PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS research tool and a valid predictor of cognitive performance under some conditions. Of greater interest, decreased vigor rather than increased fatigue appeared to be the psychological state that was most closely related to cognitive performance. This is consistent with reports that while fatigue decreases and vigor increases following periods of reduced workload, performance changes are more closely related to the amount of vigor improvement rather than to subjective fatigue decreases (Bricker & Hams, 1999). Subjective assessments such as the SOAP that do not assess vigor appear to be limiting their predictivepotential. ACKNOWLEDGEMENTS This research was supported by a grant from the Office of Naval Research (N00014-99-1-1034). The views expressed in this article are those of the authors and do not reflect the official policy or position of the Office of Naval Research. The authors thank Dr. Susan Chipman, the ONR Technical Monitor. We are extremely grateful to the personnel of the SERE School, Brunswick, Maine for all their cooperation and assistance during the present work. In particular, we would like to thank CDR J. M. Doherty for all his help and direction. REFERENCES SOCIETY 45th ANNUAL MEETING- 2001 905 Heuer, H., Spijkers, W., Kiesswetter, E. & Schmidtke, V. (1998). Effects of sleep loss, time of day, and extended mental work on implicit and explicit learning. Journal of Experimental Psychology: Applied, 4, 139-162. Hockey, G.R.J, Wastell, D.G., & Sauer, J. (1998). Effects of sleep deprivation and user interface on complex performance: a multi level analysis of compensatory control. Human Factors, 40, 233-253. McNair, D. M., Lorr, M., & Droppleman, L.F. (1992). Manual for the Profile of Mood States (rev.ed.). San Diego, CA: EDITS. Orasanu, J. M., & Baker, P. (1996). Stress and military performance. In J. Driskell & E. Salas (Eds.), Performance under stress. (pp. 89-117). Hillsdale, NJ: Lawrence Erlbaum Associates. Slaven, G.M. & Windle, C.M. (1999). Cognitive performance over 7 days in a distressed submarine. Aviation, Space, and Environmental Medicine, 70(6), 604-608. Retzlaff, P.D., King, R.E., Marsh, R.W., & French, J. (1997). The Development of the Sustained Operations Assessment Profile (SOAP). (AL/AO-TR-1997-094). Brooks AFB: Armstrong Laboratory. Wickens, C. D. (1996). Designing for stress. In J.E. Driskell&E. Salas,(Eds),StressandHuman performance, Mahwah, NJ: Lawrence Erlbaum. Bricker, T. A. & Harris, W.C .(1999). Managing workload with fatigue self-reports. Proceedings of the Human Factors and Ergonomics Society 43rd annual meeting, Houston, TX. Callister, J.D., Percival, G.L., & Retzlaff, P.D. (1999). Stress and fatigue during aircrew survival training. Proceedings of the Tenth International Symposium on Aviation Psychology, 10 (2), 843-847. Elsmore, T. F., Naitoh, P., & Linnville, S. (1992). Performance assessment in sustained operations. Naval Health Research Center Report No. 92-30 Hancock, P.A., Harris, W.C., & Harris, S.C. (2001). Information processing changes following extended stress. . Proceedings of the Human Factors and Ergonomics Society, 45, 901-905.
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