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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.
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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-
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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.
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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
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8, 15.oo
p.. 230
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= 240
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220 ,_...................................
210
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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
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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
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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.
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