Monitoring Metabolic Status Predicting Decrements in Physiological and Cognitive Performance (2004) / Chapter Skim
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5 Strategies for Monitoring Cognitive Performance
5 Strategies for Monitoring Cognitive Performance
Pages 159-194
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From page 159... ...
As noted earlier in this report, combat service members are routinely exposed to a wide variety of physical and environmental stresses that, if ignored, will ultimately degrade operational performance. Heat stress and dehydration pose major threats to the cognitive readiness of ground combat service members, and these factors can be expected to exacerbate the fatigue from sleep loss and strenuous work.
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From page 160... ...
Depriving humans of proper restorative sleep produces attention lapses and slower reaction times, which are associated with poor performance (Krueger, 1991~. It has been determined that sleep-deprived personnel lose approximately 25 percent of their ability to perform useful mental work with each 24-hour period of sleep loss (Belenky et al., 1994~.
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From page 161... ...
In addition, Wilkinson (1964) reported that while reaction-time tasks and vigilance tasks are most degraded by sleep loss, more interesting learning tasks and performance tasks often are less affected, presumably because the subject's level of interest provides greater motivation and ability to resist attention lapses or outright sleep episodes (although, as warned by Dinges and Kribbs t1991]
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From page 162... ...
Thus despite the known dangers of fatigue and the established need to accurately measure it in some contexts, it is clear that much work remains to be done on monitoring technologies that can accurately predict moment-to-moment performance fluctuations. Clearly sleep loss from prolonged duty periods is a major threat to unit readiness in the operational environment.
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From page 163... ...
Sleep Quality Examination of the structure and sequence of an individual's sleep cycles offers crucial information about the restorative value of the sleep period. Although adequate sleep duration exerts a substantial impact on subsequent cognitive function, it is also important that the sleep be of high quality.
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From page 164... ...
found that chronic sleep reductions of even 2 hours per night result in performance decrements on vigilance tasks, and that even after 7 consecutive days of shortened sleep, there is no evidence of an adaptive response. Furthermore, these authors reported that severe sleep restriction not only hampered a wide variety of functions during the deprivation period itself (including the ability to accurately drive through a simulated course)
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From page 165... ...
. However, besides utilizing direct measures of physiological indices to help predict performance, predictive computerized models have been developed to estimate fatigue and cognitive performance capacity based on what is generally known about sleep and circadian influences.
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Note that SAFTE is based on the concept of a sleep reservoir that quantifies the impact of sleeprelated processes on cognitive readiness, or "cognitive effectiveness." Sufficient sleep time fills the sleep reservoir, and hours of wakefulness deplete the reser
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From page 167... ...
. Cognitive readiness or effectiveness is predicted based on the level of the sleep reservoir and the time of day (circadian phase)
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From page 168... ...
For example, model predictions accounted for 89 percent of the variance (degradations) in throughput on serial addition-subtraction across 72 hours of sleep loss in one study, and 98 percent of the variance in throughput on a variety of cognitive tests across 54 hours of sleep deprivation in another (Hursh et al., 2004~.
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From page 169... ...
SAFE predictions were initially validated via comparisons with laboratory data collected during several studies of sleep deprivation and shift work. Select variables were used from tests of visual vigilance, continuous memory recall, psychomotor tracking, and the Multi-Attribute Task Battery.
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From page 170... ...
These standard recordings have been used for years to document and understand "normal sleep," as well as to investigate a wide array of clinical complaints, including excessive daytime sleepiness, insomnia, and a number of sleep disorders (Carskadon and Dement, 1994; Dement, 1976; Hauri and Orr, 1982; Roffwarg, 1979)
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From page 171... ...
There are plans to employ the Sleep Watch in upcoming field exercises so that Watch-based alertness measures can be correlated with aspects of real-world performance. Once this tool is optimized, it will offer a fielduseable method for monitoring operator fatigue levels and for warning wearers of impending cognitive performance failures associated with insufficient sleep.
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From page 172... ...
is significantly elevated by even moderate sleep loss (i.e., sleep loss resulting from 18-20 hours of continuous wakefulness) , and research has repeatedly established that the fatigue from insufficient sleep affects both EEG
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From page 173... ...
New analysis routines, better equipment, automated artifact-correction algorithms, and new types of high-impedance electrodes will ultimately make widespread real-time monitoring of cognitive readiness (via measures of brain activity) feasible in field settings.
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From page 174... ...
EEG Measures Combined with Performance Measures Sleep-watch measures, EEG assessments, or other physiological parameters may be the ultimate strategy to monitor the cognitive states of ground combat service members, but combined physiological and performance measures may be a better alternative for vehicle operators. Caldwell and Roberts (2000)
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From page 175... ...
FOG measurements have been used in a wide range of applications, such as the recording of REM during sleep research (Andreassi, 1989~. It has also been found that long-duration eye closures during blinking are related to reduced alertness (Stern, 19804.
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From page 176... ...
This is a technique that may one day be useful for monitoring vehicle operators in field environments, but the equipment involved makes it unlikely that PERCLOS can be employed to assess the operational readiness of ground combat service members. Other Ocular Measures There are a number of commercial products available that measure fatigue.
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From page 177... ...
As a result, Leder and colleagues (1996) "...expect to be able to unobtrusively collect spontaneous eyelid activity in ambulatory subjects engaged in their routine activities," including "changes in blink rate associated with fatigue and loss of alertness or vigilance." OTHER CENTRAL NERVOUS SYSTEM MONITORING TECHNOLOGIES In addition to the technologies described above, there are other methods of studying central nervous system changes that may offer information about cognitive status.
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From page 178... ...
reported that 24 hours of sleep deprivation produced significant decreases in relative regional glucose metabolism in the thalamus and prefrontal and posterior-parietal cortices of the brains of 17 volunteers. Once again, both alertness and cognitive performance declined in conjunction with changes in brain activity.
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From page 179... ...
Of course heart rate has long been used as an indicator of physical effort, but it has also been proven useful for studying mental effort and other aspects of psychological and cognitive status. Thus the monitoring of heart rate as an indicator of cognitive stress may be useful for optimizing task demands with the aim of avoiding levels of cognitive fatigue that could lead to a breakdown in alertness or performance capacity.
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From page 180... ...
can be used to predict cognitive performance. Tasks that have been examined include the Stoop color-word conflict task, continuous performance tasks, and working memory tasks.
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From page 181... ...
These and other psychophysiological measures are not widely used for the assessment of cognitive readiness per se, but they can provide insight into psychological or work-related factors that ultimately can influence operator status. Since all of them can be assessed via nonintrusive, skin-mounted sensors, their potential utility for future applications should not be dismissed; however, each measure poses different challenges in terms of both recording and analysis.
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From page 182... ...
found that speech signals (word duration and fundamental frequency) recorded from aircrews in B-1B long-range bomber simulators tended to fluctuate parallel to the circadian cycle, like subjective and cognitive performance, during sleep deprivation.
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From page 183... ...
In fact, a 1990 review of 50 years of research on voice analysis techniques indicated that while this is a promising area of research, the results have not shown voice analyses to be reliable techniques for determining the type or degree of reaction to stress or workload in operational settings (Ruiz et al., 19903. Studies on the utility of voice analysis for the prediction of changes in cognitive readiness are virtually nonexistent.
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From page 184... ...
Only a small subset of the strategies will likely be suitable for operational settings. Based on a general review of the literature, it appears that the most promising techniques for accomplishing real-time, continuous assessments of footsoldier cognitive readiness in military field settings are: (1)
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From page 185... ...
. In light of these facts, automated, onboard alertness monitors would be an obvious choice for fulfilling a much-needed fatigue countermeasure role.
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From page 186... ...
Aviat Space Environ Med 65:21-26. Brookhuis K
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From page 187... ...
for maintaining aviator performance during 64 hours of sustained wakefulness: A simulator study. Aviat Space Environ Med 71:7-18.
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From page 188... ...
Aviat Space Environ Med 58:205-210. Comperatore CA, Caldwell JA, Stephans RL, Chiaramonte JA, Pearson JY, Trast ST, Mattingly AD.
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From page 189... ...
Aviat Space Environ Med 58:1165-1170. Hansen AL, Johnsen BH, Thayer JF.
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Change in heart rate and salivary cortisol. Aviat Space Environ Med 59:511-516.
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1992. Measurement and analysis methods of heart rate and respiration for use in applied environments.
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Aviat Space Environ Med 61 :266-271.
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From page 193... ...
Aviat Space Environ Med 50:625-634. Spencer J
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From page 194... ...
J Sleep Res 3: 16-25. Whitmore J
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