1. Chapter 13: Stress and workload
Describes factors that influence human performance
Direct effect on performance (interfere with perception and action)
Indirect effect through psychological mechanisms, such as arousal
Long-term debilitating effects
Objective: To modify the work environment to reduce or eliminate stressors

2. Objectives
Understand range of stressors and their effects (physical and psychological)
Workload prediction and measurement
Difficulties with monitoring tasks: Vigilance decrement
Sleep loss and disruption (circadian desynchronization and sleep quality)

3. Four effects of stressors
Psychological experience
Physiological change
Information processing performance, usually degrades
Long-term health

4. Environmental stressors
Noise
Lighting
Motion
Vibration
Whole body vibration
Sickness inducing low frequency motion
Thermal (heat, cold)
Air quality

5. Psychological stressors
Cognitive appraisal
Level of arousal
Performance decrements with over arousal
Perceptual narrowing
Cognitive tunneling
Working memory loss
Revision to dominant behaviors based on LTM
Strategic shifts, tendency to take immediate action

6. Remediation of psychological stressors
Change nature of task, more people
Simplify design of displays, controls, and procedures
Train so emergency procedures are dominant long-term memory
Emergency stress management strategies (don’t react immediately)

7. Workload
Workload affects immediate task performance and can degrade future performance through fatigue
Considerations for timeline model
Distribution of task time should be considered (use 90th percentile)
Time required/Time available<.80 to avoid overload
TR/TA modulated by resource requirements
TR/TA does not equal effort
Time stress and task scheduling
People focus on tasks believed to be important and available
Train to speed processing
Train to calibrate importance

8. Measurement of mental workload
Primary task performance
Higher workload makes performance worse
Secondary task measures
Measures of reserve capacity
Mental arithmetic, time estimation, memory, reaction time
Physiological measures
Heart rate variability, pupil dilation
Subjective measures

9. Mental workload measurement dissociations
Higher motivation, higher effort, better performance
Performance and arousal curve
Change in subjective performance criteria
Multiple measures are often used to understand particular situation

10. Underarousal and vigilance
Maintaining vigilance in low workload situation can be fatiguing and stressful
Effects of vigilance decrement
Time
Event salience
Signal rate
Arousal level

11. Vigilance enhancement: Enhance arousal and make detection easier
Signal enhancement
Frequent rest breaks
Vigilance declines in as little as 20 minutes
Introduce false signals
Stimulants
Caffeine
Music
Conversation
Avoid sleep disruption

12. Considerations regarding sleep and fatigue
Cost and safety consequence of fatigue
Affect on performance
Factors affecting fatigue
Sleep
Circadian rhythm
Workload and activity
Mitigation strategies

13. Why does alertness matter?
Automotive accidents over 24 hours

14. Why does alertness matter? Error rates in reading meters

15. Cost of fatigue related accidents
200,000 crashes and 4,000 deaths/year in roadway accidents due to fatigue
70 Billion/year roadway accident costs related to fatigue
Fatigue can reduce performance to level of 0.08 BAC after 24 hours of continuous activity

16. Fatigue and its affect on performance
Highly affected
Judgment
Learning new material
Planning
Less effected
Motor activity/physical tasks
Tasks involving highly interesting material

17. Factors affecting fatigue
Time of day (circadian rhythm)
Time since last sleep
Time on task, hours of work
Amount and quality of sleep (sleep debt)
Sleep inertia
Circadian desynchronization
Lack of environmental stimulation

18. Circadian desynchronization
=Circadian rhythm does not match day/night cycle
=Mismatch between when your body wants to sleep and when you need to be awake
Shift work
Fast rotation worse than slow
Delayed shift better than accelerated (get up late)
An extended day allows the body to extend the circadian cycle in line with the unconstrained 27-hour cycle

19. Circadian desynchronization
Jet lag
Eastbound worse than westbound, similar to delayed shift
Allow one day for each time zone for recovery
Weekend effect

20. Fatigue mitigation/Endurance management
Get more and better sleep: Sleep hygiene/management
No caffeine before bed
Consistent sleep periods, with 8 hours per day in a single period
Attitude, as in medical interns
Quiet, dark place to sleep
Napping
More than 15 minutes, but no more than 90 minutes
Stop at least 10 minutes before work

21. Fatigue mitigation/Endurance management
Sleep credit: sleep more before sleep deprivation period
Less effective: Drugs
Melatonin, to support circadian synchonization
Caffeine, to boost alertness
Less practical: Curtail operations
Siesta
Avoid nighttime operations

22. Objectives
Understand range of stressors and their effects (physical and psychological)
Workload prediction and measurement
Difficulties with monitoring tasks: Vigilance decrement
Sleep loss and disruption (circadian desynchronization and sleep quality)