1. Stress, Workload, Accidents, & Errors
Information
Processing
Stressors
Experience
Health
Direct (e.g., vibration)
Physiological arousal
Indirect
Direct (e.g., lighting, noise)
Input
Performance
Figure 13.1 A representation of stress effects. (Wickens et al, pg.325)
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2. Environmental Stressors
Effect
Stressor
Health
Input
Indirect / IP
Performance
Light X
Noise
Vibration
Motion Sickness
Heat/Cold
Air Quality
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3. Psychological Stressors
Fear, embarrassment, loss of esteem, etc.
Effects
Perceptual / attention narrowing or tunneling
 cognitive tunnel vision
working memory loss
strategic shifts, e.g., tendency to react too quickly
Effect depends on individual factors –
personality traits
level of experience
life stress
- and on level of physiological arousal induced by the
stressor.
Yerkes-Dobson law
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4. Workload and Performance
Yerkes-Dobson law
Low arousal  ________________
Moderate arousal  ____________
Overarousal  _______________
Note optimal level of arousal (OLA)
improvement in performance due to “trying harder” (e.g., threat of loss caused by psych stressor motivates one to work harder and perform better.)
Effects of overarousal:
attentional and/or cognitive tunneling (good if you are focusing on the correct solution, but bad if not)
working memory loss
long-term memory may be enhanced (tend to engage in the most available thoughts)
some strategic shifts (e.g., “do something now”)
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5. Workload Overload Underload Measures Effects Remediation
Time req’d / Time avail. (TR/TA)
Primary task measure
Secondary task measures
Physiological Measures
Subjective Measures
TR/TA
signal detection task performance
Effects
Fatigue
Performance decrement
Workload disassociation
Future performance
Vigilance decrement
Remediation
Automation
Task sharing
Training (performance, task management)
Reduce length of vigil, increase rest breaks
Signal enhancement
Increase level of arousal
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6. Workload Measures Time required / Time available (TR/TA) ratio
Based on task analysis
Percentage computed per time unit on task timeline
Useful predictor, but difficult to construct
Primary task measures
measure the influence of mental workload
Secondary task methods
measure the reserve capacity
Physiological measures
allow non-intrusive measures
Subjective measures
SWAT, TLX, etc.
FUNCTIONAL
MENTAL
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7. An example using NASA TLX
Form two teams. Each team will follow the instructions given to you.
You have 1 minute to complete the task.
The team that comes closest to completing their task with the fewest errors will “win.”
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8. Relative workload scores:
Enter your workload scores below:
What does this say about the relative workload of the two tasks?
What does this say about the subjective nature of the workload scores?
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9. Sleep loss and desynchronization
Fatigue effects on performance
accident rates directly due to fatigue
performance on exams
effect on medical treatment, decision making, etc.
See figure 13.6, pg. 346
Causes
deprivation
disruption
phase in circadian rhythms
desynchronization – shiftwork strategies
Remediation
get more sleep!
napping
sleep credits
sleep management
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10. Your turn …
On the following pages you will find a checklist of variables that increase the effort demanded by a task. For each of the variables:
define the specific effect in your own word
identify relevant theories, experimental results, or principles from what we have learned so far this term
provide an example of good design
provide an example of bad design
Use the table on the following pages. The first row is filled in as an example.
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11. Demand checklist Definition Relevant theories, etc. Good design
Bad design
Legibility
How easy is it to see the data
signal detection theory
ATC screen in which incoming aircraft ‘stand out’
weather radar in which cloud cover obscures indicators of tornadoes, etc.
Visual search demand
Display organization
Compatibility
Consistency
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12. Demand checklist (cont.)
Definition
Relevant theories, etc.
Good design
Bad design
Number of modes of operation
Prediction requirements
Mental rotation
Working memory demand
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13. Demand checklist (cont.)
Definition
Relevant theories, etc.
Good design
Bad design
Unprompted procedures
S-R compatibility
Feedback
Precision of action
S-R-K
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