Stress, Workload, Accidents,

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Stress, Workload, Accidents, Errors
Figure 13.1 A representation of stress effects.
(Wickens et al, pg.325)
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Environmental Stressors
Effect Effect Effect Effect
Stressor Health Input Indirect / IP Performance
Light X X
Noise X X X X
Vibration X X X
Motion Sickness X
Heat/Cold X X X X
Air Quality X X X
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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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Workload and Performance

• Yerkes-Dobson law
• Low arousal ? ________________
• Moderate arousal ? ____________
• Overarousal ? _______________

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Workload
Overload Underload
Measures Time reqd / 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 Fatigue Vigilance decrement Future performance
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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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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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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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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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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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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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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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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Demand checklist (cont.)
Definition Relevant theories, etc. Good design Bad design
Unprompted procedures
S-R compatibility
Feedback
Precision of action
S-R-K