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Stress, Workload, Accidents, & Errors

Figure 13.1 A representation of stress effects. (Wickens et al, pg.325)

Information

Processing

Stressors

ExperienceHealth

Direct (e.g., vibration)

Physiological arousalIndirectDirect (e.g.,

lighting, noise)

Input Performance

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Environmental Stressors

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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WorkloadOverload Underload

Measures

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

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 checklistDefinition

Relevant theories, etc.

Good design Bad design

LegibilityHow 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.)

DefinitionRelevant

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.)

DefinitionRelevant

theories, etc.Good design Bad design

Unprompted procedures

S-R compatibility

Feedback

Precision of action

S-R-K