Chapter 12. Stress and Human Error

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Chapter 12. Stress and Human Error

• STRESS
• stressors (Fig 12.1) environmental factors,
  psychological factors, time pressure
• produce phenomenological experience emotional
  or affective
• physiological change observable, often linked
  with phenomenological experience
• affect characteristics of information processing,
  not always degrade performance
• Stress Effects on Performance
• developing models that will accurately predict
  stress effects is challenging
• ethical considerations make it difficult to carry
  out controlled experiments
• human performance response to stressors appears
  to be inconsistent and unpredictable
• the pattern of inferred human stress response
• stress was a causal factor in the errors made in
  the events, yet the causal inferences will always
  be ambiguous
• there have been a series of efforts to capitalize
  on stress imposed for other reasons, to gain
  insights into performance
• a number of studies have examined that effects of
  stressors in more controlled laboratory
  environments
• Stress Component Effect
• Arousal
• easiest way to measure the quantitative levels of
  many stressors is through physiological measures
  of arousal HR, pupil diameter, catacholomine in
  the blood or urine

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• associated with improving the level of
  performance
• most stressors increase the level of arousal but
  sleep loss and fatigue will decrease arousal
• Selective Attention Narrowing
• increased selectivity or attentional narrowing
  results from a wide variety of different
  stressors
• usually degrade performance may actually
  facilitate performance with focused attention
• Selective Attention Distraction
• simply impose a distraction, thus divert
  selective attention away from taskrelevant
  processing
• Working-Memory Loss
• negative effects of anxiety, perceived danger,
  noise
• The Yerkes Dodson Law
• an inverted U-shaped pattern relating stress to
  human performance (Fig 12.2)
• at the lower end of the arousal scale, increasing
  stress by increasing arousal will increase
  performance
• higher levels of arousal, stress begins to
  produce the attentional and memory difficulties
  that cause performance to decrease
• the optimum level of arousal greater
  performance for simple task than complex
• Perseveration
• high level of stress will cause people to
  perseverate or continue with a given action or
  plan of action that they have used it in the past
• combined effects of stress on attentional
  narrowing and perseveration can contribute to a
  pattern of convergent thinking or cognitive
  narrowing and tunneling that can be dangerous in
  crisis decision making
• stress will enhance the confirmation bias

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• Strategic Control
• the characterization of a set of strategies that
  the human will consciously adapt to cope with the
  perceived stress effects in Fig 12.3
• adaptive closed-loop model of stress -- appraisal
  and strategic choice
• operators not respond to the stressor per se, but
  to the perceived or understood level of stress
  (cognitive appraisal)
• selection of the appropriate or inappropriate
  strategies -- four major categories of adaptive
  responses
• Recruitment of More Resources
• try harder or acceleration (time stress) can be
  adaptive but it has risks
• long-term costs of fatigue and possible health
  risks
• acceleration may eliminate redundancies ?
  confusions and errors
• shift in the speed-accuracy trade-off, toward
  faster but more error-prone performance
• Remove the Stressor
• Change the Goals of the Task
• people adaptively invoke qualitatively different
  performance strategies under higher stress
  conditions ? a simpler and less effortful
  strategy is often chosen ? people to abandon
  compensatory strategies in favor of simpler
  non-compensatory ones, which are simpler,
  quicker, and require less WM more stress
  resistant
• humans adapt by choosing a simpler and more
  efficient strategy
• stressors even produce performance improvement
• Do Nothing

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• Moderating Effects
• Other Stressors -- one stressor may reduce rather
  than amplify the effect of another
• Personality
• locus of control those with an internal (self)
  locus of control are less stressed
• action-oriented (more proactive and effectively
  filter less relevant material) vs. state-oriented
  (more reactive and more inclined to accelerate
  performance)
• Training and Expertise
• highly skilled operators are more immune or
  buffered from the negative effects of stress
• automaticity ? pure expertise in routine
  performance is not sufficient
• greater repertoire of strategies available
• greater familiarity with the stressors
• Stress Remediation
• Environmental Solutions
• Design Solutions -- emergency procedures
• Training
• HUMAN ERROR
• human error is the primary cause of 60 to 90 of
  major accidents and incidents
• result of bad system design or bad organizational
  structure rather than irresponsible action
• the error was only one of a lengthy and complex
  chain of breakdowns
• Categories of Human Error An Information
  Processing Approach

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• Mistakes
• failing to formulate the right intentions
  shortcomings of perception, memory, cognition
• knowledge-based mistakes
• incorrect plans of actions are arrived at because
  of a failure to understand the situation
  (incorrect knowledge) ? influences of many biases
  and cognitive limits
• insufficient knowledge of expertise to interpret
  complex information
• poor displays either present inadequate
  information or in a poor format
• rule-based mistakes
• operators know the situation, and they invoke a
  rule or plan of action to deal with it
• the choice of rule if-then logic
• choice of a rule guided by frequency and
  reinforcement
• Slips
• the right intention is incorrectly carried out
• capture errors the intended stream of behavior
  is captured by a similar, well practiced behavior
  pattern
• intended action involves a slight departure from
  the routine, frequently performed action
• either stimulus or action sequence are closely
  related to now inappropriate action
• action sequence is relatively automated and
  therefore not monitored by attention
• pouring orange juice rather than syrup on the
  waffles while reading the newspaper
• Lapses
• failure to carry out any action at all

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• Mode errors
• closely related to slips but also have the memory
  failure characteristic of lapses
• pressing the accelerator of a car to start when
  the transmission is in the reverse mode
• a joint consequence of relatively automated
  performance or of high workload and of improperly
  conceived system design
• Distinction Between Error Categories
• the ease of detectability
• detection of slips relatively easy
• preventing slips system and task design
• preventing mistakes design features related to
  effective display or on training
• Human Reliability Analysis
• to predict human error (Fig 12.5)
• technique for human error rate prediction (THERP)
• Human error probability (HEP) the ratio of the
  number of errors made on a particular task to the
  number of opportunities for errors ? from
  databases of actual performance or estimated by
  experts (heavily biased and not always terribly
  reliable)
• event tree or fault tree (Fig 12.6)
• HEPs can be modified by performance shaping
  factors, multipliers(expertise or the stress)
• Lack of Database
• Error Monitoring
• Nonindependence of Human Errors
• first error ? resulting frustrations and stresses
  ? increase the likelihood of a subsequent error

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• Integrating Human and Machine Reliabilities
• to integrate actuarial data of human error with
  machine data to estimate system reliability
  difficult to justify ? nonindependence issue ? a
  considerable challenge to estimate reliability
• Errors in the Organizational Context
• human error as only one small component in a set
  of more serious organizational deficiencies
• local triggers or active failures the tip of
  the iceberg
• resident pathogens or latent conditions the
  base of the iceberg (Fig 12.7)
• Error Remediation
• Task Design
• Equipment Design
• minimize perceptual confusions
• Make the execution of action and the response of
  the system visible to the operator
• Use constraints to lock out the possibility of
  errors
• Offer remedies
• Avoiding multimode system
• Training
• Assists and Rules
• memory aids or procedures checklists
• Error-Tolerant Systems
• errors are undesirable but inevitable

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