Pilot In-flight Complex Decision Making May be Impaired by Mild Hypoxia


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Stephen Legg
Centre for Ergonomics, Occupational Safety and Health,
School of Management,
Massey University,
Palmerston North, New Zealand

(P18, Thursday 27, Civic Room 3, 10.30)

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Pilot In-flight Complex Decision Making May be Impaired by Mild Hypoxia

  1. 1. Centre for Ergonomics Occupational Safety and Health (CErgOSH) Our strengths
  2. 2. 1Centre for Ergonomics, Occupational Safety and Health 2School of Sport and Exercise Science 3School of Psychology 4 School of AviationOHSIG Conference presentation27 Oct 2011 *Massey University Research Fund Summer Studentship 2010 and 2011 Study also supported by the NZDF Defence Technology Agency
  3. 3. This video available athttp://youtu.be/Y4JoXT3or3M
  4. 4.  Symptoms of hypoxia are dependent on the level of hypoxia (i.e. the altitude), are deceptively insidious, initially very subtle and progressive: ◦ Visual: reduced colour perception, peripheral vision, acuity, and dimming ◦ General: euphoria, task fixation, personality changes, fuzziness, amnesia, mental confusion, loss of self criticism, poor judgement and decision making ◦ Neuromuscular: clumsiness, fine tremor, slurring of speech, slowing of movements, „hypoxic flap‟ ◦ Times of useful consciousness Altitude Time of useful consciousness 18,000 ft 10-15 min 25,000 ft 2-3 min 40,000 ft About 30 seconds
  5. 5.  Evidence for the effects of mild hypoxia is mixed ◦ Reduced complex reaction times, but well learned tasks unaffected at 5000 and 8000 ft (Denison et al 1966) ◦ Impaired novel task learning under mild hypoxia (Crow and Kelman, 1969, Farmer et al 1992) ◦ Simple tasks - logical reasoning and a vigilance - unaffected at 8000 ft (Morgan and Green 1972, Fiorica et al 1971) ◦ Slower judgement time at 7000 ft but accuracy unaffected (McCarthy et al 1995) ◦ No effects on visual function at 7000 ft (Corban et al 1995) ◦ Impaired sleep quality at about 8000 ft (Muhn et al 2009)
  6. 6. Our concern Mild hypoxia associated with exposure to aircraft cabin altitudes of 8000 ft may be an unrecognised factor contributing to impaired decision-making performance of aircrew in uncertain, novel, or emergency situations, and may be a factor that could have contributed, and may contribute in the future, to aircraft accidents HypothesisMild hypoxia (equivalent to cabin altitudes of about 8000 ft) impairs complex cognitive (decision- making) task performance (especially when there are additional multiple stressors and task demands)
  7. 7. Study design Familiarisation session 15 studentsHypoxicator delivers normoxic or hypoxic air equivalent to 8000 ft First exposure Second exposure (Hypoxia or Normoxia) (Hypoxia or Normoxia) Counterbalanced presentation Physiological measurements Cognitive Tasks Psychomotor task • SaO2 • HR Complex decision • Reasoning task making tasks • Memory task
  8. 8. Normoxia Normoxia or mild hypoxia 0 30 60 90 120 150 Time (min) Rest period Rest period Cognitive tasks Cognitive tasks Cognitive tasks• SaO2• HR
  9. 9. Physiological results Heart Rate (bpm) 100 90 98 98 1% 85 HR (bpm) 96 80SaO2 (%) 75 94 70 92 90 91 1% 65 60 88 55 86 50 Normoxia Mild Hypoxia
  10. 10. Simple joystick „steering‟ task ◦ Keep white disc inside yellow target with joystickBraking task ◦ Press foot pedal when lights come on. Duration ~10 minutes: 15 brake trials, 35-50 seconds apartMeasurements ◦ Time outside target ◦ Braking reaction timePrediction based on previous research ◦ No significant effect of mild hypoxiaResults ◦ No significant effects
  11. 11. Belief bias People find logic tasks (syllogisms) difficult when believability of conclusion conflicts with logical validity of argument Syllogism All mammals can walk Whales are mammals Whales can walk Unbelievable conclusions incline people to think syllogisms are invalid Believable conclusions incline people to think syllogisms are valid Belief Bias makes judging the validity of Conflict (unbelievable) syllogisms hard and Nonconflict (believable) syllogisms easyDual process Reasoning while doing another mental task (i.e. the logic task) causes poorer performance on Conflict syllogisms but not Nonconflict syllogisms ..... because Conflict syllogisms require much more concentration and deliberation to judge correctly
  12. 12. Reasoning Task – Belief bias/Dual process task Method ◦ 12 logical syllogisms for each block Example of a valid conflict syllogism  6 conflict syllogisms,  6 non-conflict syllogisms  Half valid, half invalid ◦ Random presentation Measurements ◦ Accuracy ◦ Response Time Prediction ◦ Mild hypoxia will reduce performance on Conflict and Invalid (i.e. difficult) syllogisms but not Non-conflict and Valid (i.e. easy) syllogisms Results ◦ No change in Accuracy ◦ Conflict syllogisms judged more slowly in mild hypoxia at 30 & 90 min ◦ Invalid syllogisms judged more slowly in mild hypoxia at 30 min
  13. 13. 1. Reading Span measure of Working Memory (WM) ◦ Processing Component  Judge the semantic and/or syntactic sense of sentence He was a fanatical yellow of football, rugby, and cricket. ◦ Memory Component  Recall last word of each of a set of 2-6 sentences  Cricket in the previous sentence2. Event-based Prospective Memory (PM) ◦ PM = Remember to do something when a specific event occurs ◦ PM task = press F whenever you see the letter string “ean” in a sentence Everyone knew his distinctive purple beanie and shoes.
  14. 14.  Method ◦ 60 sentences, divided up into 15 blocks ◦ 10 blocks contained a PM trial (a word with „ean‟ in it) ◦ At the end of each block, subject prompted to recall the last word of each of the sentences in the block Measurements ◦ Working Memory span – number of last words recalled correctly ◦ Sentence sense error rate ◦ Prospective Memory score – number of times an „ean‟ word was correctly spotted Prediction ◦ Working Memory span, Sentence sense error rate and Prospective Memory score will all be reduced by hypoxia Results ◦ Reduced WM span at 90 min ◦ No effect on Sentence Sense Error rate ◦ No effect on Prospective memory ◦
  15. 15.  Psychomotor task ◦ As predicted, no effect of mild hypoxia on psychomotor task Complex cognition tasks ◦ Reasoning  Reasoning accuracy not noticeably affected by hypoxia  Time to reason affected by hypoxia, particularly for „harder‟ logical operations (i.e. conflict syllogisms and invalid syllogisms) that require concentration and deliberation ◦ Working Memory  Working memory span reduced by hypoxia after 90 min  Hypoxia had no effect on Sentence Sense Error Rate and Prospective memory
  16. 16. ConclusionsTentative evidence that mild hypoxia (equivalent tocabin altitudes of about 8000 ft) can affect aspectsof complex cognitive decision-making in novel and stressful situations
  17. 17. Limitations of this study Small sample size (n =15). We will be collecting data for at least 10 more subjects to increase statistical power Students are not pilots Limited face validity of the complex cognitive reasoning and memory tests for aviation Future study plans The effects of varying durations and levels of mild hypoxia in an increased sample size of pilots with more refined tests of complex cognitive performance (with higher face validity) and of risk judgement in a flight simulator  The effects of combined exposure to mild hypoxia, dehydration, circadian dysrhythmia (jet-lag) and sleep deprivation (loss of and disturbed sleep)