Stephen Legg Centre for Ergonomics, Occupational Safety and Health, School of Management, Massey University, Palmerston North, New Zealand s.j.legg@massey.ac.nz (P18, Thursday 27, Civic Room 3, 10.30)

2. Centre for Ergonomics Occupational Safety and Health
(CErgOSH)
Our strengths

4. 1Centre for Ergonomics, Occupational Safety and Health
2School of Sport and Exercise Science
3School of Psychology
4 School of Aviation
OHSIG Conference presentation
27 Oct 2011
*Massey University Research Fund Summer Studentship 2010 and 2011
Study also supported by the NZDF Defence Technology Agency

5. This video available at
http://youtu.be/Y4JoXT3or3M

6.  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

7.  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)

8. 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
Hypothesis
Mild 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)

9. Study design
Familiarisation session
15 students
Hypoxicator 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

10. 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

12. Physiological results
Heart Rate (bpm)
100 90
98 98 1% 85
HR (bpm)
96 80
SaO2 (%)
75
94
70
92
90
91 1% 65
60
88 55
86 50
Normoxia Mild Hypoxia

13. Simple joystick „steering‟ task
◦ Keep white disc inside yellow target with joystick
Braking task
◦ Press foot pedal when lights come on. Duration ~10
minutes: 15 brake trials, 35-50 seconds apart
Measurements
◦ Time outside target
◦ Braking reaction time
Prediction based on previous research
◦ No significant effect of mild hypoxia
Results
◦ No significant effects

14. 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 easy
Dual 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

15. 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

16. 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 sentence
2. 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.

17.  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
◦

18.  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

19. Conclusions
Tentative evidence that mild hypoxia (equivalent to
cabin altitudes of about 8000 ft) can affect aspects
of complex cognitive decision-making in novel and
stressful situations

20. 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)