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Experimental Design: The Smell of Fear
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Experimental Design: The Smell of Fear


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These slides are from a first year undergraduate lecture introducing concepts of experimental design in a light-hearted way. Two approaches to tackling the question "can you smell fear?" are …

These slides are from a first year undergraduate lecture introducing concepts of experimental design in a light-hearted way. Two approaches to tackling the question "can you smell fear?" are contrasted. Firstly students watch a short clip from the TV series Brainiac Science Abuse and having discussed what is right/wrong with this approach they design better ways to address the same question, before finally we consider the methodology used in an academic paper on the topic (Prehn-Kristensen et al (2009) doi:10.1371/journal.pone.0005987). The latter is published in an open access journal PLoS ONE where "Under the CCAL, authors retain ownership of the copyright for their article, but authors allow anyone to download, reuse, reprint, modify, distribute, and/or copy articles in PLoS journals, so long as the original authors and source are cited. No permission is required from the authors or the publishers."

Chris Willmott, University of Leicester.

Published in: Health & Medicine, Technology

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  • 1. Experimental Design Chris Willmott 2/01b Henry Wellcome Building [email_address] MB1031 Introduction to Medical Bioscience B
  • 2. Introduction to session
    • value of scientific data relies on research being conducted in an appropriate way
    • quantity of data is no substitute for quality
    • in addition to ‘wrong’ findings there may be cost in terms of time , money and harm if experiment badly designed
    • purpose today = to begin to consider aspects of good (and poor) experimental design
  • 3. The smell of fear
    • watch this short clip describing an experiment to investigate whether you can smell if someone is afraid
    • having watched the clip, consider: - what was good about the design of the expt? - what was wrong with the experiment?
  • 4. Good aspects of Brainiac expt?
    • included a negative control (no fear, no sport)
    • all subjects carried out their activity for same time
    • all subjects were “sniffer” by same person
    • all subjects were same gender
    • … but little else is good
  • 5. What was wrong with this expt?
    • only one “sniff-er”
    • only three “sweat-ers”
    • was not the same person on crane/running/relaxing
    • distance nose-to-armpit not same in all cases
    • may have been other explanations for the observed differences, e.g.
      • natural body odour differences between the three
      • use of deodorant
      • eating of smelly foods
    • olfactory fatigue/adaptation may have occurred
  • 6. Design a better version
    • work with those sitting near you to design a better experiment looking into whether it is possible to smell fear
  • 7. A more scientific approach Prehn-Kristensen et al (2009), PLoS ONE 4(6): e5987
  • 8. Sweat donors
    • N= 49, of whom 28 (57%) male
    • Removal of as many confounding factors as possible:
      • had to be non-smokers
      • European origin
      • not taking medication
      • no history of neurological, psychological, endocrine or immune disease
      • no garlic, onion, asparagus or spicy food for >24 hrs
      • no deodorants
      • only odourless soap (provided)
  • 9. Sweat collection
    • Sweat collected (different days, same time of day) from all participants under two different conditions:
      • for 60 mins prior to final oral exam of degree
      • for 60 mins during sporting activity = control (10 min intro, 10 min cycling, 10 min rest, 10 min cycling, 10 min rest, 10 min cycling)
    • All donated sweat pooled into one of 4 groups:
      • male, anxious (MA)
      • male, sport (MS)
      • female, anxious (FA)
      • female, sport (FS)
  • 10. Sweat collection
    • Saliva samples taken from donors at various timepoints to monitor cortisol and testosterone levels
    • Immediately before exam/after exercise, donors asked to rate their emotions ( anxiety , joy , surprise , anger , sadness , disgust ) and their feelings of happiness , arousal and dominance
  • 11. Test participants
    • N = 28, of whom 14 (50%) male
    • Removal of confounding factors:
      • all right-handed
      • all non-smokers
      • not taking medication
      • no history of neurological, psychiatric, endocrine or immunological diseases
      • no upper respiratory tract diseases
      • no brain injury
      • no concerns about being in MRI scanner
    • Written informed consent, paid
  • 12. Test procedure (1)
    • Prior to scan, participants asked to rate each odour (MA, MS, FA, FS) on scale of 0 to 8 for:
      • intensity
      • pleasantness
      • unpleasantness
      • familiarity
    • Also asked whether feelings of happiness, arousal or dominance affected
    • No significant differences between ‘anxiety’ samples and ‘sport’ samples reported
  • 13. Test procedure (2)
    • Odour delivered to participants via adapted oxygen mask whilst in MRI scanner
    • System validated using rose-smelling odour with 8 participants (= positive control)
    • Each of 4 odours (MA, MS, FA, FS) given 20 times in random order
    • Asked to click yes/no for odour detection
    • Breathing belt around chest confirmed breath taken
    • Patterns of brain activity also recorded in each case
  • 14. fMRI results: Anxiety - Sport
  • 15. Conclusions
    • Questions about perception : conscious mind did not detect difference anxiety v sport
    • fMRI scans : but subconscious mind did demonstrate differences
    • Authors consciously recognise limits : findings about anxiety do not necessarily translate to other chemosensory signals