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Detecting deception. A lie: a deliberate attempt by one person to mislead another No prior warning of this intent To detect a lie, we need to understand why lies fail Speech content, mannerisms Will tell us what to look for Problem: How do we know when we have caught a liar?

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detecting deception
Detecting deception
  • A lie: a deliberate attempt by one person to mislead another
    • No prior warning of this intent
  • To detect a lie, we need to understand why lies fail
    • Speech content, mannerisms
    • Will tell us what to look for
  • Problem: How do we know when we have caught a liar?
    • Error 1: He was lying and we missed it
    • Error 2: He wasn’t lying and we said he was!
misses false accusations
Misses & False accusations
  • “we can detect lies with 96% accuracy” what does it mean?
    • We can only work out this number if we know base truth
  • Base truth is when we know the actual truth about the event
    • Normally happens in experiments
    • Not normally available in the field unless the person confesses to lying
  • We must trade off one type of error against the other
    • A problem of all hit/miss decisions on a yes/no event
limits of decisions
Limits of decisions
  • Your decision will be balanced on two poles
    • Being too lenient, and increasing your chance of him getting away with it if he actually lied
    • Being too conservative and increasing your chance of falsely accusing him if he is actually innocent
  • So why not just be extra conservative, if we think he is actually lying?
    • Because we don’t know the base truth! So all decisions are compromises between these
why do lies fail
Why do lies fail?
  • Some external reasons
    • Someone rats them out, physical evidence is found
  • Sometimes the liar exposes the lie
    • Some behaviour or statement may reveal the lie
  • But beware! Contradictions are tricky!
    • A contradiction can be a sign of a lie
    • But truth can contain contradictions too (bad memory, etc)
lying on the fly
Lying on the fly
  • To effectively lie, you need time to prepare
    • Get the story straight
    • That way, it will flow naturally when telling it
  • When being questioned, a non-prepared lie may become apparent
    • Show signs of thinking about answer
    • Pause, averting gaze, speech mannerisms
    • Can only be taken as a sign of lying depending on the context
emotions and lying
Emotions and lying
  • Faking an emotion is hard
    • Either showing one you don’t feel or suppressing one you do
  • Some signs of emotion are ‘reliable’ (extremely hard to fake)
    • Narrowing red edge of lips (anger)
    • Eye muscle movement in Duchenne’s smiles (happiness)
    • Could be faked by Stanislovskian method
  • Concealing emotions in harder than faking them
concealing an emotion
Concealing an emotion
  • One emotion is generally concealed by trying to express another
    • Eg. Hide sadness by attempting to smile
  • This can fail in two ways
    • Leakage (part of the masked emotion escapes) – eg. Brow remains raised even when smiling
    • Produce a deception cue (behaviour which doesn’t fit in with the rest of the lie) – eg. Smile may not be held for long enough
further role of emotions
Further role of emotions
  • Even if the lie is not about emotion, emotions probably play a role
    • Fear, guilt, happiness (“dupe delight”), excitement
    • Not in every lie
  • Whether emotion is felt depends on various factors
    • Characteristics of the liar
    • Characteristics of the target
    • Content of the lie
  • Each type of emotion has two effects
    • Increase in level of arousal
    • Specific behavioural changes
examples of emotion in lying
Examples of emotion in lying
  • Fear
    • Chance of punishment is high
    • Lie is not practiced
    • No experience of success with the target
    • Known that target is suspicious
  • Guilt
    • Values shared with target or target respected
    • No personal benefit from the lie
    • Lie not authorized by an institution
  • Duping Delight
    • Allies of the liar are watching
detecting lies by behaviour
Detecting lies by behaviour
  • Several channels to consider
    • Face, body, voice, paralinguistics
  • No one channel provides more information than the others
    • Each can provide some, combinations can provide more
  • Showing these behaviours does not guarantee lying
    • “Othellos’s error”
    • Need to consider the context of the behaviour
    • Would a truthful person show those emotions in that circumstance?
experiments in lying
Experiments in lying
  • Experiments would be useful
    • Allow us to tell which cues are linked to lying
  • How does one experiment on lying?
    • Get people to lie/not lie
    • Measure various cues and see if they are useful predictors
  • What about high stakes?
    • Lying about something silly will not give a level of arousal matching a real world situation
    • But creating a high stakes situation increases the motivation to not be caught (ruins the experiment!)
example riggio friedman 1983
Example:Riggio & Friedman (1983)
  • Undergraduate volunteers
  • Subject sits alone in front of video camera
  • Given a folder with pictures
    • Each had instructions on whether to describe the picture or lie
  • No punishment/reward for lying
  • Extremely well controlled experiment
    • But very unlike a real lying situation
example eckman et al 1989
Example: Eckman et al (1989)
  • Student nurse subjects
    • The study was part of their course
  • Had to describe, as they watched, a gory video and lie
    • Spoke to a person in the room who could not see the video
  • Control group who described a pleasant video without lying
  • Well controlled, realistic experiment
    • Base truth is known
    • High stakes situation
    • More generalizable to real situations
getting cues from eckman s study
Getting cues from Eckman’s study
  • Looked for cues in various domains
    • Facial expression (using FACS)
    • Voice (stress, pitch, volume, etc)
    • Body movement (mannerisms, suppression, etc)
  • Asked judges (observers) to look at videos
    • Asked if the subjects were lying or not
    • Asked them to infer about personality and affect
  • Analyze these to find if there were reliable cues to predict lying
ekman s results
Ekman’s results
  • Indicators in facial expressions
    • Duchenne’s smiles in rue enjoyment
    • Leakage smiles (micro-traces) in lying
  • Indicators in voice / text
    • Pitch increases in lying
    • Number or self-references (‘I’/’me’) decreased in lying
  • Best predictor is in combining both expression/voice data
    • Accurate assignment rate of 96%
    • Comparable with best published polygraph results (see later)
why the changes when lying
Why the changes when lying?
  • Duchenne’s smiles are automatic
    • Difficult to fake
  • Leakage smile (ie. other emotions leaking through)
    • Emotions of lying, or about the nasty film?
    • Probably lying; smiles different to miserable smiles and compliance smiles
    • In another experiment (no lying) leakage smiles did not occur
why the changes when lying1
Why the changes when lying?
  • Changes in self-reference
    • Could be due to simultaneous planning of the lie
  • Changes in voice pitch
    • Fear of being caught? Arousal from the film? Both?
    • Probably lying (also been found in lying studies without nasty films)
  • Note: the indicators are clear, but the reasons why they occur are not!
looking at videos of lying
Looking at videos of lying
  • Note: subjects only told they were seeing a conversation!
  • Only text cues (what was said) and mannerisms made a difference
    • Duchenne’s smiles, Leakage smiles, voice pitch etc not used
  • The most important predictors of lying were ignored!
    • Most useless behaviours were focussed on
    • In social world, people act to maintain lies (?)
ekman s conclusions
Ekman’s conclusions
  • Some lying cues can be found
    • They cut across channels (not simple)
    • Face and voice together provide a high hit rate
  • BUT: observers who are not privy to the lie do badly at spotting it
    • Observers ignore these cues
    • Focus on content of the conversation
    • This is a terrible predictor of lying
    • Question: Can observers be trained to ignore useless cues and focus on reliable ones?