Detecting deception
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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?