1. 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!

2. 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

3. 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

4. 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)

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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?

11. 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!)

12. 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

13. 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

14. 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

15. 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)

16. 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

17. 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!

18. 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 (?)

19. 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?