Detecting deception

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?