1. Lie detector
Week 5

2. How many times do people lie a day?
Diary studies of lying
77 college students reported telling 2 lies a day,
70 community members told 1
DePaulo, Kashy, Kirkendol, Wyer, & Epstein (1996). Lying in everyday life. J Pers Soc Psychol.

3. When do people start lying?
When theory of mind develops.
Lying requires metacognition – knowing that other people have minds
Thus, lying is a cognitively effortful process

4. History of lie detectors
Ancient Hindus: If deception leads to fear, and fear inhibits the secretion of saliva, then an accused individual shouldn’t be able to spit out rice after chewing it because it will stick to the gums.

5. History of lie detectors
16th and 17th centuries “dunking test”: People who denied being witches were dunked in water.
If she floated to the surface = guilty (because witches are supernaturally light or because water is so pure a substance as to repel a witch’s evil nature) sentenced to death.
If she didn’t float to the surface = innocent (and dead)

6. History of lie detectors
1920s, psychologist William Moulton Marston invented a device, the first “lie detector” test, that measured systolic blood pressure

7. Pop culture https://www.youtube.com/watch?v=Vj0PsC7iaBs

8. Comparison Question Test
Notice Jack first measures the baseline (responses towards mundane questions) and then the actual questions of interest.
This baseline-experimental manipulation methodology is scientifically sound!

9. Comparison Question Test
Relevant questions concerning the alleged misdeed
“Did you steal $200 from your employer?”
Questions that try to force people to tell a lie that’s irrelevant to the alleged misdeed
“Have you ever lied to get out of trouble?”

10. Uncontested assumptions
People get nervous
Polygraphs detect heart rate (HR), skin conductance (SC), and blood pressure (BP)
HR, SC, and BP are under control of the autonomous nervous system; it’s difficult (not impossible) to control these indices voluntarily
Lie detection follows signal detection logic (next slide)

11. Signal detection logic
LIE

12. Problem Anxiety The many-to-one problem Lying Shock at being accused
XXX
Worry

13. Problem 2. Some people do not get anxious when lying psychopaths
3. Polygraph examines are prone to confirmation bias
the tendency to see what they expect to see
Classic exposé (1989):

14. Conclusion
The “lie detector” is an arousal detector.

15. Would ‘truth serums’ work?
Truth serums increase both revealed truths, lies, and plain nonsense. So in the end, you still can’t tell which is which.

16. So what can be done? Apparently, aphasics are better at lie detection
Aphasics have damage to left hemisphere  severe deficits at understanding spoken sentences
Their brain develops compensatory ability at judging nonverbal behaviors
Etcoff et al. (2000). Lie detection and language comprehension. Nature.

17. Current state of lie detection
We know many clues to deception – whether we can detect them reliability is another question
Most lie detection theories promises a ‘better than chance’ hit rate.
But we still don’t have a good tool that promises legally/ethically acceptable reliability hit rates, minus the false alarms.
DePaulo et al. (2003). Cues to deception. Psychological Bulletin.

18. Nice reads
Lilienfeld , S. O., & Lynn, S. J. (2009). 50 Great myths of popular psychology: Shattering widespread misconceptions about human behavior.
Vrij, A. (2000.) Detecting lies and deceit: the psychology of lying and implications for professional practice. Wiley series in psychology of crime, policing and law.