Lie Detection


Lie Detection

How lie detectors work:
Measure involuntary physiological reactions to emotional stress
– Heart rate variability (stressful situations cause an increase in sympathetic activity “fight or flight”, which increases heart rate variability)
– Skin conductance (small increases in sweat gland activity in the palms and soles is controlled by the sympathetic nervous system.  Increased conductance = increased arousal)
– Blood pressure
– Respiratory rate

Ways to beat a lie detector
– Superficially raise your sympathetic level during the “control” period
– Superficially lower your sympathetic level during the relevant period

Can people really fool a lie detector test?
– Gary Ridgway; American serial killer known as “The Green River Killer”, convicted of 48 separate murders but confessed to nearly double that.  Killed prostitutes in Washington during the 80s/90s.  His first 5 victims were found in the Green River.  He was arrested in 1984, at which point he took and passed a polygraph test.  He was arrested again in 2001, when DNA evidence matched him to the crimes.

– Aldrich Ames; Soviet double agent.  Compromised more CIA assets than any Soviet mole in American history.  Passed 2 polygraph exams in 1986 and 1991.  Apparently, the KGB told him to get a good night’s sleep, relax, and pretend he was good friends with the test administrator.  He was eventually arrested after surveillance evidence accrued.  He compromised over 100 US intelligence operations and his info led to the execution of at least 10 US sources.

– Bill Wegerle failed 2 polygraph tests in Wichita, KS, while under suspicion of killing his wife.  One given by police, one given by an examiner he hired to clear his name.  He was never arrested or convicted, but was largely suspected of, and shunned for, the crime by his community for about 20 years.  Eventually, evidence linked his wife’s death to the BTK killer, a serial killer from the Wichita area, and effectively cleared his name.

How accurate is the polygraph test?
– Very little scientific credibility
– Businesses selling polygraph equipment claim validity of 90-100%, but a survey of over 400 forensic psychologists puts the validity at about 61%.  Still better than chance alone, but given the stakes, it doesn’t seem to be an admissible form of evidence.

– In 2007, polygraph testimony was still admitted in 19 states, but was up to the discretion of the trial judge in federal court.  It is still used extensively by attorneys and law enforcement agencies, including the LAPD.  Most commonly, it is used in post-conviction supervision of sex offenders.

How can a Good Guy To Know use lie detection strategies?

– First off, don’t buy a polygraph.  It’s largely pseudoscience at this point.
– Look for sociological signs of deception:

1) Eye movements

2) Body movements
Timing and duration of emotional gestures are off normal pace.


Expressions are often limited to only movements of the mouth when someone is lying, rather than the whole face if they’re telling the truth.

When people touch their face/throat/mouth, it usually is a sign of discomfort

Liars will tend to place objects between themselves and you

3) Speech patterns

Typically, statements with a contraction are more likely to be truthful (I didn’t do it, versus, I did not do it)

Liars will include unnecessary details while recanting their story in an effort to convince you

Be suspicious if someone uses the words “never” or “always”

*Trick*  Try switching the subject quickly.  A liar will often follow you to the new subject, glad to have gotten away with their deception.  Someone who is telling the truth will probably be confused about the subject change, and will want to return to the dispute so that they can effectively clear their name.

Poker Table Lie Detection

Common tells include dilated pupils (in a well-lit room), strong/rapid pulse seen either in the temple or at the carotid, the “prey response” (sitting still/quiet, like a rabbit when a predator is close).

Likewise, people may try to hide their naturally heightened state by engaging in worthless, forced conversation, exaggerating gestures, or trying to move the focus off of them.

Unfortunately, you’re really just trying to detect a stress response, which can occur during a bluff (most commonly), or when someone has a great hand (less common, but devastating to you).


None of these techniques should be used by themselves.  You’ll get better accuracy if you notice a number of these phenomena occurring simultaneously.  Obviously, these are all dependent on the individual in question, and you’ll be much more likely to catch a lie from someone you know, because you can judge against their baseline.  Also, and most importantly, I make absolutely no claim that the above suggestions have good evidence of their efficacy over time and over a large number of liars.  Use cautiously.

Most of this info was pulled from Wikipedia or websites created for entertainment purposes only.

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