Polygraphs?

[kwigibo]

I've just been reading about them on Randi.org, and their opinion is, not surprisingly, that they're completely bunk.

It got me to thinking, my only experience with polygraphs has been in movies and on TV. I don't have much idea as to how they're supposed to work, other than that they measure your pulse-rate or something. Of course, even with what little I knew, I never thought that there was any substance to it, as if there were any constant connection between physiological functions and lying that applied equally to all people, or even to one person.

But, I am still curious as to its supposed nuts and bolts, and also about any experiences people have had with them. According to the Randi site, multitudes of US governmental departments swear by the device, especially law enforcement and defense (even though they rarely count as evidence in court anywhere anymore, I think). And I'm also under the impression that in the US, many employees are subject to polygraph tests, for a plethora of reasons.

So, anyone know how they 'work'?

Anyone ever been subjected to a 'test'?

:)

[LeftCoast]

Originally posted by kwigibo
I've just been reading about them on Randi.org, and their opinion is, not surprisingly, that they're completely bunk.

It got me to thinking, my only experience with polygraphs has been in movies and on TV. I don't have much idea as to how they're supposed to work, other than that they measure your pulse-rate or something. Of course, even with what little I knew, I never thought that there was any substance to it, as if there were any constant connection between physiological functions and lying that applied equally to all people, or even to one person.

But, I am still curious as to its supposed nuts and bolts, and also about any experiences people have had with them. According to the Randi site, multitudes of US governmental departments swear by the device, especially law enforcement and defense (even though they rarely count as evidence in court anywhere anymore, I think). And I'm also under the impression that in the US, many employees are subject to polygraph tests, for a plethora of reasons.

So, anyone know how they 'work'?

Anyone ever been subjected to a 'test'?

:)

Check out AnitPolyGraph.org (http://www.antipolygraph.org/). Especially look at this document (http://www.antipolygraph.org/lie-behind-the-lie-detector.pdf) - which should go a long way to answering all of your problems.

[Loren Pechtel]

Originally posted by kwigibo
I've just been reading about them on Randi.org, and their opinion is, not surprisingly, that they're completely bunk.

It got me to thinking, my only experience with polygraphs has been in movies and on TV. I don't have much idea as to how they're supposed to work, other than that they measure your pulse-rate or something. Of course, even with what little I knew, I never thought that there was any substance to it, as if there were any constant connection between physiological functions and lying that applied equally to all people, or even to one person.

But, I am still curious as to its supposed nuts and bolts, and also about any experiences people have had with them. According to the Randi site, multitudes of US governmental departments swear by the device, especially law enforcement and defense (even though they rarely count as evidence in court anywhere anymore, I think). And I'm also under the impression that in the US, many employees are subject to polygraph tests, for a plethora of reasons.

So, anyone know how they 'work'?

Anyone ever been subjected to a 'test'?

:)

As normally used they are bunk.

However, they can be used in *SOME* situations with great reliability if it's done right.

They are too vulnerable to various factors to ever be counted on for detecting *LIES*. However, if they are used to detect knowledge it's another matter--quite reliable and failures will be false negatives, not false positives.

Ok, you've got a corpse and a few suspects. First, make sure they don't know the details of the crime (you'll have to prohibit newspapers from publishing crime scene photos for this to be of much use.) Then you give them a bunch of statements to read, one at a time (these must be based on the actual crime, a generic list isn't possible):

She was wearing a red blouse
She was wearing a green blouse
She was wearing a white blouse
She was wearing a blue blouse

Her blouse was still on
Her blouse had been ripped open
Her blouse had been ripped off
Her blouse had been removed normally

She was wearing a red skirt
She was wearing a blue skirt
She was wearing blue jeans
She was wearing a green skirt

and so on. Lets say each set has 4 options and there are 20 such sets. You note which statement the person reacts most strongly to. If he reacts most strongly to the true one of each set, what are the odds of that being chance? Try 1 in 4^20--about 1 in a trillion. Note that this does *NOT* prove guilt, only knowledge. If he story doesn't explain why he knew, though, you've got your perpetrator.
Unlike using it for lie detection there's no stigma attached to the question and thus you aren't going to get false positives on it. (To be sure you sit a few innocents down also just to make sure there's nothing about the questions that causes a hotspot on the right answers.)

Note, also, that this should pass a 5th amendmant challenge--while you are saying things you aren't testifying. Every word is provided to you by the tester. If the courts can compel DNA and the like they should be able to compel this.

[beowulf_king]

I've taken the polygraph twice recently for an application to a government job...and I can tell you for a fact that they do not work.

I've visited antipolygraph.org, and everything they say is true.

Basically, the polygraph measures three things. Your heart rate (blood pressure), breathing speed, and galvonic skin response (amount of sweat). What they look for is changes in these. Meaning, if you are asked a question and you like, your heart rate should increase, your breathing pattern should change, and your galvonic skin response should jump. But these changes don't only occur when lying. They occur when you are nervous. They occur when you are afraid (fear of failing a polygraph).

The polygraph is less in detecting a lie, but forcing the person to admit things they would normally not admit. During both of my tests, the polygrapher stopped in the middle of the "interview" and started questioning me about how I was giving a response and wanted me to come clean. They explain how everything is ok, the government doesn't care about what you did, and they just want to know this stuff incase someone tries to blackmail you. During the first test, they stopped me on a question of whether i committed a serious crime...which I have never done. They questioned me for about 30 minutes while I denied that I have ever done anything. Of course I failed (but the agency I applied to is known to fail people on the first try, and even the second). During the second polygraph, they stopped on a question of if I had committed a crime against a person (robbery, hit & run, extreme racism, etc.). The same process of questioning me and telling me that it's ok what I did and no one will know about it. But then the worst part happened. He started talking about baptism and how that's a cleaning of your sins, and that if I admit anything I will be cleansed of my sins. Praise the lord, I'm saved...too bad i'm an atheist :) . Again I denied everything and the polygraph eventually ended. I'm still waiting for the results on this. In the waiting room, I had time to talk with other applicants and they all said they underwent the same process of being accused of lying.

One of my main objections to the polygraph is that because I "failed" my first one, what is the chance that my second polygrapher will pass me and make the other one look bad?

In the end, there is no scientific proof of the polygraph. The reactions it measures are sometimes expressed by individuals lying, but everyone is different. Some people may have no response, and some people may have a response to any question. (Kinda like showing a picture of a clown to people. Most people will be fine, but a few will be freaked out). And even getting a positive reading in no way says you are lying. Plus, with all the false positives (and false negatives), it's totally illogical to base anything off of a polygraph.

Anyway, hope this answers some questions.

[Betenoire]

Interestingly, fMRI (functional MRI) has shown that when people lie, a specific part of their brain lights up, as opposed to when they're telling the truth. You can stick anybody in a MRI machine and use it as a highly accurate lie detector.

[Loren Pechtel]

Originally posted by Betenoire
Interestingly, fMRI (functional MRI) has shown that when people lie, a specific part of their brain lights up, as opposed to when they're telling the truth. You can stick anybody in a MRI machine and use it as a highly accurate lie detector.

Practical for court yet??

[Peregrine]

When I was in the Army (counterintelligence) one of the Detachments in my unit was the Army Poligraphy group, and many of the poligraphers were my friends.

A polygraph serves one purpose, an interigation tool. It scares the hell out of people, and they will confess. One of the poligraphers would travel around the world running polygraphs on people with clearances suspected of drug use. Before issuing the test he would have the person write down every drug that they take. In almost every case the person will admit to using illegal drugs.

But the one thing that has stuck with me was one of the guys told me, "Never take a polygraph. I can make anybody fail a polygraph even if they did nothing wrong."

[Deacon Doubtmonger]

Originally posted by beowulf_king
Basically, the polygraph measures three things. Your heart rate (blood pressure), breathing speed, and galvanic skin response (amount of sweat). What they look for is changes in these. Meaning, if you are asked a question and you lie, your heart rate should increase, your breathing pattern should change, and your galvanic skin response should jump. But these changes don't only occur when lying. They occur when you are nervous. They occur when you are afraid (fear of failing a polygraph).
The reverse is also true: since lying becomes easier with practice, like any skill, people such as car dealers could beat a polygraph with ease ... and what do you suppose happens when they actually start sincerely believing that a lemon is a creampuff?

Usually, though, the way to beat one is to obliterate the difference between the "baseline" reading that starts the test and the readings that occur on the allegedly dishonest responses, rendering the entire test invalid. Pressing the big toe on a thumbtack hidden in the shoe is one favorite method.

He started talking about baptism and how that's a cleaning of your sins, and that if I admit anything I will be cleansed of my sins. Praise the lord, I'm saved...too bad i'm an atheist :) .
So I'm waiting for the day the pastoral magazines advertise "Use of the Polygraph to Induce Confession of Sin in Atheists, Agnostics, Backsliders and Other God-Resistant Subjects." :p

[Loren Pechtel]

Originally posted by Peregrine
But the one thing that has stuck with me was one of the guys told me, "Never take a polygraph. I can make anybody fail a polygraph even if they did nothing wrong."

Of course. It's easy to scare people who don't know the truth about the machines.

[Betenoire]

Originally posted by Loren Pechtel
Practical for court yet??

Within ten years it'll be technically practical.

But, hell, juries don't understand and accept DNA evidence yet. Try explaining MRIs and they'll run screaming when you get to "Nuclear Magnetic Resonance"