I’d think that even innocent people would naturally be nervous, stressed, a little or a lot crazy even, while taking a lie-detector test. How does the polygraph tell between nerves and lies?
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It can’t. This is why they are not admissible in court.
Polygraphs measure skin conductivity (sweat), heart rate, breathing, all of which are detectable signs of stress. There is no way to detect lies, and an individual can fool a polygraph by remaining entirely calm.
It bases your “lies” on the control questions at the beginning and the differences between them. Is your name Bob? do you live at so-n-so? Are you sitting down? is your shirt green? These are to establish a baseline of when you are telling the truth. So lie then.
Better yet, just tell them no, I’m not going to do it. And ask for your lawyer.
Polygraph tests are very inaccurate. They don’t differentiate honest nervousness and deceptive answers very well at all. Their most powerful use is the reactionaries people have when invited to take one. If people believe they work, then the their reaction to being told to take one speaks volumes. They are inadmissible in court because they are only slightly more accurate than just guessing whether someone is lying.
Thanks, y’all. I’m very into the true crime rerun channels and the polygraph is used every now and then during interrogations. Now that I think about it, it’s not used that much. I can definitely understand how it is a tool to coerce rather than to prove.
Like its cousin, the [Scientology E-Meter](https://en.wikipedia.org/wiki/E-meter), the polygraph is a prop for an interrogation.
Its purpose is to make the subject think that the interrogator can read their feelings, thereby making it feel useless to lie.
The polygraph displays output that relates loosely to the subject’s emotional state. It doesn’t tell whether you are lying. It tells whether your skin sweat and oil are changing, which has to do loosely with being nervous or excited or horny or needing to go to the bathroom or a whole bunch of other things.
But people are really good at thinking that things are more strongly connected than they really are. If you were to try deliberately to get a signal out of a polygraph or e-meter, by tensing your muscles or thinking about something shameful *(your brother’s underwear?!)*, you would see that it did give a signal! But that signal doesn’t mean “lie”. It means “change”.
And that is what makes it an effective prop. It is more impressive than a machine that just randomly goes “ping”, because it does relate to *something* that’s *somehow* connected to the subject’s thoughts.
And so it is a prop that constantly conveys, “I know what you really think, I know what you really did, your body tells me things that your lips are not willing to admit. The output of this machine is your real truth, and it is already on your permanent record. You may as well do the thing that will make that record look acceptable.”
(If the interrogator used a gun instead of a polygraph, it could still be a prop, but would convey, “Your life is in my hands, I can kill you if you displease me.” That’s a technique some interrogators use sometimes, usually to extract false confessions for political purposes; but it’s not the same one that the polygraph is used for.)
Incredibly poorly. If you’re nervous you’re going to fail a “lie-detector” test. They’re not admissible as evidence in court because they’re so unreliable, but confessions made by people who don’t know that can still be used to convict.
Polygraphs work by establishing a baseline ie your pulse, temp, skin conductivity etc when they ask you easy questions like is your name x, are you x years old etc. Once that is established then they ask some non pertinent questions just to keep you relaxed and then throw in the actual questions they are interested in in between easy and normal questions. If your bio responses change drastically when answering the pertinent questions, then it typically indicates deception.
They don’t work at all.
So why do they still exist?
Questioning someone exists along a spectrum, from casual chats, to cross examination in court, to police questioning, interrogation, ending with torture.
The one thing they have in common is you *always* want the subject to think you know more than they do. It has two benefits. Firstly, if you already know, the subject isn’t telling you something new, merely corroborating. This can make a submission psychologically easier. Secondly, at the interrogation/torture end of the spectrum, you want your subject to be scared to lie. As mentioned, if the subject thinks you know more than they do, or, you can prove you know more than the subject, they will be unwilling to lie if there are consequences (being caught lying or pain).
The polygraph simply lets interrogators pretend they know more, so the subject is psychologically unwilling to lie.
I’ve taken a polygraph twice. Failed both due to extreme anxiety. Basically, they lie to you about their effectiveness. Following the test, both tried to get me to confess to the crime in question, pulling the “do the right thing” card.
If you’re in a situation where the outcome determines your level of freedom, then you know they only have the prosecution’s interests in mind. They’re designed to coerce confessions.
There is no detectable difference between a lie and nervousness. They aren’t admissible in court unless you agree to it.
They can’t so if you’re ever in a situation where cops ask you to take one, DONT. Ask if you’re under arrest, if not, leave, if yes, ask for a lawyer and don’t say anything till they get there. Guilty or innocent you don’t say shit.
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