Like – if it’s based on a person’s physiological responses, isn’t it possible that a response to a question like “did you murder your hamster” would register as a lie due to the increase in heart rate and blood pressure cause of anxiety associated with being accused of something?
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As others have said, they really don’t. It’s absolutely not a hard science at all.
Occasionally they’re just used as a simple intimidation tactic. Good cop / Bad Cop stuff … except instead of having bad cop yell “I KNOW THAT YOU’RE LYING,” you have the machine do it. “THE MACHINE KNOWS THAT YOU’RE LYING.” In that setting, you might as well hook the subject up to an etch-a-sketch. There’s no useful data coming out. You’re just trying to get the person to confess.
However, sometimes they are used and you actually do want to get some useful information. So you make a whole day of it. Or evne 2 or 3 days, potentially. It can be a hell of a process.
To start with, you acclimate the person. Spend a while with them hooked up to the machine, and asking questions that aren’t really important. Start with simple stuff: “Where were you born, what year did you graduate high school, what was your first pet’s name, etc.” Turn it into a conversation. It helps to create a baseline, because even simple conversation is more tense when you’re hooked up to weird machines, in a strange room, with strange people asking you questions.
From there you start asking awkwardly probing questions that aren’t really important, but are designed to illicit an emotion response. “Have you ever had homosexual thoughts (assuming the subject isn’t openly gay). Have you ever taken prescription medication that wasn’t yours. Have you ever shoplifted or stolen from any of your jobs. How would you rate your own dick: small/medium/large.”
You’ll certainly get some kind of a reaction from some of those questions, and again, it’s used as a baseline. You’re not being accused of anything (yet) they’re just getting a reading for what makes you squirm, and how that shows up on the machine. From there, they can start getting into more specifically probing questions and use all of the previous responses to try and gauge a reaction.
Of course… it’s all easy enough to muddy by simply putting a rock in your shoe. Pressing down on the rock will cause your body to react internally. Doing this during the “baseline” portion will prevent them from having a useful comparison. And there are other ways to muddy the results. Even just crossing your legs, clenching up your butt-cheeks hard enough or holding your breath can register on the machine.
Of course… of course… a muddy result can also be useful data itself. It tells you that the person is probably doing this on purpose, and trying to hide something. You’re not going to get a printout with exactly what they’re trying to hide, but you know that they’re hiding something, and smart enough to try and deceive you. And that’s good to know.
Another fucked up bit of trivia: although polygraph tests can’t be used as evidence in trial (unless all parties consent as some others have mentioned), they can be used as the basis for probationary decisions. So if you fail a polygraph test your PO can determine that you violated your probation whether you actually did or not.
They’re bullshit and no one should ever agree to taking one because nothing good can ever come of it for the person being “tested.”
I want to second u/rhombiodus here and say – they don’t.
But what you suggested is essentially how they are supposed to work.
The idea is they get a reading of your heart rate, breathing rate, etc. when you are answering normal questions truthfully (is your name yoteachcaniborrowpen?)
Then, they ask you the ‘real’ questions (did you strangle Mr. Body?). The idea is that lying is stressful, which causes your heart rate and breathing rate to ‘spike’.
So you look for these spikes compared to the easy questions, and say ‘lie’ or ‘not lie’.
It’s utter BS. There was a 400-page plus report commissioned by congress that was put together by tons of experts in the field that concluded there was no evidence whatsoever to support polygraphs. It’s not admissible in court. The only reason it’s still around is to threaten people into confessing and use it against you if you refuse one – because the fact you refused IS admissible (AFAIK).
Source: psych prof
It’s not a lie detector, it’s a stress detector.
they start by questionning you on common things; non stressful questions. Is your name Joe, etc.
And while doing that, they check your physiological reactions (heart rate, sweating, breathing, etc).
Then they move on to ask you questions about the thing they want to check (ie: did you kill Bob?).
They do so with the assumption that if you are truthful, you won’t really be *more* stressed out. And that if you are lying, you will be *more* stressed out, and therefore have physiological reactions that are different than when you are honest.
But keep in mind this whole thing is also an interrogation: the polygraphist could try to get you to confess by suggesting or indirectly implying you failed the polygraph.
“Any reason the polygraph would show you are lying?”
Is a type of question that might throw off some lying people into thinking some kind of red light flashed on the machine. And then they will start talking and backtracking their story and boom: the story is broken.
It’s not rare for people leaving a polygraph to feel like the polygraphist think they are lying, to feel lile they failed the test. That’s part of the strategy to push a lying person to talk more, to overjustify to the point of contradicting themselve.
They don’t. Which is why they aren’t accepted as true lie detector tests.
They’ll have you answer spare questions to calibrate the test. But even still, this doesn’t work 100% of the time.
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