I don’t have the firmest grasp on the way a polygraph functions, but I’ve just had this thought a lot.
Could a polygraph help people uncover repressed memories? For example if a person suspects they were being harmed as a child, but can’t remember details, could a polygraph help them get more answers? Like by asking specific questions maybe related to what a person suspects happened and detecting how they respond.
Or, is a polygraph only useful to detect truth/a lie about things someone is certain about and remembers fully?
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No, and there’s a couple of reasons.
A polygraph isn’t a machine that magically tells you if something is true or not. A polygraph measures your blood pressure, heart rate, respiration rate, and skin conductivity. Skin conductivity is measured because water with salt in it, like your sweat, conducts electricity well, so if you sweat your skin will conduct electricity better.
The way a polygraph works is that the person running the machine asks you a number of baseline questions that they know the answer to and that you wouldn’t like about like “what is your name” and “when were you born.” This is to see how your body reacts to those questions. Then they ask the relevant questions. The idea is that if you are lying the stress from lying will increase your blood pressure, heart rate, respiration rate, and cause you to sweat, which will allow the machine to detect these things and indicate that you are lying.
Polygraphs are notoriously unreliable and they are not allowed as evidence in any court in the United States. A person with training can beat a polygraph. Additionally someone who is nervous, for example because they’ve been accused of a crime and are hooked up to a lie detector, can create a false positive.
Even if the machines were reliable it wouldn’t help prove that a repressed memory was real because the machine is only going to detect a different response if the person knows that what they are saying is not true. If the person genuinely believes that the repressed memory is real then the machine would not show any difference between that memory and something that was true, because that person believes it to be true.
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