This is because the polygraph instrument that detects physiological responses is often called a Lie Detector.
Although the instrument and the examination aim to detect changes in our physiological response to questions asked by the examiner i.e. changes that occur when a person is not being truthful, polygraph experts prefer to call the process ‘truth verification’ rather than lie detection.
The term ‘lie detector’ portrays the ideology that the instrument will detect any lie told by someone undergoing an examination. However, in reality there is no such thing as a typical "lie response."
People lie for a variety of reasons. Some lies have no great consequence associated with them. Some term these lies as ‘little white lies’. For example telling someone you like their new hair style when you actually think the opposite.
However, some lies are associated with larger consequences, such as the loss of a job, loss of a relationship or even imprisonment.
In other words, just because a person tells a lie, it doesn’t mean that they will have a reaction and if they do, it will be different to the reaction that someone else would have.
So if polygraphs exams or lie detector tests don't actually detect lies, what do they detect?
Rather than the lie itself, it is the reason for telling the lie that is most important.
When a person has done something wrong, such as commit a crime, there is the realisation that if caught there will be consequences. Our instinct for self-preservation makes us want to avoid being punished for what we did. This is usually accomplished by lying. However, because a person understands the potential consequences they face if caught in the lie, the body's self-defence mechanism activates when the examiner questions the person on the related subject.
The polygraph instrument and the examiner will recognise when the body's systems activate.
However, the response can be different, unlike the response when a person is being truthful.
The term lie detector would seem to presume that a lie is always detected but in reality not everyone that takes a polygraph exam is being untruthful.
In these cases, the lie detector actually verifies when a person is telling the truth. Hence the term ‘truth verifier’ is preferred by professionals to the term lie detector.
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