A common question regarding lie detection is, 'What physiological responses do lie detector tests evoke?'. This will entirely depend on whether the person is telling the truth or not. Although not everyone will react (physiologically) in the same way when telling the truth and/or telling a lie, it is widely accepted that there ‘standard’ ways that people do react and it is the aim of a lie detector tests to pick up on these.
Lie detection using a polygraph is based on the premise that lying and truth-telling elicit different physiological responses in subjects. But what are these responses and how do they alter when someone is lying? Between 1917 and 1925 four scientists established that when individuals were being deceptive their blood pressure increased. The underlying physiological state has been described as being either fear, arousal or excitement based and these states have been closely associated with deception, which has provided the rationale for the relevant-irrelvant questioning format. Other research has identified that when being deceptive a person’s heart rate may also increase; their respiratory rate may go up and they may perspire (more heavily). All of these factors can be picked up by the polygraph machine.
The problem that seems to exist is that not every person will react in the same way to lie detector tests, as we are, after all, individuals. Some people may be able to stay calm and relaxed and show no physiological responses despite lying, whereas others telling the truth may react negatively to the test and elicit physiological responses that would usually be associated with lying. This is where the expertise of the examiner comes in. A well-versed professional examiner is able to accurately analyse the responses during the test and whether the person is lying or simply of a nervous disposition Obviously no machine or human can be correct 100%, but a combination of a polygraph and a professional examiner has been shown to provide far great accuracy than chance.
Learn more about lie detector tests here: http://www.liedetectortest.ie