Interviewers ask a number of control questions during the test and then compare the responses to the key questions. It finishes with a post-test interview, where the person will be able to explain any responses they showed. He says that it requires sitting down and practising with a trained examiner.
But for those who don't have a qualified questioner to hand - what methods can work? But he cautions that most examiners will be able to spot any covert attempt to beat the test.
The credibility of the polygraph was challenged almost as soon as it was invented in , and there is much debate about its accuracy. Dr van der Zee says that, because taking a lie detector test can be a stressful experience, it can sometimes present innocent people as guilty.
So whilst the polygraph is quite good at identifying lies, it is not very good at identifying truths," she says. But Prof Grubin says there are a number of different reasons why a test may be inaccurate. These include the questions being poorly formulated and the interviewer misreading the results. However, he says that interviewing victims presents a separate problem. This means a victim, especially one recounting a traumatic experience, may appear as if they are lying because they are in an emotional state.
Mixed in with the control questions are relevant questions. In a drug case, for example, a polygrapher will ask, "Did you ever use an illegal drug? If the former reactions are greater, the examinee passes; if the latter are greater, he fails. In essence, an examinee's lie only counts as a lie if it registers as more of a lie than his or her control lie.
So here's how you beat the test: Change your heart rate , respiratory rate, blood pressure and sweat level while answering control questions.
Send your control lies off the charts. By comparison, your answers to the relevant questions whether they are truths or falsehoods will seem true. The most common technique is to demonstrate to the suspect that the machine will be able to tell which card the suspect picks from a deck.
If he is guilty, it is important to make him afraid of being caught. This leads some interviewers to increase their control over the environment, sometimes opting to use a secretly-marked set of cards, essentially relieving the polygraph from having to perform any real deception detection.
The suspect must believe in the ability of the lie catcher. Signs of fear would be ambiguous unless matters can be arranged so that only the liar, not the truth teller, will be afraid.
They know they can get away with it, and if they know it, they are more likely to be able to do so. When a suspect does not confess, some polygraph operators will browbeat the suspect, telling the suspect that the machine has shown that the suspect is not telling the truth.
By increasing detection apprehension, the hope is to make the guilty confess. The innocent suffer the false accusations but supposedly will be vindicated. Unfortunately, under such pressures some innocents will confess in order to obtain relief. Anyone can learn how to spot deception. Forensic Science. Updated: Apr 15, Does it work?
The person's breathing rate The person's pulse The person's blood pressure The person's perspiration. Polygraph FAQ How accurate is a lie detector test? The estimated accuracy of the polygraph test stands at 87 percent.
Can an innocent person fail a polygraph test? The polygraph tests whether a person is lying or not by tracking breathing rate, blood pressure, perspiration and heart rate.
0コメント