Lie Detector

Lie Detector

 

Perhaps you have heard about the Lie Detector / Polygraph, read about it or seen it in a movie. Maybe you were once a subject in a polygraph test. The lie detector, also known as a polygraph machine, is used by interrogators to endeavor to determine whether the subject is telling the truth. In essence, the machine uses physiological parameters to check whether someone is lying. This is based upon the notion that someone who is telling a lie or who is guilty might exhibit some changes in parameters such as pulse, breathing rate, blood pressure, perspiration and even limb movements.

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The Lie Detector in Detail

Perhaps you have heard about the Lie Detector / Polygraph, read about it or seen it in a movie. Maybe you were once a subject in a polygraph test. The lie detector, also known as a polygraph machine, is used by interrogators to endeavor to determine whether the subject is telling the truth. In essence, the machine uses physiological parameters to check whether someone is lying. This is based upon the notion that someone who is telling a lie or who is guilty might exhibit some changes in parameters such as pulse, breathing rate, blood pressure, perspiration and even limb movements.

Who came up with this idea of lie detection? You can guess that he had a medical background and an interrogator’s mind. John Larsson, a Californian police officer who was also a medical student, invented the lie detector test in 1921. It was lauded as a great idea and earned the inventor accolades for his ingenuity. Larson’s invention lives on today.

Doubts have been expressed as to the reliability of the test as some people believe they can “beat” the polygraph by manipulating their own physical responses. Evidence from lie detector tests is not admissible in Australian courts and can’t be used here to test whether someone has acted criminally. Regardless, the lie detector machine is here to stay and it may help some people get peace of mind regarding a personal or family concern. If the subject is willing to take part and both parties understand the potential limits of the testing process, the polygraph can possibly help resolve problems that have no other solution.

Cases Where a Lie Detector Can Help

Primarily, the Polygraph is useful for the investigation of personal and domestic disputes. Its most common use is in gaining an insight into whether there is evidence of infidelity by a cheating partner or spouse. Other examples include investigating the existence of addictions or other issues within the family, such as historical actions that cannot be investigated in another way. If you have a nagging question that you believe a polygraph could help solve, get in touch with an investigator today and see whether a lie detector test is what you need.

The Polygraph Testing Procedure

At the start of the polygraph, the examiner usually explains the technique to be employed during the test to the subject. At this point the examiner also discusses the essence of telling the truth which can tend to make a guilty person cautious about telling lies. Typically, there is a stimulation test which is also termed the ‘stim test.’ In the stim test, the subject is asked to tell a lie. There are two techniques which are typically then be used to test a subject.

The Control Question Technique (CQT)

After the stimulation, there are a series of questions put to the person being interviewed. The Polygraph examiner alternates between relevant questions and diagnostic or control questions. There are also irrelevant questions that don’t have much bearing on the result of the test.

The autonomous physical arousal detected upon asking the relevant questions and the control questions is what the examiners use to analyse the veracity of the subject’s answers. A greater response to the control questions relative to the relevant questions point to truthfulness. On the other hand, if someone experiences greater responses to relevant questions, then the examiner judges this as indicative of possible deception.

The Guilty Knowledge Test

Besides the CQT, examiners can also use the Guilty Knowledge Test (GKT) which is alternatively called the Concealed Information Test. Here, the examiner is someone who has no prior knowledge of the crime or subject incident that is being investigated. To some extent, this method works to correct the errors that might arise in the Control Question Technique.

The GKT has multiple choice questions, and the interviewee is expected to choose one. The questions focus on the subject incident. It could be something like ‘Was the car a Mercedes or Rolls Royce?’ If the subject answers a number of questions correctly and exhibits a larger reaction to the correct answers, it can be inferred that the subject knows these facts to be true. This technique is only effective if the subject actually knows the answer the questions.

The Uncertainty of a Lie Detector test

The Lie Detector / Polygraph proponents speak of a 90% validity score but this has not been enough to silence those who criticise it. False positives occur with polygraph tests and the main reason is that there is no concrete evidence of its accuracy that can be generally agreed on. Physiological signs of anxiety can be displayed by an innocent subject who is worried about the procedure, by a guilty subject and potentially by a person who has trained to beat the machine.

Despite some of its shortcomings, the Polygraph has many uses worldwide. It can be a useful investigative tool in the right circumstances. Get in touch today to get a quote for your investigation.