The Lie Detector Test

How Does It Work?: The Lie Detector Test

The central nervous system is divided into two subdivisions, a voluntary portion and an involuntary portion. The voluntary portion governs things that you and I want to do. If you wanted to drive a car there would be various actions which you would need to engage in, in order to drive a car such as unlocking the car, sitting in the car, turning the key in the ignition etc. All of these actions are voluntary actions.

The involuntary portion of the central nervous system works in the back ground, sometimes we do not even realise it is working. When a person becomes too hot and they start to sweat or if a person becomes too cold and starts to shiver, the sweating and shivering are all involuntary actions which we cannot control and take place without our conscious effort. When a person tells a lie it is not physiologically easy for the body, it takes an effort, it takes energy, and it causes cognitive activity, resulting in the body involuntary reacting when a lie is told.

The polygraph test or lie detector works by identifying these involuntary changes in our physiology which are recorded by the computerised polygraph instrumentation and sensors.

What Does The Test Involve?: The Lie Detector Test

The Polygraph Examination is broken down into three phases, “pre-test”, “in-test” and “post-test”.

The pre-test which is the first phase of the examination is where the examiner will provide the subject with an overview of the process, the examinee will also be advised of their rights and told that the test is voluntary. The examinee will then be required to complete a medical and consent form.

A full explanation of the how the instrument and sensors work will be given.

A pre-test interview will them be conducted between the examiner and subject in order to ascertain the purpose of why the subject is taking a Polygraph Test. This is an important part of the process in order to establish the details surrounding the purpose of the test and allegations made, which will later play a key part in test question construction.

The “in-test” phase will involve the examiner attaching the sensors to the subject’s person and conducting an “acquaintance test”. An “acquaintance test” allows the subject to get accustomed with the sensors and to settle any nervousness or anxiety. It also allows the examiner to ensure the subject is co-operating and is able to follow the instructions given. An Acquaintance Test must be conducted for validity purposes.

On completion of the Acquaintance Test, the questions pertaining to the subject’s issue of concern will be reviewed with the subject prior to The Polygraph Test.

The examiner will then go onto the testing phase which is carried out in several phases. During the testing process, the computerised equipment, instruments and sensors will record the subject’s physiological changes in the form or several charts.

The third and final phase is the “post-test”. During the “post-test” the charts will be analysed

In this part the charts are examined and examiner may discuss the result with the examinee depending on the requirement.


What are the Possible Results?

The first results which can be given are Deception Indicated (DI)/Significant Reactions (SR) which means that the examiner has deemed the subject to be deceptive in the answers given.

The second results which can be given are No Deception Indicated (NDI)/No Significant Reactions (NSR) which means that the examiner has deemed the subject to be truthful in the answers given.

The third result which can be given is No Opinion (NO) which occurs when the examiner is unable to reach a conclusion after data analysis.

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