Lie-detection tests: The methods used and its efficacy

lie detection
Representative image. Photo: Maxx-Studio / Shutterstock

Lie-detection tests have been in the news for a while now. It apparently assumes a vital place in crime investigation scenarios. Investigators rely on these tests to find out if a person’s statement is true.

The investigators relied on lie-detector tests in the 2012 Arushi Talwar murder case and the 2008 Sheen Bora killing. (In the Sheena Bora case, the Central Bureau of Investigation refused to heed to the plea of accused Indrani Mukherjee to put her through a lie-detector test).

Investigating agencies use three kinds of tests to ascertain if a person is stating the truth. These are polygraph test (or lie-detector test), narco-analysis, and brain mapping.


In polygraph or lie-detector tests, the heartbeat, breathing rate, and blood pressure is ascertained continuously during questioning. The general understanding is that the heart and breathing rates would go up if a person lies.


In this test, a medical doctor injects sodium pentothal or sodium amytal, both known as truth serum, into the body of those being questioned. The person being questioned slips into a semi-conscious state and the idea is that the subject would not have the capability to think and state a lie.

It is said that the military intelligence units depended on this method during World War II.

Brain mapping

This method involves the use of electrodes to map the neural structure of the person being questioned. For example, the person being questioned would have told the investigators that he was unaware of a person. They then suddenly show him a photo of the person. Then, the brain waves would be different and the agencies can ascertain if he is lying or not.


The efficacy of these methods is still disputed by experts. Some are of the opinion that these methods, which have no accuracy, could lead to wrong inferences. As of now, these tests can only be conducted only with the consent of the one being questioned. In 2012, a US official called Russel Ties came out against such tests. He said he was subjected to the tests 20 times and argued that one could manipulate the results with proper training. He listed out these ‘tricks’ and these are available on the internet.