Polygraph Unmasked: Process, Controversies, and the Power of Questions

In a world driven by truth-seeking and reliability, the polygraph, often heralded as the lie detector, stands as a fascinating marvel and a subject of intense debate. Since its inception, this device has captivated minds and sparked controversies, aiming to unravel the intricacies of human honesty.

Lying is an inseparable part of human behavior, especially when a person does something wrong and does not want to be caught. The culprits of any criminal offense always try to avoid conviction by telling lies or framing false stories in front of the investigator.

However, an experienced forensic investigator may easily detect if the person is lying or not although some hardcore criminals can be difficult and bold which may not be detected easily. There is a saying “A lie has no legs” and forensic investigations prove this every time a criminal is convicted.

As we delve into the realms of deception detection, this blog post explores the history, mechanics, and ethical implications surrounding the polygraph. From its humble beginnings to its contemporary role in law enforcement and beyond, join us on a journey through the intricate web of science, skepticism, and the pursuit of uncovering the truth.

Process of Polygraph

Polygraph is a procedure of lie detection based on the study of the functioning of different body systems which is conducted on a person to detect lies. It is also known as a lie detector which measures the physiological responses of a person when they are questioned to detect if a person is lying or not.

There were many inventors of polygraph machines but the most common one in use was invented by John Keeler.

Principle of Polygraph

The principle of polygraph is based on the fact that a person can deceive another person but not oneself. When a person lies, a mixture of emotions including fear and anxiety is produced which stimulates the sympathetic nervous system and causes physiological changes. These changes are recorded by the machine which can be indicative of deception. A person having expertise in reading the polygraph can interpret the results.

The important physiological changes considered for the study are:

  • Skin reaction
  • Blood pressure
  • Respiration rate 
  • Pulse 

The test carried out involves asking questions that are suggestive and require answers in the form of ‘Yes’ or ‘No’. The difference in the above-mentioned physiological changes before and after the questioning indicates that the examinee may be deceptive.

Components of Polygraph Machine

  • ChairThe examinee is asked to sit on the chair comfortably
  • Arm Cuffit is placed around the arm of the examinee to measure the blood pressure and pulse.
  • Belt A belt is wound around the chest of the examinee to record the respiration rate.
  • ElectrodeAn electrode connection is attached to the tip of the index finger for recording the galvanic skin reaction.

When these connections are made on the body of the examinee, the questions are asked of him. Usually, 8-10 questions are asked from the examinee. The responses of the concerned physiological process are recorded on a single paper which a polygraph expert analyses.

Types of Questions Asked 

The results of the polygraph are interpreted by the responses achieved depending on the nature of the questions asked by the examinee. The following types of questions asked are:

  • Relevant Questions

These are the questions that concern the incidents related to the offense.

  • Irrelevant Questions

These are the questions which do not relate to the incidents

  • Control Questions 

They are also known as comparison questions because they compare responses to relevant questions with responses to other questions that are intended to generate physiological reactions even in non-deceptive examinees. It determines the level of truthfulness which varies in genuine and deceptive examinees.

In the genuine answers, the level of truthfulness is quite high without any anxiety, whereas in the deceptive examinee, the truthfulness level is low and it is presumed that the relevant questions create a greater level of concern and therefore a stronger physiological response.

Before the polygraph examination, a pretest interview is conducted with the examinee. During this interview, the examinee is informed about the examination process, the types of questions that will be asked, and the purpose of the test. The main goal of the pretest interview is to influence the emotional state and expectations of the examinee during the test.

The examinee is led to believe that the machine is capable of detecting every lie. As part of this process, the examinee is asked to deliberately tell a lie, which is then detected by the machine, reinforcing the examinee’s confidence in the machine’s reliability. This demonstration is also known as a ‘stim test’. At times, this is done to mislead the examinee, preventing them from attempting to deceive the polygraph examination.

After the commencement of the pretest interview, a polygraph examination is conducted and the examiner forms a combined graphical result of the response. So it can be said that a polygraph examination is a consolidated impression of the interview or interrogation technique and a psychophysiological measurement or testing technique.

Usually, a polygraph examination is used by investigating agencies to examine deceptive criminals. However, in countries like the United States, Israel, Japan, and Canada, polygraph is used in pre-employment screenings in law enforcement agencies. It is also used in the screening of the employees of security agencies.

Controversies Related to Polygraph

The results of the polygraph examination are inadmissible in court because it has a high percentage of false positivity.

In 1923, in Frye vs the United States, the District of Columbia Court rejected the scientific validity of the polygraph because the technology did not have significant acceptance at that time. This was the incident that made the courts think about deciding to accept any kind of scientific evidence.

In India, the first case when the court adopted the results of polygraph took place in 2008 where a woman was convicted of murdering her fiance. However, in 2010, the Supreme Court of India declared the use of polygraph, narco analysis, and brain mapping on the suspects as illegal if the examinee did not give consent. It is mentioned in Article 20(3) which states that- No person accused of any offense shall be compelled to be a witness against himself. However, the polygraph test is legal in India if the defendant requests it.


A polygraph examination is a psychophysiological test that helps to reveal the deception of a person. Although the positive results have a percentage of about 87-90 percent, the false positivity rate is also high which limits its admissibility in courts. However, it can be accepted by the court if both the parties related to the case agree to the conduction of the examination. 

A polygraph test is a useful method of lie detection but has certain limitations that need to be worked upon so that it becomes acceptable in courts without any controversy.

Suksham Gupta

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