Justice

Polygraph is the main tool for lie detection

A computer system for recording and processing a person’s psychophysiological reactions, the so-called polygraph, is the main modern tool for detecting lies. It consists of special sensors that record various physiological parameters of the interviewed person. The sensors are connected to the data collection unit. This block, in turn, is connected to a laptop with a special software complex for statistical processing and data presentation in graphic and numerical formats. A photo of the hardware complex of the polygraph examiner is presented below.

The basis of a modern polygraph consists of nine sensors that record seven different physiological parameters of the human body, namely:

• Dynamics of chest breathing and diaphragmatic breathing;
• Physical and tonic components of the skin-galvanic reaction of a person;
• Blood pressure dynamics;
• Plethysmograms (PPG and FPG);
• Tremor (motor activity and facial expressions);
• Energetics of speech signal.

Polygraphs of different manufacturers can differ in the design and sensitivity of the sensors, the degree of stability of the polygraph and its protection against external vibrations and radiation, the capabilities and versatility of the software. The most popular models used in Ukraine are Polarg, Kris, Barrier, Lafayette.

Specialists of the Agency for lie detection and personnel security “Justice” use survey methods developed and tested in well-known schools of polygraph experts in the Russian Federation and the USA. The method is chosen depending on the type of services provided by the polygraph examiner.

What is instrumental lie detection based on

An interview with the help of a polygraph consists in the fact that the interviewee is asked questions, and the lie detector records all physiological changes during the time that the person answers the questions.

When a normal person lies, physiological changes occur, which are recorded by the polygraph sensors. Testing practically does not establish the lie itself, as such, but records the physiological changes in the body that accompany it.

The reputation and trust of the polygraph is growing, and therefore quite often guilty people who do not admit to committing a crime to the police or even to their own lawyer are forced to confess before the prospect of a polygraph test.

An innocent person, as a rule, tries to cooperate, is not afraid of exposure and, accordingly, does not give the same physiological reactions as a guilty person. Undoubtedly, the polygraph test itself causes concern even for an innocent person, but a well-trained polygraph operator will explain the principle of operation of the equipment used, the testing procedure, discuss the questions that will be asked, and also take into account the background level of excitement when answering the questions.