It is not too difficult for a sophisticated liar to deceive a person. It is enough to demonstrate sincerity in the conversation, open gestures and a convincing tone. But even a trained professional in the field of human relations is unlikely to be able to mislead a polygraph. That is why such a device is also called a lie detector.
What is a polygraph
The polygraph is a rather complex technical system for conducting psychophysiological research using special methods. The procedure of examination with a lie detector consists in removing from the subject a number of physiological parameters that arise in response to verbal and other stimuli that are significant for him.
It is believed that with the perception of pre-prepared questions or visual images, memory processes and traces of stress are activated. Acting according to a well-thought-out plan, the researcher identifies the subject's reactions to the questions presented to him. The results are displayed on a computer screen or recorded by a special device on a paper tape.
Polygraph device
Several designs of lie detectors are known. They can be analog devices that write parameters sequentially with a pen or other writing device on paper. Today, digital lie detectors, designed on the basis of computer technology, are more often used. In any case, the polygraph has a sensor unit, sensors for reading information and a device for recording test results.
The list of reactions that are subject to registration on a polygraph may be different. It is determined by the complexity of the device and the technique used. Usually the device takes measurements of respiration, galvanic skin response, blood pressure and some other characteristics of the cardiovascular system. A tremor sensor is also often used to register subtle tremors of the limbs. The facial expression sensor is used less frequently.
How a lie detector works
The polygraph registers signals that come from sensitive sensors attached to certain parts of the subject's body. The survey technique is based on the fact that fluctuations in the level of a person's arousal cause a significant change in indicators. In other words, when a person is worried about hearing a significant question for him, the emotional background and associated physiological characteristics immediately change.
It is generally accepted that insincerity or outright lies when answering an expert's question leads to an increase in the level of arousal. With a truthful answer, this does not happen. Such a difference in responses to stimuli can be associated with feelings of guilt or the emergence of a person's fear of exposure of his lie and subsequent punishment. The reliability of the polygraph test results is considered very high. Modern methods of research and processing of results make it possible to identify deliberate attempts to deceive the polygraph.
