Logging channels of polygraphs

At first, let’s put several questions, the answers to which will be given below:

  1. Which logging channels of physiological reactivity must be provided in each professional polygraph?
  2. Readings of which sensors must be necessarily taken into account in the combined decision on the level of physiological reactivity to stimuli presented (question)?
  3. How to rank the logging channels indications in order of importance when analyzing polygraph chart?

In the majority of polygraphs the same logging channels are used. Typically, individual sensors. are used for registration of each type of physiological activity of the human body. They distinguish the so-called primary and secondary sensors. The group of primary sensors include those that are designed to fix physiological activity of high and medium level of accuracy. Accordingly, secondary sensors include fixing low physiological activity.

One of the first polygraph
That’s how it all started…

Sensors used in the work of polygraph

Sensors of high level of accuracy:

  1. KGR (galvanic skin response), fixing the dynamics of electrodermal activity (both resistance and conductivity);
  2. PG (plethysmogram), fixing the dynamics of peripheral cardiovascular activity (arteriolar tone and heart rate).

This is predetermined by the fact that the dynamics of the above-mentioned physiological activities is not subjected to conscious distortion, a person cannot change the process of his perspiration, and the tone of his smallest arteries by force of will in a matter of seconds.

Sensors of medium level of accuracy:

  1. DH (breathing), fixing the dynamics of respiratory activity (as a rule, simultaneously two sensors are applied - thoracic and diaphragmatic breathing). Due to the fact that the physiology of the respiratory system, in addition to functioning in automatism mode is subjected to conscious distortion of the depth and frequency of breathing, both inhalation and exhalation.
  2. TRM (tremor), fixing the dynamics of physical activity. Due to the fact that a fixed position of the body in course of the study of psycho-emotional stress may manifest both as involuntary (unconscious) physical activity, and intentional (conscious) movements.

Sensors of low level of accuracy:

  1. ARD (blood pressure), because at the level of sub-extreme informational stress, which are the result of research procedure, the reactivity of the main blood vessels (arteries), are often low informative.
  2. MKF (microphone), fixing the dynamics of acoustic activity. In connection with the fact that the respondent, usually unconsciously (subconsciously) varies the volume, time and pitch of his response, but may consciously (intentionally) change these parameters.

For example, with a sharp and loud response, diaphragm reduces. Artery and vein pass through it. As a result, hemodynamics (blood flow) is impaired for a short time, which is the cause of further activation of physiological reactivity.

In addition, manufacturers complement polygraphs with various additional sensors, that record the changes of pupil diameter, skin temperature, difference of arterioles tone on the body and head (according to Vinogradova-Sokolova phenomenon), microactivity reactivity (complex visual - activity reaction according to A.R. Luria) etc.

However, with all their variety, the most promising sensor is considered to be the one for fixation of the dynamics of induced brain potential (as background wave processes and the specifics of the changes in confirming or concealing information by the respondent). This logging channel will finally allow to capture the dynamics of changes in the "causal factor" (in the presented stimulus of psychic activity). As it is known, the polygraph in its current embodiment allows you to record only "investigation factors" that appear at the physiological level.