«Lie detector» based on Evoked Potentials
Strategy is based on the neurophysiological method of Evoked Potentials study.
The method P300 of Cognitive Event-Related Potentials is used as base.
Test is carrying out for to reveal the reactions on presenting a familiar object.
Characteristic of procedure:
(variant — Visual Evoked Potentials).
1. Characteristics of the stimulus:
Stimulus — a photographic scene, present at the monitor 17″-20″ from distances 1,5-2,0 m.
Binocular stimulation; full field.
Duration of stimulus — 40-80 mS.
Frequency of presenting a stimulus — 0,5-2 Hzs.
Probability of significant stimulus — 10-20 %, nonsignificant — 80-90% (pseudorandom interleaving of significant and nonsignificant stimuluses — 1 significant to 5-10 nonsignificant stimuluses).
2. Characteristics of the recordings:
One-Canal abduction (the 10-20% International System of electrode location):
Active electrode — Oz;
Reference electrode — Fz;
Ground — A1(2).
Sensitivity: 10 mkV.
Bandwidth: 0,5-100 Hzs (1-50 Hzs).
Automatic rejection: 5 sens.
Max. impedance level: before 10 kOm.
Analysis time: 500 mS (350-1000 mS).
Number of epochs: 50-300 (separately on significant and nonsignificant stimuluses).
3. Evaluation of result:
If significant stimulus is a familiar object really, the reaction is shown as the additional positive wave (cognitive response) with Latency order 300 mS.
Note: Cognitive reaction is primary in the method and is not controlled by a volitional checking.