Effect of a countermeasure which reduce physiological responeses in the detection of deception

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The dependent measures in a polygraph test are autonomic activities such as respectively, electrodermal, and cardiovascular responses. Recently, however, event-related potentials (ERPs) are expected as the index for detection of deception.Countermeasures are deliberate techniques that might be used by the suspects to alter their physiological reaction. A number of experiments have indicated that it is possible, indeed quite easy, to train guilty examinees and prepare them for a polygraph examination in such a way that they will be found truthful with a high probability. A possible approach for dealing with countermeasure manipulation is use of guilty knowledge test (GKT) that are based on ERPs instead of autonomic measures.In this research, we examined effects of a mental countermeasure on the GKT based on P300 (one of the ERPs). This research demonstrated that...1.A mental countermeasure inhibited the P3 amplitude. But there was a significant difference between amplitudes to relevant stimulus and to irrelevant stimulus because countermeasure inhibited the P3 amplitude not only to the relevant stimuli but also irrelevant stimulus.2.When subjects name were presented as relevant stimulus, the accuracy of GKT based on ERP in countermeasure condition was 81% and in non-countermeasure condition was 94%. There was no significant difference between accuracy of those GKTs.3.When jewels which subjects were stole in mock crime were presented as relevant stimulus, the accuracy rate of GKT based on ERP in countermeasure condition was 50% and in non-countermeasure condition was 79%. There was no significant difference between accuracy of those GKTs.It is concluded that GKT based on ERP is protected against a mental countermeasure.