[Effects of a mental countermeasure on the physiological detection of deception using the event-related brain potentials].

This study focused on the effects of a mental countermeasure on the detection of deception using the P300 component of event-related brain potentials. Thirty-three subjects were divided into two groups: a countermeasure (CM) group and a non-countermeasure (NCM) group. The CM group was instructed to count backwards by sevens during the experiment. Relevant stimuli were subjects' own family names and irrelevant stimuli were four other typical Japanese family names. The subjects were required to press a button when the name stimuli were presented on a CRT display. The use of the mental countermeasure significantly prolonged reaction time to the stimuli and reduced overall P300 amplitudes. The P300 amplitudes to the relevant stimuli, however, were consistently larger than those to the irrelevant stimuli in both groups. The correct detection rate of the relevant stimuli was 81% in the CM and 94% in the NCM group, but the difference was not statistically significant. These findings indicate that deception can still be detected by using P300, in spite of the use of the countermeasures by subjects.