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Polygraphic Examinations in Japan: Application of the Guilty Knowledge Test in Forensic Investigations

There are two main types of psychophysiological detection of deception in Held practice: the guilty knowledge test (GKT) and the control question test (CQT). A survey carried out for members of the American Psychological Association and the Society for Psychophysiological Research proved that many of the members consider that the GKT is superior to the CQT in its validity. Moreover, several experimental studies reported that the GKT produces fewer false positive errors (classifying an innocent suspect as guilty) than the CQT. In spite of these issues, the GKT is used less in North America and there are several researchers who insist that it is inapplicable in real-life criminal investigations. In Japan, however, the GKT has been extensively and successfully used in criminal investigations since the 1950s. Moreover, basic studies of the GKT, such as visual presentations of evidence, an automated diagnostic method by a computer and detecting guilty knowledge by using event-related brain potentials, are actively carried out in many Japanese laboratories to improve the method's reliability. In an effort to encourage the application of the GKT as an effective and scientific method in criminal investigations, this paper describes the status of the GKT in Japan.