In 1959, David Lykken, U. of Minnesota, compared electrodermal responses to crime-related information with those to equally plausible neutral items. He demonstrated that participants who committed a mock crime exhibited stronger electrodermal responses to crime-related items as compared to neutral alternatives. Innocent subjects, who remained ignorant of the relevant details of the mock crime, showed a non-systematic response pattern across the different test items. Thus, this Guilty Knowledge Test (GKT), later called the Concealed Information Test (CIT), allows for identifying crime-related knowledge. The CIT is accepted by the scientific community. (Verschuere, B., Ben-Shakhar, G., & Meijer, E. (2011). Memory detection: Theory and application of the concealed information test.)
The CIT is based upon a sound psychological construct called the “Orienting Response” (OR). The OR, triggered by a change in the environment, was first mentioned by Pavlov (1927) and later elaborated on by Sokolov (1963). The OR elicits physiological responses in the form of a rise in skin conductivity, respiratory suppression, reduction in pulse amplitude and heart rate deceleration.