Mental and Physical Countermeasures Reduce the Accuracy of the Concealed Knowledge Test
The effects of a physical (pressing the toes to the floor) and a mental (counting backward by sevens) countermeasure on the concealed knowledge test (CKT) were examined in a mock crime experiment with 40 subjects. Some knowledgeable subjects were informed about the nature of the CKT and were trained in the use of a countermeasure, whereas others remained uninformed. All subjects were offered a monetary reward if they could produce a truthful outcome. Subjects were tested using standard field techniques and instrumentation. The physical and, to a lesser extent, the mental countermeasures reduced the accuracy of the CKT. These results clearly demonstrate that the CKT has no special immunity to the effects of countermeasures.
Honts, Charles R.; Devitt, Mary K.; Winbush, Marcus; and Kircher, John C.. (1996). "Mental and Physical Countermeasures Reduce the Accuracy of the Concealed Knowledge Test". Psychophysiology, 33(1), 84-92.