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 menta l (counting backward by sevens) countermeasure on the concealed knowle dge test (CKT) were examined in a mock crime experiment with 40 subjec ts. Some knowledgeable subjects were informed about the nature of the CKT and were trained in the use of a countermeasure, whereas others re mained 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 e xtent, the mental countermeasures reduced the accuracy of the CKT. The se results clearly demonstrate that the CKT has no special immunity to the effects of countermeasures.