MENTAL AND PHYSICAL COUNTERMEASURES REDUCE THE ACCURACY OF POLYGRAPH TESTS

Effects of countermeasures on the control-question polygraph test were examined in an experiment with 120 Ss recruited from the general comm unity. Ss were given polygraph tests by an examiner who used field tec hniques. Twenty Ss were innocent, and of the 100 guilty Ss, 80 were tr ained in the use of either a physical countermeasure (biting the tongu e or pressing the toes to the floor) or a mental countermeasure (count ing backward by 7) to be applied while control questions were being pr esented during their examinations. The mental and physical countermeas ures were equally effective: Each enabled approximately 50% of the Ss to defeat the polygraph test. The strongest countermeasure effects wer e observed in the cardiovascular measures. Moreover, the countermeasur es were difficult to detect either instrumentally or through observati on.