The role of comparison questions in physiological detection of deception.

Comparison questions in physiological detection of deception were studied with 60 "guilty" and 60 "innocent" participants in a mock crime experiment. Different types of comparison questions were used in four conditions: relevant-irrelevant (R-I) participants answered only relevant and neutral questions; trivial directed lie participants were instructed to lie to three of the six neutral questions; personal directed lie participants were instructed to lie to personally relevant questions; and probable lie participants received traditional probable lie comparison questions. Respiration, cardiovascular, vasomotor, and electrodermal activity were recorded. Manipulation of the comparison questions produced different patterns of physiological responses for innocent but not for guilty participants. The R-I test produced an unacceptable rate of false positive decisions.

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.

Polygrapher's dilemma or psychologist's chimaera: a reply to Furedy's logico-ethical considerations for psychophysiological practitioners and researchers.

We respond to Furedy's article in this journal where he raised an issue he referred to as the "Polygrapher's dilemma" (Furedy, J.J. (1993) Int. J. Psychophysiol., 15: 263-267). Furedy claimed that the control question test, the most commonly applied psychophysiological detection of deception test, is inherently subjective and harmful to subjects in both the field and the laboratory. Fortunately, Furedy's arguments were based on inaccurate representations of the control question test and on flawed logic. To correct Furedy's misrepresentations, we present an accurate description of how the control question test is used and evaluated. We then examine the results of empirical research that address Furedy's concerns. Furedy's concerns are found to be lacking on almost all counts. Finally, we discuss the findings from several studies that Furedy failed to mention but are directly relevant to the issues he raised.

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 community. Ss were given polygraph tests by an examiner who used field techniques. Twenty Ss were innocent, and of the 100 guilty Ss, 80 were trained in the use of either a physical countermeasure (biting the tongue or pressing the toes to the floor) or a mental countermeasure (counting backward by 7) to be applied while control questions were being presented during their examinations. The mental and physical countermeasures were equally effective: Each enabled approximately 50% of the Ss to defeat the polygraph test. The strongest countermeasure effects were observed in the cardiovascular measures. Moreover, the countermeasures were difficult to detect either instrumentally or through observation.