Detection of Deception

Psychophysiological Techniques

The common element of all approaches to psychophysiological detection of deception is the recognition that external stimuli such as verbal questions may induce physiological reactions in the interviewee. These approaches combine practical applications of psychology with practical applications of biology. Hence, the term psychophysiology is used.

Polygraph testing is the most widely known of these techniques. During an interview, polygraph instruments make continuous recordings of physiological reactions from the interviewee's autonomic nervous system. The polygraph examiner reviews a short set of questions (about ten) with the examinee prior to putting the instrument attachments on the person for recording the physiological data. The attachments monitor changes of at least three types: changes in respiration during the question set, changes in blood pressure, and changes in sweat gland activity. There are no physiological reactions that the polygraph examiner can specifically associate with the telling of a lie. The reactions being recorded and evaluated are stress or fear reactions caused by what medical experts call the “fight-or-flight syndrome.” The autonomic nervous system responds to a perceived threat by rapidly making changes in the body that are somewhat predictable in their form if not in their magnitude. Questions [Page 501]that directly inquire whether the subject has committed the act under investigation (called relevant questions) pose a serious threat to the subject who is lying. of course, these questions also provoke reactions for the truthful or innocent subject, because of the threat posed by being falsely accused or fear that the examiner may make an error. So, the question set has comparison questions, as well as irrelevant questions, which allow the examiner to distinguish between liars and truth tellers with a high degree of accuracy.

An FBI recruit undergoing a polygraph test at the FBI Academy in Quantico, Virginia, showing that the test is used to detect deception in all aspects of criminal justice work.

© Anna Clopet/Corbis; used with permission.

Of the psychophysiological techniques used for forensic detection of deception, polygraph testing is the only one that has been subjected to large-scale scientific scrutiny. Hundreds of studies on the validity and reliability of polygraph testing have been completed, and U.S. government agencies (as well as those in other nations) continue to conduct and contract out additional research. Other techniques, such as computerized voice stress analysis, kinesic interviewing, or scientific content analysis, have yet to establish a body of supporting research to form a scientific basis necessary for expert witness testimony in a courtroom

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