Polygraphs

When researchers developed means for measuring visceral responses and
discovered that these responses are associated with emotions, it was not long
before the possibility of detecting lies was raised. The use of a polygraph to
detect lying is based on the assumption that people will feel anxious or guilty
when asked a question that has personal, emotional significance to past
deeds. The polygraph tester measures and compares physiological responses
to both control questions and relevant questions to infer lying. For example,
if a person is suspected of murdering John Smith on May 16, the tester may
ask the control question: “Have you ever hurt someone?” Because everyone
has hurt someone at one time or another, and probably feels guilty about it,
some level of emotional response will be registered in changes in heart rate
and respiration. The relevant question is “Did you kill John Smith on May 16?” Supposedly, the innocent person will show a greater emotional response
to the control question than the relevant question. The perpetrator
of the crime should show a greater emotional response to the relevant question
because of its extreme emotional significance.

The use of polygraph testing is surrounded by controversy. Although
some liars can be detected, if a perpetrator does not feel guilty about the
crime—or does not believe that the polygraph can measure lying—he or she
will not show the expected response to the critical questions about the
crime. In addition, research has shown that some innocent people will become
so anxious when asked “relevant” questions that they are mistakenly
viewed as guilty. The American Psychological Association has expressed
grave concern over the validity of polygraph testing. The U.S. Congress has
outlawed the use of preemployment testing to predict who might, for example,
steal inventory. Despite the reservations of the American Psychological
Association, however, security agencies and defense industries are allowed
to use polygraph testing.