clarity regarding the mechanisms purported to cause differential responses to relevant and comparison question in relevant-irrelevant or comparison question polygraph tests. Various theoretical accounts have been advanced to explain differential psychological responses to relevant and comparison questions (differential arousal, stress, anxiety, fear, attention, or orienting). Although these theories all concur that a guilty individual responding to relevant question should evince a different psychological state than when responding to a comparison question, these theories differ with respect to the variety of psychological states that an innocent individual might experience in responding to relevant question and comparison questions. Although these differences are important for understanding the possibilities for false positive test results, we have found no studies reporting tests among the theories. Relatedly, various theories have been proposed to map the diverse psychological states presumed to be associated with deception to peripheral physiological responses. We found no tests among these theories, either. Indeed, most research on the comparison question polygraph has been atheoretical about the underlying mechanisms.

The situation is somewhat different with research on concealed information polygraph testing, which has consistently drawn on the theory of the orienting response. This research has emphasized developing and testing procedures that are resistant to threats to validity that can arise from differential reactions to relevant and comparison questions among examinees who have no event-related information to conceal. It uses the same physiological measures as other polygraph research, however, and in this respect shares the limitations of other polygraph test formats.

Polygraph research has not made adequate use of well-developed theoretical models of the physiological processes underlying the peripheral measurements taken by the polygraph. Those models are not reflected in the instruments or measurement procedures used in polygraph testing. Theoretical developments about the separable neurophysiological control of peripheral responses that appear similar (e.g., Dienstbier, 1989; Berntson, Cacioppo, and Quigley, 1991, 1993; Cacioppo, 1994) have seldom been considered in polygraph research, nor do the physiological measurement procedures and devices used in polygraph tests conform to the standards established by the scientific research community (e.g., Dawson, Schell, and Filion, 1990; Dawson, 2000). There is now an extensive body of literature on the sympathetic and parasympathetic influences on many organs that are in turn reflected in psychophysiological measures. Many of the measures used in polygraph testing, such as heart rate, reflect both sympathetic and parasympathetic influences. Several very different physiological mechanisms can result in identical changes in heart rate. There are now measures available that allow for the disentan-



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