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The Polygraph and Lie Detection
nomic measures to psychological processes that are closely tied to deception. Brain activity can be measured with modern functional imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI, often referred to as functional MRI or fMRI when used to relate brain function to behavior), as well as by recording event-related potentials, characteristics of brain electrical activity following specific discrete stimuli or “events.” The third class of techniques attempts to achieve detection of deception from demeanor: these techniques usually involve careful observation of specific behaviors of examinees (e.g., voice, facial expression, body movements, choice of words) that can be observed with human sense organs but may also be measured with scientific equipment. The fourth class is based on overt, direct investigations and includes employment questionnaires; background checks; and employee surveys, questionnaires, and paper-and-pencil tests. We consider each of these in turn.
The polygraph is the best-known technique for psychophysiological detection of deception. The goal of all of these techniques is to detect deception by analyzing signals of changes in the body that cannot normally be detected by human observation. The physiological phenomena recorded by the polygraph are only a few of the many physiological phenomena that have been characterized since the polygraph was first introduced and that might, in principle, yield signals of deception.
The polygraph relies on measurements of autonomic and somatic activity. That is, it analyzes signals of peripheral physiological activities associated with arousal and emotion. The traditional measures used in polygraph testing are cardiovascular (i.e., changes in heart rate and blood pressure), electrodermal (i.e., changes in the electrical properties of the skin that vary with the activity of the eccrine sweat gland), and respiratory (see Chapter 3). These are among the oldest measures used by psychophysiologists.
A wider variety of visceral events can now be recorded noninvasively, including myocardial contractility, cardiac output, total peripheral resistance, skin temperature (thermography), and vascular perfusion in various cutaneous tissue beds (Blascovich, 2000; Cacioppo, Tassinary, and Berntson, 2000a). Several of these measures provide clearer information than traditional polygraph measurements about the underlying neurophysiological events that produce visceral adjustments. Given appropriate measurement contexts and controls, for instance, respiratory sinus arrhythmia can be used to reflect cardiac vagal activation, and myocardial contractility (e.g., as assessed by pre-ejection period) can be used to