Some techniques for detecting deception are based on the interpretation of subtle signals in behavior or demeanor, defined here as activities of an individual that can be observed with the usual human senses, without physical contact with the individual and therefore, potentially, without the individual’s knowledge. Demeanor includes, among other things, gaze, posture, facial expressions, body movements, sound of the voice, and the patterns and content of speech when one person talks to another during an interview, interrogation, or any other conversation. We use the term detection of deception from demeanor to refer to efforts to discriminate lying from truth-telling on the basis of such cues. There can be a fine line between such detection and peripheral measurement of autonomic responses, as suggested, for example, by thermal imaging techniques. These techniques can detect both phenomena that a trained observer can learn to discriminate (such as blushing) and others that are beyond the capabilities of human senses because they involve infrared emissions. Because thermal imaging primarily measures infrared emissions, we classify it with techniques for the psychophysiological detection of deception.
Several authors have reviewed the large body of research connecting lying or truth-telling to cues from demeanor (Zuckerman, DePaulo, and Rosenthal, 1981, 1986; Zuckerman and Driver, 1985; DePaulo, Stone, and Lassiter, 1985; DePaulo et al., 2001; Ekman, 2001). Because this research is rooted in social psychology more than in law enforcement or counterintelligence practice, it has a somewhat different flavor and focus than the polygraph research (reviewed in Chapters 4 and 5). Many of the studies, for example, concern everyday “white lies” and other deliberate untruths that may be quite different psychologically from serious lies or truth telling, such as occur about suspected criminal activity or espionage. Their findings may not transfer to such practical settings. Some of the reviews do not analyze results in a way that shows how many subjects were correctly or incorrectly classified as liars or truth-tellers and how many could not be classified. Also, many of the studies focus on specific demeanor cues or classes of cues, rather than on building a full capability for detecting deception from demeanor by combining information on any aspects of demeanor that might provide useful information. For such reasons, large segments of the research have very limited practical relevance for criminal or security investigation contexts. In addition, most of the research has limitations in terms of external validity, as does most polygraph research: for example, the stakes are almost always low, and there are no negative consequences for being judged to be lying. In this context, it is worth noting the results from one meta-analytic study (DePaulo et al., 2001) indicating that the associations of demeanor indica-