facial expression, various body movements, posture, and various measures of speech). The evidence suggests that such measures are likely to have the greatest success when lies have high personal relevance, when the stakes are high, when the liar knows he or she is telling a lie when it is being told, and before there has been opportunity to practice and rehearse the lie (Ekman, 2001; DePaulo et al., 2001). So far, however, no research has been done combining all of the behavior measures and testing their accuracy under the appropriate circumstances.

Given the apparent potential for the detection of deception from demeanor and the difficulty and limited effectiveness of objective measurement so far, the question arises whether it might be possible to train observers to make accurate judgments from demeanor without formal measurements. Without training, most observers, even experienced law enforcement personnel or security officers, cannot do much better than chance, and their confidence in their judgment is unrelated to accuracy (Ekman and O’Sullivan, 1991; Ekman, O’Sullivan, and Frank, 1999). Some groups, however, do perform better than chance in detecting lies from demeanor just by viewing videotapes. A group of U.S. Secret Service agents averaged 64 percent correct judgments when chance performance was 50 percent, with about half of them achieving an accuracy level of 70 percent or more (Ekman and O’Sullivan, 1991). No studies have yet been done to determine if those who do poorly in detecting deception from demeanor can be trained to become very accurate. However, a review of the research on training effects in deception studies showed a moderate improvement (Frank and Feeley, 2002).

The research on the detection of deception from demeanor includes the presumption that liars experience more stress than truth-tellers, especially in high-stakes circumstances, and that this stress shows in various channels, including in the voice. Recent meta-analytic evidence shows consistent associations of lying with vocal tension and high pitch (DePaulo et al., in press). Applied efforts to develop measures of voice stress for the detection of deception have not been very successful, however.

As early as 1941, Faye and Middleton attempted to use human judgment of voice responses to determine deceptions of subjects told to answer a series of questions either truthfully or untruthfully. Their methodology yielded correct judgments for truthful responses at essentially chance levels and slightly higher rates of correct judgments for untruthful