deception. Buller et al. found that this did not elicit as much suspicion as probes from nonsuspicious receivers. Burgoon et al. (1995) found that some receivers engaged in a more dominant interview style to engage with their deceiver, which represents a more aggressive and "unpleasant" style of questioning that aroused suspicion on the part of the deceiver. Emotion Emotion plays a central role in IDT as a motivation and result of deception. Emotion can motivate deception, with the sender relying on relevant knowledge (informational, relational and behavioral familiarity) to achieve goals such as self-gratification, avoiding a negative emotional outcome or creating a negative emotional outcome for the target of deception. Emotion can be a result of deception, since a physical response occurs in the sender (usually arousal and negative affect). Leakage The concept of leakage predates the development of IDT and was developed by Miron Zuckerman, et al., who created a four-factor model to explain when and why leakage is apt to occur. Leakage in deception is manifested most overtly in nonverbal signals; studies indicate that over 90 percent of emotional meaning is communicated non-verbally. Humans are sensitive to body signals, and communication is often ambiguous; something is communicated verbally and its opposite non-verbally. Leakage occurs when nonverbal signals betray the true content of a contradictory verbal message. Facial expression is difficult to read, and the Facial Action Coding System (FACS) is a means of uncovering deception. Small facial movements, known as micro-expressions, can be detected in this system using action units. Micro-expressions and action units Action units (AUs) can be examined frame by frame, since these micro-expressions are often rapid. Paul Ekman’s research in facial deception has found several constants in certain expressions, with the action units relating to lip-corner pulling (AU12) and cheek-raising (AU6) qualifiers for happiness in most people. Brow-lowering (AU4) and lip-stretching (AU20) are disqualifiers for happiness. According to Ekman, emotional leakage appears in these fleeting expressions. Ekman's research has received much attention in the popular media, but it also has been heavily criticized on both experimental and theoretical grounds. His theory that micro-expressions are effective markers for detecting deception is no longer considered to be well-supported. One criticism is that the theory "confounds emotion and deception", like use of the polygraph in assuming that an innocent person and a guilty one will feel different emotions in a situation which has severe possible outcomes. Concerns with