The most commonly associated class of indicators of deceit is arousal. Engaging in deceit is theorized to be distressing, causing liars to experience increased arousal such that the sympathetic nervous system excites the body in response to an imminent fight-or-flight event or potential threat monitoring invoked by the security motivation system (Woody & Szechtman, 2011). It is these cardiorespiratory and galvanic skin physiological responses that are captured by the polygraph and are the impetus for most of the commercial products that have been billed as lie detection systems.
Previous research has revealed that liars often do exhibit one of two types of response patterns: either a generalized activation response or greater tension. Negatively valenced arousal can be revealed through greater pupil dilation or instability, postural shifting, fidgeting, random trunk and limb movements, hand adaptor gestures such as touching the face, neck or head with the hand, or lip adaptors
such as biting, licking or puckering the lips. Tension, on the other hand, can manifest itself through frozen and rigid postures, lack of gestures or a tightening of the muscles in the vocal folds, which causes them to vibrate faster and produce a higher pitch (fundamental frequency) when speaking (Titze & Martin, 1998).
Although arousal is the most commonly acknowledged overt manifestation of deceit, it should be noted that the relationship between deception and arousal is not deterministic.
First, deceit does not inevitably trigger arousal. White lies, lies told for the benefit of the target, lies that are sanctioned by a given culture or community, lies that are sanctioned by an experimenter or authority, omissions, exaggerations and evasions, and the like may not cause the perpetrator of deceit to experience
Second, internal experiences do not necessarily translate into external observable cues. People are capable of masking, minimizing, and replacing distress and arousal signals with outward displays that are socially appropriate and do not reveal the true internal state (P. Ekman, 1992; Fridlund, 1991).
Third, a variety of factors other than deceit can cause arousal. Truth tellers, for example, may show signs of arousal if accused of wrongdoing or if questioned by authority. People may blush because they are embarrassed, even though they are not being deceptive. If both liars and truth tellers exhibit signs of arousal, then such signs cannot be used to identify truth.
Fourth, different people may exhibit arousal in different ways. For example, one person may swivel in a chair, whereas the next person may “freeze” into a fixed posture with virtually no movement. Put differently, arousal can take many, substitutable forms (Judee K. Burgoon, Kelley, Newton, & Keeley-Dyreson, 1989).
Finally, the indicators of arousal may be feeble and transitory (DePaulo et al., 2003; Hartwig & Bond, 2011), eluding detection because humans or instrumentation lack the sensitivity to capture them or because detection efforts are ill-timed (Hamel,
Burgoon, Humpherys, & Moffitt, 2007). For all these reasons, there is a lack of one-to-one correspondence between truth and arousal indicators, which undermines the diagnostic value of such indicators.