One of several theoretical explanations for the psychophysiological mechanisms underlying arousal during deception. According to this ‘concern-based’ model, examinees physiologically respond to test questions to which they are lying out of concern that their deceptions will be detected and adverse consequences will follow. The greater the fear, the greater will be the response. While incomplete and unproven, this remains a prevailing theory taught to PDD practitioners because it appears to have some face-validity. Unfortunately, it ignores the large body of scientific literature dealing with cognition, emotion and behavioral conditioning. One obvious exception relates to those instances where the PDD test continues to be effective even when there are no or trivial consequences for detection, or when directed-lie comparison questions are used.