Polygraphers claim that it is the form and mix of questions that are the keys to their success. It is in this crucial pretest phase that the polygrapher's deception comes into play, for he wants the innocent subject to dissemble while answering the control questions during the actual test. The assumption underlying the Control Question Test is that the truthful subject will display a stronger physiological reaction to the control questions, whereas a deceptive subject will react more strongly to the relevant questions. That is the heart of it. Modern lie detection relies on nothing more than subtle psychological techniques, crude physiological indicators, and skilled questioning and interpretation of the results.
Critics claim that polygraphy fails to take the complexities of lying into account.
For some people lying can be satisfying, fulfilling, exciting, and even humorous, depending on their reasons for lying. Other people feel little or no emotion when lying. Still others believe their lies and think they are telling the truth when they are not. Moreover, the theory holds that deception produces distinctive physiological changes that characterize lying and only lying. This notion has no empirical support.