Lying, goes the rationale, is deliberate, and the knowledge and effort associated with it will make a person upset enough to display a physical reaction like a speedup of the heartbeat. The variables measured usually include the galvanic skin response, blood pressure, abdominal respiration, and thoracic respiration. There is no specific lie response. The polygraph merely records general emotional arousal. It does not distinguish anxiety or indignation from guilt.
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, polygraph theory holds that deception produces distinctive physiological changes that characterize lying and only lying. This notion has no empirical support.