Have you ever watched The Maury Show and waited for the Lie Detector Test results to come back? On the show, those results are treated like conclusive evidence when in reality, the credibility of polygraph tests is dubious.
How does it work anyways? Polygraph tests measures psychological signals that commonly reflect anxiety, typically changes in respiration, skin conductance, blood pressure, and palm sweating. It relies on the premise that humans have a Pinocchio response, a supposedly perfect physiological or behavioral indicator of lying.
Here's the scary part: Studies have found that polygraph tests are actually biased against the innocent (Iacono & Patrick, 2006)! The obvious flaw with the test is that it is actually an "arousal detector," which does not always correspond with lying; it confuses physiological arousal with evidence of guilt. Those being tested could display physiological arousal for other reasons besides the guilt of lying, for example, nervousness caused by the fear of being incriminated for a crime you did not commit.
Wait a minute! If polygraph tests are so unpredictable, why does Maury Povich and many law enforcement units use them for interrogation and lie detection purposes? The answer is lies within human perception. Oftentimes, when someone's polygraph test detects guilt, it will provoke a confession - sometimes useful, but, varyingly unreliable. This is why most US courts do not accept polygraph tests as evidence.
So, when you're watching guilty pleasure reality shows like The Maury Show, the shocking lie detector results may not ascertain the guilty party.