Maybe it's because we've come to distrust computer programs so much. Or maybe our own insecurities cause us to think other people are able to see through us.
In any event, this test produced results described in Meet Brad, the AI interrogator: Virtual persona taught to tell when people are REALLY telling the truth tell an interesting story.
Researchers built a virtual interrogator which was a computer program that conducted an interview while lie detector type measurements were taken from the subject. What the researchers found was that the device was only effective if subjects believe the system was being controlled by a human, not a computer.
Brings to mind the old joke:
Husband to wife: You're lying.
Wife: No I'm not.
Wife to Husband: You're lying.
Husband: How did you know?
The real value of the polygraph is if the test taker believes it will work. The technician tells the subject that the test says he/she lied. Faced with this scientific proof plus a convincing human, the test taker then confesses.