Polygraph tests -- also called "lie detectors" -- have been around so long that they're a permanent part of the way American's picture law enforcement operations. In the movies and on television, the police can hook a suspect up to a polygraph machine and make a clean call about their guilt after just a few questions.
Well, it really doesn't work that way. Psychologists say that the machine is better described as a "fear detector," than any kind of lie detector. To detect a "lie," the polygraph machine measures such things as a suspect's:
- Rises in blood pressure
- Changes in breathing
- A quickening heart rate
- Increased sweating