And afterwards we go over the results in detail. If a subject is lying, he usually tells me so before we ever get to that point. Some people believe they can beat it by taking drugs. But I want them to come in here in their normal physical condition. If the guy I'm talking to is a heroin addict, I don't want him going through withdrawal.
Polygraph measures the body's normal responses.
His body still responds to threats the way our most remote ancestors did, and one is generally unable to control autonomic responses such as blood pressure and palm sweating. Four groups of 20 people were told to drop off or pick up packages from two doormen at a building. The doormen then were presented with four photographs and asked to identify who had picked up the packages. Experts in various methods of detection tried to make the same determination from among those in the the four photos. The fingerprint expert was right 100 percent of the time, polygraph 95 percent, handwriting expert 94 percent and the eyewitness testimony of the doormen was right 64 percent.