Hi SAHS,
Just a little side point: I thought that a lie detector test could not actually be used by itself as the sole evidence for a legal conviction. Does the law on this vary among different states?
In most states, a lie detector test cannot be used against a criminal defendant. In some states, it can be used, depending on the judge and jurisdiction involved.
I?ve heard that it is possible for some people to ?fool? a lie detector machine so that it doesn?t pick up evidence of lying. (There must be some mental ?trick? to that.)
It is nearly impossible to fool a lie detector, as it measures too many human responses for a person to control. Some few people have been able to fool a lie detector if they are trained and practiced many times on a polygraph machine. The notion that we can fool it is mostly myth. The very few cases where it proved inaccurate, have led courts to not trust it entirely.
If it?s possible that a lie detector may fail to pick up actual lying, is it also possible that such a machine may give a false indication of lying when a person may actually not be lying due to extreme anxiety or some other factor?
No, this cannot happen. A person is first checked out several times on a polygraph to calibrate all of their nervousness and feelings of anxiety. Once this calibration is complete, then the polygraph can commence.
Has there been any scientific research into the validity of these machines one way or the other?
Yes. I used to have the links, but they are on my old PC. There is good science on polygraphs. However, there are many "junk" sites that are against lie detectors that are not good science.
A defense attorney once stated to me that the odds of a person being able to "fool" a lie detector are about one in a million. But, for the courts, a defense attorney will argue that it is one in a million too many. - Jim W.