问答题 Lie detectors are widely used in the United States to find out whether a person is telling the truth or not. 21 Polygraphers, the people who operate them, claim that they can establish guilt by detecting physiological changes that accompany emotional stress. The technique adopted is to ask leading questions such as: "Did you take the money?" or "Where did you hide the money?" mixed in with neutral questions, and measure the subject"s electrical resistance in the palm or changes in his breathing and heart rate. Such apparatus has obtained widespread recognition.
Whether lie detectors will ever be adopted on a similar scale in Britain is still a matter of opinion. 22 At first sight, it appears obvious that any simple, reliable method of convicting guilty people is valuable, but recent research sponsored by the U.S. Office of Public Health not only raises doubts about how lie detectors should be used but also makes it questionable whether they should be employed at all.
23 The point is that, apart from many of the polygraphers being unqualified the tests themselves are by no means free from error, primarily because they discount human imagination and ingenuity. Think of all those perfectly innocent people, with nothing to be afraid of, who blush and stammer when a customs officer asks them if they have anything to declare. Fear, and a consequently heightened electrical response, may not be enough to establish guilt. It depends on whether the subject is afraid of being found out or afraid of being wrongfully convicted. 24 On the other hand, the person who is really guilty and whose past experience has prepared him for such tests can distort the results by anticipating the crucial questions or deliberately giving exaggerated responses to neutral ones!
The success rate of up to 90% claimed for lie detectors is misleadingly attractive. If we refer such a figure to a company with 500 employees, twenty of whom are thieves, the lie detector could catch 18 of them but in doing so would place 32 innocent employees under suspicion. The problem for the management would therefore become one of deciding how much industrial unrest they are prepared to cause in order to eliminate theft. 25 What concerns research workers even more, of course, is the fact that a certain number of innocent people are bound to be convicted of crimes they have not committed.