Judy Newton, Age 11, Of Kentfield, Calif., for her question:
How does a lie detector work?
Its scientific name is the polygraph, which comes from two older words meaning many and write. This comp1ex gadget records several processes that go on continuously in the human body and writes its records on a revolving chart. A trained expert is needed to use it and read its reports.
We laugh when we are happy and cry when we are sad. We are used to the idea that emotions of light hearted joy cause our faces to wrinkle with smiles, and emotions of pain cause tears to roll down our cheeks. We know that changing motions cause changes in our bodies and in what we do.
Experts claim that our emotions cause far more subtle changes in certain processes of the body, such as the breathing and heart beat, the unconscious blood pressure and muscle tension. Our emotions, these experts claim, react to every word we speak, and these changing emotions can be recorded on the complex polygraph. This gadget is called a lie detector because it is used to detect the reactions of a person's body when he or she is not telling the truth. Perhaps it should be called a truth detector.
A person tested with a polygraph is seated in a chair and fitted with meters. One meter records the rate of his breathing, another records changes in pulse and blood, pressure. Another records electrical charges of the skin caused by perspiration, another records the reflexes of muscle tenslon. The person being tested is qu=stioned by a trained expert, and the bodily reactions caused by his answers are charted in graphs on a revolving drum.
Such a complicated gadget, you might think, can prove without doubt whether the person is telling the truth or not, whether someone is guilty or innocent of the crime in question. The polygraph machine may indeed root out the truth. But its graph must be read by human beings, and sometimes even the experts cannot be sure what they mean.
Chances are the blood pressure of a guilty person increases, and he tends to hold his breath. But a scared or nervous person may react in the same way, or he may react with guilt to some unrelated minor misdeed of his childhood that just happened to pop into his head. Because of these arid other weaknesses, most law courts refuse to accept a polygraph test. As reliable evidence what's more, no American can be compelled to confess his own guilty secrets. So, just in case this mechanical detective can make a person reveal the guilty truth about himself, no American can be forced to take a polygraph test.
The experts are divided for and against the usefulness of the polygraph. Most law enforcement officials think it helps to weed out the innocent from the guilty. But after it had been used at oak ridge to test the reliability of experts entrusted with our defense secrets, the atomic energy commission decided against it. The polygraph, it was felt, may or may not be able to spot a character weakness which may or may not be a security risk. But this contribution was far outweighed by the indignation of true blue citizens who felt that the detective machine was being used unfairly t0 challenge their loyalty.