Heidi Vance, age 10, of Staten Island, New York, for her question:
How does a lie detector work?
The older folk tell us and tell us to speak the truth, but often they forget to tell us why. Actually, the simple truth is like two and two which makes four. %en we tell a lie, it is like trying to add two and two to get six or some other impossible number. It just won't work out to the right answer. This wastes a lot of useful time and often leads to a maze of misery. The lie detector tells us even more about this. It proves that even our bodies like us to tell the truth.
Experts call the lie detector a polygraph because it draws a whole family of. jiggly graph lines. It works because our bodies like us to tell the truth. When we tell deliberate lies, we feel secretly upset and our bodies try to protest. The polygraph has a special chair and a number of sensitive instruments that report these secret protests.
Most of the time we do not notice our besting hearts and breathing lungs. These operations go on quietly behind the scenes. The polygraph instruments report slight changes in these and other quiet operations. One keeps a record of the pulsing heart. Another is a tube placed around the chest. It keeps a record of breathing. The person being tested sits in the special chair. It has instruments to check the palms of the hands for temperature and perspiration. Other instruments check muscles in the arms and legs. All these sensitive gadgets keep records of how the body is carrying on its secret operations. Their reports are relayed to metal fingers that write them on the graph paper.
When a normal person tells an outright lie, the body feels emotionally upset. This upsets the pulse and the breathing, perhaps the temperature and perspiration. Maybe a few muscles twitch. The polygraph notes all these slight changes and writes them on the records.
This complicated tattle tale machine must be run by a trained expert. He starts by asking a few innocent questions, just to see how the body reacts when a person tells the simple truth. Then he asks a series of carefully planned questions. If the person believes that the answers are truthful, the graphs jog along in normal ups and downs. But when a normal person tells a deliberate lie, the jiggly graphs go wild. However, it takes an expert to read what they mean.
The polygraph works because emotions change the body's normal operations. This happens when a normal person tells a deliberate lie, but lots of other things also can be upsetting. Maybe something nasty happened at home, maybe a question recalled a painful memory. These emotions may show up in the record, even though a person is truthful. So the polygraph is not perfect.
The expert makes allowances for a few upsets from outside. But once in a while he has to cope with a failure. A few people can tell lies without feeling emotionally upset about it. Most likely they cannot grasp what is true or false, or even care. The rest of us do care, and our bodies are much happier when we tell the truth.