Gary Vanicek, age 12, of York, Neb., for his question:
HOW DOES A LIE DETECTOR WORK?
A person cannot be forced to take a lie detector test. Co operation from the subject is absolutely necessary. The person submitting to the test sits in a chair with a blood pressure and pulse cuff on his arm and a respiration tube around his chest. Galvanic reflex electrodes are placed on his hand and the chair has devices that measure muscular movements.
A lie detector is also called a polygraph. It is a device that measures various physical reactions to questions asked. It records with an ink tracing the body activities related to blood pressure, pulse and breathing as questions are asked.
Emotional responses to questions are reflected in the way a person reacts to quizzing. An expert who is trained in the use of the polygraph can make a determination if the subject is telling the truth or telling a fib.
One of the popular lie detectors is called the Reid Polygraph. It records changes in blood pressure, pulse and varying reflexes of the skin to a slight amount of electricity.
A continuous record of the various activities of the body is made during the questioning. Ten questions are usually asked with four related to the matter being investigated and the remaining six broken down into four unrelated questions to establish a ''normal'' reaction and the final two dealing with minor incidents similar to the one under investigation.
If a person lies when he answers questions, a change in breathing or blood pressure will usually take place. Other body responses may be indicated, but breathing and blood pressure are the two most reliable items for this test. If the subject tells the truth on other questions, there usually is no change in his breathing or blood pressure.
A person who is being completely honest could well show signs of nervousness that would be recorded on the tracings. But his nervous condition would continue throughout the test, including when certain ''control'' questions were asked.
The polygraph is a most accurate piece of equipment, although results from it cannot be used as legal evidence in court trials.
One of the first polygraphs used was made by John A. Larson in 1921. An improved model was made by Leonarde Keeler in 1926, and then John E. Reid in 1945 developed an instrument that recorded not only blood pressure, pulse, breathing and skin reflexes but also muscular pressures.