The lie detector, as the polygraph has been named by some repertorial genius, is much more accurate and efficient than some people would have you believe. The courts have not as yet accepted its evidence, I believe, as being final. But it is used with increasing respect by detective bureaus.
Basically the lie detector is an instrument which has long been used in physiologic laboratories to record in ink on a moving strip of paper the blood pressure and the pulse.
It has long been known that the rate of the pulse and the blood pressure are influenced by emotional states. The youth who sees the young lady of his dreams feels his heart rate go up about twenty beats a minute. The elder who does not like the way the stock market is going pounds the table until his blood pressure rises and his face looks like an over-ripe tomato.
One of the earliest clinical cases we have knowledge of is Galen’s account of a great patrician lady who fell ill in Rome. Her husband asked Galen to examine her. The old doctor said he could see that her trouble was functional and he heard from one of the servants that she was very fond of going to the theater. So with his finger on her pulse he asked her which dancer she enjoyed the most, naming them over one after another. When he mentioned Pylades he noticed that her pulse skipped a few beats. He concluded that her illness was due to a secret love for Pylades.
The lie detector carries out the same idea more accurately. Chief August Vollmer in 1921 started a young student at the University of California, John Larson, to make practical tests.
One of the crucial experiments consisted of having test subjects select one card from a pile of ten. Then with the lie detector adjusted each of the ten cards was shown and to the question, “Is this the card you selected?” they were required to answer “No” each time.
Now the subjects were trying to outwit the lie detector and of course each one lied at one point. But the detector revealed the time of the lie so often that only four out of 75 subjects could beat it.
When Larson got through his studies he had records on 400 criminals of all kinds, and a workable basis for future deductions.