There may be a choking up of the throat. They may become flushed in the face. Based on this general common sense observation, law enforcement individuals who had psychological and physiological training decided in about 1920 that if they could obtain an instrument to record certain physiological, changes with regard to suspects in criminal cases, they might be in a better position to perhaps determine whether or not the person has been telling the truth.
They developed an instrument which was eventually called the polygraph or so-called lie detector.
Through the years it has been used by law enforcement. It is primarily used, as I said before, as an investigative aid, and it has been helpful in that it can provide investigative direction to people in the law enforcement profession.
Mr. Specter. What is its level of reliability in indicating patterns of deception?
Mr. Herndon. There has been no conclusive scientific objective study in that regard, and as of today there are no valid statistics with regard to its actual objective reliability.
Mr. Specter. What is your opinion as to its level of reliability in measuring patterns of deception in a normal person?
Mr. Herndon. Well, the polygraph, of course, measures certain physiological responses which have to be interpreted. It must be clearly understood that the physiological responses that are portrayed on a polygraph chart can often be caused by things other than deception, such as fear, anxiety, nervousness, dislike, and many other of these emotions.
A polygraph examiner has to be extremely skilled and conservative in his estimation as to whether or not it is deception. I cannot give you any clear-cut personal opinion as to the validity of the technique with regard to its percentage of reliability.
Mr. Specter. Aside from an opinion as to percentage of reliability, what is your opinion in a very general way as to the ability of a well-trained, conservative examiner to detect a pattern of deception in a normal person under appropriate standards of administration?
Mr. Herndon. Based on a hypothesis of all factors you mentioned, a polygraph examiner under ideal conditions can generally interrogate a person, and if he has been able to obtain what he considers good control questions, he then may be able to come up with a conclusion which would indicate whether or not a person is deceiving or not.