The Polygraph: A Valuable Investigative Aid
Early Forms of Lie Detection
Throughout history, mankind has used various combinations of common sense and artifice to determine truthfulness. In ancient Babylon, the following observation was inscribed on a tablet: "When a man lies, he looks down at the ground and moves his big toe in circles." The implication is that a liar cannot look you in the eye.
A Chinese tablet dated approximately 1000 B.C. recorded an inscription which, translated, reads as follows: "The accused chews a mouthful of rice. He spits it out. If it is wet, the accused is truthful; if it is dry, the accused is lying." The Chinese believed that a truthful man's mouth would secrete saliva when he was questioned, whereas a liar's mouth would remain dry and thus not secrete any saliva.
In 1500 B.C. in India, a priest put lampblack on the tail of a donkey and led the donkey into a dark room. Suspects were told to go into the room and pull the "magic" donkey's tail, for the "magic" donkey could determine dishonesty. When the suspects returned from the room their hands were examined. Those with clean hands obviously did not pull the donkey's tail, indicating their fear of being exposed, and, consequently, their dishonesty.
The Development of the Polygraph
The word polygraph comes from Greek and it means "many writings." In 1790, Thomas Jefferson was the first man known to use the word "polygraph" to describe one of his inventions which could be made to repeatedly re-write words or messages.
In 1885, Cesar Lombroso, of Italy, recorded changes in the blood pressure of suspects during questioning in an attempt to determine the guilty party. He was successful in the first case he experimented with this method, a murder investigation with three suspects.
In the 1920's, John Larson was the first to record simultaneously, for lie- detection purposes, the breathing and cardio response of a human; he called the instrument the polygraph. In the 1930's to late 1940's, Leonarde Keller trained at Berkeley under John Larson. He patented the "Keeler Polygraph" and is legally considered to be the inventor of the polygraph. Keeler later developed the first polygraph device to measure breathing, skin resistance and cardio responses together.
In the late 1940's, John Reid further developed the polygraph technique by devising known lie and guilt-complex questions. These questions were specifically designed to elicit certain physical thought to clearly indicate truthfulness or dishonesty. The Reid Polygraph also measures arm and leg activity to use as a factor in determining truth.
The Modern Polygraph
Today's polygraph is an instrument that records three major physiological changes: (1) cardio response, measured in terms of blood pressure variations, heartbeat and pulse wave; (2) skin resistance, which is affected by the amount of perspiration; and (3) breathing. These changes may vary and are affected by the amount of emotion the person is experiencing. All of these reactions are recorded on a moving chart which is then analyzed by the polygraphist.
All polygraph examinations are strictly voluntary, and the average examination lasts approximately two hours. The initial phase, which is termed the pre-test interview, is an opportunity for the polygraphist to learn about the examinee's medical history, physical condition, psychological background, as well as what the examinee believes are the highlights of his or her life. This information allows the polygraphist to determine whether a person is suitable for testing.
The polygraphist then proceeds with a thorough explanation of how and why the polygraph works. Afterwards, the polygraphist discusses the issue in question with the examinee. For instance, if the examinee is suspected of committing a criminal act, the polygraphist discusses the criminal act allegedly committed by the examinee. The examinee is asked to relate to the polygraphist his understanding of the crime and why he believes he is a suspect.
The polygraphist then fine tunes the test questions prepared for the examinee. Approximately ten questions are asked during the actual examination, five of which relate directly to the crime. Prior to the actual examination, however, the test questions are read to the examinee, word-for-word.
Following this procedure, the actual testing begins. The ten test questions are usually asked three separate times, with a rest period between each test. After analyzing the polygraph chart, the polygraphist will come to one of three opinions about the examinee, i.e, that he or she is either truthful, dishonest, or indefinite.
(Most indefinites are resolved by a re-examination conducted at a later date). If the person is found to be dishonest, a post-test interview is attempted to arrive at the truth.)
There are presently 23 polygraph schools in the United States. At most schools, emphasis is placed upon the theory and actual operation of the polygraph, the most effective testing procedures, test question wording, chart analysis and both pre-test and post-test interviewing.
Classroom courses are usually six weeks long and consist of 257 hours of instruction. The classroom work is followed by an internship program during which the schools's staff reviews the first 30 cases conducted by the newly trained polygraphist.
Since the profession is continually being expanded and improved upon, it is necessary for a polygraphist to have continual training in the latest techniques. Conscientious polygraphists will attend at least one professional seminar every year.
Use in Law Enforcement
he primary purpose of the polygraph is as an investigative aid. In Pennsylvania, evidence pertaining to the polygraphist's opinion or the results of the polygraph is not admissible as evidence against the accused at trial. Accordingly, the polygraph is used as a supplement to an investigation, never as a substitute.
The majority of polygraph examinations conducted involve the testing of actual suspects. On occasion, complainants, informants and witnesses may also be examined. This will periodically occur when their allegations seem questionable or when their versions of the facts are in doubt. The polygraph helps to assess the credibility of the allegations. Hundreds of man hours may be saved when an individual confesses to having made a false report.
Licensing of polygraphists helps to ensure that only qualified persons enter the profession. In the United States today, approximately 21 states maintain licensing requirements.