An Early Lie Detector Test

Photograph

By: Anonymous

Date: 1915

Source: Corbis

About the Photographer: This photograph, originally from the Bettmann Archive, is currently owned by Corbis, a photo agency headquartered in Seattle, Washington. Corbis licenses images for use in magazines, films, television, and advertisements.

INTRODUCTION

Crime investigators have always been concerned with determining whether or not a suspect is telling the truth. When people lie, they tend to undergo certain characteristic physiological changes such as fidgeting, facial flushing, and avoidance of eye contact. If these physiological changes could be measured accurately, then scientifically based lie detection might be possible, and the results presented as evidence in a trial.

Cesare Lombroso (1835–1909), a pioneering figure in criminology, was the first person to use a machine that could measure changes in blood pressure and pulse as a means to assess a suspect's honesty. During World War I, William Marston (1893–1947), a graduate of Harvard University, developed a similar machine for use in detecting espionage and helped introduce its use into the American legal system.

The modern polygraph was invented by police officer John Larson. It measures blood pressure, respiration, and pulse while a suspect is being questioned. The multiple outputs of the device produce several lines on graph paper, which is the source of the device's name—polygraph. In 1939, Leonard Keeler, a student of Larson's, added measurement of skin conductance to the polygraph and, thus, introduced the version of the instrument that is still used today. The photograph below shows a suspect being interrogated using a primitive polygraph, probably based on blood pressure and pulse measurements.

PRIMARY SOURCE

AN EARLY LIE DETECTOR TEST

See primary source image.

SIGNIFICANCE

The status of the polygraph evidence in U.S. courts has always been somewhat controversial. Generally, evidence from a polygraph test is only admissible by prior agreement. In 1923, a defendant named James T. Frye appealed his murder conviction on the grounds that the court had not taken into account results of a blood pressure test. His conviction was, however, upheld, and, as a result, the federal court instituted the "Frye Test," which requires the scientific community to judge the validity of new methods, such as the polygraph test. Experts were required to prove the value of forensic tests outside the court before these tests could be used as evidence.

The Frye case did not deter the developers of the polygraph, and they continued to refine the device. As the device came into wider use, it became clear that the skill of the examiner and the questions asked are as important as the performance of the device itself. One important aspect of a polygraph examination is the use of a neutral control question as a baseline. The assumption is that this neutral question will elicit a lower response than questions related to the crime. Even with the use of the control question, the possibility remained that innocent people might be angry and frightened while being interrogated, causing their polygraph results to resemble those expected of a guilty person.

The modern polygraph is a small portable device. Rubber tubes are placed on the chest and abdomen of the suspect, a blood pressure cuff is placed on the arm, and small metal plates are applied to the fingers. When each question is asked input from three physiological responses—skin resistance, blood pressure, and respiration—is recorded as traces on a chart. A scoring system is used, based upon deviations from baseline on the chart. From this, the examiner decides whether the suspect is telling the truth, is lying, or whether the result is inconclusive.

The American Polygraph Association claims a high degree of accuracy for the device, as long as the examiner is skilled and a reliable instrument is used with a validated testing and scoring system. However, one study showed an error rate of eighteen to fifty-five percent among a group of six interpreters. Another, which used actual criminal investigation data, showed the examiners were right sixty-three to seventy-six percent of the time. These studies seem to show that the accuracy of polygraph results can depend heavily on the skill of the examiner. Some defendants, desperate to prove their innocence, may call for a polygraph test only to fail the test due to the stress of the experience. Others, who are guilty, may give a performance on the polygraph that makes them appear to be innocent because they are not very emotionally responsive.

The case of Roger Keith Coleman, convicted of rape and murder in 1982, illustrates the importance of timing and setting when administering a polygraph test. Coleman asked for a polygraph test to prove his innocence, but was only allowed to take the test on the day set for his execution. No second opinion was allowed nor was a second test permitted. It is hardly surprising that Coleman "failed" the test, given the stress he must have been under. He was executed later that day.

The polygraph also has been used in employment screening, but this application of the device was outlawed in the U.S. in 1988, except for certain sensitive positions. It is also sometimes used in civil litigation. While other forms of lie detection, such as hypnosis and the use of hypnotic drugs or "truth serum" have limited credibility, a new truth-detection technique that does look promising is brain fingerprinting. This technique involves recording brain activity in response to questions about crime details of which only the perpetrator would have knowledge. Studies have not yet compared the accuracy of the polygraph with brain fingerprinting but, when they do, the results should be fascinating.