The Truth About The Lie Detector

IS THE LIE DETECTOR CONTROVERSIAL? ITS MAIN INVENTOR denied that he had invented anything. Its early developers admitted that it could not detect lies. The United States government has published many studies critical of its performance, yet key elements of our national security rest on its reliability. Lie-detector advocates say the device is virtually infallible; detractors say it is grossly inaccurate. Police embrace the technology; scientists scorn it. It’s widely used in the United States and almost unknown in Europe. It induces confessions from hardened criminals, but a child can learn to beat it.

In 2002 a committee of the nonprofit National Research Council completed an exhaustive review of lie-detector screening. While admitting that it works in some cases, the committee’s chairman disparaged the device as a “blunt instrument” and concluded that “overconfidence in polygraph screening presents a danger to national security objectives.” Yet use of the lie detector is booming. A device that purports to detect untruthfulness has enormous appeal.

The lie detector emerged in a period of scientific optimism when researchers were eager to use physiological tools to delve into the human mind. In the mid-1890s the Italian psychiatrist and criminologist Cesare Lombroso speculated that measuring a person’s heart rate and blood pressure could reveal an emotional response connected with deception. He tried the technique on criminal suspects and found a man accused of a robbery to be innocent. His conclusions were later verified by the police. In Lombroso’s device, the subject inserted his hand through a rubber membrane into a container of water. Instrumentation measured the volume of blood flowing into the hand and recorded it on smoked paper. A drop in blood pressure, Lombroso said, meant that the subject was lying.

Two decades later an Italian professor of criminology named Vittorio Benussi tried a different approach. In 1914 he asserted that he could identify a lying subject by tracking the person’s breathing pattern. The ratio of inhalation to exhalation was larger after a lie, he said, and smaller after an honest answer. Despite their findings, neither researcher established a reliable method for identifying liars. Nevertheless, they opened up the possibility that a person’s physiology, if carefully monitored, could reveal deception.

The man who carried these ideas to the United States, where they would find fertile ground, was Hugo M’fcnsterburg, a flamboyant German brought over by the psychology pioneer William James to take charge of a laboratory at Harvard. M’fcnsterburg was eager to apply the science of the mind to forensics. In 1908 he proposed that courts might use blood pressure and other physiological changes as a deception gauge. A few years later the notion was taken up by one of his students, a Ph.D. candidate in psychology who had already received a law degree from Harvard. William Marston is sometimes credited as the inventor of the lie detector, though he always said that he originated a technique, not a device.

Marston was an energetic researcher who, with his colleagues, performed more than 10 million calculations to test Benussi’s respiration theory. When they were done, he rejected the method as too complicated. Instead he latched on to the measurement of blood pressure as a key to detecting prevarication. He hailed his discovery, which came to be called the Marston Deception Test, as “the end of man’s long, futile striving for a means of distinguishing truth-telling from deception.”

The basic technique was to ask questions while recording the subject’s blood pressure five times a minute, using an inflatable cuff and stethoscope. Marston plotted his findings on a graph and drew a curve over the discontinuous data. “The behavior of the blood pressure … constitutes a practically infallible test of the consciousness of an attitude of deception,” he asserted.

HE PUBLISHED HIS FINDINGS IN 1917, AND WHEN NEWS papers got wind of his work, they coined the term lie detector . Marston became the technology’s first great promoter; his enthusiasm set rolling the modern history of the lie detector, and his zeal eventually tarnished the device’s scientific credentials. At first he was content with an academic career, but later he set himself up as a popularizer of psychology, often employing the lie detector as a prop. In a 1928 stage presentation he used his technique to examine blonde, brunette, and redheaded showgirls at the Embassy Theatre in New York in an attempt to demonstrate the connection between emotional response and hair color. (That same year his book The Emotions of Normal People introduced the DISC [Dominance, Influence, Steadiness, Compliance] personality scale, which remains in use today.) By 1938 he was appearing in advertisements for Gillette, explaining that on the basis of “an astounding series of tests,” the lie detector had revealed “the naked truth about razor blades!”

“The Lie Detector goes to the heart of the situation,” Marston insisted. “It is a psychological medicine, if you like, which will cure crime itself when properly administered.” He saw the device from a moralistic rather than a strictly technical perspective: The lie detector would strip “the criminal’s magic cloak of deceptive invisibility.” Later researchers distanced themselves from Marston’s extravagant claims, but his influence would continue to shadow the field.

One important legal principle that came out of the Marston era was a 1923 U.S. Court of Appeals decision that limited the use of lie-detector test results as evidence in federal courts and established criteria for evaluating all scientific testimony. In 1920 James Alphonso Frye had confessed to the murder of Robert Brown, a Washington, D.C., physician. Frye later recanted. Marston examined him using the blood-pressure method and found his denial credible, but the trial judge would not allow the jury to hear Marston’s evidence.

When the issue went to the court of appeals, it ruled that scientific evidence “must be sufficiently established to have gained general acceptance in the particular field in which it belongs.” Marston’s technique, the justices decided, did not meet what came to be known as the Frye test. But though lie-detector evidence continued until recently to be banned from federal courts, each state could set its own standards for judicial acceptance. As early as 1924 an Indiana court allowed testimony about a lie-detector test. Other states adopted a variety of criteria for deciding whether the results could be admitted.

(Marston, by the way, left behind another artifact that would prove just as durable as the lie detector: Wonder Woman. He created the character in 1941 and scripted her adventures in the comics until his death in 1947. He equipped his skimpily but patriotically attired Amazon with a magical lasso whose embrace forced victims to tell the truth.)

In 1921 Marston’s ideas about lie detecting caught the imagination of John Larson, a police psychologist in Berkeley, California. Larson began experimenting with and refining Marston’s concept, adding a version of Benussi’s respiration evidence to the mix. Instead of relying on intermittent measurements, he created a machine that tracked cardiac and respiratory activity continuously, recording the values on paper. He called his equipment an ink polygraph , after a similar device that the Scottish cardiologist James Mackenzie had introduced in 1902 to record blood flow.

One of the early tests to which Larson put his machine was picking out the shoplifter from a group of 38 University of California coeds who lived together in a dormitory. He used a technique of alternating relevant questions (“Did you take merchandise without paying?”) with irrelevant ones (“Is your name Jane?”). The thief was so chagrined by having the machine uncover her deception that she later admitted to the crime.

Larson was as much a skeptic about the lie detector as Marston was a booster. He questioned some of Marston’s assumptions, did not believe polygraph results should be introduced in court without supporting evidence, and eventually lost faith in the technique. The results it did achieve, he decided, came mainly from intimidating the subject. In later years he stated the matter succinctly: “The lie detector, as used in many places, is nothing more than a psychological third degree.”

Leonarde Keeler, who as a high school student had worked with Larson at the University of California, was the next to advance the technology. In 1926 he built Larson’s concept into a standard, portable machine, and in the 1930s he added another pen to record changes in the electrical resistance of the subject’s skin caused by perspiration and other factors. This “galvanic skin response” had been known since Luigi GaIvani’s investigations of animal electricity in the 1790s. Some researchers had already raised the possibility that it might vary in some distinctive way under the stress of lying.

The Keeler polygraph became the archetype of the lie detector. Most of the machines developed since have been variations on it, measuring blood pressure, pulse, respiration, and skin resistance. Keeler was a true believer, yet he readily admitted that “there is no such thing as a ‘lie detector.’” He compared his techniques to the art of medical diagnosis. The polygraph, like any other medical instrument, yielded valuable data about the subject. The user had to interpret it to derive a conclusion.

The different measuring devices combined in Keeler’s polygraph had been developed in the late nineteenth century to give doctors and physiologists objective data about the human body. Scipione Riva-Rocci invented the modern blood-pressure cuff in 1896. He devised a rubber bladder, wrapped it firmly around the upper arm, and inflated it until it blocked blood flow in the brachial artery. A gas-pressure gauge gave the examiner a reading of the height to which the compressed air pushed a column of mercury. The blood-pressure gauge in a modern polygraph records both the rapid oscillations of the pulse and the slower increase or decrease in blood pressure.

To record breathing, the polygraphist fastens a corrugated rubber tube across the subject’s chest. Each inhalation expands this sensor and draws air up a separate tube, activating a bellows attached to a pen inside the machine. A third pen measures skin resistance. Electrodes attached to two fingers send a minute electric current through the subject’s hand. A Wheatstone-bridge circuit determines the resistance by comparing it with a known resistance inside the machine. The result is amplified and sent through a galvanometer, which moves the pen.

ALL THESE DEVICES TRY TO DETECT PHYSICAL REACTIONS associated with the autonomie nervous system, the part of the nervous system that regulates involuntary actions. These reactions are presumed to reflect the subject’s thoughts about the veracity of his or her statements. Lie-detector scientists have put forth a number of theories about how this works, most of them assigning a primary role to the subject’s fear of detection. However, a wide range of emotions can set off the autonomie system, generating reactions that vary from one person to the next. No one disputes that the polygraph detects sweaty palms, blood-pressure shifts, and changes in breathing. But what do these things mean? Is the reaction actually fear? Or is it embarrassment? Or anger over being asked an intrusive question? Could it be a reaction to an unrelated memory that a question has evoked?

The gap between physiology and cognition is a chasm that few research scientists were willing to leap in Larson’s day. Studying the machine’s reliability and accuracy was left to specialists in the polygraph field, many of them trained only in law and police work. Over decades of research they consistently judged the machine’s results to be highly accurate, usually in the range of 90 to 95 percent. Yet the laboratory conditions in which their studies were performed were very different from real life.

In the laboratory a researcher can tell an experimental subject to lie or tell the truth, but that’s not the same as examining an actual criminal suspect whose freedom may depend on the answer (and who may be a practiced liar). A man accused of murder and a college student who has acted out a theft can’t be expected to share the same emotions. On the other hand, research conducted with uncontrolled subjects lacks a reliable means of getting at the “ground” truth—that is, knowing whether the subject is lying or not.

One of Keeler’s innovations was the “stimulation” test. This was intended to convince the subject, before the main part of the examination began, that the polygraph was infallible. The object, which remains the key to all successful lie detection, was to increase the subject’s emotional response, to make him or her fearful that any deception would be immediately apparent to the polygraph operator.

This response could be generated in a number of ways. The subject might be asked to select a playing card, examine it, and answer no to everything the operator asked about it. The operator would ask questions (“Is it a red card? Is it a face card?”) and tell the subject whether the answer was a lie or the truth, eventually announcing what the card was. To make sure the test worked, the operator used a marked deck.

During the 1930s and 1940s law-enforcement agencies across the country began to adopt the polygraph for criminal cases. The FBI resisted the trend because the incorrect identification of a kidnapping suspect in Florida had soured the bureau’s director, J. Edgar Hoover, on lie detectors. The military services tested the device for use in intelligence work during World War II. By 1948 Keeler was offering police and military personnel a six-week course in polygraph operation at the nation’s first polygraph school.

Researchers continued to try to refine and improve the lie detector, focusing in particular on the interrogation format. A lawyer named John E. Reid developed the “reviewed control” question in the 1950s. This was a means of inducing the subject to tell a known lie in order to provide a base against which the polygraphist could compare the subject’s other responses. An operator might ask, “Have you ever stolen anything?,” assuming that the subject would lie in response. The aim was to distinguish the reaction to lying from simple nervousness. Besides eliciting known lies, Reid also elicited known truths, using “guilt complex” questions, which asked about a fictitious crime. The subject would truthfully disclaim any involvement in the crime, the point being to judge the subject’s general reaction to an accusatory inquiry.

REID EMPHASIZED THE IMPORTANCE OF MAKING AN EVAL uation based on all available information: the subject’s tone of voice, gestures, and facial expression and the known facts of the case, as well as the data on the polygraph chart. Skill at evaluating information beyond the actual tracings is thought to explain why on-the-scene testers are usually better at detecting deception than polygraph experts who review charts after the fact. Yet this difference belies the claims that polygraphy is an objective scientific technique; you might just as well ask the police officers who interviewed a suspect for their opinion. That’s why many polygraph detractors consider the lie detector to be an interrogation technique, not a scientifically valid procedure.

During the 1960s Cleve Backster, who instituted the polygraph program at the CIA, tried to minimize operator bias by standardizing and quantifying the reading of lie-detector charts. He also refined even further the methods for conducting a polygraph interview. At the same time, David T. Lykken, a psychologist who would emerge as a leading lie-detector critic, was developing the “guilty knowledge test.” This idea, which goes back to Lombroso, is to present the subject with details about the crime (“The victim was wearing a sweater. Was it red … blue … brown?”). A guilty party, asked to repeat each word, would presumably show a physiological reaction to the crime element, while an innocent person would not. No complicated interrogation technique or intrusive questions were needed. However, this technique is limited to interrogations that center on a specific incident, and the polygraph operator must be aware of details about the crime that are not widely known (and that the criminal has noticed and remembered).

By 1960 use of the lie detector in the United States had increased tenfold in a single decade. The polygraph had found a new role: employee screening. Leonarde Keeler had envisioned a role for the device in private business as early as 1931, but only after World War II did corporations embrace the technology. Companies used lie detectors as an economical way to select prospective employees and investigate internal theft, with periodic tests acting as a deterrent to malfeasance. Polygraph schools sprang up around the country, and some corporations kept polygraph specialists on salary.

Lie detecting became something of a craze, with one Dallas firm conducting 42,000 polygraph tests on its applicants in 1964 alone. The polygraph was seen as a kind of mental X ray that could root out a prospect’s narcotics use, undisclosed pregnancy, previous thefts from employers, or plans for staying with the firm. Employers tried to uncover political beliefs and attitudes that they thought might diminish an applicant’s rapport with management. The government turned to the polygraph to test potential employees in intelligence and defense posts, asking about everything from Communist sympathies to unconventional sexual practices. Law-enforcement agencies continued to use the lie detector too, but by the 1970s employee screening had surpassed criminal investigation as the primary use of the technology.

To the extent that polygraph screening did work, it did so in part because of the intimidation factor: It encouraged employees or candidates to reveal information that they might otherwise have hidden. During a lie-detector test the subject is given a chance, before or after the exam begins, to admit any wrongdoing or suspicious activity that might influence the results. After the machine is switched off, the subject can be asked to explain indications of deception on the chart. Eager to clear themselves, subjects may admit to peccadilloes or even major crimes. “It’s amazing what people will tell you,” one polygraph operator has said.

Critics believe that such interrogations amount to invasions of privacy. Pope Pius XII condemned lie detectors in 1958 because they “intrude into man’s interior domain.” A 1963 congressional study declared, “There is no ‘lie detector,’ neither mechanical nor human,” and advised a reduction in government reliance on the technique. In 1974 another congressional committee recommended that government agencies stop using lie detectors altogether.

Massachusetts passed the first ban on compulsory polygraph tests for employment in 1959. A few other states followed suit, but in 1988 a federal law, the Employee Polygraph Protection Act, made it illegal for an employer to require a lie-detector test for job applicants or employees. Firms involved in certain industries, such as security, were exempt, though, as were all lawenforcement and other government agencies.

The technology of lie detection has remained remarkably stable since Keeler established the basics in the early 1930s. Over the years just a few inventors have introduced changes. One added a second respiration sensor so that thoracic and abdominal breathing could be tracked separately. Another introduced an amplifier to let the blood-pressure cuff work at a lower pressure. Many modern machines are fully electronic, equipped with pressure sensors instead of mechanical tambours to convert data to pen movement. Lie detectors began to be connected to computers during the 1990s, with digital readouts replacing the tracings of ink on paper. Researchers have fulfilled Cleve Backster’s wish by removing human judgment from the process, devising algorithms to let the machine itself evaluate the data and apply the “deceptive” label according to a point system.

It has long been known that certain physical and mental countermeasures can create false or inconclusive results on a polygraph test. If the subject bites his tongue, performs mental gymnastics (such as math problems or word puzzles), or evokes emotional imagery, he can beat the test, particularly if he has had a chance to practice the techniques in advance. Motion sensors and muscular-tension monitors have been added to machines to reveal some of these tricks, but it is still generally acknowledged that countermeasures can significantly reduce a lie detector’s accuracy.

The admissibility of polygraph evidence in court has continued to be a point of contention. In 1978 a man named Floyd Fay was arrested for a murder in Ohio. With little hard evidence against him, the prosecutors offered Fay an opportunity to clear himself by taking a polygraph test—with the stipulation that the results could be used in court. Confident of his innocence, Fay took the test, failed, and was convicted. He served three years of a life sentence before the real killers were found.

TODAY 35 STATES ALLOW THE RESULTS of lie-detector tests to be used in court when both sides agree to their admissibility. In New Mexico there is no restriction on such evidence. In 1993 the U.S. Supreme Court, revising the Frye test, gave federal judges more leeway in deciding whether lie detectors could be used in trials.

Critics point out that a polygraph expert can in effect supplant the jury, which is assigned by our legal system to make decisions about the veracity of witnesses. The technique also raises the issue of self-incrimination. How voluntary are confessions elicited by a lie-detector test, which is usually administered without a lawyer present? In terms of coercion, one critic noted, the polygraph falls “between the rubber truncheon and the diploma on the wall.”

In 1983 the Congressional Office of Technology Assessment undertook yet another major review of polygraph validity. The report found the equipment hard to assess but concluded that the polygraph’s ability to detect lies was only slightly better than guessing. It was particularly critical of the lie detector’s role in screening, as opposed to criminal investigation. The study stated: “It appears that the NSA [National Security Agency] (and possibly the CIA) use the polygraph not to determine deception or truthfulness per se, but as a technique of interrogation to encourage admissions.”

The lie-detector controversy boiled over again in 1999 with accusations of Chinese espionage at the Los Alamos nuclearweapons laboratory. When Congress demanded action, the Department of Energy scheduled lie-detector exams for hundreds of its research scientists. Many of the targets denounced the polygraph as junk science, an “undependable piece of electronic flimflammery,” in the words of David Dearborn, a weapons designer at Lawrence Livermore National Laboratory. Forcing employees to undergo lie-detector interrogation would undermine morale, they said, even as it created a baseless sense of security. The CIA mole Aldrich Ames had managed to pass several lie-detector exams while he betrayed American secrets to the Russians. The scientists’ vehement protests, which succeeded in reducing the scope of the testing program, were what prompted last year’s National Research Council study.

Use of the polygraph as an intelligence tool has proliferated even though, as one NRC panel member put it, “No spy has ever been caught using the polygraph.” Polygraph use in law enforcement also continues to grow. Beginning in 1994, Louis Freeh, the director of the FBI, mandated polygraph tests for all applicants for employment at the bureau. Outside government, the once lucrative market for employment screening has been seriously abridged. Private polygraph experts today market their services for “fidelity testing,” offering to point the finger at cheating spouses. They promise to sort out accusations of child abuse in custody disputes and allegations of workplace sexual harassment. Some states require convicted sexual offenders to take periodic lie-detector tests as a condition of their parole.

Many lie-detection professionals advocate continued use of the technique because, whatever its scientific merits or shortcomings, it works. It uncovers most liars; it elicits confessions; it deters wrongdoing. Ideally, the polygraph should not be used as the sole criterion in assessing truthfulness but as one of several tools, like standardized tests in college admissions or computerized image analysis in diagnosing cancer.

The NRC committee discussed some innovative technologies, such as brain-wave monitoring, magnetic resonance imaging, and thermal tracking of facial blood flow, all of which look like more trustworthy indicators of deception than the data used in polygraphs. It remains to be seen whether these new approaches will replace Leonarde Keeler’s 70-yearold measures. One thing is certain, however. The controversy over what a newspaper of the 1920s called an “almost magical contraption” is unlikely to diminish any time soon.