The Basics of the Polygraph Process
Polygraph tests, commonly referred to as lie detector tests, have a storied history that can be traced back to the late 19th century. Originally designed for practical purposes, the development of these tests and the science that underlies them was intended to introduce a brand-new method of truth verification. The tool has largely evolved in a professional context, but their original intention as a scientific method is important to know as a basis for determining how they hold up in a legal context.
The term polygraph denotes a device or machine designed to measure physiological changes in the human body, including blood pressure, pulse rate (or heart rate), perspiration levels and respiration. The most common form of lie detection incorporates all of these elements into a single graphic output — hence, the "poly" prefix, which means "multi" — that a trained examiner analyzes to determine the truthfulness of an accused. However, the basic polygraph machine has evolved from its original purpose and now has many variants. Some even exist in a modern utilitarian form that a subject may use independently to create a computer printout record of physiological fluctuations in a private setting, which can then be considered by a trained examiner. A polygrahic chart indicates the normal or baseline levels of these key physiological substances, which increases when a person recognizes a perceived threat, for example. This increase is read by the machine as a sign of truthfulness or deception depending on the context . The machine itself does not make this judgment, however; it is merely a device. A trained examiner will analyze the resulting printout. This modern advancement in usability has helped make polygraph tests more widely available and accessible. Polygraphs are thought to work because physiological changes in the human body are measured during a person’s response to a perceived threat, such as being caught in a lie. The slight stress that the brain perceives as life-threatening is then transmitted to the nervous system and affects the internal organs, which then produces distinctive physiological indicators that a trained examiner may interpret as a relative increase or decrease in a given baseline substance. These small changes might go unnoticed if not recorded on a polygraph machine. The basic premise behind a polygraph test is that the physiological stress produced when a person lies will show up on the polygraph as a change in the above-mentioned baselines. It is worth noting that while this is a psychological reaction, it does not mean it is a conscious decision. The brain perceives the question as a threat and then automatically responds by producing a specific physiological response. Therefore, even a person who is unaware of the polygraph machine or lies unknowingly may wonder why they "failed" a polygraph test. They may not even realize they answered a question incorrectly. A polygraph test tracks involuntary responses rather than purposeful lying.
Statutory Language and Guidance For Polygraphs
The legal definition of a polygraph test is the measurement of responses to questions in a way that indicates the truth or deception of an answer. The physiological measurements are assumed to be connected to truthfulness, lies or both.
A polygraph test is governed by a set of rules and regulations that is set at both the federal and state level. According to the Employee Polygraph Protection Act, or EPPA, this law limits the use of polygraph tests for certain work situations while allowing for their use for other purposes. This law also determines when a polygraph test may be used, and prevents employers from having employees take a polygraph test as a condition of their employment.
While there is no federal law that prohibits the use of polygraphs in criminal cases, such as murder, theft or other crimes, many states do not permit the use of polygraphs in criminal cases. In fact, the law in many places keeps polygraph tests out of court. Rules of Evidence are written for many states, and Article X of the Federal Rules of Evidence also prohibits the use of polygraphs in court.
The polygraph test is a type of lie detection that measures three responses that are assumed to correlate with deception. A polygraph test is usually not used by itself, but it is rather one factor that is used along with other law enforcement investigative techniques and procedures.
Polygraph Mechanism
Polygraphs, commonly known as lie detector tests, do not measure truth or deception in the way their common moniker would imply. While a polygraph examiner attempts to measure physiological responses that indicate a person’s veracity, the connection between those responses and the truthfulness of their answers is anything but a foregone conclusion. The physiological responses measured by the polygraph include blood pressure, respiratory rate and galvanic skin response, which measures the conductivity of the skin’s surface that changes as a function of sweat gland activity. The polygraph machine uses an inflatable rubber tube, called a pneumograph, to measure respiration in the form of air pressure. An individual’s blood pressure is monitored using a conventional finger cuff and a one channel plethysmographic sensor attached to the tip of the finger. To measure galvanic skin response, two electrodes are placed on the palmar surface of the index and middle fingers of the participant’s non-dominant hand.
A polygraph examiner will typically conduct a pre-test interview with a subject, the objective of which is for the examiner to get to know the examinee, build rapport and gain a better understanding of the examinee’s mindset and the reason for the test. During this portion of the test, the examiner also may ask the examinee to provide a "stim test," which is designed to establish a baseline physiological response upon which the examiner can measure any deviations from the baseline. The stim test typically consists of three irrelevant questions and three relevant questions. For example, the examiner will ask the examinee to say "my name is ____" or "I live at 123 Main St." while at the same time instructing the examinee that he/she should answer the question in a way that requires a "No" response. The purpose of this is to gauge an examinee’s physiological response to making an intentional false reply.
Admissibility and Weight of Polygraph Results
As mentioned above, the general consensus is that polygraph results are inadmissible in court. However, not all courts are in strict compliance with this exclusion policy. Some courts will accept lie detector evidence if it fulfills the Daubert criteria for expert opinion evidence. This means that polygraph evidence can be presented if its potential to reach a correct answer is sufficiently high.
Some courts, such as civil courts in Illinois, are more sympathetic to the admissibility of polygraph results. In Illinois, Georgochak v. Georgochak has established sufficient criteria to put polygraph evidence on more of an equal footing with other expert evidence. Some other states are also willing to consider polygraph evidence as long as they do not require its admission in all cases and careful evidentiary safeguards are observed. In most cases, polygraph evidence is rejected by the court; therefore, the admissibility of polygraph evidence still varies by state and country.
Several criteria have been established for the admissibility of polygraph results in court. These criteria include:
If polygraph examinations are performed in accordance with primarily the Polygraph Protection Act of 1988 and later amendments, and National Center for Credibility Assessment policies, these can be used to help the courts assess the truthfulness of testimony. While individual courts will maintain their own standards for admissibility, a well-trained examiner can still present polygraph test results with an explanation of the methodology used to assess the truthfulness of the statements made by suspects or witnesses. This will allow the court to objectively assess the truthfulness of statements made in the trial, thereby using the polygraph to help judge the overall credibility of the statements made.
Polygraphs: What a Court Looks at Before Submitting to the Jury
Judicial attitudes vary regarding the admissibility of polygraph results as evidence. Some courts view expert testimony regarding the polygraph examination as admissible; others rely upon general acceptance standards for admissibility motions, while still others consider the polygraph as irrelevant. Polysomnographic data were viewed as admissible in a 1979 decision of the United States Court of Appeals for the Eleventh Circuit. The Supreme Court of Georgia has also held expert testimony about issues of polygraph use admissible.
Expert testimony and evidence of scientific validity and reliability on matters about which expert testimony is admissible should generally be considered relevant by courts. However, admissibility of this testimony is not guaranteed. Many courts have refused to admit expert testimony on the scientific validity and usefulness of polygraph examinations. The Supreme Court of North Dakota, in State v. Doran, based its opinion concerning the exclusionary rule for polygraph evidence upon the Daubert v. Merrill-Dow Pharmaceutical, Inc. standards for admissibility of expert testimony on scientific matters, which first allows or denies admission for scientific reliability or validity, and relevance. The evidence of scientific validity and reliability provides a basis for establishing its relevance.
Courts often rely upon polygraph testing to determine credibility and mental state. Courts are generally skeptical of polygraph examinations’ ability to detect falsehoods. Such examinations rely upon an assumption that a physiological response indicates a lie. If individuals maintain a body position or answer truthfully, the polygraph cannot measure discrepancies in physiological states. Because of this reason, the reliability of polygraphs generally is lower, perhaps substantially so, for nondiagnostic purposes.
To overcome reliability concerns, the Daubert v. Merrill-Dow Pharmaceutical, Inc. standard may be applied to polygraph evidence. In Daubert, the Supreme Court determined that Frye’s general acceptance standard was superseded by the Federal Rules of Evidence. Daubert requires a trial court to determine the admissibility of expert testimony based upon scientific validity and reliability as a prerequisite to considering relevance. The court must ask and answer the following questions regarding scientific testimony:
(a) whether the theory or technique has been tested;
(b) whether it has been subject to peer review and publication;
(c) its known or potential error rate; and
(d) the existence and maintenance of standards controlling its operation.
The Daubert rule for determining reliability or validity of polygraph examinations is broader than the original Frye rule. Frye generally defined general acceptance as majority or plurality of experts in a particular field, while Daubert specifies standards of reliability as relevant evidence and likely basis for conclusions.
Polygraphs 101: Critique and Issues
The use of polygraph exams has long been met with some skepticism and controversy in the scientific community. Critics of these tests note that there is a lack of scientific evidence supporting many of the basic tenets of their use, and say that inaccuracy can lead to wrongful convictions. The National Academies of Sciences, Engineering and Medicine have indicated that polygraphs are not accurate enough to be accepted as evidence in court (or disallowed as evidence, as in some U.S . government agencies) and that the scientific evidence of their accuracy falls short of the standards generally required for acceptance into the courtroom.
Concerns have also been raised about the ethics and legality of using polygraph tests as part of the investigative process. Some critics maintain that they unfairly target certain individuals, and that physicians who administer these tests may run the risk of liability if false positives are indicated. Federal regulations even ban employers from using polygraph tests for most private jobs.
Admissibility of Polygraphs: Case Law
Polygraphs are often used in public and private sector employment. They have become an acceptable method for employers (on a voluntary, not mandated basis) of determining whether an applicant for employment or an employee has engaged in criminal behavior and/or drug use. Polygraphs have been used in law enforcement for many decades. State and federal courts have accepted their use. One of the most interesting uses of polygraph testing in the public sector have taken place in Ohio State Highway Patrol cases. The patrol instituted a Drug-Free Work Place Policy. An internal investigation into agents who had been found to use illegal drugs during the course of their employment with the patrol, and use of the polygraph was one part of the investigation. The results were not being accepted by the court, e.g., past use of legal drugs were also being tested. The court rejected the tests because of the errors involved in such testing. The Ohio State Supreme Court ultimately rejected polygraph results as a result in Ohio v. Doss 48 Ohio St. 3d 405; 550 N.E.2d 409; 1990. In this case, the court seized upon the question, "Should evidence obtained from a polygraph test be admitted at a criminal trial?" The court ruled on the issue of whether the results of a polygraph test are admissible in court. The majority opinion written by Justice Douglas, found that the test was unreliable and therefore inadmissible. Three of the judges filed concurring opinions supporting the exclusion of the evidence, but the reason for that exclusion differed from that offered in the majority opinion. Two judges dissented in favor of admissibility. However, the fact that the majority opposed the admission of the test did not completely settle the issue. Others seized upon the word "reliable" and found polygraphs reliable. Some in law enforcement and the courts objected to the general application of the decision as it discussed lie detection. Many of the defendants who were accused of crimes offered polygraph tests, and some courts found the tests admissible in their cases. In spite of this, the holding did uphold the original holding if the Doss case without any discussion of how other courts had applied it.
Polygraphs: Alternatives
While the polygraph is the most commonly used lie detection test in criminal investigations, there are other methods that law enforcement officers or private investigators can use as an alternative to polygraph testing. While there is limited scientific data on these alternatives, polygraph skeptics and accepted alternatives include the following:
Magnetic Resonance Imaging (MRI): This testing is based on the fact that the human brain has a distinctive reaction to each stimulus. The theory behind the MRI is that the part of the brain that experiences guilt, or trying to conceal a lie, is separate from the part of the brain that authorizes the speech. Researchers found that the area of the brain that processes speech is not activated when a subject is lying, whereas the area associated with the feeling of guilt consciously recognizes the lie, causing the test subject to dwell on the guilt being concealed, and the brain circuits of the two areas are separated by a corpus callosum. This MRI test could make for a more reliable lie detection tool, but it has yet to be accepted as a mainstream part of criminal investigations.
Brain electrical activity (BEAM): This test measures the electrical activity of the brain to assist in the detection of lies. Research has shown that the electrical activity of the brain differs when an individual tells the truth as opposed to when he or she is withholding the truth. The difference between truth-telling and lie-keeping is a side effect of the continuous "lying" monologue that takes place in a person’s subconscious while he or she is concealing the truth.
Voice Stress Analysis (VSA): This polygraph alternative listens to minute changes in voice patterns. Even when the sonogram shows that the words have been spoken calmly, it may also register previously undetectable muscle spasms and microtremors that result from a person’s stress response to the questions. The stress response of lying, even if not consciously recognized, is manifested in different muscles than those that are used to speak.
Functional Magnetic Resonance Imaging (FMRI): The basis of this method is that blood flows away from the frontal lobes when a person lies. An FMRI scan measures an individual’s blood flow in the M1 area of the brain, and a lie registers as an increase in oxygen levels on the scan, while a truth registers as a decrease.
Polygraphs in the Future
As technology continues to evolve, so too may the way in which courts and the legal system regard polygraph results. Some experts suggest that alternative lie detection methods, such as voice stress analysis and brain fingerprinting, could give the court more confidence in the reliability of the results. While these technologies are still in the research and development phase, their potential applicability in the legal system could be considered if they prove to be more accurate and reliable than polygraph testing.
It is also possible that experts will develop new techniques to make the polygraphing process itself more accurate or to back up the results. For example, some researchers are looking into ways of visualizing the body’s autonomic responses through thermal vividness, in which cameras detect slight changes in facial temperatures revealed through physiological responses. With only a few degrees of change in thermal temperature being needed to indicate a true physiological response , this technology could potentially complement or serve as a replacement for the traditional polygraph.
From a legal standpoint, however, the future of polygraphing remains clouded in ambiguity. While courts have consistently ruled that the admissibility of polygraph test results lies solely in the discretion of the trial judge, this may be the case until further experience with more advanced polygraph operation occurs. Higher courts may yet develop further rules surrounding the admissibility of this technology, should it continue to become more advanced and trustworthy.
With the continuing controversy over polygraph use in criminal cases, it’s difficult to say for sure where this technology will land in the court system several years from now. While it isn’t likely that polygraphs will ever become the primary line of evidence in a courtroom, they will probably continue to serve as a supplemental tool to be weighed along with other evidence in determining the outcomes of cases.