Leonarde Keeler administers polygraph tests to two murder suspects, the first time polygraph evidence was admitted in U.S. courts.

The Genesis of the Modern Polygraph: Leonarde Keeler's Legacy

Born on October 30, 1903, and passing away on September 20, 1949, Leonarde Keeler holds a significant place in the history of forensic science as the co-inventor of the modern polygraph instrument. His fascination with the detection of deception began early, influenced by his namesake, the polymath Leonardo da Vinci, which led him to prefer the informal moniker 'Nard.' While attending Berkeley High School, Keeler was not only a diligent student but also an adept amateur magician, a pursuit that likely honed his understanding of human perception and misdirection, making him uniquely predisposed to the study of truthfulness and deception.

Keeler's journey into the realm of lie detection truly began when he was captivated by the work of Dr. John A. Larson, a Canadian-American police officer and psychologist, who developed an early version of a deception detection instrument. Larson's pioneering device, which he termed the 'cardio-pneumo psychogram,' measured basic physiological changes. Recognizing its profound potential, Keeler dedicated himself to refining and advancing Larson's initial concept. By the mid-1920s, while working under Larson at the Berkeley Police Department and later at the Scientific Crime Detection Laboratory at Northwestern University School of Law, Keeler significantly enhanced the machine. His crucial innovations included the addition of a galvanic skin response (GSR) component, which measures changes in skin conductivity, alongside improvements to the blood pressure and respiration sensors, and the introduction of continuous chart recording. These advancements transformed Larson's prototype into the multi-channel, continuously recording apparatus we recognize today as the modern polygraph.

Understanding the Polygraph: How It Works (and Doesn't)

A polygraph, widely recognized as a "lie detector test," is a sophisticated device or procedure designed to measure and record several physiological indicators simultaneously. These typically include a person's blood pressure, pulse rate, respiration patterns (breathing), and skin conductivity (often referred to as galvanic skin response or GSR). These measurements are taken while an individual is asked and responds to a carefully structured series of questions. The fundamental premise underpinning the use of the polygraph is the assumption that deceptive answers will elicit involuntary physiological responses that are measurably different from those associated with truthful statements. Proponents believe that the stress and emotional arousal linked to deception trigger specific changes in the autonomic nervous system, which then manifest as detectable shifts in these physiological parameters.

However, a critical challenge to the polygraph's validity stems from the scientific reality that there are no distinct, specific physiological reactions that are uniquely associated with the act of lying itself. While deception can certainly induce stress and anxiety, these physiological responses (such as an increase in heart rate or perspiration) are not exclusive to lying. They can also occur due to general anxiety, fear of being disbelieved, indignation at being accused, or even strong emotional reactions to the questions asked, regardless of truthfulness. This inherent ambiguity makes it exceedingly difficult for polygraph examiners to definitively differentiate between physiological responses caused by deception and those resulting from other forms of emotional arousal or stress. Furthermore, many polygraph examiners traditionally prefer to use their own subjective individual scoring methods rather than relying on computerized, objective techniques. This preference often stems from a desire to more easily defend their personal evaluations, which can introduce examiner bias and further compromise the standardization and objectivity of the assessment.

The Control Question Test (CQT): A Common Methodology and Its Flaws

To overcome or mitigate perceived problems with earlier methods, such as the relevant-irrelevant testing technique (which primarily compares responses to direct questions about a crime with irrelevant baseline questions), the Control Question Test (CQT), also known as the Probable Lie Test, was developed. The CQT attempts to differentiate between reactions to "relevant" questions (specific to the incident under investigation) and "control" questions (designed to elicit a probable lie from both innocent and guilty individuals, typically about past misdeeds or general honesty). The theory posits that a guilty person will react more strongly to the relevant questions, while an innocent person will react more strongly to the control questions due to uncertainty about their own past truthfulness on the control questions.

Despite its theoretical basis, further examination of the Control Question Test has indicated that it is significantly biased against innocent subjects. While the relevant questions in the CQT are intended to elicit a stronger physiological reaction from individuals who are lying, the same physiological reactions may, paradoxically, also occur in innocent individuals. This phenomenon often arises from the intense fear of false detection, the stress of the interrogation process itself, or deeply held emotional convictions about their own innocence. Therefore, even if a significant physiological reaction occurs, the underlying reason for that response may be rooted in stress or fear rather than actual deception. A critical flaw is that innocent individuals who are unable to think of a "lie" related to the control questions – or who react with significant stress to the direct accusation of the relevant questions – may inadvertently produce a physiological pattern indicative of deception, leading to a "failed" test. This means that a truthful person, simply by being anxious or emotionally responsive, can appear deceptive.

Polygraph Use and Its Scientific Limitations

Across various countries, polygraphs are employed as an interrogation tool, particularly with criminal suspects or candidates vying for sensitive public or private sector employment positions, especially those requiring high-level security clearances. In the United States, numerous law enforcement and federal government agencies, including the Federal Bureau of Investigation (FBI), the National Security Agency (NSA), and the Central Intelligence Agency (CIA), alongside many police departments such as the Los Angeles Police Department (LAPD) and the Virginia State Police, utilize polygraph examinations to interrogate suspects and screen potential new employees. Within the US federal government, a polygraph examination is also formally referred to as a Psychophysiological Detection of Deception (PDD) examination. Administering such a test in the United States typically costs more than $700, contributing to a substantial $2 billion industry built around these assessments.

Despite their widespread use, assessments of polygraphy by respected scientific and governmental bodies consistently suggest that polygraphs are highly inaccurate and may be easily defeated by countermeasures. Countermeasures are deliberate actions or mental strategies taken by an examinee to alter their physiological responses during the test, such as tensing muscles, biting the tongue, or engaging in specific thought patterns, thereby manipulating the test results. These bodies generally conclude that polygraphs represent an imperfect or, more critically, an invalid means of assessing truthfulness. A comprehensive 2003 review of existing research by the prestigious National Academy of Sciences (NAS) concluded unequivocally that there was "little basis for the expectation that a polygraph test could have extremely high accuracy." Echoing this sentiment, the American Psychological Association (APA) states that "Most psychologists agree that there is little evidence that polygraph tests can accurately detect lies." This broad scientific consensus highlights the significant gap between the popular perception of the polygraph as a "lie detector" and its actual scientific validity and reliability.

Frequently Asked Questions About the Polygraph

Who invented the modern polygraph?
The modern polygraph instrument was co-invented by Leonarde Keeler, who significantly refined the earlier concepts developed by Dr. John A. Larson. Keeler enhanced the device by adding more physiological sensors, such as the galvanic skin response (GSR), and introduced continuous chart recording.
What physiological indicators does a polygraph measure?
A polygraph measures several physiological indicators, primarily including blood pressure, pulse rate, respiration patterns (breathing), and skin conductivity (galvanic skin response or GSR). These are monitored for changes indicative of arousal or stress.
Is the polygraph test scientifically proven to detect lies?
No. Major scientific organizations, including the National Academy of Sciences and the American Psychological Association, conclude that there is little scientific evidence to support the claim that polygraph tests can accurately detect lies. They consistently point to the lack of unique physiological responses associated with deception and the test's vulnerability to countermeasures.
What is the Control Question Test (CQT)?
The Control Question Test (CQT), or Probable Lie Test, is a common polygraph methodology designed to compare an individual's physiological responses to "relevant" questions about an incident with "control" questions about general past honesty. It aims to differentiate between truthful and deceptive responses, though it has been criticized for being biased against innocent individuals.
Are polygraph results admissible in court?
In most jurisdictions within the United States, polygraph results are generally not admissible as evidence in criminal courts due to concerns about their reliability and scientific validity. However, their use can vary depending on specific legal precedents and agreements between parties in certain contexts.