As children, we all knew Pinocchio’s nose grows longer when he lies, but in Italian author Carlo Collodi’s original version of The Adventures of Pinocchio, his nose grew longer when he became anxious and not only when he lied, thus capturing the essence of the polygraph test.  Another myth to be debunked is that a polygraph is a ‘lie detector’ test. There is no device that determine whether someone is lying.  There are devices that can indicate physiological states of anxiety, which can manifest due to a number of reasons, not just when lying. It is also a myth that psychopaths can fool polygraph tests.

The Polygraph

A polygraph is a device that measures autonomic nervous system physiological arousal indicators like blood pressure, pulse, respiration and skin conductivity, when attached to a person answering questions. Although there are no specific physiological reactions directly linked to lying, it is generally accepted that the autonomous nervous system is activated when a person is feeling anxious, therefore the device should indicate when a person is comfortable (because they are truthful and have nothing to hide) or if they are uncomfortable, which could be attributed to being deceptive but this could be attributed to another reason, which begs investigation. 

Since polygraphs measure arousal, results can be influenced by mental disorders such as anxiety disorders, post-traumatic stress disorder (PTSD), hypoglycemia, psychosis, depression, substance-induced states (nicotine, stimulants), substance-withdrawal state (alcohol withdrawal) or other emotions. In short a polygraph cannot differentiate anxiety caused by deceit from anxiety caused by an underlying mental disorder or some external circumstance.

In 1895 Cesare Lombrosso designed a device, called Lombrosso’s Glove that could measure changes in blood pressure, followed by Vittorio Benussi who designed a device that could measure breathing rate in 1904; and 1906 James MacKenzie also designed a similar device.  American William Moulton Marston developed a device to measure the blood pressure of German prisoners of war. Marston elaborated his design into its final version only after the war in 1921 to record changes in a person’s blood pressure and changes in breathing while giving testimony.

The first prototype of a polygraph machine is attributed to John Augustus Larson, a medical student at the University of California, Berkeley who was a police officer of the Berkeley Police Department in California in 1921. His student Leonarde Keeler updated the device, called the Cardio-Pneumo Psychograph, by adding respiratory rate and the galvanic skin response in 1939. The FBI acquired this device, which was portable. 

In 1945 John E Reid predicted that greater accuracy could be obtained by recording muscular activity simultaneously with standard blood pressure-pulse-respiration recordings.

According to Martina Vicianova in her 2015-artile Historical Techniques of Lie Detection, published in European Journal for Psychology, due to its popularity not only in law enforcement but also as a device to determine reliability of public safety employees and managers, a test of reliability was performed on the polygraph and the National Academies of Science (NAS) indicated its reliability as 81% – 91%. 

The polygraph can measure signs of nervousness, fear and emotional disturbances, but these occur not only in people are deceptive, but also in people who tell the truth. World-renown Dr Paul Ekman agrees that nervousness, fear of being accused, or other unrelated emotions can cause similar reactions, leading to false positives. This is one of the reasons why polygraph tests are controversial and often inadmissible as evidence in court. 

Vicianova confirms that the polygraph does not detect lies but instead measures physiological responses postulated to be associated with deception. None of these responses are specific to deception, nor are they necessarily always present when deception occurs. Vicianova refers to a  2003-report of the National Research Council, Committee to Review the Scientific Evidence on the Polygraph finding that when used by well-trained examiners and in conjunction with other techniques, it appears to offer a useful adjunct in identifying those who attempt to deceive.

Dr Paul Ekman in his blogs Do Lie Detectors Actually Work and The Body’s Betrayal: What Physiology Reveals About Deception points that the polygraph exam does not detect lies, it detects signs of emotion. “If there are no universal signals for deception, then it should come as no surprise that there are no fool-proof methods to determine if or when a person is lying; at least, not without requiring the use of additional tools and techniques to investigate further.”

The Face, A Mirror of Emotions

Dr Paul Ekman’s most interesting work centres around the study of micro-expressions related to emotions. He found a high agreement across members of diverse Western and Eastern literate cultures on selecting emotional labels that fit facial expressions. Universal expressions included those indicating wrath, grossness, fear, joy, loneliness, and shock. In the 1990s, he expanded the list of basic emotions, including a range of positive and negative emotions that are not all encoded in facial muscles, to include amusement, contempt, contentment, embarrassment, excitement, guilt, pride in achievement, relief, satisfaction, sensory pleasure, and shame. 

To my mind guilt, embarrassment and shame would be significant emotions to identify when interrogating a suspect. Charles Darwin in his 1872 The Expression of the Emotions in Man and Animals, describes shame manifesting in the physical form of blushing, confusion of mind, downward cast eyes, slack posture, and a lowered head. Ashamed people feel that their entire self is worthless, powerless, and small and they also feel exposed to an audience. Therefore it is not advisable to extract a confession in a person’s own home in the presence of their family members or children. 

People feel guilty when they realize they have not lived up to expected moral standards.  Guilt is not the same as remorse. Remorse is when a person regrets an action that caused harm and wants to atone for it.

Embarrassment is the lesser of the emotions, expressed when a person is confronted by a socially unaccepted act, committed either by the self, or someone they feel responsible for. It is a self-conscious emotion.

Dr Paul Ekman, Wallace Friesen and Joseph Hager expanded Swedish anatomist Carl-Herman Hjortsjö’s system to taxonomize human facial movements and developed the Facial Action Coding System (FACS) where anatomically possible facial expressions are deconstructed into the specific “action units” (AU) and their temporal segments that produced the expression. The FACS manual is over 500 pages in length and provides the AUs, as well as Ekman’s interpretation of their meanings.

In their Words:

Statement analysis involves an investigator searching for linguistic cues and gaps in a subject’s testimony or preliminary statements. Ideally, the technique would guide investigators to ask follow-up questions to uncover discrepancies. Avinoam Sapir created Scientific Content Analysis (SCAN), and I was trained by him.  I found his method very effective – not just in a criminal investigation but also in a therapeutic environment.  Sapir says that a fundamental principle of statement analysis is that “denying guilt is not the same as denying the act. When one says: ‘I am not guilty’ or ‘I am innocent,’ they are not denying the act; they are only denying guilt.”.

In 2016, the High-Value Detainee Interrogation Group (HIG), a federal agency group consisting of the FBI, the CIA, and the United States Department of Defense, released a report which found that studies commonly cited in favour of SCAN were scientifically flawed and that SCAN’s evaluative criteria did not withstand scrutiny in laboratory testing.

The Voice

Voice Stress Analysis is based on the tenet that the non-verbal, low-frequency content of the voice conveys information about the physiological and psychological state of the speaker. This computer programme differentiates between stressed and non-stressed outputs in response to stimuli with high stress seen as an indication of deception.

In 2003, the National Research Council concluded, “Overall, this research and the few controlled tests conducted over the past decade offer little or no scientific basis for the use of the computer voice stress analyzer or similar voice measurement instruments“.

The Brain

A lie is conceived in the mind and is expressed through the body. 21st-Century researchers in neuroscience have been focussing on whether Functional Magnetic Resonance Imaging (fMRI) could indicate which parts of the brain are activated when subjects use artificial memories. Artificial memory could be explained as ranging from a non-malevolent imagination, such as creating fiction, to at worst, intentional deception or lying.

In their 2002-article titled Brain Activity during Simulated Deception: An Event-Related Functional Magnetic Resonance Study, Professor DD Langleben of the Department of Psychiatry, University of Pennsylvania, and his colleagues found increased activity in the anterior cingulate cortex (ACC), the superior frontal gyrus (SFG), and the left premotor, motor, and anterior parietal cortex was specifically associated with deceptive responses. Their results indicate that cognitive differences between deception and truth have neural correlates detectable by fMRI; inhibition of the truthful response may be a basic component of intentional deception, and the anterior cingulate cortex and superior frontal gyrus are components of the basic neural circuitry for deception.

Research in this field is promising. It seems brains-scans are able to detect if someone is deliberately deceptive. Submitting a person to a brain scan of course has all kinds of financial and legal implications, which may not be practical in law-enforcement.

Serial Killers and Polygraph tests

The discovery of a body in July 1982 in Seattle heralded the onset of what was known as the Green River killings in America. In 1984, Gary Ridgway was identified as a suspect, but he passed the polygraph test.  In 2001 he was arrested due to a DNA match and confessed to killing more than 72 victims. He was convicted on 49 counts of murder. 

In 1986, Bill Wegerle of Wichita, Kansas was suspected of murdering his wife Vicki Wegerle and he failed two polygraph tests, one administered by the police, the other conducted by an expert that Wegerle had hired. He was not arrested or charged. In 2005 DNA evidence from the Wegerle murder matched that of the BTK serial killer, Dennis Rader, exonerating Wegerle.

The question often arises can psychopaths fool polygraphs since they do not experience remorse of guilt, implying their physiological arousals will not be triggered. Researchers Christopher Patric and his colleagues in their 1989 -article titled Psychopathy, threat, and polygraph test accuracy (in Journal of Applied Psychology) conducted an experiment in prison involving known psychopaths and non-psychopaths and found that “guilty psychopaths were detected just as easily as guilty nonpsychopaths, and the majority of guilty subjects (87%, excluding inconclusives) were correctly identified. However, innocent subjects were identified with only 56% accuracy, and an analysis of false positive errors suggested that the subjective impact of the threat was a critical factor in these outcomes.” 

A 2004-article titled Efficacy of Detecting Deception in Psychopaths Using a Polygraph, published in the NCJRS Virtual Library of the US Department of Justice, states: “a common myth is that the psychopath’s deception is invisible to the polygraph. However limited as it is, research evidence suggests otherwise”.

In my opinion if one approaches the topic from the premise that these devices and methods measure physiological indicators of stress, anxiety and discomfort, and they do not function as “lie detectors”, they can be very useful tools in the sphere of criminal investigations, when conducted by experienced examiners, despite the criticism of pseudoscience.  Perhaps they are best coupled with an experienced interrogator who can identify facial micro-expressions, and explore underlying emotions or mental illnesses. Signs of stress warrants further investigation. For example, when I participated in a private investigation into on-line gambling fraud, in fairness, all employees were screened. Surprisingly, the tea-lady failed the test.  A gentle probing revealed she had taken some teabags home on some occasions and she felt very guilty about this.  The method – in this case I used SCAN – proved successful in identifying a suspect, who confessed when I followed up with an interrogation, and was prosecuted.

Top image: Resin sculpture of Pinocchio and Sebastian used in Guillermo del Toro’s Pinocchio (2022) (CC BY-SA 4.0)

By Dr Micki Pistorius