The lie detector test: An American “innovation” in the British criminal justice system
On January 21 2020, the Home Office and the Ministry of Justice announced a range of proposals, thereby reinforcing the British government’s counter-terrorism agenda. This package of measures was prompted by the most recent terrorist atrocity at London Bridge on November 29 2019. Among the proposals was one for submitting terrorist offenders to a lie detector test, thereby proving that they were “reformed”, prior to their release from prison. Robert Buckland, the Justice Secretary, emphasised that the lie detector test was “about the authorities assessing the risk posed to the public by offenders”. The aim was to identify ‘superficially very compliant’ so-called ‘sleepers’, who posed a risk of engaging in further terrorist activity upon premature release, as indeed was the case with the perpetrator of the November 2019 attack.
The basis of a lie detector test, also known as a polygraph test, is that people who are attempting to deceive their questioners display a range of predictable physiological responses. Thus, a deliberate liar apparently breathes rapidly and heavily, while his/her heart pounds and races. He/she also sweats profusely, while his/her blood pressure shoots up dangerously. These changes can be measured in the modern polygraph machine, which simultaneously records patterns of breathing, pulse rate and volume, changes in skin conductivity, and blood pressure. There is, however, no specific combination of physiological responses that can conclusively prove that someone is actually lying.
To better understand the rationale for testing, it is worth digressing, to take a brief look at the history of lie detection. William Marston, a psychology student, used his wife Elizabeth as an experimental subject to demonstrate a relation between emotional state and blood pressure. In 1915, while measuring systolic blood pressure with a cuff applied to his wife’s arm, he demonstrated a rise in blood pressure when she “got mad or excited”. She must have been a most remarkable woman, going on, years later to inspire the comic superhero Wonder Woman, in 1941. Marston pursued his research during the First World War, while attached to the US War Department. His aim was to develop a tool for interrogating suspected spies. After the war, he turned his attention to the criminal justice system, but had no success in convincing the courts to accept his evidence. His 1921 doctoral dissertation at Harvard was aptly titled “Systolic blood pressure symptoms of deception and constituent mental states”.
The polygraph was subsequently developed for forensic use by John Augustus Larson, a trained psychologist, beginning in 1921. He introduced the continuous monitoring of blood pressure, and used his device during investigations conducted by the Berkeley Police Department in California. His device went through several modifications over the years. Today’s devices are the products of a succession of digital and electronic upgrades of Larson’s original device, which is currently on display at the Smithsonian Institution in Washington DC.
Lie detection remains popular in the country of its origin. In the US, polygraphs are widely used by federal, state and local agencies, such as the FBI, CIA and NSA, along with many police and fire departments, both for screening new employees in sensitive occupations as well as, where relevant, for the interrogation of criminal suspects. The Employee Polygraph Protection Act 1988, however, specifically prohibits private companies, other than those involved in moving cash or drugs, from using lie detector tests to screen potential employees.
Many several unresolved issues remain. Polygraph testing is by no means standardised. Individual polygraph examiners may choose to use their own screening procedures, which may include a consent procedure, a pre-test interview, an optional stimulation test, followed by the actual test. Even the pattern of questioning is not consistent between examiners. The American Polygraph Association (APA) was formed in 1966 in response to some such criticisms. According to its website, “the APA provides the highest standards of professional, ethical and scientific practices for its 2700 + members”. However, while the APA accredits training programmes in the US and several other countries, including Canada, Israel and Singapore (but not the UK), it does not certify individual polygraph examiners. In the UK, a code of ethics and standards for best practice for polygraphic examinations have been developed by the British Polygraph Society (BPS), in conjunction with the APA. However, these guidelines are neither mandatory nor actually enforceable.
In most jurisdictions in the US, polygraph findings are inadmissible in a court of law as expert testimony. Nonetheless, in the UK, the Ministry of Justice has, since 2014, been using lie detector tests on selected sex offenders before their release. In addition, the injudicious use of lie detectors tests in the public arena led to the demise of ITV’s The Jeremy Kyle Show in May 2019, following the death by drug overdose of a 63-year-old contestant, Steve Dymond, ten days after he had failed a lie detector test while appearing on the programme.
Overall, there is a lack of scientific consensus, including within professional bodies of psychologists and criminologists, in favour of the polygraph. Lie detection tests are thus frequently regarded as being “pseudo-scientific”. Indeed, there are many accomplished liars who can train their responses to deceive their interrogators and pass with flying colours, while many innocent people may become more anxious at the time of testing than their guilty counterparts. The techniques may also be subject to examiners’ race, gender and age biases, held consciously or otherwise.
It remains to be seen how lie detection will help with the fight against terrorism. Human honesty is a particularly difficult entity to test reliably. Meanwhile, another potential application of lie detection testing comes to mind. Polygraph devices could be potentially used to scrutinise selected politicians, to help differentiate deliverable promises from those that are merely blatant lies.
Ashis Banerjee