Opinion: The truth of lie detection
Polygraph tests do not measure lying directly, but rather possible signs that a person could be deceiving
By Suresh Dharur
In Liu Cixin’s ‘Three Body Problem’, the Hugo award-winning sci-fi trilogy, humans make first contact with ‘Trisolarans’, an alien civilisation whose unique feature is that they communicate through direct transfer of thoughts. As a result, they are incapable of lying or keeping secrets.
For humans, on the other hand, deception is a key trait. In fact, human beings have no foolproof way to know if someone is telling the truth. We only depend on our intuitive skills to look for clues like body language, inconsistencies in what people tell us, or their behaviour. But apart from this, we are largely left to trust their words, as we have no way of accessing their own inner world. Human behaviour is complex and people can deceive in a variety of ways all the time.
Patchy and Ineffective
However, we have not given up on this task. Over the decades, continuous efforts have been made to develop techniques to detect when someone is lying. A polygraph or lie detection test is one such method that is widely used, though patchy and ineffective. It works by picking up changes in blood pressure, heart rate, breathing and skin conductance, which is believed to be indicative of someone not telling the truth.
The efficacy of the lie detection tests has once again come under the spotlight in the Kolkata rape and murder case. The CBI has conducted polygraph tests on at least ten people, including principal of RG Kar Medical College Sandip Kumar Ghosh and the main accused Sanjay Roy, in connection with the gruesome rape and murder of a trainee doctor.
One wonders why investigators routinely opt for this procedure when its scientific validity and efficacy are highly questionable.
In 2010, the Supreme Court, in the case of Selvi versus State of Karnataka, noted that there was little empirical evidence to bolster the argument that these tests provide reliable leads for investigators. It also ruled that no lie detector tests should be administered “except on the basis of consent of the accused” in accordance with the fundamental right against self-incrimination as enshrined under Article 20(3) of the Constitution. Despite the Supreme Court’s cautionary stance, the administration of these tests continues to be prevalent in India.
In a 2010 paper published in the Indian Journal of Medical Research, it was observed that lie-detection techniques have faced a number of criticisms, and their effectiveness in revealing “concealed knowledge in applied real-world settings” remains uncertain. It contested the reliability of polygraph tests, pointing out that the test’s underlying principle itself is flawed — parameters such as heart rate and blood pressure have not been proven to be uniquely indicative of lying.
No Scientific Basis
Most psychologists and scientists agree that there is little basis for the validity of polygraph tests. The courts in the United States have repeatedly rejected the use of polygraph evidence because of its inherent unreliability.
There is no evidence that any pattern of physiological reactions is unique to deception. An honest person may be nervous when answering truthfully and a dishonest person may be non-anxious.
Since its inception almost 100 years ago, the polygraph has remained largely unchanged. It concurrently monitors cardiovascular, respiratory and electrodermal outputs of the human body. A blood pressure cuff monitors the blood flowing in and out of your heart, and a second apparatus measures pulse. Rubber tubes placed on the chest track air entering and exiting your lungs. Finger plates track the sweat seeping through your skin.
The theory behind the polygraph is that when people are lying, they experience a different emotional state than when they are telling the truth. However, humans have a tendency to lie from a very young age, mastering the white lies very early in life. Polygraph tests do not measure lying directly, but rather possible signs that a person could be deceiving the interviewer. This information is then used in conjunction with everything else that is known about the person to form a clearer picture of whether or not they are being truthful.
Interrogation Tool
In fact, polygraph testing is an interrogation tool, not a lie detector, as demonstrated by the emphasis on disclosures made during the interview process. Now, the question is whether those disclosures could have been made through normal investigation processes and whether the process relies on convincing offenders that the machine can detect lying.
Some scientists dub it as “zombie forensics”. It risks giving investigators a false sense of security that if the machine says someone is telling the truth, then they must be. A 2003 report from the National Academy of Sciences in the US concluded that there is little basis for believing that a polygraph test result will be accurate. It said lie-detector tests did a poor job of identifying spies or other national security risks and were likely to produce accusations of innocent people.
Beating the Machine
Similarly, a 2019 study conducted in the United States flagged high false positive rates and noted that individuals can train themselves to beat a polygraph. The psychological changes that a polygraph test looks for can be produced by states other than lying. Additionally, the alleged physiological signs that accompany lying may not be uniformly applicable across cultures, ethnicities, genders and age. The interpretation of lie detection results may vary.
The lie detection test involves the injection of a drug called sodium pentothal, inducing a hypnotic or sedated state. The assumption is that a subject in such a state is less inhibited and is more likely to divulge information. Because the drug is thought to weaken the subject’s resolve to lie, it is often referred to as a “truth serum.”
The polygraph, narco-analysis and brain-mapping raise serious concerns related to the professional ethics of medical personnel involved in the administration of these techniques and the violation of human rights of an individual.
The ability to definitively distinguish truth from lies will always hold an allure. We believe in the lie detector test because we long for a form of justice that is swift, certain and non-coercive. But after 100 years of mixed results, it is time to acknowledge the human conscience will neither be perfected nor mechanised.
(The author is a senior journalist)
