Can polygraph tests be fooled? Neurologists weigh in on lie detector accuracy
As the investigation into the horrific rape and murder of a trainee doctor in Kolkata continues, two key suspects – Sanjay Roy and former college principal Sandip Ghosh – have undergone polygraph testing to verify the truthfulness of their statements. Commonly known as a lie detector test, the polygraph examines physiological responses like blood pressure, breathing and sweat levels that could indicate deception or anxiety. However, just how reliable are these tests? I spoke to leading neurologists to gain expert insight into how polygraph examinations work and whether it's possible to mislead the results.
Polygraph tests function by recording several bodily parameters simultaneously as questions are asked, explained Dr. PN Renjen of Indraprastha Apollo Hospitals. Physiological changes from a person's normal baseline are taken as signs that their answer may not be fully truthful. The basic logic is deceptive responses trigger measurable alterations in factors like pulse, breathing and skin conductivity. However, Dr. Renjen acknowledged various countermeasures can potentially skew results, like controlled breathing, tensing muscles or mental math during control questions. Some may even use drugs to disguise responses, making fooling a test possible in theory.
Individual differences and a person's ability to stay calm also color accuracy rates. The American National Research Council reviewed polygraphs in 2003 and found screening accuracy was comparable to a coin toss. Specific investigations may fare better, but reliability remains imperfect. With concerns over validity, most US courts reject polygraph evidence. Dr. Bhupesh Kumar also pointed out numerous studies suggest much lower success levels than proponents claim, usually around 80-90%. “We must approach results cautiously as variables change per individual,” he stated.
While polygraph testing provides one tool in the ongoing Kolkata case investigation, neurologists agree the technique's limitations necessitate corroborative evidence. The search for truth will require evaluating all findings judiciously to achieve justice for the departed medical student.
