Lie Detection

Pioneering criminal anthropologist Cesare Lombroso invented the first mechanical lie detector in 1895. He adapted a medical instrument called the sphygmograph which could measure changes in a suspect's blood pressure and pulse over the course of an interrogation. The device was an early form of polygraph.

The principle, which familiar to us now, assumed that if the subject attempted to deceive his interrogator, a change in heart rate and blood pressure would accompany the lie. Whatever the suspects says about his or her involvement in a crime, his or her heart will tell the true tale.

In fact, Lombroso's machine was a mechanical incarnation of Edgar Allen Poe's imagination. Poe published The Tell-Tale Heart in 1843, a story of mayhem and murder. When the murderer is interrogated by police about the fate of a missing person, he denies his involvement. At the same time, his own body betrays his guilt with a deafening and tell-tale heartbeat that compels him to confess his crimes. The killer's heart does precisely what Lombroso expected to find in his suspects 50 years later.

The modern polygraph is based on the very same assumptions as Poe's and Lombroso's inventions. Lying causes stress and stress causes changes in heart rate and blood pressure.

Numerous studies indicate that the modern polygraph has a 80-90% accuracy rate. But this is in an experimental setting. There is huge debate in the legal system about the efficacy of such machines in the real world where the argument goes that habitual liars are not stressed by deception. This, of course, is impossible to find out, but a conundrum that fMRI scans may circumvent.

fMRI | The Polygraph | Trial by Fire

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