New brain scanners claim to distinguish truth from lies. Should we trust them?by Ian Leslie / September 23, 2009 / Leave a comment
Published in October 2009 issue of Prospect Magazine
A murder case in India last year attracted unusual scientific attention. A 24-year-old woman called Aditi Sharma was accused of killing her former fiancé, Udit Bharati. Aditi had married another man, but she had met Udit at a McDonald’s, where she allegedly laced his food with arsenic.
After she was arrested, Aditi agreed to take a brain-scanning test to prove her innocence. Investigators placed 32 electrodes on her head, before reading the allegations to her in the first person—“I bought arsenic”; “I met Udit at McDonald’s”—along with neutral statements like “The sky is blue.” Adit failed the test—according to prosecutors, the parts of her brain where memories are stored buzzed when the crime was recounted. The judge deemed this proof of “experiential knowledge” of the crime, and she and her husband were sentenced to life in prison. It was the first time anywhere in the world this technology had been used to make a conviction.
A foolproof—or rather liar-proof—machine has long been a law enforcement dream. For much of the 20th century, the polygraph held out such a promise. But it doesn’t detect lies, exactly: it measures a suspect’s physiological responses to stress, such as increases in blood pressure or heart rate. And so it can produce a guilty reading on innocent suspects who are merely nervous, and is vulnerable to the well-prepared liar who can control their emotions.