For one, individuals with psychopathologies or drug use
(overrepresented in the criminal defendant population) may have very different brain responses to lying, says Phelps. They might lack the sense of conflict or guilt used to detect lying in other individuals.
Laken concedes that they've tested the machine on a rather limited population-18-50 year-olds with no history of drug use, psychiatric disease, or serious traumatic brain injuries. But he says he is content for his clientele to be restricted to "relatively normal people" like
Martha Stewart and Lewis "Scooter" Libby - neither of whom has actually used the technology.
There's another drawback: If a person actually believes an untruth, it's not clear if a machine could ever identify it as such. Researchers including Phelps are still debating whether the brain can distinguish true from false memory in the first place. "In law, we're concerned with acting human beings [who] can intentionally falsify or unintentionally falsify," says Stephen Morse, professor of law and psychiatry at the University of Pennsylvania. "To the extent that we're trying to get at the truth, we need a valid measure to understand [the difference]."
