A recent study by UC-Berkeley forensic psychologist Leanne ten Brinke has found that our odds of detecting a lie increase significantly if we register that detection subconsciously (through implicit association tests) and are not asked to actually accuse someone of lying. But even taking the higher, subconscious rate of success into account, human beings can be fooled. Is there any way to be sure someone is telling the truth?
Given the state of neuroscience, you might think a brain scan would do the trick. But in this segment from the PBS miniseries Brains on Trial, Alan Alda talks to Duke legal bioethicist Nita Farahany about the practical limitations of using fMRI technology as a more admissible substitute for polygraph tests in criminal cases. So far, the jury's still out (so to speak):
And polygraph tests have long been discredited—to the point where many industrialized countries, including the United States and at least one Australian province (the High Court hasn't ruled on the matter yet), consider them inadmissible as evidence.
Does this mean we can't tell if someone else is lying? Not necessarily. These studies, and these legal standards, deal with the blanket question of how well an unspecified human can assess whether another unspecified human is being deceptive—a scenario we never actually encounter in our day to day lives. Maybe you can tell when one friend is lying, but not others. Maybe you can convincingly lie about some things, but not others. Maybe some of us have remarkably good instincts while others among us have remarkably bad instincts. Maybe there really are good and bad liars. We just don't know.
And it's hard to address any of these possibilities in a definitive way, because most of the studies that address our ability to lie and/or our propensity to get caught deal in aggregate results drawn from relatively small sample sizes in controlled settings. But ten Brinke's experiment, and others like it, may bring us closer to understanding just how people lie—and why some of us don't get away with it.