RENEE MONTAGNE, host:

More than a century into the scientific exploration of lying, we still can't say for sure whether someone is telling the truth. That has enormous consequences. Take the fight against terrorism, for example. The search for accurate information has led the Bush administration to seek legal justifications regarding interrogation and torture.

To begin a three-part series about deception and the efforts to identify it, NPR FBI correspondent Dina Temple-Raston separates fact from fiction about the polygraph.

DINA TEMPLE-RASTON: Here's the first thing you need to know about the polygraph: It isn't really a lie detector; it's an anxiety detector.

(Soundbite of movie, "Meet the Parents")

Mr. ROBERT DE NIRO (Actor): (As Jack Byrnes) Now, I'm going to ask you some questions. And all you have to do is answer yes or no.

Mr. BEN STILLER (Actor): (As Greg Focker) Okay.

Mr. DE NIRO: All right. Let's give it a whirl.

TEMPLE-RASTON: Who can forget Robert De Niro's interrogation of his prospective son-in-law in "Meet the Parents"?

(Soundbite of movie, "Meet the Parents")

Mr. DE NIRO: Did you fly on an airplane today?

Mr. STILLER: Yes, I did.

Mr. DE NIRO: No peeking. Did we eat pot roast for dinner tonight?

Mr. STILLER: Yes.

Mr. DE NIRO: Was it undercooked? Relax. Relax. The needles are jumping.

TEMPLE-RASTON: The polygraph is misunderstood. While it can show when someone gets anxious, it can't definitively say what is triggering their nervousness. And that's the rub.

In 2003, the National Academy of Sciences concluded in a report on polygraphs that the machine was lacking. When it was used to investigate a specific incident it performed, in the academy's words, well above chance, though well below perfection - hardly a ringing endorsement.

(Soundbite of music)

TEMPLE-RASTON: What we consider to be the modern polygraph was actually invented in the 1920s. It was a time when Prohibition was in full swing and law enforcement had its hands full with bootleggers and crime syndicates.

A Berkeley, California beat cop named Leonarde Keeler invented a machine he claimed detected lies. Americans were utterly receptive to the idea. It was a time when quacks were pushing truth serums and people were exploring the unconscious mind and the afterlife.

The prospect of a machine that could definitively tell liars from truth-tellers fit into the fashion of the times. Keeler's machine measured pulse rate, blood pressure and respiration and what he called electrodermal responses. That's a fancy name for sweaty palms. Subjects were told to answer yes or no questions while their physical responses were recorded by ink pens on paper. By the end of the 1930s, polygraphs were an integral part of local police work.

Mr. BILL MAJESKI (Polygrapher, New York Police Department): You know, clearly, the body gives off signs of deception. It's a question of trying to identify the best way of reading those signs.

TEMPLE-RASTON: That's Bill Majeski. He's a veteran NYPD polygrapher who agreed to hook me up to one of those old-fashioned Keeler machines.

Frankly, the machine looks a little menacing. It is a size of a briefcase and there's a tangle of copper wire connected to metal knobs. Majeski unpacks the contents. There is a blood pressure cuff and some hoses and, yes, even light chains. Okay. The machine is scary.

What's all these wires and…

Mr. MAJESKI: Well, it's clearly intimidating…

TEMPLE-RASTON: …pins?

Mr. MAJESKI: …clearly intimidating…

TEMPLE-RASTON: Uh-huh.

Mr. MAJESKI: …to a certain extent. And that's one of the reasons why so much time is spent preliminarily.

TEMPLE-RASTON: A good polygrapher can spend hours with the subject before actually firing up the machine.

Mr. MAJESKI: Well, you know, clearly, you're measuring levels of anxiety and emotion. But the thing is that you establish a norm for the person that you're going to be testing. So essentially, what you're doing is just spending a fair amount of time with that individual to get to understand that person and clearly calm him down. I will never do a polygraph test if a person is in a high state of anxiety.

(Soundbite of polygraph machine)

TEMPLE-RASTON: The sharp needle-like pens are tracking my heartbeat, my breathing and my blood pressure. Majeski started a mock test. You can hear that the rhythm of the pens really doesn't change.

Mr. MAJESKI: Do your friends call you Dina?

TEMPLE-RASTON: Yes.

Mr. MAJESKI: Do you work for NPR?

TEMPLE-RASTON: Yes.

Mr. MAJESKI: Are you going to be truthful with me today?

TEMPLE-RASTON: Yes.

Mr. MAJESKI: Are you absolutely sure?

TEMPLE-RASTON: Yes.

Mr. MAJESKI: All right. That's (unintelligible).

(Soundbite of laughter)

TEMPLE-RASTON: Majeski says good polygraphers aren't like the ones we see in the movies. They don't wear white coats and sinister expressions. Instead, the best ones go into a polygraph test actually rooting for the person they are administering it to.

Mr. MAJESKI: The psychology behind this is that when I do a test, as with any good examiner when they do a test, they view the subject as being a truthful subject.

TEMPLE-RASTON: Mm-hmm.

Mr. MAJESKI: And you go forward with that premise. The natural reaction, you know, by a truthful person is they're a little nervous. They don't want to be blamed for something they didn't do. So they're looking for some helping hand.

TEMPLE-RASTON: Of course, that is the problem. The subjective opinions of polygraph examiners play a huge role in whether people pass or fail. Studies show for example that senior staff members at organizations rarely fail the test, but as many as 40 percent of the applicants for entry level positions don't pass. Is that because polygraphers don't want to fail their bosses?

Daniel Langleben is a psychiatrist and neuroscientist at the University of Pennsylvania.

Dr. DANIEL LANGLEBEN (Psychiatrist, Neuroscientist, University of Pennsylvania): It's not very well understood, but interaction - face-to-face interaction between an examiner and an examinee is a factor.

TEMPLE-RASTON: Mm-hmm.

Dr. LANGLEBEN: What are the effects of the factor is not clear. It's not known. To me, an unknown is equal to problem.

TEMPLE-RASTON: And there are lots of problems. The polygraph didn't catch Aldrich Ames, the CIA agent who spied for the Soviets. And Wen Ho Lee, the Department of Energy scientist, was wrongly accused for being an agent for the Chinese government after taking a polygraph.

Paul Root Wolpe is at the Center for Bioethics at University of Pennsylvania.

Dr. PAUL ROOT WOLPE (Faculty Associate, Center for Bioethics, University of Pennsylvania): There's just no question in my mind that if we had an effective lie detector, that the pressure to use it - security purposes, in courtrooms, even in sensitive employment settings — will be so strong that it will make its way into those settings. I think it'll be very, very difficult to stop it.

The reason polygraphy hasn't done that yet is because it is just not good enough. It's not reliable enough. But if we had a very reliable lie detector, that would be, I think, a very big challenge for us.

TEMPLE-RASTON: And that's a challenge that science is taking up in spades. There are new machines that look for brain activity patterns when a subject is lying and computers that track micro expressions that can tip someone off to untruth.

In the age of terror, the perfect lie detector has become a top priority for law enforcement. But so far, it's been elusive.

Dina Temple-Raston, NPR News, Washington.

MONTAGNE: One California company has found a way to take pictures of the brain that, it says, track a lie as it's being formed.

Unidentified Man: What we are able to do is to look inside people's brains and verify that they're telling the truth.

MONTAGNE: Lie detector tests have been largely banned from courtrooms. Find out why at npr.org. And tomorrow, more on lying.

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