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Lie Detection

by Steven Novella, Oct 31 2011

I recently received the following e-mail:

I have a question about science into deception and detecting lies.

Particularly to do with the show, ‘Lie to Me’ and the Cal Lightman character. The show is supposedly based on some science about deception. Wikipedia says the lead character is loosely based on Dr. Paul Ekman.

The notion that because we’re hardwired to communicate our feelings through facial and bodily expressions making deception difficult (which would leave specific and unconscious tells) seems to me sensible and I would’ve liked to have believed it, bought the book by Ekman and tried to learn to read micro-expressions.

However I keep hearing that under controlled conditions that no one, not experienced detectives, scientists, judges nor average people of the street demonstrate can discern lies from truths any better effectively than pure chance.

Is this stuff about microexpressions and truth wizards based in any reality at all, and if so, how limited or useful is it really?

This is an excellent question. Many of the pseudosciences we cover are so obvious and extreme that anyone with basic critical thinking skills and a modicum of scientific literacy should be able to smell them a mile away. So I enjoy also covering topics that are on the edge of legitimate science and pseudoscience, where even an experienced skeptic would have to do some digging or ask an expert to figure our how legitimate the claim is.

Claims for lie detection are generally highly problematic, although not completely pseudoscientific. There is a body of rigorous science, but the difficulties in applying that knowledge in a practical way to the question of lie detection tend to be overwhelming.

Indirect Markers

The first problem that is often pointed out with lie detection is that the technology is not detecting lies – but the markers of behavior that correlate with lying. The polygraph, for example, measures physiological stress, which is assumed to correlate with psychological stress, which is assumed to correlate with lying. But there are nervous interviewees who display stress without lying, and their are cool liars who do not reveal stress even when they are lying.

Group vs Individual

Another primary limiting factor is that individual variability tends to be greater than commonality in terms of behavior. When doing research you can look at correlations one of two ways. You can take a group of subjects who are known to be lying and another group known to be telling the truth and compare them. When you do this you can find statistical differences between the groups.

We can therefore make statements about the kinds of behavior people display when they are lying. But this is not the same thing as indicating if one individual is lying (called single-subject truth-verification). This has been a primary (but not only) problem with the polygraph test, for example.

Therefore with this type of technology we can only make statistical statements about the probability that someone is lying or telling the truth. This renders the technique not entirely useless, but questionable, especially in some applications, like the courtroom.

If, however, we can get close to 100% accuracy in comparing groups, then it becomes more reliable to apply the technique to the individual. This is the promise of a new technology using fMRI scans to see what is happening inside the brain when people lie vs tell the truth. The idea is that we may be able to control our voice and facial expressions, but not what is happening inside our brains.

fMRI Lie Detectors

Studies with fMRI have been impressive. In a concealed information test model some studies have found a 100% correlation between lying and prefrontoparietal lie activation. Overall correlation is above 90%. It seems our brains go through a different process when fabricating a lie than when recalling the truth, which makes sense.

A recent review summarized the types of studies done:

Since an initial publication in 2001,37 several papers on the BOLD fMRI methodology have reported differential patterns of blood flow in various brain regions in experimental paradigms in which subjects were instructed to lie or deceive in one task condition and respond truthfully in another task condition. The task paradigms included forced-choice lies (i.e., responding yes when the truth is no and vice versa)37,38; spontaneous lies (i.e., saying Chicago when the true answer is Seattle)39; rehearsed, memorized lies39; feigning memory impairment40,41; and several variations of the Guilty Knowledge Test,42,43 including lying about having a playing card,44–47 lying about having fired a pistol (loaded with blanks) before the scanning session,48 lying about the location of hidden money,49,50 and lying about having taken a watch or ring.51

The most consistent finding is activation of the certain prefrontal areas with lying. The hypothesis is that this area is needed to suppress saying the truth, which would otherwise be the default response to a question. The research summarized above, however, is of the group kind. There have only been a couple of studies looking at the accuracy of lie detection in individuals. These studies show about a 90% accuracy of this technique.

Still, fMRI lie detectors have a similar problem to that of polygraphs. In the polygraph someone who is fearful or anxious may display the same autonomic findings as someone who is lying, generating a false positive. Likewise, the fMRI is detecting (probably) not a lie but the suppression of a response. There may be many reasons in a real life situation when an innocent person would want to suppress a response, generating a false positive.

There are other problems with applying this technology as well.


Lie detector researchers have known for a long time about countermeasures – techniques that individuals can use to foil a lie detector.

Ganis et al recently explored whether lie detection countermeasures would affect the fMRI model of lie detection. Their research confirmed that 100% of subjects who are lying display characteristic changes on fMRI scanning. However, when typical countermeasures were employed the detection rate was reduced to 33%. If their findings are correct, this would put fMRI lie detection in the same camp as the polygraph.

Micro Expression

Finally we get to the issue of microexpressions. This is the basis of the TV series Lie to Me. There is little science behind microexpressions, however. I found one peer-reviewed study specifically on microexpressions as lie detection, which found some correlation but is not sufficient to support this technique as a form of lie detector.

The basic idea, originated from Paul Eckman, is that when we conceal our true emotion, the real emotion leaks through with brief “micro”expressions. If someone is pretending to be happy when they are really sad, they will frown briefly.

If true, again we have a marker for lying, and not really a test for lying. Microexpressions would reveal that someone is concealing their true emotions, but not why they are doing so.

The microexpression concept has not been studied enough to conclude that it is legitimate. If it holds up under adequate replication then we still have all the problems inherent in lie detection – it is looking at a proxy of lying, there are likely to be effective countermeasures, and variation in individual personality and situation may overwhelm and true signal of deception.


The various lie detection technologies have collectively discovered interesting facts about human emotion and deception. They have not, in my opinion, yielded an effective lie detector, capable of high levels of accuracy despite deliberate countermeasures. The more recent technologies – fMRI and microexpressions – also need to be researched in real world applications to see how generalizable their principles are.

I would not rule out that an effective lie detection technology can be developed. The most promising approach seems to be with brain scanning. But we are not there yet.

49 Responses to “Lie Detection”

  1. tmac57 says:

    On a more philosophical note,what would likely be the effect on society,government,and personal liberties,if we were to invent a truly infallible lie detector?
    At first blush,it sounds like an enormously useful tool,but where could something like that also go wrong?

  2. Clearly there would be a huge potential for abuse. However, I could envision a high threshold for a specific court order for using such a technique. If you are indicted for a crime, for example, then it could be used.

    • The Midwesterner says:

      You’re forgetting about the Fifth Amendment. A person cannot be compelled to give testimony against themselves. In your scenario, they would have to be asked about the crime they’re charged with, which can’t happen unless they waive their Fifth Amendment right.

      Also, even if we didn’t have a Fifth Amendment, while you may envision a high threshold, I doubt that most prosecutors would, particularly in our current political climate. It’s not that difficult to get an indictment against someone and most defendants aren’t even indicted. They’re charged by complaint, which is a document in which a government attorney (they’re called different things depending on the jurisdiction) only needs to establish probble cause and get a judge’s signature to charge a defendant. Probable cause is not nothing but it’s not a particularly high threshold. We would be on one extremely slippery slope.

      • tmac57 says:

        That’s the kind of thing that I was interested in exploring when I posed my hypothetical scenario.
        The prospect of ‘knowing’ the absolute ‘truth’ of a crime seems very seductive on the surface of it.But as always,there can be unintended consequences associated with seemingly expedient solutions.

      • Wrong says:

        Even if you didn’t use it to judge the guilty, it is plausible that the innocent could use it to prove their innocence. That at least would help prevent false imprisonment and punishment.

    • Steven, you forgot to mention even more problems with fMRIs:

      1. They’re not operating in real time.
      2. Their resolution level is still WAY too crude to pinpoint brain areas small enough for us to say, “He’s lying!”

  3. Max says:

    “Therefore with this type of technology we can only make statistical statements about the probability that someone is lying or telling the truth. This renders the technique not entirely useless, but questionable, especially in some applications, like the courtroom.”

    No test is 100% accurate; not a mammogram, not even DNA matching. You just have to consider its sensitivity and specificity, and take it for what it’s worth.

    As unreliable as the polygraph might be in the courtroom, the jury is looking at even less reliable markers of lying like body language.

  4. Max says:

    “When doing research you can look at correlations one of two ways. You can take a group of subjects who are known to be lying and another group known to be telling the truth and compare them.”

    What’s the second way?

  5. d brown says:

    I think a sociopath would not have real emotion to leak. There was some work with what part of the brain is active when lying. If you were remembering the truth, one part of the brain is working. Making up something and it’s another. But if they were remembering the lie they had made up??

    • Wrong says:

      Novella noted that the study did test the effects of using pre memorised lies, but I haven’t looked over the results. That would be interesting, is a fictional memory equal in value to the truth, measurement wise?

      Also, I don’t believe Sociopaths are completely emotionless: They usually don’t exhibit normal emotions, or empathy, and have highly manipulative personailities, but generally they serve their own ends, and deliberately do things that please them. That was my understanding of it anyway, most of the sources on the internet differ in definition or testing, or venture into highly suspect language tests.

      • Well, some linguists theorize that language originated in part *inwardly* and not just socially. Under these theories, part of language’s value is in helping us and our subselves to get and keep “our stories straight.” In this line of thinking, pre-memorized lies might indeed work well.

    • strumpfhosen says:

      Yes, my opinion is that a sociopath would not have real emotion to leak.

  6. The Midwesterner says:

    In my job I have listened to testimony from many thousands of witnesses in both criminal and civil cases. I sit closer to them than anyone else in the courtroom and frequently stare at them for their entire testimony. While I make judgments about their truthfulness, there is no way I – or anybody else – can tell with certainty who is telling the truth and who is lying. One reason is the very meaning of lying. It’s frequently not just the difference between a statement that is aboolutely true and one that is absolutely false. We all see and perceive things differently, so any number of witnesses may tell a similar story with glaring differences yet none is actively trying to deceive anyone. When we are accused of doing something wrong – even if we’re not the defendant – we try to minimize or explain away our perceived wrongdoing. We sorta, kinda lie, leave out a few things, maybe allude to something that isn’t quite true but maybe is partially true. Sometimes witnesses tell a story in which most of it seems true and coincides with all the other evidence but then a part of the story couldn’t possibly be true. Are they lying outright about that part? Do you dismiss all their testimony because of that part? It’s common for witnesses to have given a verbatim statement about an event shortly after the event and long before a trial. They may then be asked the same question but give a conflicting answer. When called on it, many witnesses will tell you that what they’re saying at the trial is the truth even though the original statement was given much closer in time to the event and they acknowledge that it’s likely the events were fresher in their mind when they made the earlier statement. These are usually good people who are simply called to testify as fact witnesses and have no interest in the outcome of the case so have no reason to fabricate.

    During jury selection, jurors are frequently asked what tools they will use to determine credibility. Most answer body language: eye contact, nervousness, etc. It’s then pointed out to them that being on a witness stand is pretty daunting and many witnesses are nervous. Most jurors acknowledge that, ultimately, all the evidence has to fit together – not prefectly – but enough so they are convinced of their verdict. Ultimately, I think juries do a very good job. There’s only been a few times when I think they got it wrong – and I could be the one who was wrong.

    Given the enormous variability in how we process events in our minds and then relate that information to one another, no matter the setting, it’s hard to imagine that any scientific test is going to be able to detect an untruth. Certainly if someone tells you they can tell when a witness in court is lying, they’re lying – or badly deceiving themselves.

    • Max says:

      “The foreman of the jury in the Casey Anthony trial said that his work experience [as a high school phys ed teacher] trained him in reading people, which made him suspicious of the testimony of Casey Anthony’s father, George Anthony, a report says.”

      Was he deceiving himself?

      • The Midwesterner says:

        Jurors are told they can and should use their common sense, their life experiences, anything they normally use in making judgments in daily life. It’s common in jury selection for attorneys to ask prospective jurors if they think they’re good judges of character. I have yet to hear one answer no. However, I’m guessing we’ve all met people who seem particulary gullible or get involved with people who we think are less than stellar but they can’t see it. So my answer is yes and no. He apparently did use his life experiences, which is completely valid, and, of course, to each a verdict, he and every other juror has to make judgments and decide what is credible and what is not. However, I don’t believe anyone has any “special” ability to determine when someone is lying, including this juror.

      • Max says:

        Common sense is the opposite of specialized knowledge and training, which jurors are instructed NOT to use.
        But I think we agree that the phys ed teacher was fooling himself about his special ability to read people. It’s like Creationists who think their work experience in engineering trained them to understand biology.

      • tmac57 says:

        Common sense,like beauty,is in the eye of the beholder.

      • The Midwesterner says:

        I don’t know of a situation where jurors are instructed not to use specialized knowledge. They are usually asked about any such knowledge in jury selection and either attorney is free to use a peremptory strike (a just-because removal of a prospective juror) or argue that the juror should be removed for cause, meaning they have some bias that would taint them. One thing I always find amazing is that attorneys are terrified of scientists on juries, believing all scientists see things only in black and white and, therefore, will make awful jurors.

      • tmac57 says:

        “believing all scientists see things only in black and white and, therefore, will make awful jurors.”
        Haha! That is so ironic.

      • Max says:

        “I don’t know of a situation where jurors are instructed not to use specialized knowledge.”

        Here you go

        “If you have such a special expertise, and if it relates to some material issue in this case, it would be wrong for you to rely on that special expertise to inject into your deliberations either a fact that is not in evidence or inferable from the evidence, or an opinion that could not be drawn from the evidence by a person without that special expertise. The reason it would be wrong to do so is that you must decide this case only on the evidence presented to you in this courtroom.”

        They don’t want jurors to play expert witness.

      • You bet he was. Dunning-Krueger effect. (My mnemonic for that? Brian Dunning overestimates how much of a skeptic he is and Freddy Krueger overestimated how scary he was.)

    • Max says:

      I’m skeptical that juries do a very god job.

      “A recent study of mock juror decision-making at Cornell University showed that 85% of prospective jurors showed ‘pre-decisional bias’ in their decision-making… In our experience conducting mock trials over the past 26 months since the formation of Isosceles Consulting, we have found that only 12.4% of jurors change their verdicts between the conclusion of opening statements and the end of trial.”

      • The Midwesterner says:

        “Harry Plotkin is a jury consultant in Los Angeles. Mr. Plotkin specializes in assisting
        trial attorneys in jury selection and crafting persuasive opening statements and trial strategies.” I read over your link, admittedly quickly, but my first impression was that it was an advertisement for Mr. Plotkin.

      • Max says:

        Yeah, he writes about how to manipulate the jury. Interesting stuff.

      • The fact that jury selection (which I assume is linked to his comments on jury manipulation) is such a big deal (Maj. Nidal Hasan last week asked for a “jury consultant”) shows that juries probably don’t always “get it right.”

        And, in many cases, judges are even somewhat hamstrung, at least compared to the continental European system, where the presiding judge can conduct his/her own cross examination of witnesses.

    • tmac57 says:

      Your comment is very interesting.You appear to have a well grounded and savvy perspective on the jury trial process.Given that,from your experience,do jurors have the same kind of grounding in the way they evaluate evidence,or do they tend to make decisions more from their ‘gut’?

      • Max says:

        Judges literally make decisions from their gut, and I assume the jury isn’t any better.

        “As a case study, one of the judges started in the morning by granting parole to about 65 percent of the prisoners; that percentage dropped to near zero by the end of the first session, then rebounded to about 65 percent after the snack break. The same pattern repeated in the second and third sessions.”

      • Max says:

        Supreme Court Justices John Paul Stevens and Antonin Scalia believe the fringe theory that Shakespeare’s works were actually written by Edward de Vere.

        In a visit to Shakespeare’s birthplace in Stratford-upon-Avon, Justice Stevens observed that the purported playwright left no books, nor letters or other records of a literary presence.
        “Where are the books? You can’t be a scholar of that depth and not have any books in your home,” Justice Stevens says. “He never had any correspondence with his contemporaries, he never was shown to be present at any major event — the coronation of James or any of that stuff. I think the evidence that he was not the author is beyond a reasonable doubt.”

        This goes against mainstream academic opinion, which makes me wonder whether an academic approach to trials would do better than jury trials, which are more like a debate.

      • tmac57 says:

        PhD level professional jurors whose verdicts must be vetted through peer review.Each aspect of the evidence considered by appropriate experts (forensics,psychology,physics,biology etc.)
        I foresee big job opportunities.

      • Good fucking doorknob. That new movie about this? The only thing I don’t get is why isn’t it an Oliver Stone product?

      • The Midwesterner says:

        As it turns out, the entire judicial system, from the US supreme court to the lowliest clerk is populated completely by human beings, all of whom are subject to biases, weird beliefs, sometimes fuzzy thinking, deficits in their knowledge base. Jurors come from the same pool of less-than-perfect beings. That’s one of the reasons for the many layers and many people it takes to get a case completely resolved, and even then, we know of situations where it’s later proven to be wrong.

        As to gut feelings, I’m going to guess that there are many definitions and whatever it is is used by jurors, along with whatever scientific evidence is available in a trial, to make a decision. Most people who have served on jury duty will tell you it’s a lot harder than it looks. The music doesn’t get more dramatic when a witness is telling a great truth or a great lie. There are rarely any smoking guns. There’s lots of tiny bits that need to be tied together. It’s extremely rare that someone confesses from the witness stand – or the back of the courtroom. Jurors have gotten into great fights while deliberating and sometimes can’t come to a unanimous decision. The system we have is no more perfect than we are, but so far no one has come up with a better one.

      • tmac57 says:

        What about the ‘CSI effect’?

  7. Max says:

    Don’t know about microexpressions, but I know that fake smiles involve the mouth but not the eyes.

    • Myk Dowling says:

      I suspect that’s BS. Pretty sure I can fake a smile including my eyes. Actors do it all the time.

  8. d brown says:

    Sociopath’s are not emotionless. But their’s are not like ours. That they are different can be found out, but not if they are telling the truth. I think I read the main emotion is anger when they are not getting what they want. I remember reading of a study that had actors playing a trail. and then mock jurys read the same thing on paper. The actors phony emotion fooled them most of the time. The more you read about how the system really works the more fearful you are of being in it. Why do you think years ago, an Association of Prosecutors wanted the use of DNA stopped because of the damage to peoples faith in the system it would cause.

  9. BillG says:

    What constitutes a lie? Exaggeration, embellishment or salesmanship? Perhaps control of one’s inhibitions, patience or simply displaying civility? Does the brain process this differently with a justification: a glitch contrasted from blatant fabrications?

    I would hazard millions wake up every day living a lie, be it their job, spouse or general existence.

    Regardless, I think your correct Steve “we are not there yet”. A true lie detector may always be a fantasy until we tackle our ignorance on what consciousness is.

  10. Phea says:

    Pamela Meyer gave a very interesting talk recently called, “How to spot a liar.” The link is:

  11. The Midwesterner says:

    To tmac57 re CSI Effect – Attorneys, particularly prosecutors, are quite concerned about this because in so many cases, there is no “scientific” evidence presented, either because none exists or because none is necessary. (In a rape case where the defense is the victim consented, it doesn’t matter whether the defendant’s DNA is found; he’s admitting having sexual contact.) Defense attorneys worry jurors may be easily swayed by scientific evidence and not listen to anything else. Both sides attempt to deal with this in jury selection. After a trial is concluded, jurors are free to discuss anything they want about the case and their deliberations. Attorneys frequently send out surveys asking them for information or attempt to speak to them right after a verdict, but most jurors aren’t interested in responding so it’s difficult to know how real the CSI effect is, at least as far as I know.

    • tmac57 says:

      Thanks for the reply.This keeps coming up in news stories,and I have wondered how much of it is real,and if it was having any significant effects.

  12. d brown says:

    Oh say, you can buy voice stress analyzers. Larry Flinn had a PI run Nixon’s Watergate speech in one. Flinn printed the speech with the graft along said the words. It sure looked like it worked. After that Pols only talked about mom and the flag. The lies were from spokesmen.

  13. Maria says:

    For the record, when I was 19, I lied on a polygraph test…and was not caught. So much for that “lie detector.”

    • Max says:

      Or are you lying to us now?

      • Wrong says:

        It’s not all that hard: If you can fake stress, you can stuff up what they percieve as a lie. Some people simply don’t stress, and aren’t caught either. I want to take one, just to see whether I could beat it. That would be fun.