Detecting the Lie

The most well known lie detecting test today is the polygraph. But is the really a good test to catch a liar? It is based on physiological responses such as blood pressure, respiration rate and electrodermal skin response such as sweating. All of theses responses are present when the person is under stress, not only when they are lying. How could a polygraph test determine whether a person is just stressed or stressed about covering up their lie? Scientists are looking at various tests to find one that could be better than the polygraph to detect the lie.

This is a Ted Talk by Pamela Meyer author of Liespotting.

In Robin Marantz Henig's article “Looking for the Lie” she goes through various tests scientists are working on in order to detect deception.

f-MRI Tests

Working at the University of Pennsylvania starting in 2000, psychiatrist Daniel Langleben performed a study looking at the brain using an f-MRI during deception. The study was an early step in mapping lying in the brain because it is practically impossible to set up natural conditions of lying in an f-MRI lab. The procedure for the study was simple. Langleben had his 18 participants lie about a specific card- the 5 of clubs. To make sure that there was no emotional connection with that card, he screened out compulsive gamblers from his participants. The participants were given a specific amount of cards and then watched cards flash before them in the f-MRI. They were to be honest in saying if they had that card or not except for the 5 of clubs. When that card flashed before them, they were instructed to lie and say that they didn't have it in their pocket when they actually did.

What Langleben found is that there are regions of the brain that are more active then when telling the truth. Marantz reports that, “lying was associated with increased activity in several regions of the cortex, including the anterior cingulate cortex and the superior frontal gyrus.” These regions of the brain are part of the pre-frontal cortex. These are some of the same areas that light up when a person is performing an improvisation (Berkowitz). This shows that some of the decision making processes occur in the same part of the brain for deception as for improvisation. According to Langleben, “the prefrontal cortex-thre reasoning part of the brain-was generally more aroused during lying than during truth-telling, an indication that it took more cognitive work to lie.” In comparison to improv, it takes cognitive work to get to the point where a flow state is obtained. The cognitive works are very similar between both improv and lying.

Langleben performed this study again in 2003. This time he gave his subjects the choice of two cards to lie about or the choice not to lie at all. In this version of the study he found activation in some of the same regions as before which established a pattern for deception in specific parts of the cortex. There was activation in the parietal cortex which interested Langleben because the parietal cortex is activated during different types of arousals such as increased sweating when lying. This finding might in fact give validation to the polygraph test and give it more credibility.

Stephen Kosslyn a psychologist at Harvard looked at Langleben's study, but said that the areas of the brain light up for other tests such as the the Stroop test and therefore determined that that area couldn't be what he termed as the 'lie zone'. He therefore performed his own test to determine if there was a difference in the areas of the brain that lit up between rehearsed lies and spontaneous lies. He had his subjects (10 people, all in their 20's) rehearse a lie which he helped them create from a notable work experience or vacation experience. He found that that there was a difference in brain activation between a rehearsed lie and spontaneous one.He said that both involved memory but the areas were different. For a spontaneous lie part of the frontal lobe involved in working memory lit up while for the rehearsed lie part of the anterior frontal cortex involved in retrieving episodic memory lit up. This means that there is more involved in lying than originally thought, and it is a complicated process involving many parts of the cortex.


Jennifer Vendemia a psychologist at the University of South Carolina has been studying lying using the EEG. She is using a different type of cap that has 128 electrodes instead of of 12 electrodes so that she can find where the electrical impulses are coming from when a person lies. She is looking at a specific type of brain wave known as event-related potential or E.R.P. According to Marantz the E.R.P wave “represents electrical activity in response to a stimulus, usually 300 to 400 milliseconds after the stimulus is shown. It can be a sign that high-level cognitive processes, like paying attention and retrieving memories, are taking place”. Vendemia has studied 626 undergraduates and their E.R.P waves when they are lying. In this study, Vendemia presents statements that the students have to respond to as either true or false depending on the color of the statement. She found that students typically take longer, up to 200 milliseconds longer, to lie than to tell the truth. There were changes in certain E.R.P waves when lying, especially in the regions that lit up in the fMRI scanner. These regions are “the parietal and medial regions of the brain, along the top and middle of the head.”

Vendema can detect changes in the brain waves within 240-260 milliseconds after the statement is presented. But it takes 400 to 600 milliseconds longer for the person to actually respond true or false to the statement.

Facial Recognition

Paul Ekman has developed at Facial Action Coding system that can detect lying as easily as the EEG. His system includes “a precise categorization of the 10,000 or so expressions that are created by various combinations of 43 independent muscles in the face.” Ekman says that “facial expressions are hard-wired into the brain and can erupt without an individual's awareness about 200 milliseconds after a stimulus…a facial expression can give away your feelings before you are even aware of them, before you have made a conscious decision about whether to lie about those feelings or not.” His system is based on microexpressions that last less than a half a second. It is these microexpressions that indicate incongruity between the emotions and words of a liar. But it is not only the microexpressions that give away a liar. According to Ekman voice, hand movements,posture, and speech patterns all vary from how the person normally talks. He also says that word choice is also a clue. When someone is lying their language changes to be more in third person and they might also try to buy time as they figure out what to say.

Ekman's program can be taught to anyone, and has a 95% accuracy. He has been teaching this to various officials, but the government is not willing to use it because they will only use a machine.

Physiological Responses

In addition to the other tests that are being looked at for lie detection there are ones that are looking at different physiological response tests that are different than the polygraph.

At the Dodpi facility at Fort Jackson, SC a thermal scanner is being studied. This produces a computer image of a person's face and how much heat it is emitting, detected by the specific color of that region. There is a specific region of interest, just inside each eye, which gets hotter when a person lies. It also gets hotter with other cognitive tasks so it is important to find a “specific signature for deception” so that there are not false positives.

There are other machines that are being developed to detect lying such as an eye tracker which looks at the fixation, duration, rapid eye movements, and scanning path. This determines if the subject is looking at something they have seen before, and is thought of as a mute version of the Guilty Knowledge Test. In addition there is more research on detectors that are looking for increased physiological processes that are related to lying. According to Marantz these include:

  • a sniffer test that measures levels of stress hormones on the breath
  • pupillometer that measures pupil dilation
  • a near-infared-light beam that measures blood flow to the cerebral cortex

All of these machines are being worked on to be a replacement for the polygraph. But are any of theses tests more accurate than the polygraph? Some people are worried that they will fall into the same trap. We shall see what the future brings in terms of lie detection, and how it impacts our everyday lives.


Marantz Henig, R. (2006, February 5). Looking for the Lie. New York Times, 155(5348), 46-83. Retrieved April 29, 2013