The Polygraph Dilemma

dollarphotoclub_76207749-e1450156501621-680x416Psychological Detection of Deception (or PDD for short) has become a regular feature of popular crime television culture in modern times. Most commonly referred to as a lie detector or polygraph test, it is shown to be the one stop solution of every investigative dilemma. As with other forensic sciences, misrepresentation of this technique leads to misinformed opinions about the polygraph test and what it entails.  Let’s ‘debunk’/disprove or confirm the prevalent notions about the Lie Detector tests and see if we can ‘trick’ or fool the test effectively.


Before one can disprove, we must determine what a Polygraph test is and what does it measure? The test relies on certain subconscious and physiological changes that one’s body undergoes when they lie or misrepresent any information. These changes include increased perspiration, faster heart rate, respiratory rate and skin surface temperature. Before conducting the actual test, the forensic psychologist conducts what is referred to as the Pre-test or Control Question Test (CQT). This involves certain questions to be posed to the subject, the answers to which are already known and inconsequential. For e.g. “What f110626yz16is your name?”, “What is your age?” etc. The purpose of the pre-test is to establish a control or base line for all physiological functions with which the test results can be
compared. They then ask questions to which they know the person would have reason to lie about.  If the subject is trying to deceive the psychologist, in theory, their deception would be visible in the data collected in the form of the physiological changes. The results can be classified into four types, positive (lying), negative (not lying), false positive (saying the truth but appears as lying) and false negative (lying but appears as saying the truth).


The science behind the polygraph states that when a person knowingly lies, it leads to a certain physiological changes in functions that are being monitored during the test.

  1. The first being respiratory rate. Pnuemographs are used to detect the expansion of the lungs in order to identify minute changes in the subject’s breathing pattern, which is directly associated with the feeling of anxiety and nervousness, thereby pointing to deception.
  2. The second most common physiological function measured is the heart rate or blood pressure of the subject. The blood pressure and heart rate both noticeably increase when a person is anxious in order to maintain normal functionality under stress.
  3. cheat-a-polygraph-testThe polygraph also tracks the Galvanic Skin Resistance (GSR) or the minute perspiration on the fingertips of the subject. Also known as electro-dermal activity, the tips of one’s finger are extremely porous and are most likely to sweat. The “galvanometers” attached to the subjects figure tips measure the skins ability to conduct electricity. If one perspires more, the galvanometer would reflect this in its result and since increased perspiration is also a known sign of anxiety and uneasiness, it can be concluded that said subject was lying.
  4. Lastly, modern polygraphs have started using pressure pads which detect micro-contractions of the muscles caused by the subconscious mind while lying.
  5. More recent and more advanced Polygraphs have begun to rely on more advanced science and also measure skin temperature to ensure that one cannot ‘trick’ the polygraph. 

As is visible, the Polygraph test is not an actual lie detector but just a detector of the symptoms of anxiety which are often associated with people who are lying. As noted by the National Academy of Sciences in a study conducted by them in 2003 on the reliability of the polygraph test, the test results are a level greater than chance, yet short of perfection. The study concluded that the polygraph may have some utility but little basis for the expectation that a polygraph test could have extremely high accuracy The study also takes into account that a person can be anxious or nervous for many reasons and not necessarily because he or she is lying.

polygraph-testing-opelousas-laThe study, however conclusive, does not stop the general populous from coming up with a myriad of ways to defeat the polygraph.  The myths and notions are largely divided into two categories, those which deceive the test by addressing the questions asked and those which try to falsify the baseline or control. Further, they can be categorized as mental or physical methods. Most of these myths rely on the fact that a lie detector test is inherently biased against the truth. In theory, the CQT is supposed to be answered truthfully thereby allowing the subject to be calm. This work against him or her being questioned as the more relaxed one is during the initial questions, the more likely they are to fail the polygraph.

The first part of these notions focus on a more basic and fundamental understanding of PDD. Some of them are maintaining a generally calm attitude during the questioning, taking deep breaths, not paying great attention to the questions and thinking about a happy memory. Tricks like these address the main questions asked during the test itself. This is the direct approach which would require a greater amount of skill and control over subconscious functions. The direct approach must be tackled as a group as they all try to achieve the same thing, preventing the polygraph from detecting the lie by fooling the body itself into thinking its telling the truth.

OLYMPUS DIGITAL CAMERAIn the direct approach, the baseline is accurate but the test itself is fooled. For example, if a person keeps themselves distracted by a happy thought during the questioning, their mind would not react to the gravity of the lie and the situation they are in at the time and in turn would not make subconscious physiological changes such as micro-perspiration or increased heart rate which then, would not be seen on the test. Such ways to cheat a polygraph are very direct but can only be mastered by practice even after which, they cannot be air-tight. They will almost always fail against modern polygraphs which also detect minute changes in skin temperature caused by increased blood flow and expansion of arteries. For that reason, those wanting to beat the polygraph rely on the second form of cheating a polygraph.

The second and more popular approach to beating a Polygraph test is by corrupting the CQT result. This makes the baseline which is supposed to be the control against which the actual test will be seen, appear higher than it actually is. This causes any lie that is said in the actual test be masked or merge with the control and will be considered true in the test.


The first of these “mythical tactics” to beat the polygraph is the trick of keeping a pin or a tack under your toe in your shoe. When the psychologist asks you questions during the CQT, answers to which are non-incriminating, the person to press down on a tack under their toe while answering. This would cause a sharp pain which would trigger an adrenaline secretion in the body which directly increases the heart rate and perspiration.  This would lead the forensic analyst to associate that exaggerated reading with the truth thereby corrupting the baseline itself. At this point, even if the answer to the actual test is a lie, it would be camouflaged and would not particularly stand out.

In fact, this myth is true and in theory would work but forensic analysts are trained to look for such methods by what they refer to as “countermeasures” which allow the psychologist to tell if someone is trying to deceive the polygraph. These countermeasures included an irregular heartbeat and irregular breathing etc.


The second myth states that if you breathe irregularly during the whole test, it gives false positive results. The myth requires the subject to breathe deeply and hold their breath for 2 seconds and repeat this process during the CQT and then during the actual test do the same before every question. They say that manipulating your breath as mentioned above causes an increased amount of oxygen intake with every breathe which would need to be compensated with a faster heartbeat to distribute the oxygenated blood over the body. This would also lead to increase in the blood pressure thereby masking the lie on the sheets of the forensic analyst considering the baseline was incorrect to begin with.

This is not an airtight getaway simply because the polygraph measures a lot more than BP and heart rate. The perspiration under the pressure of lying along with any pressure pad attached to their’s body would still give results, irrespective of the breathing pattern. Further, the aforementioned countermeasures which can be detected by the forensic psychologist can still be detected.


Another very common myth says that if a person counts backward from 10 to 1, the brain functions engaged would cause you heart rate to rise and also distract one from the importance of the questions. This myth tries to minimize the emotional impact of the relevant question asked to you. Though this can be near impossible to detect, it can more than often have only a minimal impact on the actual test result, considering that the involuntary physiological changes are very hard to suppress.


Lastly, if one clenches their anal sphincter while answering questions, one can fool the body into increasing the heart rate by putting constant stress on the glutus muscle section. The more stress one puts, the more oxygen the muscles would require forcing the heart to beat faster and in turn triggering increased perspiration etc. This method sounds like a long shot because, in fact, it is. Forensic psychologists are trained to detect these physical methods of hiding the lie. They apply the aforementioned countermeasures one of which includes pressure pads over the body which would easily detected the glutus muscles being clenched. Therefore, this myth is more rumour than fact.

It has been accepted by the courts that lie detector tests or polygraph tests, however efficient cannot be reliable and that there shall always be a chance of the result being false positive or false negative. This is expressed in the case of Selvi v. State of Karnataka (Selvi v. State of Karnataka, 2010) where the Supreme Court of India held that it is better that a person who is guilty be let go rather than an innocent be jailed. However, should these tests gain legal validation in court in the near future, this would be a good argument to make for how difficult it is to beat the tests.

Written by Garv Bhatia (JGLS ’14)

Edited by Poulomi Bhadra


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s