Lie detector tests are based on the theory that people will exhibit different physiological responses when they are lying. The test measures physiological changes like heart rate and blood pressure as well as perspiration.
A typical test starts with “control questions” and then moves on to relevant questions. The examiner then compares responses to determine if the subject is lying.
Physiological Responses
A polygraph test measures the subject’s physiological responses to a series of questions. This can include their heart rate, blood pressure, sweat glands, and skin conductance. The examiner looks for changes to these responses that are more common in those who are lying than those who are telling the truth.
Some studies show that when people lie, their heart rates increase and their breathing patterns change. This is because liars need to be able to think quickly to construct an elaborate lie and keep it consistent, which can be tiring. Their body also needs to get more oxygen-carrying blood to their brains to make this happen, so they breathe faster.
However, this type of response is not unique to liars and can be a result of many different factors, including stress, anxiety, or a medical condition. Furthermore, it can be difficult to distinguish between a genuine and false response. As a result, it is possible for a truthful person to fail a polygraph test for a reason that has nothing to do with lying. I recommend this website for more Lie Detector Test.
Lie Detection Tests
There are many different lie detector tests, some using newer technologies like fMRI brain scanning. But most work on the same basic premise: that liars show increased arousal in response to certain questions, while truth tellers do not.
An examiner hooks up a series of sensors to your body (a blood pressure cuff, two pneumographs that measure breathing and electrodes placed on your fingers) and then asks you a series of questions. The examiner mixes relevant questions, which relate to the crime or issue at hand, with control questions that don’t.
The examiner looks for irregularities in your physiological responses to the question-related and control questions. A successful result is a “deception not indicated,” while a failed result means the examiner found that you were lying during the test. It’s important to understand that the changes in your physiology that lie detector tests look for are involuntary and difficult to manipulate. For example, infamous Soviet spy Aldrich Ames was able to pass his polygraph test by taking sedatives and applying antiperspirant to keep his sweating under control.
Lie Detection Equipment
In a polygraph test, sensors attached to the body record physiological responses (such as heart rate, blood pressure and respiration) as the subject answers questions. These responses are then reproduced as line graphs on a piece of continuous paper or displayed on a computer, alongside the particular questions asked. The examiner then traces out patterns that might indicate lying. It takes a trained polygraph examiner to interpret these signals, and a skilled one can detect most lies—though not all of them.
Researchers estimate that the average person can tell when a person is lying by observing subtle changes in the subject’s physiology that sensitive equipment can pick up and record. But it’s not foolproof, and it is not a good substitute for interviewing tactics that can spot deception and elicit more honest answers. For example, expert interrogators often use facial microexpressions to catch people in lies. But that’s not available to everyone, and some liars are simply more adept at hiding their emotions from sensors.
Lie Detection Techniques
Since World War I, people have developed techniques to spot deception by measuring physiological responses. One of the most well-known is the lie detector test, which is still used by law enforcement agencies and in some government positions (as noted by Wired).
The polygraph is a device that attaches sensors to your body, including a blood pressure cuff, two pneumographs (to measure breathing), and electrodes to measure skin conductivity. A computer then records the resulting digital signals and analyzes them for signs of lying.
The examiner starts by asking three or four simple questions to establish a baseline for your responses. Then, he asks relevant questions about the suspected crime and “control” questions that are unrelated. He looks for a greater reaction to the relevant questions and a lesser response to the control questions, which he believes would indicate you’re being dishonest. While there are ways to cheat a lie detector test (taking sedatives, applying antiperspirant, holding your breath during the test), this usually doesn’t affect the results significantly.
