Whether you are under investigation or applying for a government job, you may be subjected to a lie detector test. Though controversial, this method is based on the idea that people who are lying increase their physiological responses to questions designed to spot deception.

Physiological responses are recorded on moving graph paper by sensors hooked up to your arms and legs. We’ll explore how these signals work and why they are thought to indicate deception.

Physiological Responses

Physiological responses such as heart rate, respiration and perspiration are looked for in a polygraph test. These responses are allegedly associated with anxiety that results from lying. They are monitored by a combination of rubber tubes attached to the chest and abdomen, metal plates on the fingers, a blood pressure cuff and galvanic skin sensors that measure sweat gland activity.

During the lie detector test, the examiner asks a series of control questions (generally, vaguely threatening ones that don’t relate to the case at hand) followed by core questions related to the incident in question. The examiner assumes that if a person’s physiological responses to the critical questions are larger than their responses to the noncritical questions, they may be lying. For more info, do visit this website Lie Detector Test.

Early theorists believed that deception was a mental act that required effort, and they proposed that these efforts could be detected through physiological changes. However, experimental tests have been unable to distinguish placebo-like effects from the real biological response to a lie.

Behavioral Responses

Humans have been trying to find reliable ways to detect lies for centuries. In ancient China and India, authorities “detected” a lie by asking the suspect to chew a rice grain and then spit it out.

In the modern era, polygraph tests use a combination of medical instruments to measure autonomic responses such as skin conductivity, blood pressure and breathing. The examiner analyzes the recorded data to determine if the subject is being truthful or lying.

The premise behind the test is that questions that are relevant to a liar will trigger different physiological responses than non-relevant ones. The examiner will decide the subject is telling the truth if their physiological responses to relevant questions are smaller than their reactions to comparison questions. However, researchers have found that the same underlying biological changes are caused by things like fear, anxiety, alcohol withdrawal and psychosis, all of which can cause a person to appear to be lying.

Detection Methods

The theory behind polygraphs and more recent devices such as the computer voice stress analyzer is that most liars exhibit certain changes in their physiology that sensitive equipment can detect. A number of scientific studies support this theory, although a study using an index based on precise measurement of all facial movement yielded a false-positive rate of 58 percent.

Most polygraph examiners begin the test with “control questions” that are unrelated to the subject under investigation. This allows the examiner to establish a baseline reaction and ensure that the examinee answers the relevant questions honestly.

Some people attempt to fool the lie detector by implementing countermeasures. These include taking sedatives to minimize anxiety, applying antiperspirant to counter sweating, or inflicting pain on oneself (such as the infamous spy Aldrich Ames did by sticking a nail in his foot after every question). These tactics can skew results and make it harder for an examiner to distinguish between truthful and lying responses.


Lie detector tests have been the subject of controversy for nearly as long as they’ve existed. These machines look for typical stress responses to lying, including higher blood pressure and heart rate. However, people can learn how to control these responses. Some, like the infamous Soviet spy Aldrich Ames, can pass a lie detector test by simply taking sedatives and applying antiperspirant to minimize sweating.

In addition, a person can change the results of a polygraph by putting more emotional weight on what’s being asked. They can also use physical countermeasures such as biting their tongue or moving a leg muscle to skew the results.

Generally, private employers are forbidden from using these kinds of tests on their employees through the Employee Polygraph Protection Act (EPPA). But some exceptions do exist for companies involved in ongoing investigations of economic loss such as theft or embezzlement. In these cases, a company may require an employee to take a lie detector test.