A lie detector’s name is a bit deceptive. This machine, called a polygraph, does not have the ability to determine lie from honest answer, but rather allows for a skilled technician to compare the way that a person’s body is responding to different types of questions. The polygraph is based on the idea that the body will display signs of increased anxiety when someone is lying, and tries to help a polygrapher determine these signs and when they are elevated.


History Of The Polygraph

There had been numerous attempts to construct a lie detector throughout the late 19th century, but it wasn’t until John A Larson, a psychologist living in Berkeley, California, began studying police procedures that a breakthrough occurred. Larson wanted to invent a way to make police interrogations easier, and working off of what he knew of deception he created a device that would measure three main physiological elements: blood pressure, heart rate, and perspiration.


How It Works

The polygraph has long sensors that send data back to the main machine showing the poolygrapher exactly how the person is responding to the interrogation. The polygraph measures blood pressure, heart rate, and perspiration—all factors considered by psychologists to be important in determining if someone is lying.  The real way that the polygrapher is able to determine lie from truth is not in simply seeing these numbers rise, but in the polygrapher’s ability to compare the way that the person in the test responds to control questions and to relevant questions.


Control Questions And Relevant Questions

Ehow points out that most polygraphs will ask roughly ten questions , four of them being relevant questions and six being control. As the Law Dictionary explains, hand. Instead, they are questions that come from information the polygrapher already knows about the person they are interrogating. These can range from the person’s address, name, or age to the current day of the week or what they do for a living. The idea is to use these control questions to establish their body’s response to speaking confidently and truthfully.

Then, the polygrapher moves into the relevant questions, the ones where it is important to know if the person is telling the truth. A trained polygrapher can compare the relevant responses to the control responses and determine if there was a significant enough change to believe that they weren’t answering honestly. It isn’t perfect, or completely guaranteed, technology, but it remains an incredible tool that we can use to try and fight deception.