Lie Detector/ Polygraph

United States v. Scheffer, 1998

A military court had decided that exclusion of polygraph evidence violated the Sixth Amendment right to present a defense. The high court disagreed: "A fundamental premise of our criminal justice system is that 'the jury is the lie detector.'" The court decided polygraphs aren't scientifically valid enough and the jury should be able to detect lies by the criminal

False Positives

Although polygraph machines look scientific and measure responses such as sweating and increased pulse rate with accuracy the polygraph accuracy rate at around 65 percent; the test generates a lot of false positives. People who are telling the truth but whose polygraph test suggests they are lying. Must say base questions to establish norms

How to Beat it

Change your heart rate , respiratory rate, blood pressure and sweat level while answering control questions. Send your control lies off the charts. This way when you are asked real questions the lies will be calmer than those in your control questions and will register as the truth. Pain is also used to create a false norm that is high therefore lies aren't registered as anxious responses

When Used

Even though the polygraph now has a tarnished legal reputation, modern-day version of the exam are still used in job screenings, background checks, and reality television shows. Still not valid in a court of law

Inventors of the Polygraph

John Augustus Larson and James Mackenzie

P300 technology

The technique involves a subject wearing electrodes and a headband while being shown images on a computer screen, allowing an examiner to determine if the subject has stored information that she shouldn't. The images can be evidence. Specific response if the witness has seen it beforehand

National Research Council

an organization of scientists - conducted a systematic evaluation- concluded that the test is lacking in scientific validity actually is only 65% valid Organizations say 90%

Temporal lobe

associated with memory encoding and retrieval, it is involved in checking whether the mental imagery is correct Lying creates images you've never actually seen

Polygraph

measures the activity in the limbic system- the anxiety felt by the person- Lying makes this conflict within us creates a reaction because we have to fight our body's normal (truthful) responses, and the resulting reaction causes some of the changes seen with a polygraph instrument in dishonest people.

Components of Polygraph

sensor measures body movements blood pressure cuff- records pulse and blood pressure rubber tubes- placed over abdomen and chest for breathing metal plates- attached to fingers for sweating

Administrating

the test administer asks basic questions to establish a base and determine the output accurately. It was found that with examinees untrained in tricks designed to beat the test, have more mistakes in tests they administer. specific-incident polygraph tests "can discriminate lying from truth at high rates though below perfect

Compulsive Liars

up to 26% more white matter in the prefrontal cortex than most people. That's why they are more capable of making connections between thoughts not actually connected. "Creative" enough mentally

Frontal lobe

when activated, it is involved in suppressing or inhibiting the truth

Limbic system

when activated, it is involved in the increased anxiety from the deception