by Derek Paulson

Lie detector tests have become a popular cultural icon — from crime dramas to comedies to advertisements — the picture of a polygraph pen wildly gyrating on a moving chart is readily recognized symbol.

The instrument typically used to conduct polygraph tests consists of a physiological recorder that assesses three indicators of autonomic arousal: heart rate/blood pressure, respiration, and skin conductivity.

Most examiners today use computerized recording systems. Rate and depth of respiration are measured by pneumographs wrapped around a subject’s chest. Cardiovascular activity is assessed by a blood pressure cuff. Skin conductivity (called the galvanic skin or electrodermal response) is measured through electrodes attached to a subject’s fingertips.

Polygraphs don’t really detect anything meaningful except that the subject is under stress – and simply being given a polygraph is sufficient to trigger the stress.

The real value of the polygraph test is to work as a placebo to trick the suspect into thinking they will be caught in a lie.  This in turn amplifies behaviors for concealing lies – which makes the lies much easier to catch by a trained observer.  If the criminal believes the lie has been ‘found out’ they are much more likely to confess.

There are also all sorts of cool tricks that can be used to amplify the placebo effect and convince the individual that they have been caught in a lie.

For instance, an individual interviewing for a security clearance at an agency with a high level for security clearance relayed the following experience.

He was taking a polygraph, about half way through they had asked a question about ‘Have you ever engaged in criminal behavior’ to which he answered ‘No’.

The technician showed him a big squiggle on the polygraph and explained that it had detected a lie.  The interviewee maintained his innocence.  The technician then called his supervisor, who came in wearing a white lab coat, and closely examined the squiggle, confirming that it indeed showed evidence of a lie.

The guy thought about it for a while, and finally confessed to something – which resulted in him being disqualified for the position.

The reality is that it was almost certainly just a random squiggle, that the machine hadn’t detected anything, that the first technician lied, and that the supervisor was a planned action simply to amplify belief in the placebo using the expert authority trick – to give the exact result – people to confess since they were certain that they were caught.

The problem of course is that investigators who aren’t aware of the real value of a polygraph – think that it really can ‘detect lies.’