Terrorist returned to jail for failing lie detector test – one of the first carried out under new powers

David Barrett tests the government’s state-of-the-art lie detector tests, which are now used on terrorists

A feeling of stress is an integral part of the lie detector test.

There’s an element of theatrics to the process, the experts tell me as I’m outfitted with a bewildering array of medical monitoring devices.

The body reacts to the act of lying the same way it reacts to an unexpected knock on the window at night, the examiner says.

Primitive physiological responses show measurable changes in blood pressure, breathing rate, sweating and blood density in the extremities – often described as “fight or flight”.

“You have no control over that,” adds the reviewer grimly.

I’m fitted with sensors on three fingers – a ‘plethysmograph’ to measure blood density and two that measure sweat levels – plus a blood pressure cuff and two strap-like ‘pneumographs’ around my chest to monitor breathing rate .

DAVE BARRETT: There's an element of theatrics to the process, experts tell me as I'm outfitted with a bewildering array of medical monitoring devices

DAVE BARRETT: There’s an element of theatrics to the process, experts tell me as I’m outfitted with a bewildering array of medical monitoring devices

There’s also a motion detector on my chair to make sure I stay absolutely still during the test, which is video-recorded for evidence.

I undertake what is called a ‘surge’ test – a form of calibration experiment that is conducted before offenders begin the ‘real’ exam which asks them about their activities.

The test subject – me, in this case – is told to deliberately tell an untruth so that the examiner can study how the body reacts.

I am ordered to lie about a series of colored numbers posted on the wall in front of me.

Each question is read by a synthesized voice on a computer, so no human speech inflections affect the test.

The 25-second intervals between questions only add to the tension.

DAVE BARRETT: I'm fitted with sensors on three fingers - a 'plethysmograph' to measure blood density and two that measure sweat levels - plus a blood pressure cuff and two strap-like 'pneumographs' around my chest to monitor the breathing rate.

DAVE BARRETT: I’m fitted with sensors on three fingers – a ‘plethysmograph’ to measure blood density and two that measure sweat levels – plus a blood pressure cuff and two strap-like ‘pneumographs’ around my chest to monitor the breathing rate.

Going through the numbers one to six printed in black and red, I have to answer “No” to the question “Is the number four red?”

I know it’s wrong, and everyone in the room can see it’s wrong, because the number four is actually printed in red.

But the important thing is to demonstrate that the technology can record what happens involuntarily in my body when I lie – and that the examiner can correctly interpret what he sees on his laptop screen.

It seems like such a simple exercise.

But knowing that the barely perceptible responses of my body are being observed, measured and recorded makes it a disconcerting experience.

It’s a bit like going to the doctor’s office for test results, going to a job interview, or waiting to hand in the exam paper at school, all rolled into one.

Then the examiner shows me the results – a graph illustrating how the sweating and blood pressure peaked as I said that little canard.

DAVE BARRETT: It's a bit like a visit to the doctor's office for test results, a job interview or waiting to hand in the exam paper at school, all rolled into one

DAVE BARRETT: It’s a bit like a visit to the doctor’s office for test results, a job interview or waiting to hand in the exam paper at school, all rolled into one

Even the anticipation of having to lie had pushed the numbers up on the chart.

“It’s very clear to me that even though there were no consequences for you here in this scenario, the test showed when you were lying and when you were telling the truth,” the reviewer says.

“There were clear physiological responses.”

I’m relieved that my lie was exposed.

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