THE ROUGH GUIDE TO PSYCHOLOGY
The polygraph test, still widely
used in America, faces the same
problem. The squiggly lines
produced by measures of heart
rate, breathing, and sweatiness are
merely signs of stress – so again,
the nervous innocent could end
up being categorized as a liar. And
cunning criminals may well be able
to trick the system – by such ploys
as biting their tongue during the
control questions (for example, “is
your name Jack?”) they can distort
the assessment.
What we do know for sure about
lying is that it’s more mentally
demanding than telling the truth.
This should mean that if the mental
demands of a situation are ratch-
eted up, liars will struggle more
than truth-tellers. That’s exactly
what Vrij found in a 2007 study in
which he used the device of asking people to tell their stories backwards
- a task that is known to be cognitively tricky.
Vrij invited students take part in a mock theft, half of whom later
acted as liars. The demands of telling their story backwards exposed
significantly more differences between the liars and truth-tellers than
did the task of telling their story forwards. In the reverse-story condition,
the liars gave fewer auditory details, gave less context, hesitated more,
spoke more slowly, moved their feet more and blinked more. By contrast,
among the students who told their stories forwards, the liars differed
from the truth-tellers only in the fact that they moved their hands and
fingers less, probably because of a deliberate effort to appear calm.
Most importantly, when police watched video clips of the students, they
successfully identified far more of the lying students based on the back-
ward story-telling compared with the traditional forward story-telling.
An issue that’s generated a great deal of excitement in recent years
involves using brain imaging to determine whether someone is lying. In
fact, companies such as No Lie MRI have started springing up in America,
claiming to offer just such a service. Although there is research that shows
North Carolina police operating a
polygraph test in 1962.