more and his/her blood pressure and heart rate rises. This is
an idea that has been around since the 19th century. The first
polygraph was invented in 1921 by a medical student named
John Larson. Here “poly” means many, and “graph” is the
graphical representation of some data. This method involves
deducing lies through analyzing physiological responses to
a series of questions asked by the interviewer. Only a part
of the test includes recording instruments and questioning
techniques. A typical examination has a phase in which the
subject is guided through the process, where the technique is
explained and each test question reviewed. This interview is
conducted to ensure that the subject understands the ques-
tions and to induce a fear of being deceptive.
Source: http://www.studioprops.net
The instrument typically used to conduct polygraph tests con-
sists of a polygraph recorder that has three indicators of au-
tonomic arousal: heart rate/blood pressure, respiration and
perspiration. Heart rate and blood pressure data are collected
by an arm encircling cuff placed on the upper arm. Changes
in respiration are detected by pneumographs, an instrument
for recording the thoracic (spine area near the thorax) move-
ments or volume changes during respiration. The measure-
ment of sweat, which is scientifically known as the measure-
ment of galvanic skin resistance, is detected by a two-piece
galvanometer attached to two of the subject’s fingertips. The
galvanometer records how much current is passed through
the skin by sending a small electrical current. If a subject per-
spires, the conductivity of the skin increases thereby increas-
ing the amount of current
passed. All the information
provided by these instru-
ments is recorded by the pol-
ygraph graphically. That is,
information is given out as a
graph in real time. Experts can
detect small changes in these
graphs and detect whether a
person is lying or not.
The accuracy of polygraphs
has highly been questioned
throughout its existence.
Some people, such as spies,
are specially trained to dis-
guise their feelings and can
easily pass a polygraph test.
Furthermore, the end result
depends heavily on the poly-
graph examiner. Hence the re-
sult is heavily biased. Howev-
er, these tests are still carried
out today due to a number of
reasons. The willingness to
face a polygraph test shows
that the suspect has nothing
to hide, and at the same time
the idea of facing a test can
provoke fear and can prompt
the guilty to confess.
More advanced methods to
detect lies through physiolog-
ical changes have been pro-
posed and implemented ever
since. Facial thermal imaging
is a technology that maps fa-
cial blood flow. Anxiety is as-
GAUGE Magazine University of Peradeniya
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