This presentation is regarding the technology involved in the polygraph machine. It describes the procedures involved in carrying out the so called 'Lie detector ' test for criminal investigation and other purposes.

1. POLYGRAPH MACHINE
 BY- VIPUL CHAVAN
 11-509
 Biomedical Engineer

3. INTRODUCTION TO POLYGRAPH
 A polygraph measures and records several physiological
indices such as blood pressure, pulse, respiration, and skin
conductivity.
 Commonly referred to as “lie detector”.
 Invented in 1921 by John Augustus Larson.
 US federal government agencies such as the FBI and the
CIA and many police departments such as the LAPD use
polygraph examinations to interrogate suspects and screen
new employees.
 Within the US federal government, a polygraph
examination is also referred to as a psychophysiological
detection of deception (PDD) examination

4. General theory behind polygraph
Arousal  Increased ANS activity
○Sweating
○Respiration changes
○Vasoconstriction
○Pulse rate
○Blood pressure
○Specific patterns of arousal during questioning
could indicate guilt or lying

6. Polygraph – Relevant/Irrelevant Test
 Earliest method of polygraph testing
 Two kinds of questions
 Relevant
○ Deal with issue at hand
 Irrelevant
○ Deal with outside facts or details
 Assumption:
 A liar or guilty person will be more aroused by relevant
questions than Irrelevant ones, while an innocent person
will show no difference
○ So, if arousal(relevant) > arousal(irrelevant) = lying

7. Polygraph – Comparison Question
Test
 Most common method of polygraph interrogation
◦ Developed by John Reid
 Begins with extensive pre-test interview
 Three kinds of questions:
◦ 1. Irrelevant
 Is your name Orenthal James Simpson?
◦ 2. Comparison (aka probable lie)
 E.g. “Have you ever physically harmed someone”
◦ 3. Relevant
 E.g. “Did you kill Nicole Brown Simpson”

8. • A liar become more aroused by lying to
the relevant questions than the
comparison questions
• An innocent person will be more
aroused by the comparison questions
• Arousal(relevant) > Arousal(comparison) =
guilty