王育軒
蘇亭維
吳昱輝
Polygraph
Referred to as “lie detector”
 Identify truthful or deceptive answers to
questions.
 It often takes 2~3 hours for a polygraph
exam to be done with high accuracy.

Principles
When a person lies, his/her autonomic
nervous system will make a response of
fear.
 Generally increase heart rate, sweat,
and complexly suppress breathing.
 Measures physiological indices such as
blood pressure, pulse, respiration, and
skin conductivity while answering
questions.

Polygraph Devices
Pneumographs
Respiratory rate
 Rubber tubes filled with air
 The air inside the tubes is displaced
when muscles expand
 Employ transducers to convert the
energy of the displaced air into
electronic signals

Blood-pressure cuff
Blood pressure and heart rate
 As blood pumps through the arm it
makes sound
 The change in pressure caused by he
sound displace the air in the tube

Galvanometer
Galvanic Skin Resistance (GSR)
 Measure the ability of skin to conduct
electricity
 We sweat more when we’re under
stress

Polygraph Devices
Polygraph Data
Polygraphy Exam
A kind of forensic science
 It’s important for the examiners to
carefully design the questions and the
atmosphere
 A well trained examiner
can improve the accuracy
to about 80% ~ 99%

fMRI
Functional magnetic resonance imaging
 Using MRI technology that measures
brain activity by detecting associated
changes in blood flow
 When an area of brain is used, blood
flow to that region

BOLD
Blood Oxygen Level Dependent
 Shows the uses of oxygen by the brain
 Identification of portions using more
oxygen

Lie Detection
Placing a magnetic band on head
 When detecting changes in the
peripheral nervous system, fMRI
catches the lie at source.
 Lying can be distinguished due to
increased prefrontal and parietal lobe
activity
 Lies can be distinguished 78% of the
time

Myth Buster