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Electrodermal Activity and Polygraph

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on 15 April 2015

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Transcript of Electrodermal Activity and Polygraph

Electrodermal Activity and Polygraph
Biopac Student Lab ® Lesson 9
Reflection -
What We Learned
How to pass the lie detector
As the polygraph( lie detector) principle focus on: physiological response
Easy to cheat : take drugs
Try to breathe normally such as maintaining a breathing rate of 15-30 breaths per minute
Bit tongue to reduce stress response

I. Count and touch

Basic questions:
Heart rate ↓ ,  EDA ↑ ,
             Respiratoryrate ↓

It is about...
Uses three types of measures:
Electrodermal activity (EDA), respiration, and heart rate

Which are associated with

somatic and special sensory stimuli
cognitive behavior and emotion

III. Yes-No Questions
Subject remains seated and relaxed
faces the Director and listens for instructions
Director asks Subject ten prepared questions and notes Subject’s response
Subject may answer “yes” or “no”
truthfully or dishonestly

Physiological response differences
deceptive and nondeceptive answer

Polygraph as a lie detector
based on:
the involuntary control of automatic nervous system
falsification answer

  autonomic output→ related physiological change→ measured value change

Generally, lying: heart rate↑, start sweating         (EDA increase), respiratory rate↑
Electrodermal activity (EDA)
Human skin: ability to conduct electricity, relay info. within body parts
Measure sweat on our fingertips , sweat → conductivity ↑

Galvanic skin response:
fluctuation of skin’s electrical conductivity which represent EDA
Galvanic skin response
= Galvanic skin resistance(GSR) + Galvanic skin potential(GSP)
GSR: electrical resistant between two electrode within inch apart
GSP: electrical potential between two electrode within inch apart

Two electrodes connected two different fingers
Measure the
electric current
Which proportional with

II. Colored Squares result
Darker colors (e.g black and brown)
Had the higher value
All of measurements increased

Brighter colors (e.g. white and pink)
Had presented lower values
All of measurements decreased

III. Yes-No Questions result
Heart rate↑
Start sweating (EDA↑)
Respiratory rate↑
According to the results,

1. The subject was answering some
basic questions

not change too much

2. The
colour tone
affected emotion of the subject
revealed by changes in her respiratory rate, heart rate, and skin resistance

3. When the subject was
her respiratory rate, heart rate, and EDA increased significantly

1. The subject’s
emotional influence

e.g. heard some funny questions

2. The subject can operate her results from controlling her physiological reactions

3. There was some data error that showed the incorrect result

4. The subject already knew the process of experiment

On the other hand:
People along with the emotion changed,
physiological state

also changed
Typically, in a person who is lying, his or her will have an emotion of distress, characterized by some eyes and eyebrows movements
We can focus on their
micro reaction
to know are they lying
Three tasks
I. Count and touch
Director asks Subject
to say full name
to count backwards from 10
to count backwards from 30 by subtracting increasing odd numbers: (30, 29, 26, 21, etc.)
Director touches Subject on side of face

II. Colored squares
Director arranges colored paper in specified sequence: White, black, red, blue, green, yellow, orange, brown, pink
holds colored paper in front of Subject
instructs Subject to
concentrate on each colored square
for about 10 seconds
lowers paper for five seconds before 

presenting net color
a) Are you currently a student? Y/N
b) Are your eyes blue? Y/N
c) Do you have any brothers? Y/N
d)Did you earn an “A” on the last physiology exam? Y/N
e) Do you drive a motorcycle? Y/N
f) Are you less than 25 years of age? Y/N
g) Have you ever traveled to another planet? Y/N
h) Have aliens from another planet visited you? Y/N
i) Do you watch “Survivor”? Y/N
j) Have you answered all of the preceding questions truthfully? Y/N

Somatic sensory stimuli
(e.g., pain, pressure, touch,) changes in emotion elicit
changes in peripheral autonomic tone and hence the EDA
e.g. the vasodilation of cutaneous blood vessels of the face (blushing) and increased sweating that often occurs in the emotional state of embarrassment

Special sensory stimuli
(vision, hearing, equilibrium, taste, smell) also affect a person’s
emotional state
e.g. the influence of color
the perception of color may affect the subject’s mood and behavior
e.g. Warm colors evoke emotions of warmth and comfort; cool colors such as green, pink, and blue
evoke feelings sadness or indifference

(2004). The Truth About Lie Detectors(aka Polygraph Tests). American Psychological Association. Retrieved from: http://www.apa.org/research/action/polygraph.aspx
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