PSYC 3210U Lecture Notes - Lecture 3: Polygraph, Ground Truth, John B. Larson
Unit 4 - The Polygraph: Lie Detector
History of the Polygraph
• Long history of using physiology to detect deception
- Bedouins of Arabia: lick a hot iron, if tongue not burnt considered
truthful
- Ancient Chinese: suspects chew rice powder and spit it out, if powder
was dry suspect was guilty
• Common principle
- If lying or guilty → feel nervous, anxious → less saliva → dry mouth
Modern Day Polygraph
• 1917: William Marston
- If blood pressure goes up -> more likely of lying
- First person to use physiology to measure if someone is lying or not
- Created wonder woman
• 1921: John Larson
- Not only blood pressure but also included heart rate, respiration, and
skin conductivity (sweat)
- Helped solve a murder case where they polygraphed the suspect
Background and Usage
• What is the polygraph?
- Tool to measure physiological activity
- Measures respiration, blood pressure and sweat on skin
• What is a polygraph exam?
- Combination interrogation + polygraph: responses to specific yes/no or
MC questions
- Examiner watched your responses to the questions
• Usage
- Criminal investigations, security pre-employment screening, disclosure
tests (most recent)
- Wil be polygraphed before entering a high security job
Comparison Question Test (Reid, 1977)
• Phase I: Pretest interview
• 10 questions developed
find more resources at oneclass.com
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- Irrelevant: neutral questions
- Relevant: relating to the specific crime
➢ On January 7 did you enter the home of Betty Brown with an axe
handle?
- Comparison: relates to possible past misbehaviours
➢ Have you ever lied to a person in authority?
➢ Before you were 25 did you ever verbally threaten to hurt someone?
Comparison Question Test Phases 2, 3 and 4
• Phase 2
- Questions asked while attached to polygraph
- Will always have comparison and relevant questions side by side
- Will do questions in 3 sets (10 questions -> break -> 10 questions ->
break and so on)
• Phase 3
- Score the physiological responses
- Assumptions
➢ Guilty will show greater response to relevant
➢ Innocent will show greater response to comparison
• Phase 4
- Examiner comes back and tells individual the results
- You failed the polygraph. You had better tell me what happened. I can
help you
• Blue line = breathing (chest and stomach)
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• Green line = skin conductivity
• Red line = blood pressure
Comparison Question Test (CQT): Problems
• Use of extra-polygraph cues
• Crucial role of examiner in preparing comparison questions
• Do innocent people show a stronger response to comparison vs relevant
questions?
Concealed Information Test (Lykken, 1981)
• Probes for concealed information – not lying
• 5 questions asked
- Multiple-choice format
- The robber dropped which of the items while escaping:
➢ A knife? A face mask? Car keys? A sack of money? A gun?
• Assumptions
- Guilty suspect will recognize the correct alternative
- Innocent suspect will give a similar physiological response to each
alternative
Concealed Information Test (CIT): Problems
• Applicability
• Examiner expectancy (gives obvious cues)
• Assumes suspect has knowledge of correct choice
• Does not confirm suspect committed offense (only assumes that suspect
has knowledge)
Practice Question #1
Durig the first years of your life, did you eer thik of hittig soeoe? This
is an example of what type of polygraph exam question?
➢ Answer: A comparison question
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
History of the polygraph: long history of using physiology to detect deception. Bedouins of arabia: lick a hot iron, if tongue not burnt considered truthful. Ancient chinese: suspects chew rice powder and spit it out, if powder was dry suspect was guilty: common principle. If lying or guilty feel nervous, anxious less saliva dry mouth. If blood pressure goes up -> more likely of lying. First person to use physiology to measure if someone is lying or not. Created wonder woman: 1921: john larson. Not only blood pressure but also included heart rate, respiration, and skin conductivity (sweat) Helped solve a murder case where they polygraphed the suspect. Combination interrogation + polygraph: responses to specific yes/no or. Examiner watched your responses to the questions: usage. Criminal investigations, security pre-employment screening, disclosure tests (most recent) Wil be polygraphed before entering a high security job. Comparison question test (reid, 1977: phase i: pretest interview, 10 questions developed.
