PSYC 2400 Lecture Notes - Lecture 4: Ground Truth, John B. Larson, Lie Detection

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25 May 2018
Department
Course
Professor
Unit 4: Deception & Malingering
Section 1: The Polygraph: Lie Detector?
History of the Polygraph
Long history of using physiology to detect deception
o Bedouins of Arabia: lick a hot iron, if tongue not burnt considered truthful
o Ancient Chinese: suspects chew rice powder & spit it out, if powder was dry
suspect was guilty
Common principle: if lying or guilty feel nervous, anxious less saliva dry mouth
o Detects anxiety, nervous, fear anything that can increase arousal
Modern Day Polygraph
1917: William Marston
o Blood pressure
Rises when lying
Wonder woman creator lasso
1921: John Larson
o included heart rate (blood pressure), respiration, & skin conductivity (sweat on
hand) as anxiety goes up
o helped solve a murder case
Background & Usage
What is the polygraph?
o Tool to measure physiological activity
What is a polygraph exam?
o Combination interrogation + polygraph: responses to specific yes/no or MC
questions
Usage
o Criminal investigations, security pre-employment screening, disclosure tests
2 types of disclosure tests: (1) treatment of sex offenders (2) condition of
sex offender release
Comparison Question Test
Phase 1: Pretest interview
10 questions developed
o Irrelevant (to the crime): neutral questions (to get a baseline reading)
o Relevant: relating to the specific crime
On Jan 7th did you enter the home of Betty Brown with an axe handle?
o Comparison: related to possible past misbehaviors
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, & 4
Phase 2
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o Questions asked while attached to polygraph
Phase 3
o Score the physiological responses
o Assumptions
Guilty will show greater response to relevant
Innocent will show greater response to comparison
Phase 4
o You failed the polygraph. You had better tell me what happened. I can help you.
Polygraph Tracing
Top blue lines = respiration (one for people who breath more with stomach or chest)
Gree lie = ski odutae he ae goes up, eas they’e respoded
Red line = blood pressure
Bottom of the screen = questions (IR, SR1, C3, etc)
CQT: Problems
Use of extra-polygraph cues
o Not just physiology; pre-test, post-test, how you respond to the directions, &
examiner may be talking to lead detective which may influence the scoring
Crucial role of examiner in preparing comparison questions
Do innocent people show a stronger response to comparison vs relevant questions?
Concealed Info Test
Probes for concealed info not lying
5 questions asked
o Multiple-choice format
o The robber dropped which of the items while escaping:
A knife? A face mask? Car keys? A sack of money? A gun?
Assumptions
o Guilty suspect will recognize the correct alternative
o Innocent suspect will give a similar physiological response to each alternative
CIT: Problems
Applicability
o Only if not much pre-trail media - questions only the suspect would know
Examiner expectancy
o The way it is said may give cues
Assumes suspect has knowledge of correct choice
Does not confirm suspect committed offense
Section 2: Research on the Polygraph
Types of Research: Lab Studies
Advantages
o Ground truth known
o Control over variables
Disadvantages
o Samples used
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Usually uni students which is different from age, education and
koledge of hat’s happeig
o Generalizability
There’s ot really oittig a rie, & thus their arousal/eotios
most likely o’t e the sae
Types of Research: Field Studies
Advantages
o Real suspects
o Trained polygraphers
Disadvantages
o Ground truth not known
Don't know if they are actually guilty - even if they confessed/convicted
in court bc false confessions & sentencing happens
o Extra cues may be used
Physiological & other deception cues
Accuracy of Polygraph Tests
Comparison Question Test
o 84 92% accurate at detecting guilty
o 9 24% of innocent falsely identified as guilty
o High false positive rate
Concealed Info Test
o Around 95% accurate at detecting innocent
o 15 24% of guilty falsely identified as innocent
o High false negative rate
Countermeasures
Aythig the perso does to fool the polygraph
General state
o Drug or alcohol to diminish responsiveness
o These are easy to detect
Specific point
o Physical
If guilty, you want to make sure you respond a lot to the comparison
question
o Mental
Distract mid, so do’t respod to either
Admissibility of the Polygraph
R. v. Beland (1987)
o Polygraph results are not admissible in Canadian courts
o the polygraph has o plae i the judiial proess here it’s eployed as tool to
determine or test the rediility of itesses
Why is the polygraph still being used in police investigations?
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