Psyc 321 : Detecting Deception

Why do we lie

Evolutionary

• Adaptive

• Group interaction

What the science shows

Results synthesized from 384 studies with over 24,000 people

We are slightly better than chance

Overall accuracy = 54%

What about police

College students perform slightly better than chance, detectives do not

Problem with police is that they are trained to detect

Training based on faulty cues

Police perform worse after training

But their confidence is higher, they estimate their own accuracy at 77%

Why do we struggle

Better at identifying truth rather than deception

Poor performance for 2 reasons

• Truth bias

> generally, believe that what we’re being told is the truth

> confirmation bias, dangerous decisions theory

• Focus on incorrect cues

Faulty assumptions

lying triggers an emotional/physiological response

Detecting deception

Fundamental belief that deception produces changes

• physiological

> Evaluated using polygraph

• Behavioural

> verbal & nonverbal cues evaluated using various strategies

> observation

> statement analysis

Polygraph

As a person is questioned about a certain event or incident, it measures

1) Heart rate

2) Respiratory rate

3) electro-dermal activity (finger sweatiness)

Galvanic skin response - sweat changes conductance of skin

Uses of polygraph

• Helps in criminal investigations

> suspect asked to take a polygraph test

• Verify crime has occurred

> Victim asked to take a polygraph test

• Monitoring sexual offenders on probation

• Pre-employment screening

> Security agencies and police

Polygraph Training

In US, independent polygraph schools

• Accredited through American polygraph association

• Train police and others

In Canada, polygraph training provided by canadian police college

• 12 week course on techniques, interviewing practices and scoring

• Restricted to police officers

Polygraph research

Laboratory studies

• Simulated criminal behaviour

• Advantage : ground truth is known

• Disadvantage : lacks realism, limited real-world application

Field studies

• Real-life situations and actual suspects

• Advantage : high realism and real world applicability

• Disadvantage : Ground truth is not known

Types of polygraph tests

3 main types of polygraph tests :

• Relevant/irrelevant test

• Comparison/Control question test

• Concealed information test/ Guilty knowledge test

Relevant/Irrelevant test

2 types of questions :

1) Relevant

e.g. “Did you steal the rare gold coin”

2) Irrelevant

e.g., “Is today Monday?”

Assumption :

Larger physiological responses to relevant question = deception

Control question test

3 Types of questions :

1) Irrelevant

• Refer to identity or background

• Used to establish baseline

e.g., “Do you live in Canada?

2) Relevant

• Details about crime being investigated

e.g., “Did you assault Joe on November 11?”

3) Control

• Designed to be emotionally arousing for anyone

• Establish honesty

• Deal with prior behaviour

e.g., “Between the ages of 18 and 22, did you ever deliberately physically hurt someone?”

Control question test (cont)

Procedure

• Pre-test interview

> Control questions developed

> Examiner convinces suspect of polygraph accuracy

• Interview

> All 3 types (mostly 1 and 2)

• Analysis

> compared arousal levels

• Assumption

> Guilty suspects react more to relevant than control

> Innocent suspects react more to control than relevant

Concealed information test/ Guilty knowledge test

Assess if suspect has info that only perpetrator would know

Assumption

• Physiological response to info your recognize

• Not used in Canada or United States

• Used in Israel, Japan

Polygraph Test Accuracy

CQT

• Most studies use confessions as indicative of ground truth

• Unreliable measure

• Majority of guilty suspects are correctly indentified (84-92%)

• However many innocent suspects are falsely indentified as guilty (9-24%)

• Many are classified as inconclusive

CIT/GKT

• Mostly based on laboratory studies

• Very accurate at identifying innocent participants (up to 95%)

• Less accurate at identifying guilty participants (76-85%)

• No field studies have been conducted in North America

• Research in Israel : 98% for innocent; 42% for guilty

Admissibility in Court

United States

• First submitted in Frye v. United States - Rejected

• U.S v. Scheffer - rejected again, ultimate issue

• Admitted in some states under limited circumstances

Canada

Inadmissible

Brain-based deception research : ERP

Event-related brain potentials (ERP)

• Measure brain activity in response to a significant stimulus

• Guilty suspects : stronger response to crime vs. non-crime question

• Laboratory research demonstates relatively high accuracy levels ( 75-90% of participants categorized correctly)

• P300-MERMER had almost perfect accuracy at detecting concealed information - 99%

Brain-based deception research : fMRI

Functional magnetic resonance imaging (fMRI)

• Measures blood flow in brain

• Different brain areas are activated when a person is deceptive vs. truthful

• High accuracy rates (90%)

• Easily beaten by countermeasures

• Limitations of laboratory research

• May have powerful influence on jurors

Thermal imaging

Detects facial warming or changes in blood flow

Nonverbal cues

Underlying assumption same

Act of deception = change

Nonverbal cues are not reliable indicators of deception

• Gaze aversion, self-manipulation

Nonverbal cues (cont)

Stereotype threat

• Anxiety about conforming to a negative stereotype

Liar’s stereotype

• Liars avert their gaze, squirm, touch themselves more, and stutter

Verbal cues

Verbal cues that are indicative of honesty

• Making corrections in account

• Admitting to lack of memory

Verbal cues that are indicative of deception

• Fewer details

• Less compelling accounts

• Less cooperative and more nervous/tense