Forensic Psyc Lie Detection Flashcards
Definition of Deception
“A successful or unsuccessful deliberate
attempt, without forewarning, to create
in another a belief which the
communicator considers to be untrue”
Types of Lies (DePaulo et al., 1996)
- Outright lies
- Exaggerations
- Subtle lies
Reasons to Lie
• 5 reasons (Vrij, 2000):
–To gain personal advantage –To avoid punishment –To make a positive impression on others –To protect themselves from embarrassment/ disapproval –For the sake of social relationships • Self-oriented vs.other-oriented
Frequency of Lying
• American diary study: college students
told 2 lies/day and community
members told 1 lie/day. Most lies were
self-serving (DePaulo, 1996)
• Frequency of lying depends on:
- The personality and gender of the liar
- The situation in which the lie is told
- People to whom the lie is told
- The personality and gender of the liar:
– Extroverts lie more than introverts – Frequency of lies similar between men and women –Women tell more social lies –When dating, women lie to improve physical appearance, men lie to exaggerate earning potential
- The situation in which the lie is told:
– 90% lie to prospective date
– 83% lie to get a job
- People to whom the lie is told:
– Lowest rate of lying with spouses (1/10 interactions- mostly subtle) – Highest rate of lying with strangers – College students lie frequently to their mothers (almost 50% of conversations!)
Three ways to catch a liar
- Observe their verbal and nonverbal
behaviour* - Analyse the content of what they say*
- Examine their physiological responses
Behavioural Indicators of Deception
• Some verbal and nonverbal cues are more
likely to occur during deception than others,
depending on:
1. Emotion
2. Content complexity
3. Attempted behavioural control
Behavioural Indicators of Deception
1. Paul Ekman’s emotional
approach:
– Deception results in different emotions: guilt, fear, excitement (duping delight) – Strength of emotion depends on personality of liar and circumstances of lie – Emotions may influence the liar’s NVB NVB during deception should show signs of stress compared to baseline of typical NVB
Behavioural Indicators of Deception
2. Content complexity:
lying can be difficult to do • People engaged in cognitively complex tasks exhibit different nonverbal behaviours
- Liars may attempt to control their
behaviour
in order to avoid getting caught • When liars do this, they sometimes overcontrol themselves, resulting in behaviour that looks rehearsed and rigid, and speech that sounds too smooth • Nonverbal behaviour is more difficult to control than verbal behaviour:
Behavioural Indicators of Deception:
Verbal and Nonverbal Cues to Lying
Meta-analyses by Sporer & Schwandt (2006; 2007)
• Verbal cues:
- Higher pitch of voice
- Increased response latency
- Increased errors in speech
- Shorter length of description
• Nonverbal Cues:
- Decreased nodding
- Decreased foot and leg movements
- Decreased hand movements
• Liars do not seem to show signs of
nervousness such as gaze aversion &
fidgeting
• Professional lie detectors’ ability to accurately
classify truth and lies is about 55%
• Analyses of nonverbal behaviour are not
accepted as evidence in criminal courts
• Microexpressions:
: A fleeting facial expression
discordant with the expressed emotion and usually
suppressed within 1/5 to 1/25 of a second
• It is difficult to control facial communication and it
can betray a deceiver’s true emotion to a trained
observer (Ekman, 1992)
• Inconsistent emotional leakage occurred in 100% of
participants at least once. Negative emotions were
more difficult to falsify than happiness (Porter & ten Brinke, 2008)
Content Indicators of Deception
Statement Validity Assessment (SVA)
Developed in Germany to determine the credibility of
child witnesses’ testimonies in trials for sexual
offences
• Extended to adults and other types of cases
• SVA accepted in other European courts, but not UK
courts. Opinion in US is divided.
• Has been presented in expert testimony in US, but
main role in guiding police investigations and
decisions of prosecutors
Statement Validity Assessment
• Consists of three major elements:
- Semi-structured interview
- Criteria-based content analysis (CBCA) of
transcribed version of statement given during
the interview - Evaluation of the CBCA outcome via a set of
questions (validity check-list)
CBCA: The Content Analysis
Based on the “Undeutsch hypothesis”: –A statement derived from memory of an actual experience differs in content and quality from a statement based on invention and fantasy (Undeutsch, 1987) • Trained evaluators judge the presence or absence (or strength) of 19 criteria • The presence of each criterion strengthens the hypothesis that the account is based on genuine experience • But, absence of a criterion does not necessarily mean the statement is fabricated (Vrij, 2005)
CBCA Criteria
• General Characteristics
- Logical structure
- Unstructured production
- Quantity of details
CBCA Criteria Specific Contents
- Contextual embedding
- Descriptions of interactions
- Reproductions of conversation
- Unexpected complications during the
incident - Unusual details
- Superfluous details
- Accurately reported details misunderstood
- Related external associations
- Accounts of subjective mental state
- Attribution of perpetrator’s mental state
CBCA Criteria
• Motivation-Related Content
- Spontaneous corrections
- Admitting lack of memory
- Raising doubts about testimony
- Self-deprecation
- Pardoning the perpetrator
CBCA Criteria • Offence-Specific Elements
- Details characteristic of the offence
Why Are These Criteria Absent?
- Lack of imagination in inventing relevant
characteristics - Do not realise judgements based on these
characteristics, so don’t include them - Lack knowledge to incorporate certain
criteria - Difficult to incorporate some criteria
- Wary of including details in case they forget
- Wary of including details that can be checked
- Wary of including certain characteristics in
case their stories sound less credible
From Vrij (2000)
Validity Check List
Finally, to standardise CBCA findings, evaluators
consider alternative interpretations:
– Psychological characteristics (age, verbal and
social skills)
– Interview characteristics (types of questioning)
– Motivation to report
– Investigative questions (consistency with other
evidence)
Does SVA Work?
• Vrij (2005) reviewed first 37 experimental and
field studies on CBCA
• Field studies:
• Statements made by persons in actual cases of alleged
sexual abuse
• Clear forensic relevance, but difficult to establish
ground truth
• Experimental studies:
• Statements of participants who lied or told the truth for
the experiment
• Easy to establish veracity of statement, but differ from
real-life situations
• Results depend on methodological factors
• Field studies comparing children’s statements in
“confirmed”, “unconfirmed”, and “doubtful” cases
yield mixed results
• Experimental studies yield fewer differences
between liars and truth-tellers, but all in expected
direction
• Criterion 3 received the most support: in 80%
of studies truth tellers included more details
• Criteria 4 and 6 also received strong support:
in 69% of studies truth tellers included more
contextual embedding and reproductions of
conversation
• Cognitive criteria (1-13) received more
support than motivational criteria (14-18)
• In 92% of experimental studies, truth tellers
received higher CBCA scores than liars
• Trained evaluators often achieve above chance
classifications
• For experimental studies, Vrij (2005) reported:
– Overall accuracy of 55%-90%
– Accuracy for truths of 53%-91%
– Accuracy for lies of 35%-100%
• Truth bias: CBCA is “truth verifying method”
not “lie-detection technique
Some Concerns About SVA
• No formal decision rules, profiles for truth or
deception, or cut points
• Criteria should be given different weight (Sporer)
• Different types of lies (from subtle to outright) may
yield different levels/kinds of characteristics
• SVA assessments are subjective and inter-rater
reliability can be low, even after extensive training
• CBCA assessments of written statements are time consuming & even training may not improve accuracy
(Akehurst et al., 2004)
• Encourages short-cuts (e.g., SCAN)
Accuracy Rates of Professional Lie
Catchers
Nonverbal Behaviour Truth=55% Lie=55% CBCA 76% 68% • Chance rate = 50% • Nonverbal behaviour: Average scores of 9 studies (mostly lab studies) • CBCA: Based on 13 lab studies • Recent evidence suggests that higher accuracy rates by combining nonverbal and CBCA
A Whole Approach to Detecting Deception
• DePaulo et al. (2003) examined 158(!) cues to
deception:
– Are liars less forthcoming?
– Do liars tell less compelling tales?
– Are liars less positive and pleasant?
– Are liars more tense?
– Do lies include less ordinary imperfections
and more unusual details?
• They found evidence for all 5 of these cues in
deceptive statements
• However, many behaviours showed no
discernable links, or only weak links, to
deception
• Also, no clear cut points or profile for lies and
liars
Difficulties in Detection of Deception
- Lie detection is difficult and there is no
give-away cue - Othello Error: Truth tellers may show
similar behaviour to liars because they,
too, may experience emotions, may have
to think hard, or may have to control
themselves. - Adequate comparisons between truthtelling
and lie-telling are not made (e.g.,
small talk vs. interrogation)
4.Observers seem to have incorrect beliefs
about how liars behave and people,
including police officers, are taught wrong
cues
5.Liars can use countermeasures (e.g., can
train themselves to beat techniques).
6.Deception research is often conducted in
university labs and the stakes aren’t high
enough. It’s hard to establish ground truth
in field studies - The Brokaw hazard: Individual differences
in emotional expression, vocal and body
movement characteristics. - Individual differences in ability to control:
Some people are ‘natural liars’, or have
trained themselves to be very effective
liars. - Cultural differences in nonverbal behaviour
Guidelines for Catching a Liar
If focusing on verbal and nonverbal:
1. Be suspicious – put aside your truth bias
2. Probe – keep on asking questions
3. Do not reveal important information
4. Be informed
5. Ask liars to repeat what they have said
before
6. Watch and listen carefully and abandon
stereotypes
7. Compare liars’ behaviour with their natural
behaviour
