Suspects, Lies and Videotape: An Analysis of Authentic High

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Transcript Suspects, Lies and Videotape: An Analysis of Authentic High

Mann, Vrij & Bull
When people are lying… What
behaviours do you expect
them to have?
Background and context
Most people think that, when
lying, people:
 Avoid eye contact
 Increase fidgeting nervous
 Nervous movements
Previous research most people
decrease in non functional
movements and become
unnaturally still.
There is no relationship between
eye contact and deception
Background and context
Until now lab experiments
have required participants to
tell a lie or the truth about
beliefs and opinions.
But some of these settings
differ from real life
settings not generalizable
Background and context
Why do these kind of
experiments are not
1. Participant is asked to lie
- Some experimenters
have allowed participants
to choose if lying or telling
the truth but the lie is
told “for the sake of the
Background and context
2. Participants will usually be
videotaped and they know
their lying/truth behaviour
will be later analysed by
3. Telling lies of negligible
consequence unethical to
offer punishment for lying.
*So there is still a possibility
that high-stake liars are
more nervous and perform
nervous behaviours.
Background and context
So, to address all
these points,
another study was
designed to analyse
behaviours of
spontaneous liars.
Where? Police
department highstake situations
with suspects.
Background and context
Very difficult to catch non-verbal
behaviour in people who lie.
 Vrij & Mann (2001) analysed video
tapes of murderers– lots of insight
into the topic.
Liars may not display nervous
behaviours because they are
probably experiencing other
processes simultaneously
increased cognitive load or
attempted behavioural control.
These, could negate nervous
Background and context
Other points to be considered:
1. Liars in this study will probably have
to think hard to make their lies
convincing or otherwise sentence
Background and context
*People involved in complex cognitive tasks
make fewer movements:
- Fewer illustrators: arm and hand
movements are designed to supplement
- Self-manipulations (scratching, etc)
- Other subtle hand movements.
*Increase in cognitive load results in:
- A neglect of body language, reducing
overall movements.
- Increased speech disturbances
- Longer pauses before an answer
- Eye-blink suppression
Background and context
2. Liars often try to control their
behaviour in order to give a
credible impression to the
“Motivational impairment”:
(DePaulo&Kirkendol): the
higher the motivation to
succeed in the lie, the greater
the likelihood that liars will try to
control their behaviour.
There is a strong belief that
liars usually move away their
gaze and make nervous
movements, so liars will try to
mantain eye contact and avoid
movements. cultural
stereotype of liars.
Background and context
How does this happen?
movements and
Not aware
of body
s control
Background and context
Summary: no single
pattern of behaviour is
related to deception.
 Pinocchio’s growing
nose doesn’t exist
 We also need to
consider individual
METHOD: Participants
16 police suspects (13 males, 3 females=
4 juveniles: 3 aged 13, 1 aged 15
15 caucasian (english), 1 asian
All interviews were done in english
 Theft (9)
 Arson (2)
 Attempted rape (1)
 Murder (4)
Police detectives Kent
County, UK
Recollection of
videotaped interviews
where suspect had lied at
some point and told the
truth at another (serious
investigated files to
confirm if subjects were
lying or telling the truth
Suspects deny
evidence is shown to
them  they confess.
Results: 16 clips of
Truths and lies had to be
of the same nature
(about events, not
personal details for ex)
Number of clips per
participant varied
 For each
participant, min 2
clips: 1 truth, 1 lie
Vrij & Winkel:
differences between
lying and truthtelling behaviour are
independent of
length of the clip
Dependent variables
2 observers independently
coded 8 behaviours
Recorders where (single) blind
to truth/lie variable and
Interrater reliability inter
Ideally 2 observers coded
everything, but ethically, the
least possible people to code.
Dependent variables
Behaviours observed:
 Gaze aversion (seconds participant
looked away)
Blinking (frequency)
Head movements (frequency of head
Self-manipulations (frequency)
Illustrators (freq of arm/hand
Hand/finger movements (frequency)
Speech disturbances
Pauses (seconds)
*Strong consistency between 2 coders
Dependent variable
The total length per
minute of footage
for each behaviour
was calculated.
Result: 1 truthtelling score, 1 lietelling score for
each behaviour, for
each participant.
Lying was accompanied by a
decrease in blinking and an
increase in pauses.
As expected, individual
differences did occur and there
was no behaviour that all liars
50% showed increased head
movements and 50% a
56% showed more gaze
aversion and 44% showed less
gaze aversion
69% showed a decrease in
hand and arm movement
during deception
 33% showed an increase.
Most reliable indicator of
deception: blinking and
 81% paused longer
 81% blinked less
This study has the most extensive which
has examined deceptive behaviour in
real-life, in high-stakes setting.
2 significant differences occured:
 Suspects blinked less and paused longer
while lying.
Some support for the
cognitive load process
less blinking and longer
pauses  possible
indicators of cognitive
Blinking strongest
indication that cognitive
load affects more
suspects’ behaviour than
Nixon effect: increase in
blinking (he blinked more
than 50 times/min during
However, increased
cognitive load results in a
decrease in blinking, but
conclusions are
speculative (no
Large individual
differences were
shown probably no
typical lying behaviour
Probably the most
reliable indicator of
deception change in
the individual’s normal
DISCUSSION: Limitations
1. Different interviewers were
used for different participants
2. Sometomes more than
one interviewer was present
3. The total number of
people present, varied
depending on the number of
interviewers, attorney, etc.
In this study, experimenters
managed to control this
Researchers can’t be
sure that the clips that
they compared were
They didn’t compare
high-stake liars to
people who are trying
to plead their
innocence when
falsely accused.
The experimenters
couldn’t obtain such
Both liars and truth
tellers might
experience similar
 16 participants is not a
large sample
Difference between
this sample and the
whole population
limitation for