PSY344H5 Chapter 4: Chapter 4- Deception -2

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7 Feb 2016
Chapter 4: Deception
Polygraph: device for recording an individual’s autonomic nervous system
oMeasurement devices attached to upper chest and abdomen to measure
oAmount of sweat on skin measured by attaching electrodes to ngertips
oSweat changes conductance of skin (skin conductance response)
oHeart rate measured by a partially in"ated blood pressure cu# attached to
oAll measures amplied and can be printed/stored on computer for analysis
oUsed to measure persons physiological responses to questions asked by
oBased on ideal that deception is associated with physiological change
oPoly = many; graph = write
William Marston: psychologist and lawyer who developed systolic blood
pressure test as evidence for innocence
Polygraph training provided by Canadian police college in Canada
oRestricted to police o.cers
o12 week course covers techniques, interviewing practices, and scoring
Application of polygraph
oUsed in criminal investigations
oInsurance companies may request to verify claims
oUsed to assess and monitor sexual o#enders on probation (shows risky
behaviour; fantasies about children)
oEmployee screening
Employee polygraph protection act of 1998 restricted
private companies from using polygraph to weed out those with
criminal tendencies
Limited use to job related investigations of wrongdoing
Only Canadian security intelligence service (CSIS) and some
police departments can require polygraph
Polygraph discourse tests: polygraph tests used to uncover info about
o#enders past behaviour
Polygraph doesn’t detect lying, it shows how some questions elicit a larger
physiological response in guilty people than innocent ones
oSince many physiological states linked to lying common to other
emotional states (fear, anxiety, anger)
2 types of polygraph tests
oComparison question test (CQT): includes irrelevant questions that are
unrelated to crime, relevant questions concerning crime being
investigated, and comparison questions concerning persons honesty and
past history prior to event being investigated
Aka control question test
Commonly used to investigate criminal acts
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Includes pre-test interview (examiner learns about suspects
background, tries to convince suspect of accuracy of test by
doing a rigged test run)
Followed by series of 10 (yes/no) questions administered while
suspects physiological responses are measured
Irrelevant questions: refer to suspects identity or
personal background (not scored, used as baseline)
Relevant questions: deal with crime being investigated
Probable lie comparison questions (aka control
questions): emotionally arousing for all respondents and
typically focus on persons honesty and past history prior
to event being investigated
Relevant and comparison questions establish
Guilty people react more to relevant questions than
comparison questions
Innocent people react more to comparison questions than
relevant questions
oInnocent people know they are telling the truth
about relevant question so they will react more
strongly to general questions about honesty and
past history
Then examiner scores charts and ends with post-interview where
results discussed
Examiners in past used global scoring: incorporating all
available info, including physiological responses, suspects
demeanour, and info in case le
Today, numerically score charts to ensure decisions based
solely on physiological responses
oConcealed information test (CIT): designed to determine if person
knows details about a crime
Originally called guilty knowledge test
Does not asses deception but instead seeks to determine
whether suspect knows details about a crime that only person
who committed it would know
Series of questions in multiple choice format
Each question has only 1 correct option (aka critical option) and
four options that are foils (alternatives that could t crime but
are incorrect)
Guilty suspect assumed to display larger physiological response
to correct option than to incorrect options
Innocent person who doesn’t know details of crime will show
same physiological response to all options
Principle that people will react more strongly to info they
recognize as distinctive or important than to unimportant info
Likelihood that innocent person with no knowledge of crime will
react most strongly to critical alternative is 1/5 for each question
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Common to measure palmar sweating (skin conductance
Lack of widespread use b/c
Examiners believe in accuracy of CQT, not motivated to
use di.cult to construct CIT
For law enforcement to use CIT, salient features of crime
must be known only to perpetrator (no media
Not typically used in Canada, but used in Japan/Israel
Criticism: test will only work if suspect recalls details of crime
Criminals may have memory interference from past
Polygraph test has 3 outcomes
oTruthful, deceptive, and inconclusive
oIf deceptive, examiner tries to obtain confession
Validity of polygraph techniques
oAccuracy is determined under ideal circumstances by presenting info
known to be true and false to individuals and measuring their
corresponding physiological responses
oLaboratory studies
Volunteers (university students) simulate criminal behaviour by
committing a mock crime
Ground truth: knowledge of whether person is actually guilty
or innocent
Known by experimenter in these studies
Can compare di# polygraph tests and control for variables
But limited in real life application (participants have little to fear
if they fail test)
oField studies
Real life situations and actual criminal suspects
Compare accuracy of original examiners (those who conduct
actual evaluation of suspect) to blind evaluators
Blind evaluators only given original examiners charts and are
given no info about suspect/case
Original examiners exposed to extra polygraph cues (info about
case, behaviour of suspect during test)
Even though taught to ignore cues of suspect, many are
in"uenced by them
Di.cult to establish ground truth (physical evidence, eyewitness
testimony, DNA not available)
Reliance on confessions to establish ground truth increases
polygraph accuracy
CQT studies use confessions to classify suspects as guilty or innocent
oMost guilty suspects correctly classied as guilty
oFor innocent suspects, accuracy ranges from 55-78% (mostly inconclusive)
o9-24% of innocent were falsely identied as guilty
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