Flashcards in Forensic Psyc Eyewitness Memory Deck (21)
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Background
• Forensic investigations are an attempt
to reconstruct a past event
Physical evidence (hair, fibers, fingerprints,
DNA)
Eyewitness evidence (statements and
identification)
• Both forms of evidence are handled
very differently by the criminal justice
system
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Background
• Physical evidence
Protocols for collecting,
preserving and interpreting
physical evidence are
dictated largely by forensic
scientists.
Protocols have a scientific
foundation, grounded in
what experts suggest are
optimal ways to avoid
contamination.
Physical evidence is often
‘circumstantial
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• Eyewitness Evidence
Typically collected by non-specialists in human
memory.
Protocols for collecting, preserving and interpreting
eyewitness evidence has not incorporated scientific
psychological research to the extent that it could.
Often directly links suspect to crime.
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Why might the difference exist?
• Memory misconceptions: Loftus & Loftus
(1980), survey of 169 individuals: 84%
agreed with the statement;
• Metaphors of memory as like a videorecorder
- you just have to press ‘play’
and it all comes back to you…
“Everything we learn is permanently stored in
the mind, although sometimes particular details
are not accessible. With hypnosis, or other
special techniques, these inaccessible details
could eventually be recovered.”
• BUT psychologists know that memory is
fallible, malleable, reconstructive, susceptible
to suggestion, etc.
• So, it’s not surprising that eyewitness
testimony is amongst the least reliable forms
of evidence.
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How do we know eyewitness evidence is so
unreliable?
1. DNA exoneration case studies
“Eyewitness misidentification is the single
greatest cause of wrongful convictions [in the
US], playing a role in nearly 75% of convictions
overturned through DNA testing.” (www.innocenceproject.org)
BUT these are examples rather than scientific
evidence. They give a potentially misleading
message.
2. Eyewitness research
Over 2000 publications to date
show that errors can occur at:
Encoding (e.g., viewing
conditions)
Storage (e.g., exposure to
post-event information)*
Retrieval (e.g., interview
procedures; ID techniques)
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The Misinformation Effect
Exposure to incorrect information about
an event after it has occurred often
causes people to incorporate this
misinformation into their memories
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Three ways to encounter post-event
information:
1. Leading questions about the event
(e.g., by police officer or
therapist); Covered in Psyc1001
2. Hearing about the event from the
media
3. Hearing about the event from
other witnesses
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1. Leading Questions: Research
• Ps shown a film of a traffic
accident
• Ps asked “How fast were the
cars going when they
smashed into each other”
gave higher speed estimates
than those asked, “How fast
were the cars going when they
hit each other?”
• A week later, Ps in the
smashed condition were more
than twice as likely to recall
broken glass when in fact
there was none
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2. Media Report: Research (Wright & Stroud, 1998)
• Showed Ps pictures of a shoplifting
incident.
• Ps then read a brief summary of the
crime, which included some incorrect
details.
• Results indicated that Ps incorporated
the incorrect details from the summary
into their memories
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Co-witnesses Talk
• Eyewitness Survey (Paterson & Kemp, 2006a)
– Majority of witnesses report discussing the event
with a co-witness
– Main reason for discussing the event with a cowitness:
Providing information
– More witnesses reported that they had been
encouraged by the police to discuss the event
with co-witnesses than discouraged
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The Legal Perspective
Hearsay: “a witness’s assertions of relevant facts
should be based upon his or her own experiences”
and not those of another (Forbes, 2003, p. 59).
• American, British, (and Australian?) guidelines
discourage discussion between witnesses
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Police Survey (Paterson & Kemp, 2005)
• 74% of police reported receiving instructions to
prevent discussion
• Police reported benefits of discussion
– Refresh and reinforce memory
– Recovery from trauma
– Witnesses with different stories impeded court
– Police officers discuss with one another
• Police reported impracticalities of preventing it
– Discussion prior to arrival
– Impossible to prevent
– Mother and child
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Comparing Ways to Encounter
Misinformation (Paterson & Kemp, 2006b)
Purpose
• To investigate the relative impact of different
methods of encountering postevent information.
Participants
• 105 undergraduate psychology students
(81 females, 24 males)
Procedure
1) Stimulus: Crime video
2) 1st Delay: 1 week
3) Postevent Information:
Leading questions
Media report
Indirect co-witness information
Co-witness discussion with confederate
Control
4) 2nd Delay: 20 minutes
5) Individual Memory Task: Free recall, short
answer, and recognition questionnaire
Results
• No effect of Postevent Information Type on
memory accuracy for control items
For accurate information, direct and indirect co-witness conditions more accurate
For misleading information direct and indirect co-witness conditions less accurate
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Social Contagion of Memory
• Research has consistently shown that participants
often report misinformation that was previously
stated by a co-witness during discussion
• This phenomenon has become known as:
“Social contagion of memory” (Roediger et al., 2001)
“Memory conformity” (Wright, Self, & Justice, 2000)
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Warnings about Misinformation
(Paterson, Kemp, & McIntyre, 2011)
Purpose
• To determine whether the detrimental effects of
co-witness misinformation can be decreased by
warning participants about misinformation.
Participants
• 119 undergraduate psychology students
(97 females, 22 males)
Procedure
1) Stimuli: crime video (two versions)
2) 1st Delay: 20 minutes
3) Memory Elaboration:
Different-video group (Misled)
Same-video group (Non-misled)
No Discussion
4) 2nd Delay: 1 week
5) Warning: (general, specific, or none)
6) Individual Memory Task: Free recall,
recognition questionnaire, and identification
• For misled items, misled participants are less accurate than other conditions
For neutral items, misled participants are more accurate than other conditions
Misled participants reported more accurate propositions than non-misled participants
Warning had no effect on the recognition questionnaire or the free recall
Results
• Discussion Type and Warning had no effect
on eyewitness identification accuracy or
confidence
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Why does the misinformation effect occur?
Main theories explaining the misinformation effect:
1. Modification of the memory
a) Alteration theories
b) Coexistence theories
2. Social and demand factors (McCloskey & Zaragoza, 1985)
The different theories for the misinformation effect
have different practical implications
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Why does the misinformation effect
occur?
1a. Alteration hypothesis:
Original
information does not exist because:
i. Vacant slot explanation (Wright, 1995)
Misinformation is accepted because
individual failed to encode original
information
ii. Overwriting explanation (e.g., Loftus, 1979)
Postevent information overwrites the
original memory
iii. Blend explanation (e.g., Loftus, 1985)
Ps encode misinformation in same cognitive
structure as the original information which
results in a blend (e.g., colours, numbers).
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Why does the misinformation effect
occur?
1b. Co-existence hypothesis:
Both
memory for original event and
misinformation are stored and each
memory is capable of being recovered.
Original memory is not replaced, but is
less accessible than the subsequent
misleading information, perhaps owing
to:
Recency effect (Murdock, 1962)
Retroactive interference (McGeoch, 1932)
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Why does the misinformation effect
occur?
2. Response bias
in favour of postevent information
Due to recognition test procedure
Ps who don’t remember/notice the
critical detail in the original event and
are not given any misinformation reply
at chance rate.
Ps who don’t remember/notice the
critical detail in the original event and
receive misinformation have no reason
to doubt misinformation presented to
them (e.g, McCloskey & Zaragoza, 1985).
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Factors influencing susceptibility to the
misinformation effect
People will be less susceptible to
misinformation if:
They first make a public statement
about what they witnessed (Loftus, 1977)
There is less time between witnessing
the event and the presentation of
misinformation (Loftus et al., 1978)
The misinformation blatantly contradicts
what was originally witnessed (Loftus, 1979)
Source of the misinformation in not
credible
They are forewarned that they may
encounter misinformation (Greene, Flynn, & Loftus, 1982)
However, warning them that they have
encountered information a week after the
fact, doesn’t help combat the
misinformation effect (Paterson, Kemp, & McIntyre, 2011)
Factors that increase susceptibility to the
misinformation effect:
Age (young and old)
Hypnosis
Suggestibility (Gudjonsson Suggestibility
Scale)
Misinformation is repeated
Misinformation is peripheral
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