Eyewitness testimony and its limitations

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Eyewitness testimony and its limitations
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Why is eyewitness testimony so error-prone? 1.
Poor view of events and their perpetrators. 2.
May not appreciate events significance at the
time (e.g., con-man). 3. Changes in the
suspect's appearance (e.g. disguises). 3.
Effects of witnesses stress/arousal weapon
focus (e.g. Christianson and Loftus 1991). 4.
Elapsed time since event was witnessed. 5.
Effects of post-event information (e.g.,
witnesses own ruminations listening to other
people's accounts of it misinformation). 6.
Effects of expectations and schemas (both on
initial encoding and subsequent memory). 7. Weak
relationship between witnesses' accuracy and
confidence.
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Wells and Olson (2003) Review factors affecting
eyewitness performance. System variables - under
control of legal system (e.g. interview
procedures, lineup presentation modes,
etc.) Estimator variables - not under control of
legal system (e.g. sex and age of witnesses,
lighting conditions at time of crime,
etc.) Little evidence of effects of witness' sex
and intelligence. Effects of age, event duration,
stress/arousal, cross-race identifications.
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Can we distinguish good witnesses from
bad? Bindemann, Brown, Koyas and Russ (2012)
Considerable individual variation in unfamiliar
face recognition ability (e.g. Burton, White and
McNeill 2010). Could witnesses be tested on
this? Video of a staged theft followed by a
lineup (either TP or TA). Followed by 1-in-10
face identification test (40 trials, half
TP). Overall identification performance was poor.
(TP expt 1 22 correct identifications TP expt.
2 18). For choosers, correlation between lineup
and face identification test performance (r
.70). No good correlation for non-choosers (mixed
bag?)
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Darling, Martin, Hellmann and Memon
(2009) Measured individual differences in
response to Navon letters. Video of a staged bank
robbery followed by a simultaneous (TP) lineup.
No. of participants making correct lineup
identifications Strong global bias 14/ 25
Weak global bias 7 /25
High susceptibility to global interference when
reporting small letters was associated with
better eyewitness identification performance -
individuals with strong "global" processing bias
might be better witnesses than ones with "local"
bias.
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Exposure time and delay MacLin, MacLin and
Malpass (2001) review Increased exposure time
usually improves recognition accuracy, reduces
false identifications. Increased delay usually
decreases recognition accuracy, increases false
identifications. Bahrick, Bahrick and
Wittlinger (1975) Little effect of delay on
familiar face recognition (e.g.
schoolmates). Loftus, Schooler, Boone and Kline
(1987) People overestimate duration of events,
especially when stressed. Read (1995) Increased
exposure time can decrease performance by
increasing witnesses' readiness to make false
identifications (confuse increased familiarity
due to contextual information, with increased
familiarity from perceptual knowledge).
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Effects of expectations and schemas Allport and
Postman (1947) Picture of a black man, and a
white man holding knife. Participants tended to
recall that it was the black man holding the
knife. Bartlett (1932) "War of the Ghosts" -
memory distortions stem from attempts to make
sense of events, relate them to known facts,
beliefs, etc. Neisser (1981) James Dean and
Watergate testimony memory for gist, but
inaccurate about temporal order of events, who
said what to whom, precisely what was said, etc.
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Effects of expectations and schemas Bransford
and Johnson (1972)
Comprehension rating (1-7 scale, 1
"poor") Number of ideas recalled (out of 18).
condition no topic topic after topic before
comprehension 2.29 (.22) 2.12 (.26) 4.50 (.49
recall 2.82 (.60) 2.65 (.53) 5.83 (.49
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Effects of stress and arousal Yerkes-Dodson
"Law" (1908) inverted U-shaped relationship
between stress/arousal and performance. Easterbro
ok (1959) cue utilisation hypothesis stress
narrows attention to central items at expense of
peripheral ones. Steblay (1992) "Weapon focus"
effect decreased recognition due to presence of
a weapon. Christianson (1992) effects of stress
are an interaction between stress level and many
other factors.
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Peters (1988) Effects of stress on face
recognition. Memory for face of nurse and aide
during immunisation. Pulse rate higher for nurse
than aide. Aide identified better than nurse,
from target-present lineup. Yuille and Cutshall
(1986) Naturalistic study of recall by 13
witnesses of a violent crime. Their reports
analysed for accuracy and also compared with
earlier police reports. Accurate memories for
events 4-5 months later. Reported stress level
at time of crime not significantly related to
subsequent recall. But higher-stress witnesses
also closer and more involved in the crime.
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Odinot, Wolters and Koppen (2009) Interviewed
14 witnesses to a supermarket robbery 3 months
earlier. Used CCTV recordings to assess memory
accuracy. 84 of recalled information was
correct. Items provided in free recall were more
accurate than items produced by specific
questions (90 vs 78). Large individual
differences in accuracy (75 to 97). No effect
of misinformation from TV re-enactment of the
crime. Weak accuracy/confidence correlation
(.38). Higher levels of rumination were
associated with higher confidence levels (but not
higher accuracy). Higher levels of self-reported
emotional impact were associated wth greater
accuracy.
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Loftus, Loftus and Messo (1987) Two filmed
versions of an event in a restaurant. Version A
a man pointed a gun at a cashier and she handed
him money. Version B the man gave her a cheque
and she gave him money. Recorded eye-movements
version A subjects fixated on the weapon more
than version B subjects also showed poorer
recall of other details and were less able to
identify the robber from a photo array. Loftus
and Burns (1982) Violent and non-violent films
of a "crime". Subjects in violent version were
less able to recall details of the event. Memory
impaired for details immediately preceding the
violent scene, and for details occurring up to 2
mins earlier.
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Are experiments on the effects of stress
ecologically valid? Tollestrup, Turtle and
Yuille (1994) Lab research tells us about
unaffected witnesses of crimes but not
victims. Suspect identification rates by
real-life witnesses Victims of robbery
46 Witnesses of robbery 33 Victims of fraud
25 Maybe stress enhances recognition?
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Deffenbacher, Bornstein, Penrod and McGorty
(2004) Research confounds defensive and
orienting effects of stress, which either
impede or enhance eyewitness performance. Real
crimes likely to produce defensive responses,
Lab studies likely to produce orienting
responses. Consequence lab studies may
underestimate impairment of eyewitness
performance by stress.
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Valentine and Mesout (2009) Effects of stress
on memory for London Dungeon actor. High stress
17 recognised him. Low stress 75 recognised
him.
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Morgan et al (2004) 509 U.S. Army survival
school trainees. Mock POW experience sleep and
food deprivation, then two types of 45-min
interrogation (high-stress and low-stress). Ident
ification of interrogators by live simultaneous
lineups (15 members), and simultaneous or
sequential mugshots (with/without contextual
cues) 8 members). Overall, positive
identifications of interrogators were higher in
the low-stress condition, and false positives
were lower. Large individual differences in ID
performance 42-45 unaffected by stress 42-50
worse when stressed 8-13 better when
stressed. No relationship between confidence and
accuracy. Overall, identification performance was
poor, despite 30 min's viewing.
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Steblay (1992) Meta-analysis of studies on
"weapon focus". Fairly reliable effect. Pickel
(1998, 1999) Novelty can produce similar
effects.
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Effects of post-event misinformation Loftus,
and Palmer (1974) Confusion between
originally-witnessed event and information from
post-event questioning.
Illustration from "Psychology Themes and
Variations, Sixth Edition, Briefer Version, Wayne
Weiten"
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Effects of post-event misinformation Loftus,
Miller ands Burns (1978) Confusion between
originally-witnessed event and information from
post-event questions.
(a) Participants viewed slides of a simulated
car-pedestrian accident. (b) Half the subjects
got misleading information about the accident
while the others got no misinformation. (Told the
car went past a "yield" sign when actually it
was a "stop" sign). (c) All subjects tried to
remember the original accident "stop" or
"yield"? 75 of controls chose "stop", but only
41 of misinformed subjects.
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Influences of witnesses on each other - "memory
conformity" Memon and Wright (1999) 1995
Oklahoma bombing and hunt for "John
Doe". Wright, Self and Justice (2000) Pairs were
unaware they had seen different versions of a
storybook (present or absent "accomplice" to a
crime). Discussion produced conformity in pairs'
responses. Gabbert, Memon and Bull (2003) Pairs
saw different videos of a "theft". 60 of those
who had not seen the crime came to believe it had
occurred 30 who had seen it came to believe it
had not occurred.
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Paterson and Kemp (2006a) Witnesses are more
likely to recall misinformation provided by a
co-witness than from leading questions or
non-social sources such as the media. Paterson
and Kemp (2006b) Survey of eyewitnesses - most
reported there was at least one other witness. Of
these, 86 said they discussed the event with
their co-witness. Paterson, Kemp and Forgas
(2009) Implies that witness testimonies should
not be treated as independent observations.
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Paterson, Chapman and Kemp (2007) 77 of
witnesses said they were acquainted with other
witnesses at the scene. Hope, Ost, Gabbert,
Healey and Lenton (2008) Pairs saw two different
versions of a video one showed a girl steal
money from a wallet, other did not. 50 of
friends, 50 of couples but only 17 of strangers
said they had seen the girl steal the money, even
though this was not in their version of the
event. Amongst stranger pairings, participants
rated their partner more positively were also
more likely to accept misinformation from them.
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Conclusions Numerous factors affect eyewitness
performance at encoding and retrieval
phases. Encoding affected by stress, although
difficult to investigate experimentally. Retrieva
l is affected by operation of standard memory
effects (schemas, trace decay, interference,
etc.) plus social factors (influence of
questioner and other witnesses) plus individual
differences in witness competence. Exacerbated by
own-race bias (ORB) in cases involving cross-race
identification.