Eyewitness%20testimony%20and%20its%20limitations

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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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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 performance, increases
false identifications. Delay has little effect
on familiar face recognition (e.g. schoolmates,
Bahrick, Bahrick and Wittlinger 1975). 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 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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Loftus, Loftus and Messo (1987) Subjects saw one
of 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. Valentine and Mesout (2009) Effects
of stress on memory for an actor in the London
Dungeon. High stress 17 recognised him. Low
stress 75 recognised him.
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Steblay (1992) Meta-analysis of studies on
"weapon focus". Fairly reliable effect. Pickel
(1999) Novelty can produce similar effects.
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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.
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Influences of witnesses on each other 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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Cross-race identification (own-race
bias) Meissner and Brigham (2001) Meta-analysis
of 39 studies, over 30 years. Affects
recognition, lineups, RT studies, Photofits,
etc. Over twice as likely to identify own-race
than other-race. Less hits, more false alarms
with other-race faces than with own-race faces.
False alarms worse with short exposure times,
and long delays between study and test. ORB
accounts for 15 of variance in discrimination
accuracy. Robust finding, but reasons for it are
unclear.
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Sporer (2001b) Two aspects to ORB (a) impaired
recognition (b) shift in response bias
(increased false positives, due to increased
readiness to say "seen before"). ORB generally
strongest for Whites recognising other races -
occurs with many different races. Sporer
(2001a) Review of non-laboratory studies of
ORB. Archival studies in Britain and Germany
suggest non-Whites and non-German suspects are
more likely to be identified in lineups. Field
studies (photospread of experimenters posing as
shop "customers") show ORB.
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Explanations for Own-Race Bias (ORB) Prejudice
Only indirectly, by reducing contact with other
races. Physiognomic variability Little evidence
for this (Goldstein and Chance 1979)
. Inter-racial contact Most studies find
increased contact reduces ORB (e.g. black South
Africans Wright, Boyd and Tredoux 2003). May do
this by perceptual learning (differentiation by
focusing on task-relevant facial aspects).
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Sporer (2001b) In-group/out-group model of face
processing. 1. In-group face - automatic
configural processing. 2. Out-group - face
categorisation occurs, and step 1 is bypassed.
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Valentines (1991) Multidimensional Face Space
model
Distinctive (big nose, close-set eyes)
Narrow
Eye separation
Nose length
Long
Short
Typical
Wide
Distinctive (small nose, widely-set eyes)
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Face-space models and perceptual
expertise Valentine (1991) Other-race faces are
encoded in Multi-Dimensional Face Space with
respect to inappropriate own-race norms.
Exemplar-based model
Vector-based model
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Sporer (2001b) 5 factors influence identifying
an other-race face 1. Attentional processes at
encoding may be influenced by social disregard
cues or categorization processes (which may lead
to inadequate processing). 2. Perceptual
expertise (related to contact). 3.
Distinctiveness of target relative to other
people in that ethinic group may not be apparent
to out-group witness. 4. Difficulty of task,
affected by inter-item similarity and fairness of
a lineup (constructed by out-group member). 5.
Social factors, e.g. witness' motivation to make
a positive identification, biased lineup
instructions, police officers' expectations.
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MacLin and Malpass (2001) "Ambiguous race face
effect". Hispanic participants who saw composites
with "hispanic" hair recognised them better than
hispanic participants who saw same composites but
with "black" hair.
Bernstein, Young and Hugenberg (2007) Image
background colour affected face recognition if
participants thought it signified
in-group/out-group membership.
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Motivational factors in other-race effect? "Own
gender" bias (Wright and Sladden 2003). "Own-age"
bias (Wright and Stroud 2002 Anastasi and Rhodes
2006 Perfect and Moon 2005). Harrison and Hole
(2009) Trainee teachers better than other
students at recognising children's
faces. Difficult to explain by perceptual
expertise OR Sporer's model. Motivation?
Expertise promoted by need to differentiate
exemplars? Also explains Wright, Boyd and
Tredoux's (2003) ORB results.
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Conclusions Numerous factors affect eyewitness
performance at encoding, storage and retrieval
phases. Encoding affected by stress, although
difficult to investigate experimentally. Retrieva
l affected by operation of standard memory
effects (schemas, trace decay, interference,
etc.) plus social factors (demand
characteristics, influence of questioner and
other witnesses). Exacerbated by ORB in cases
involving cross-race identification.