Eyewitness Testimony Flashcards
Episodic Memory
Witnesses asked to remember what happened
Memory for experiences
Literal record but reconstructive process.
Remembering is not like replaying video, but rewriting a story using schemas.
Episodic Memory
Evidence
Memory of story content is affected by the ending
Memory of story content is affected by expectation; changing expectation changes memory of content
Episodic Memory
Implication
Memories may largely reconstructed
Reconstructions are fallible
Eyewitnesses can be very fallible
Stress and Memory
How does stress affect memory?
Complex interaction
Some stress can be good, too much can be bad.
Stress and Memory
Is stress bad for memory?
Children’s memory for events in a hurricane correlates with damage to house; memory / stress relationship consistent with quadratic function.
Stress and Memory
Why quadratic?
Yerkes-dodson curve
Moderate stress and arousal benefits performance
Stress and Memory
Stress narrows processing
Stress limits attention to central details;
weakens memory for peripheral details.
Malleable memory
Suggested response bias or suggested memory bias?
Response to a question may be influenced by phrasing of the question.
“do you get headaches? how occasionally / frequently?”
Is this a change in memory change in response?
Malleable memory
Phrasing biases reported memory for details
Estimates of speed are influenced by phrasing?
How fast was the car travelling when it contacted / smashed / hit / bumped / collided into the other car?
Memory for detail is affected by phrasing?
“did you see a broken headlight?” 7% yes
“did you see the broken headlight” 17% yes
The misinformation effect
Post-event information may alter memory for event information.
Misinformation
“did another car pass red car at the yield sign?”
No Misinformation
“Did another car pass red car at the junction?”
Test
Which of these slides did you see?
No misinformation - 75%
Misinformation - 41% correct
Misinformation Effect
What is it?
Personally witness an event
Read / hear incorrect details about that event afterwards
Incorrect details may infect your memory of the event.
Report what you witnessed
Misinformation Effect
Source Memory Misattribution
Attributing information in memory to the wrong source
Misinformation Effect
What affects it?
Several factors affect susceptibility, such as age and working memory capacity.
Environmental factors moderate the influence of misinformation, such as time delay and exposure time.
Physiological factors may increase the risk of misinformation, such as alcohol withdrawal, sleep deprivation.
Incorrect belief in compromised memory, such as false alcohol ingestion
Differences in memory metrics
Reaction time and confidence
Misled condition - misleading post-event information
Control condition -
neutral post event information
Reaction times and the confidence ratings show that misled subjects are certain of their responses.
Incorrect misled responses are indistinguishable from correct responses.
Powerful Misinformation
Sam Stone study
Classic study 3-6yrs misled about behaviour of class visitor called Sam Stone.
Given stereotype (pre-event)or suggested (post-event) misinformation or both.
Both types of manipulation result in false reports.
Over 20% ppts receiving both types of manipulation maintained their reports were true even when challenged.
Trained professionals could not distinguish between truth and false reports on video footage of ppt testimony.
Powerful memory error
A social contagion
social misinformation
Co-witness recall of items in a picture
Co-witness recall of details of a video event
- 2 ppts watch event separately; slight differences in events. Discuss afterwards. Free recall of event.
71% witnesses included details they did not see.
More powerful than written misinformation
Danger of interference
Natural logical inferences may act as self-generated misinformation.
- false memory for seeing schema-congruent slides that were not shown
- seeing effect slides inspired false memory for seeing ‘cause’ slides that were not shown
Casual inference errors affect memory within seconds.
Exposure time and identification accuracy
Young and old witnesses view crime
Perpretrator visible for either
12sec or 45sec; asked to pick perpretrator out of target present or target absent line up 30 mins later.
Target-present
Young - 42% wrong
Old - 45% wrong
Target Absent
Young - 90% wrong
Old - 80% wrong
False identification and weapon presence
What is weapon focus?
Presence of weapon = weaker identification, because weapon draws attention away from face and or contextually unusual objects draw attention.
False identification and weapon presence
Evidence
Face fixation time is substantially lower with weapon presence
Threatening situations reduce identification rates anyway, but presence of a weapon does so even further; effects are modest.
Ethnicity and Identification
Own-race bias or the other-race effect
Probability of identification error is about 1.5 times higher if target is different race compared to own-race.
An innocent black suspect is 55% more likely to be identified if witness is white as opposed to black.
Ethnicity and Identification
Own-race bias or the other-race effect
Why?
Popular explanation is the contact hypothesis.
The more self-reported contact with opposite race, the higher the accuracy of identification.
Alternative explanation concerns social identity.
Faces perceived as in-group may be processed differently to those perceived to be out-group faces are processed as individuals.
Facial Composites
Why use composites?
Verbal descriptions are impoverished and give a very low level of diagnosticity.
Composites allow a witness to illustrate their memory of the suspect’s face.
Facial Composites
Are composite systems useful?
Composite systems vary widely; some evidence that some systems in use are inadequate
e.g. when students created composites of classmates, others in the same class could not identify the target. Zero identification rate.
Facial Composites
Why?
People do not remember faces as a collection of features but remember faces holistically
The problem with featural composites?
Are featural composites damaging?
Using featural composite may actually weaken later identification.
3 min exposure to face;
Composite group - make composite
Yoked-control - see composite made by previous ppt
Control group - neither make nor see composite 6-photo simultaneous line-up 2-days later.
Composite Target 10% Filler 30% No-choice 58% Force-choice 30%
Facial Composites
Why?
Does the process of using feature-based facial composite systems involve destroying the holistic links between features of the face?
The identification line-up
Structure and function
Most line-ups are single-suspect, but can be multiple suspect.
Can be target-present (perpetrator is there) or target absent,
Given a line-up where the suspect is there, does the witness recognise the suspect?
The identification line-up
What makes a fair line-up?
Functional size should match the actual size of line-up
Functional size is determined by number of members that are reasonable matches to perpretrator description.
Using Line-Ups
How do witnesses identify perpetrators in a line-up?
What cognitive processes do witnesses use to complete the task?
What recommendations can psychology make to improve the accuracy and / or the utility of identifications
Using Line-Ups
Relative judgement vs absolute judgement
Absolute: choose the candidate who is the perpetrator
Relative: choose candidate most like the perpetrator relative to other line-up members.
In simultaneous line-ups, witnesses most likely use a relative judgement.
Relative judgements lead to false identification in target-absent line-ups.
The problem with relative judgement?
Relative judgement gone wrong
#3 is the perpetrator 54% choose correctly when present; when perp is removed, other witnesses make a choice.
If absolute judgement being used, what should happen?
For absolute judgements, expect 54% to make no choice.
Some do (no choice increases by 11%) but most go for the next closest match (poor #2).
Two solutions to relative judgement
Pre-line-up instructions
the perpetrator may or may not be present.
Simple instructions reduce the proportion of false identifications in target absent line-ups
Two solutions to relative judgement
Sequential line-up procedure
Many different variations sequential line-up e.g. multiple laps
Procedure is effective in reducing fale identifications in target-absent line-ups
Sequential line up
Benefits
Reduction in false identifications in target-absent line-ups
Stage mock crime; sequential or simultaneous 6-person line-up; target present or target absent.
ID suspect 50% sequential
ID innocent 17% sequential
Not there 65% sequential
Correct identifications in target present around the same level.
Incorrect identifications in target-absent substantially reduced.
Modern line-up in UK
Live line-ups are rare.
VIPER systems now common.
Foils chosen from over 20,000 person database.
Suspect and 8 foils shown sequentially 10 sec video of each person.
Line-up on DVD can be admisitered anywhere.
Witness asked to watch whole presentation before making any decisions.
Witness sometimes videoed making decision.
