PSYC 2004 Unit 7: Eyewitness
Testimony
Memory
- Changes in memory occur without awareness of distortions.
- Memories change because they are constructed and reconstructed.
- Repeated processing of memory causes it to change.
Role
- Stages of memory
- Encoding
- Information converted for storage
- Attentional saturation
- Encoding everything we see can be overwhelming and maladaptive
- Can recognize familiarity, but don’t focus on all details
- Factors that affect encoding
- Attention
- Unexpectedness
- Witness Involvement
- State of the Witness
- Storage
- Information retained in memory
- Types of Memory Retrieval
- Recall memory
- Reporting details of a previously witnessed event/person
- Recognition memory
- Reporting whether current information is the same as previous information (e.g., lineups)
- Factors affecting retrieval
- Inferences (people guess)
- Stereotypes (people fill in gaps)
- Partisanship (biases influence memory)
- Scripts/Schemas (typical vs actual info)
- Emotional Factors (anxiety blocks retrieval)
- Context Effects (cues trigger memories)
- Time (memory slippage)
- Post-event information
- Enhancing memory: Other witnesses may improve memory
- Compromising memory: Other witnesses may impair memory
- Retrieval
- Information retrieved from memory
- Factors that affect perception
- Change blindness
- Occurs when a change in a visual stimulus is introduced and the observer does not notice it.
- Stress
- Yerkes-Dodson Law: Some stress, but not too much, is optimal
Eyewitness Research
- How do we study eyewitness issues?
- Archival data
- Naturalistic observations
- Laboratory simulations (most common)
Independent variables
- Estimator variables
- Variables that are present at the time of the crime and cannot be changed
- e.g., age of witness
- System variables
- Variables that can be manipulated to increase or decrease eyewitness accuracy
- e.g., type of lineup used
Dependent variables
- Recall of event/crime
- Recall of perpetrator
- Recognition of perpetrator
- Measuring recall of information
- Amount of information reported
- Type of information reported
- Accuracy of information
- Proportion of correct information, omission errors, commission errors
- Measuring recognition of information
Aiding Eyewitness Memory
Police questioning
- Goal: collect complete & accurate information
- Fisher et al. (1987) found that police officers…
- Interrupted witnesses often
- Asked short, specific questions
- Asked off-topic questions
- Asked leading questions
- Findings replicated with more recent research
- Leading questions → Misinformation Effect
- Implications of poor questioning
- Loftus & Palmer (1974)
- “Smashed” vs. “Hit”
- “Smashed” reported higher speeds
- Affected future recall
- Did you see any broken glass?
- “Smashed”: 32% said yes
- “Hit” 14% said yes
- Wording of the question matters
- Loftus & Palmer (1974)
- Take-home messages:
- False information or information provided after an event can influence memory
- Subtle phrasing differences may bias witnesses’ responses
- Explaining the Misinformation Effect
- Misinformation acceptance hypothesis
- People guess, try to appease experimenter
- Source misattribution hypothesis
- Can recall both memories (accurate & inaccurate ones) but can’t differentiate between them
- Memory impairment hypothesis
- Original memory replaced with new, incorrect memory
Interview strategies
- Techniques to aid eyewitness memory
- Hypnosis
- Can increase amount of details
- But, these details are not necessarily accurate
- Hypnotized person is more suggestible, and is equally as confident in accurate and inaccurate details.
- Not typically permitted as evidence in Canadian courts
- Cognitive Interview
- Based on principles of memory storage & retrieval
- Used primarily for witnesses
- Memory retrieval techniques:
- 1. Mental reinstatement of context
- 2. “Report everything”
- 3. Recall event in different order
- 4. Change perspectivee
- Compared to standard interviews & hypnosis, the CI…
- Increased amount of accurate information
- 30% increase overall
- Enhanced Cognitive Interview
- Included principles of social dynamics + the memory retrieval principles used in the CI
- Additional components
- Rapport building
- Supportive interviewer behaviour
- Transfer of control
- Focused retrieval
- Witness compatible questioning
- Recognition Memory
- 1. Live lineups or photo arrays
- 2. Video surveillance records
- 3. Voice identification
Lineups
- Identification
- Suspect - a person the police suspect committed the crime (may be innocent or guilty)
- Perpetrator - the guilty person
- Lineups help determine if the suspect is the perpetrator
- Procedures
- Lineups contain the suspect and a set of foils:
- Two types of strategies for selecting foils:
- 1. Similarity-to-Suspect Strategy
- Matches lineup members to the suspects appearance
- 2. Match-to-Description Strategy
- Matches items that witness provided in description
- Identification decisions
- Target-present lineps
- 1. Correct identification
- 2. Foil identification
- 3. False rejection
- Target-absent lineups
- 1. Correct rejection
- 2. Foil identification
- 3. False identification
- Live vs. Photo lineups
- Canadian police generally use photo array because they are:
- Easier to construct
- Portable
- Suspect doesn’t have the right to counsel
- Photos are static (i.e., no variation in suspect behaviour)
- Less stressful for witness
- Video popular option used in the UK
- Lineup procedures
- Simultaneous lineup
- Present all members at the same time
- Relies on relative judgment
- Sequential lineup
- Presents members one at a time
- Relies on absolute judgment
- Simultaneous vs. Sequential Lineup
- Mixed findings
- More correct rejections for sequential lineups
- However, not all research supports this finding
- Other lineup procedures
- Show-up
- Only suspect shown to witness
- Witness is aware of who police view as a suspect
- Can result in bias
- Walk-by
- Conducted in natural environment
- Witness taken to publica location where suspect is likely to be
- Biased lineups
- Types of biases:
- 1. Foil bias
- 2. Clothing bias
- 3. Instructions bias
- Case of lineup misidentification
- Jennifer Thompson was raped at knifepoint
- Identified Ronald Cotton as attacker
- Cotton pleaded innocence
- Jennifer’s positive ID compelling evidence for conviction
- 11 years later, Cotton allowed DNA test
- Guidelines for improvement
- 1. The person conducting the lineup or photo array should not know which person is the suspect.
- 2. Witnesses should be told that the perpetrator may not be present in the lineup
- 3. The suspect should not differ from foils based on witnesses description (match to description strategy)
- 4. Witness’ confidence should be assessed prior to feedback
- *Kassin added: “lineup procedures should be videotaped”
- Guidelines for improvement
- 1. Photo lineups should be videotaped.
- 2. Inform witnesses that clearing innocent suspects and identifying guilty ones are equally important.
- 3. Lineup should be presented sequentially.
- 4. Officers should not provide feedback.
- Video surveillance Errors are still common
- Voice identification
- Accuracy increases when:
- Longer voice samples
- No Accent
- Accuracy decreases when:
- Whispering or emotion
- More foils
- Target voice occurs later in lineup