Presentation on theme: "EYEWITNESS TESTIMONY Dr. Don Hine Lecture Overview Why is eyewitness accuracy important? Key factors leading to eyewitness errors. Eyewitness confidence."— Presentation transcript:
Lecture Overview Why is eyewitness accuracy important? Key factors leading to eyewitness errors. Eyewitness confidence and accuracy. Strategies for increasing eyewitness accuracy.
Why is research on eyewitness accuracy important? Judges and jurors are heavily influenced by eyewitness testimony.
Simulated Murder Trial (Loftus, 1979) 3 experimental conditions: evidence only evidence + eyewitness evidence + discredited eyewitness Results evidence only - 12% guilty evidence + EW - 72% guilty evidence + discredited EW - 60% guilty
Why is research on eyewitness accuracy important? Judges and jurors are heavily influenced by eyewitness testimony. Eyewitnesses are often wrong!
Eyewitness error is the single largest factor leading to false convictions in the US. 2,000 – 10,000 wrongful convictions per year Eyewitness error has been implicated in 90% of convictions that have been overturned on the basis of DNA evidence.
Some Key Factors Leading to Eyewitness Errors 1. Lying 2. Reality Monitoring 3. Transference 4. Attention Failure 5. Memory Schemas 6. Post-Event Misinformation 7. Police Line-Ups
6. Post-Event Misinformation Memory of crime or accident may initially be quite accurate, but may become distorted by post-event experiences. Talking with other witnesses Talking to police Other activities
Standard Post-Event Misinformation Paradigm 1 2 3
Loftus & Palmer (1974) View slide presentation of car accident Ss were randomly assigned to one of two groups: How fast was the red car going when it HIT the blue car? How fast was the red car going when it SMASHED into each the blue car?
Results (Loftus & Palmer) HIT condition – Ss estimated the car to be traveling 34 mph. SMASHED condition – Ss estimated the car to be traveling 41 mph.
One week later... “Do you remember seeing any broken glass at the scene of the accident?” HIT Condition - 14% remember glass SMASHED Condition - 32% remember glass
1. Vacant Slot Hypothesis Original information not encoded into memory, and false post-event information is simply inserted into vacant slot.
Test of Vacant Slot Hypotheses Loftus et al. (1980) Slide show of car travelling through a stop sign and hitting another car. 2 experimental conditions. Misleading question that suggests that “stop” sign was actually a “yield” sign. No misleading information. DV - Memory accuracy for sign type.
2. Co-Existence Hypothesis Two versions of the original event are stored in memory original version altered version
3. Substitution Hypothesis Original memory is transformed or replaced by post-event information by a destructive updating mechanism.
Co-Existence or Substitution? Second-guess study (Loftus, 1979). Phase 1: Subjects view slide sequence of man reading a yellow book. Phase 2: Post-event misinformation is provided that suggests the book was blue, NOT yellow Phase 3: Recall phase in which subjects must choose from 3 alternatives (yellow, blue, and green).
Competing Hypotheses Co-Existence: subjects who choose blue as first choice should choose yellow as second choice - because both memories are stored. Substitution: subjects who choose blue as first choice, should be equally like to choose yellow or green as second choice - because original memory for yellow has been erased.
Results Subjects who chose blue as their first choice were equally likely to yellow or green as second choice.
Selection of Fillers (non-suspects) Probability of a mistaken identification is strongly affected by the selection of fillers. Good line-ups include fillers who fit the general description of the perpetrator. Bad line-ups include fillers who do not fit the description of the perpetrator.
Instructions to Eyewitnesses The content of instructions provided to eyewitnesses significantly influences their ability to make accurate identifications.
Instruction Study (Malpass & Devine, 1981) Ss witness a staged crime. Condition 1 Led to believe culprit was in lineup. No “none-of-the-above” option. Condition 2 Told culprit may or may no be in lineup. Explicit “none-of-the-above” option.
Instruction Study Results % False IDs Instruction Set Culprit Absent Lineup
Eyewitness Confidence US Supreme court explicitly lists eyewitness confidence as one key features that judges and jurors should attend to when making judgments about the credibility of eyewitness testimony.
Lawyers Beliefs about the Relationship between Eyewitness Confidence and Accuracy Brigham and Wolfskiel (1983) found 75% of the state prosecutors they interviewed believed that confident eyewitnesses were more likely to be accurate than tentative witnesses.
Jurors Beliefs about the Relationship between Eyewitness Confidence and Accuracy Studies with mock jurors consistently find that eyewitness confidence is the most powerful single predictor of jurors beliefs about whether or not an eyewitness should be trusted (Wells et al., 2001).
Eyewitness Confidence and Accuracy Most research suggests that correlations between eyewitness confidence and accuracy is very low. Wells and Murray (1984) conducted a meta-analysis of 31 studies and found an average correlation of.07.
Improving Eyewitness Accuracy Cognitive Interview Recommendations for Lineups
Cognitive Interview: Principles Principle 1 Memory retrieval is enhanced by a match between the encoding context and the retrieval context. Retrieval Mnemonics Mentally reinstate the environment and personal context at the time of the witnessed event. Interview witnesses at the scene of the crime.
Cognitive Interview: Principles Principle 2 There are multiple retrieval paths for any encoded event. Retrieval Mnemonics Describe event sequence in different orders, both forward and backward. Describe event from different viewpoints.
Cognitive Interview Studies (Geiselman et al., 1985, 1986) Ss viewed 4-minute film of violent crime Interviewed 48 hrs later standard interview cognitive interview hypnosis interview
Reasons to Prefer CI over Hypnosis Requires less interviewer training. Faster than hypnosis induction. Less susceptible to leading question effects. Some people can’t be hypnotised.
Strategies for Improving Lineups (Wells et al. 2000) Rule #1 – The person who conducts a lineup or photo-spread should not be aware of which member of the lineup or photospread is the suspect. Prevents police officers from advertently or inadvertently influencing eyewitness responses.
Strategies for Improving Lineups (Wells et al. 2000) Rule #2 – Eyewitnesses should be told explicitly that the suspect might NOT be in the lineup or photo-spread, and therefore should not feel that they must make an identification.
Strategies for Improving Lineups (Wells et al. 2000) Rule #3 – The suspect should not stand out in the lineup or photo-spread as being different from the “fillers” based on the eyewitness’s previous description of the culprit or based on other factors that would draw extra attention to the suspect.
An Example of a Good Photo-Lineup (from Wells, 2000)
Strategies for Improving Lineups (Wells et al. 2000) Rule #4 – A clear statement should be taken from eyewitnesses at the time of the identification, and prior to any feedback, about his or her confidence that the identified person is the actual culprit.
Eyewitness Testimony: Summary Eyewitness testimony has a strong influence on judges and juries. Eyewitness accounts are often inaccurate. Eyewitness confidence is often unrelated to accuracy. Accuracy can be improved by using the cognitive interview and proper lineup procedures.