crime psych Flashcards
The Persuasive Power of Eyewitness Testimony
Experimental Conditions in a Robbery/Murder Case:
Circumstantial evidence only
Circumstantial evidence plus an eyewitness declaring, “That’s the one!”
Circumstantial evidence, eyewitness testimony, and a defense lawyer discrediting the witness (e.g., proving the witness had 20/400 vision and was not wearing glasses during the crime)
Juror Convictions by Condition:
Eyewitness testimony significantly increased conviction rates, even when circumstantial evidence was weak.
Even when discredited, jurors were still likely to believe eyewitness testimony.
Eyewitness Testimony and Error
A study on a staged robbery (Wells et al., 1979) found that:
Both correct and incorrect eyewitnesses were believed 80% of the time.
Jurors placed more trust in eyewitnesses who provided trivial details (e.g., describing a hole in the perpetrator’s jeans) rather than those who focused on the suspect’s face.
Witness confidence was only modestly correlated with accuracy.
Witnesses were more persuasive when they expressed absolute certainty (e.g., Jennifer Thompson’s “100% confidence” in Cotton’s guilt).
How Memory Becomes Distorted
- schemas
- retelling bias
- Feedback effect
Schemas
Preconceptions about people, objects, or events that influence how new information is interpreted.
Retelling Bias
Testimony can be influenced by who the witness is speaking to (e.g., changing tone when speaking to defense vs. prosecution lawyers).
Feedback Effect
Witnesses given confirming feedback (“Good, you identified the suspect”) were more confident in their identification, even when they were incorrect.
Experiment on Feedback Effect:
Students watched a security camera video of a store incident and were asked to identify the suspect from a lineup (which did not include the actual perpetrator).
Despite all picking an innocent person, those who received confirming feedback were significantly more certain in their identification.
58% of participants claimed the feedback did not influence their certainty—despite clear experimental evidence that it did.
Study on Traffic Accidents:
Participants viewed a crash and were asked about the speed of the cars.
Those who heard the word smashed estimated higher speeds (40.8 mph) than those who heard hit (34.0 mph).
One week later, many who heard smashed falsely recalled seeing broken glass.
False Memory Studies:
Participants shown doctored photos of themselves on a hot air balloon ride later “remembered” the event.
In another study, children were asked weekly for 10 weeks if they had ever gone to the hospital with a mousetrap on their finger—58% later falsely remembered it happening.
Lie Detection Cues:
Face: Small expressions vs. exaggerated ones.
Body Language: Fidgeting, restless posture.
Voice: Higher pitch, more hesitations.
Verbal Style: Vague responses or excessive detail.
Uncooperativeness: Evasive behavior may indicate deception.
Complex Lies: More speech errors, slower responses, more “uh,” “um,” and pauses.
Simple Lies (e.g., omissions): Fewer errors, more confident delivery.
Factors That Influence Jury Decisions
Defendant Attractiveness
A large-scale BBC Television experiment presented a burglary case to 64,000 viewers, with only the actor playing the defendant changing:
A stereotypical “criminal-looking” defendant was convicted more often than a baby-faced actor with large blue eyes.
Implications: Racial profiling and bias in legal proceedings.
Factors That Influence Jury Decisions
The Power of Statistics in Court
Even when people understand statistics, they may not be persuaded unless the numbers are part of a compelling narrative.
Example: A DNA match with odds of 1 in 950 trillion still led jurors to conclude, “So you’re saying there’s a chance?”
Group Influences on Verdicts
Minority Influence – A consistent, confident dissenting juror can persuade others.
Group Polarization – Initial majority opinion strengthens over deliberation.
Leniency Bias – When evidence is weak, jurors tend to shift toward acquittal over time.
Conclusion
Eyewitness testimony is a powerful but fallible form of evidence. Psychological research highlights how memory distortions, feedback effects, and biases influence the reliability of witness accounts. While reforms have been proposed, including improved lineup procedures and limiting the weight of eyewitness testimony in court, the risk of wrongful convictions remains. Cases like Ronald Cotton’s serve as stark reminders of the consequences of misplaced trust in human memory.
