Case Studies for EWT

Loftus and Palmer (1974)

Leading questions

Loftus and Palmer’s aim

Students were shown a film of a car accident then were asked a series of questions about events leading to the accident. Critical question was about the speed of the car

Loftus and Palmer’s method

One group was asked “How fast were the cars going when they hit each other?”. Other groups were asked the same question but the verb was changed

Loftus and Palmer’s results

Contacted - 31mph, hit - 34mph, bumped - 38mph, collided - 39mph, smashed - 41mph

Loftus and Palmer’s conclusion

Eyewitnesses can be mislead if they are given false information after an event or during questioning. Could result in them providing incorrect details

Loftus and Palmer’s experiment 2

Participants were asked a follow up question of “did you see any broken glass?”. Yes in “smashed” group = 32%, yes in hit group = 14%. Supports substitution hypothesis - memories have been changed

Gabbert (2003)

Post event discussion

Gabbert’s method 

Participants watched a video of a crime filmed from different viewpoints. Some participants got a clear view, others got a different view. Allowed to discuss before recall

Gabbert’s findings

71% of participants recalled events they hadn’t seen but heard in the discussion. Control group - no discussion, so no mistakes were made

Gabbert’s conclusion 

Concluded that this was due to memory conformity, where participants were going along with the group 

Johnson and Scott (1976)

Negative effects of anxiety on accuracy

Johnson and Scott’s aim

To research the weapon focus effect

Johnson and Scott’s method

Participants were told they were apart of a lab study. Low anxiety group heard a casual conversation then saw a man holding a pen and had grease on his hands. High anxiety group heard an argument, a man was holding a knife and blood was on his hands. Participants were asked to identify the man from a set of pictures 

Johnson and Scott’s findings 

Low-anxiety group correctly identified the man, a mean accuracy of 49%. Accuracy dropped to 33% in the high-anxiety group

Johnson and Scott’s conclusion

Anxiety focuses attention on the weapon and away from the other details of the event

Yuille and Cutshall (1986)

Positive effects of anxiety on accuracy

Yuille and Cutshall’s aim

Investigated whether anxiety improves the memory of an event

Yuille and Cutshall’s method

Witnesses from a real-life crime were asked to take part in a study. They were interviewed 4-5 months after the shooting, interviews were compared to police interviews. Accuracy was measured by the number of matching details in each interview. Were asked to rate their stress levels at the time of the incident

Yuille and Cutshall’s findings

Their recall was accurate, matched the police reports. High-stress witnesses at the time of the incident, most accurate recall, 88% accuracy. Low-stress witness had an accuracy of 75%

Yuille and Cutshall’s conclusion 

Anxiety doesn’t have a negative effect on recall of events or the accuracy of eyewitness testimonies. May enhance recall

Geiselman (1985)

Cognitive interviews

Geiselman’s aim

To investigate the effectiveness of the cognitive interview

Geilselman’s method

A sample of 89 students watched a video of a simulated crime. 2 days later, the students were interviewed using the standard police interview or the cognitive interview

Geilseman’s findings

Average number of correct items recalled in cognitive interview 41.5 and in standard 29.3. Average number of incorrect items recalled in cognitive interview 7.3 and 6.1 in standard

Geiselman’s conclusion

The cognitive interview is effective in improving the quantity of info recalled and doesn’t lead to an increase in incorrect info