Eyewitness Testimony Case Studies

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  • Created by: Grace
  • Created on: 14-04-14 12:14

Loftus and Palmer - Eyewitness Testimony

Experiment 1:

Method: Participants shown film of car crash. Then asked a series of questions like 'How fast do you think the cars were going when they hit?' In different conditions the word hit was replaced with 'smashed', 'collided', 'bumped' or 'contacted'.
Results: Participants given the word 'smashed' estimated the highest speed (average of 41mph) and those given the word 'contacted' gave the lowest estimate (average of 32 mph)

Experiment 2:

Method: Participants split into 3 groups. One group given the verb 'smashed', another 'hit' and the third, control group wasn't given an indication of speed. A week later ppts were asked 'Did you see any broken glass?'
Results: Although no broken glass in film, ppts said they saw broken glass in the 'smashed' condition than any other.
Conclusion: Leading questions can affect accuracy of people's memories of an event.
Evaluation: Has implications for questions in police interviews. Was an artificial exp-watching a video is not as emotionally arousing as a real-life event, potentially affects recall. A laterstudy found that participants who thought they'd witnessed a real robbery gave a more accurate description of the robber. 

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Valentine and Coxon - Effect of Age on EWT

Method: 3 groups of participants (children, young adults and elderly people) watched a video on kidnapping. They were asked a series of leading and non-leading questions about what they had seen.

Results: Both the elderly people and the children gave more incorrect answers to non-leading questions. Children were misled more by leading questions than adults or the elderly.

Conclusion: Age has an affect on the accuracy of EWT.

Evaluation: This has implications in law when children or elderly people are questioned. However, the experiment was artificial and so wasn't as emotionally arousing as the same situation would have been in real lif - the study lacks external validity. The study could have seeked like an experiment into how well people remember things from TV, which isn't the same as real life.

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Loftus - Weapon Focus in EWT

Method: In a study with an independent groups design, participants heard a discussion in a nearby room. In one condition, a man came out of the room with a pen and grease on his hands. In the second condition, the man came out carrying a knife covered in blood. Participants were asked to identify the man from 50 photographs.

Results: Participants in condition 1 were 49% accurate. Only 33% of the participants in condition 2 were correct.

Conclusion: When anxious and aroused, witnesses focus on a weapon at the expense of other details.

Evaluation: The study has high ecological validity, as the participants weren't aware that the study was staged. However, this means that there are also ethical considerations, as participants could have been very stressed at the sight of the man with a knife.

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Geiselman et al - Effect of the Cognitive Intervie

Method: In a staged situation, an intruder carrying a blue rucksack entered a classroom and stole a slide projector. Two days later, participants were questioned about the event. The study used an indepedent groups design - participants were either questioned using a standard interview procedure or the cognitie interview technique. Early in the questioning, participants were asked 'Was the guy with the green backpack nervoud?'. Later in the interview, participants were asked what colour the man's rucksack was.

Results: Participants in the cognitive interview condition were less likely to recall the rucksack as being green than those in the standard interview condition.

Conclusion: The cognitive interview technique enhances memory recall and reduces the effect of leading questions.

Evaluation: The experiment was conducted as though a real crime had take place in the classroom - it had high ecological validity. The experiment used an independent groups design. The disadvantage of this is that the participants in the cognitive interview condition could have been naturally less susceptible to leading questions that the other group.

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