Reaching a verdict: Persuading a jury

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Pennington and Hastie: Effects of memory structure

Aim: To investigate whether or not presenting the evidence in the order in which an event happens (story order) influencs the jury's final verdict 

Participants: 130 students from Chicago Uni - allocated to 1 of 4 conditions 

Method: Lab experiment 

Procedure: P's listened to a tape recording of a stimulus trial before responding to some written questions 

  • they were told to: reach gulity or not guilty on a murder charge and rate their confidence in their decision 
  • The IV was how the info was presented
  • 4 conditions: prosecution= story defence= stroy, prosectuion= story defence= witness. prosecution= witness defence= story, prosecution= witness defence= defence 

Results: - When prosecution ised story order it persuaded more p's of defendants guilt - 59% - If defence used witness order when prosecution used story even more found guilty - Greatest confidence in story order, least in witness 

Conclusions: Story order is the strongest, if prosecution uses story order the likelihood of guilty verdict is over 50% 

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Loftus: Effect of expert testimony

Aim: to investigate the effect of psychological expert testimony 

Participants: 120 p's from Washington Uni 

Method: P's split into 6 groups - evidence presented to each through a booklet - Discussed evidence for 30 mins before a group verdict was asked to be given - Observers listened in adjoining room and timed the discussing of eye witness testimony

Design: Independent measures; 2 conditions, expert witness for defenece and no expert 

Independent verdict: Whether expert testimony was given or not and the testimony included weapon focus effect 

Results: -Jurors who read the expert testimony spent on average 10 minutes discussing eyewitness testimony evidence - No expert testimony Majority voted guilty - With expert testimony majority not guilty and failed to reach verdict 

Conclusion: Expert testimony prompted more discussion of eyewitness testimony. Expert testimony appeared to increase doubt of defendants guilt. Loftus clained that if both councels used expert testimony, this could confuse a jury.  

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Pickel: Investigation the effect of instruction to

Aim: To find out whether there is a difference in the jury's ability to disregard inadmissible evience depending on the stated legal reason why the evidence in admissible 

Particpants: 236 Bali State Uni - randomly assigned to one of three conditions 

Procedure: On arrival p's listened to an audiotape of trial of an individual accused of stealing $5000 from his manager's office

  • They were asked to complete a questionnaire asking them to make several decisions; one of the witnesses mentioned a past conviction for perjury. The defence objected. 
  • The judge overruled OR he agreed and said nothing else OR he agreed and explained
  • In the questionnaire, questions such as; verdict, how influenced they were by prior convition, the credibility of the witness. 

Results: - Condition 2 were able to follow instructions - Condition 3 could not follow instructions - No evidence found to support the hypothesis that the credibility of the witness would affect the jurors ability to disregard inadmissable evidence

Conclusions: Calling attention to inadmissable evidence makes it more importan to the jury and they pay more attention to it

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