Forensic - Making A Case - Interviewing Witnesses

recognising faces

weapon focus

the cognitive interview

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Bruce (1999) Experiment 1

Aim: to investigate the relative recognisiblility of internal and external features of a facial composite

Method: Three laboratory experiments

Sample: 30 staff and students from Stirling Uni were paid £2 to sort the composites. 15m, 15f (mean age of 29.2)

Procedure: stimuli were target photographs of 10 celebrities and 40 composite images produced by facial composite programs in common use by the police. each face was clean-shaven and spectacles were avoided. 3 sets of composites were used: 'complete' set, internal features and external features. Independent measures design. Asked to place composite in front of celebrity face in own time

Key Results: whole composites and external features sorted similarly (35% approx correct), internal features only 19.5% correct

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Bruce (1999) Experiment 2

Sample: 48 undergraduates at Stirling Uni, 21m, 27f all volunteers

Procedure: used photo array or line-up with distracter faces or foils making task more difficult. faces or foils made easy or hard to identify. composites presented one at a time along with the photo array and the pps had to pick out celebrity face which matched composite

Key Results: Composites of external features (42%) identified more easily than internal features (24%) - consistent across array type

Conclusions: In both, pps performed just above chance with internal features. pps performed equally well with external features or whole faces. this could indicate that there is something about the internal features of the face that does not work well when trying to reconstruct. the accuracy recall really matters and the witness will be cross examined about how certain they are of what they saw.

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Bruce (1999)


Evaluation Points:

  • determinism vs. free will
  • reductionism vs. holism

Method issues:

  • contrived situation- lacks ecological validity
  • participant variables may affect generalisability

contributes to our understanding of human phenomenon - what features are looked for/found. useful method of investigating cognitive processes

over simplistic- does not take into account other variables. ethnocentric - all uni student that are being paid or want to do the experiment

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Loftus (1987)

Aim: to provide support for the 'weapon focus' effect when witnessing a crime Method: a laboratory experiment

Sample: 36 students from Uni of Washington age 18-31. half recruited through an advertisment and paid $3.50. remainder participated for extra credit in classes                                                                                                            Procedure: 2 sets of 35mm slides. 18 slides in each; people queuing in a Taco Time. control group- person b hands cashier cheque, experimental - person b pulls a gun. all other slides identical, shown for 1.5seconds. pps told study of proactive interference. DV measured by 20-item multiple choice questionnaire

Key results: no significant difference in questionnaire. chance performance on line-up (8.5%). control - 38.9% correct/ 11.1% in weapon. no difference in confidence. eye fixation 3.72 on gun, 2.44 on  cheque.

Conclusions: pps spent longer looking at weapon, difficulty chosing from line-up. second experiment using 80 students supported findings. influence enhanced in real-life when witness is more aroused- increased attentional narrowing

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Loftus (1987)


Evaluation Points:

  • reductionism vs. holism
  • individual vs. situational

Method issues:

  • low ecological validity - won't feel full arousal of situation
  • deception- pps told it was to test for other variables

scientific information - can tell how long they look at the weapon compared to the cheque. useful applications - how it would be enhanced in real situation

ethnocentric- uses students who are paid/ given extra credit. ignores free will in indivduals - cannot intercept, can only see what is on slides/see past the sit.

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Fisher (1989)

Aim: to test the cognitive interview (CI) in the field

Method: Field experiment with actual interviews of real witnesses by serving police detectives

Sample: 16 detectives from the Robbery Division of Dade County, Florida. All experienced - minimum of 5 years with the division

Procedure: record selection of interviews-standard techniques. 4 months-88 interviews recorded, most robbery. pps divided into two groups, one group trained in CI. 7 completed-results used. 7 months more interviews recorded by 2 groups.

Key Results: 7 trained pps drew 47% more info than before, 63% more than untrained. lab-research showed no diff between CI & standard interview (85% statements correct). 94% statements were corroborated. CI's take longer

Conclusions: strong support for CI. more info obtained, no loss of accuracy.

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Fisher (1989)


Evaluation Points:

  • determinism vs. free will
  • individual vs. situational

Method issues:

  • less control of interviews
  • ethnocentric - detectives from that division may all have been trained same

CI applied to other clinical settings - therapists using to develop medical histories. still used by police forces in UK.  

ignores other human complexities - detectives ability and interviewees variables. small sample - cannot generalise for all cases/detectives

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