1

A2 Psychology: Unit G543

Making a Case: interviewing witnesses

2

Unit G543: Options in Applied Psychology

• Forensic Psychology– Making a Case

• Interviewing witnessesInterviewing witnesses

• Interviewing suspects

• Creating a profile

– Reaching a verdict• Persuading a jury

• Witness appeal

• Reaching a verdict

3

Factors Influencing Identification

• Weapon focus refers to the concentration of a crime witness’s attention on a weapon and the resulting difficulty in remembering other details of the scene

• Perception experiments have shown that people fixate their gazefixate their gaze for longer, faster and more often on unusual or highly informative objects

4

Factors Influencing Identification

• Eye fixation data– The participant is filmed while looking at

slides or a video clip and minute accurate measurements are made exactly where the eyes are scanning.

– These measurements can then be plotted to reveal the gaze concentration

5

Interviewing Witnesses: Loftus et al (1987)

Aim• To provide support for the weapon focusweapon focus

effect when witnessing a crime

Methodology• A laboratory experiment

6

Interviewing Witnesses: Loftus et al (1987)

Participants• 36 students at University of Washington,

aged 18 – 31 • ½ were recruited through an

advertisement and were paid $3.50 • The remainder participated in exchange

for credit in their psychology classes

7

Interviewing Witnesses: Loftus et al (1987)

Procedure• Participants were told it was a study of proactive interference• 2 sets of 35mm slides were shown • The 18 slides in each series showed people queuing in Taco

Time restaurant • In the control group, person B (2nd in the line) hands the cashier

a cheque • In the experimental condition, person B pulls a gun (the IV) • All the other slides in both series were identical and shown for

1½ seconds • DV measured by a 20-item multiple-choice questionnaire • Participants were also given a line up of 12 head & shoulder

photos in a random sequence, – asked to rate how confident they were of their identification on a

scale of 1 (guess) to 6 (very sure)

8

Interviewing Witnesses: Loftus et al (1987)

Results• Answers to the questionnaire about the slide showed

no significant difference between the two conditions• Chance performance on the photo line up was

calculated to be 8.5% • In the control condition, 38.9% chose the correct

person B (7 people) against 11.1% in the weapon condition (2 people)– statistically significant

• There was no difference in the confidence level of either group

• Eye fixation data showed an average of 3.72 on the gun and 2.44 on the cheque– also statistically significant

9

Interviewing Witnesses: Loftus et al (1987)

Discussion• The participants spent longer looking

at the weapon and therefore had more difficulty in picking the suspect from the line-up – 2nd experiment, using the same procedure

with another 80 psychology students, supported the findings

• This influence may be further enhanced in a real-world situation when a witness will be more aroused and is likely to have increased attention narrowing

10

Interviewing Witnesses: Loftus et al (1987)

• An unusual attack or one involving a weapon is going to affect the witness’s ability to create an E-fit of the attacker