What is eyewitness testimony?
Eyewitness testimony (EWT) is the evidence given by someone who saw an event, such as a theft or road accident. Juries trust it, especially when the witness sounds confident. But memory is reconstructive: we rebuild it from stored pieces plus expectations each time we recall it. So details can be lost or changed.
Two main things change EWT: misleading information and anxiety.
Misleading information
Leading questions
A leading question suggests the answer. In a classic study, students watched car-crash clips and were asked how fast the cars were going when they "hit" or "smashed" each other. Stronger verbs gave higher speed estimates (about 55 km/h for "hit" vs 65 km/h for "smashed"). A week later, more of the "smashed" group falsely said they saw broken glass.
- Response-bias explanation: the word only changes how people answer, not the memory.
- Substitution explanation: the word actually changes the stored memory.
Post-event discussion (PED)
Witnesses who talk afterwards often mix up their memories. In one study, pairs watched a crime from different angles; after discussing, most witnesses reported details they could not have seen themselves. This is memory contamination or memory conformity (going along with others to agree, or truly believing the other was right).
Evaluation: lab studies use video clips, so stress and consequences are low (low ecological validity). Real witnesses may be less easily misled about key facts, but more about small details.
Anxiety
- Negative effect: high anxiety narrows attention. Weapon focus: when a weapon is present, people stare at it and recall the face poorly. Here anxiety lowers accuracy.
- Positive effect: stress hormones can make memory sharper. Real witnesses to a shooting gave very accurate accounts months later, even those most stressed.
- Yerkes–Dodson (inverted U): accuracy rises with moderate anxiety and falls when it is very high. This can explain the mixed results.
Evaluation: weapon focus may be about surprise (an unusual object) rather than fear. Ethics limit how much fear researchers can create.
Improving accuracy: the cognitive interview
The cognitive interview (CI) is a police interview method based on how memory works. Its four techniques:
- Context reinstatement: mentally go back to the scene: weather, smells, feelings.
- Report everything: say every detail, even small ones that seem unimportant; they can trigger others.
- Change the order: recall from the end or middle, which breaks schema-driven "usual" stories.
- Change perspective: describe it as another witness or the offender would have seen it.
The enhanced CI adds building rapport, letting the witness control the pace, reducing distractions and asking open questions.
Evaluation: studies find the CI gives roughly a third more correct detail. It takes more time and training, and can slightly increase incorrect details too. Some police forces use only parts of it.
Try it: the leading-question test
Show two groups of friends the same 20-second video of a busy street. Ask group A: "Did you see a red bus?" and group B: "Did you see the red bus?" (there is no red bus). Count how many say yes in each group. "The" suggests it was there, so more people usually say yes.
Key formulas and definitions
- Key term: Eyewitness testimony = evidence given by a person who saw an event
- Key term: Leading question = a question that suggests an answer
- Key term: Post-event discussion = witnesses talking after the event, which can contaminate memory
- Key term: Weapon focus = attention drawn to a weapon, so other details (like the face) are missed
- Key term: Yerkes–Dodson law = performance rises with moderate arousal, then falls (inverted U)
- Key term: Cognitive interview = context reinstatement, report everything, change order, change perspective
Worked examples
1. A police officer asks, "What colour was the knife he was holding?" Why is this a problem?
It is a leading question: it assumes there was a knife and that he held it. The witness may add a knife to their memory (substitution) or say a colour just to answer (response bias).
2. Two shoppers saw a robbery. One says the robber had a beard; after chatting, the other also says beard. Explain.
Post-event discussion caused memory conformity: the second witness either went along to agree or truly absorbed the detail into their memory.
3. In a study, 18 correct details were recalled with a standard interview and 24 with a cognitive interview. What is the percentage increase?
Increase = 24 − 18 = 6. 6 ÷ 18 × 100 ≈ 33%.
4. A bank clerk at gunpoint cannot describe the robber's face but describes the gun perfectly. Which effect, and what is a counter-argument?
Weapon focus: anxiety narrows attention to the weapon. Counter: it may be unusualness (surprise) rather than fear that draws attention.
Common mistakes
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