Introduction to eyewitness testimony

Eyewitness testimony refers to the account given by someone who has observed an event, such as a crime or accident, and is often used as evidence in legal settings. However, psychologists have raised concerns about how reliable these accounts are, as various factors can influence a person's memory and recall. This leads to the use of specific research methods to investigate these influences in a controlled way.

The way questions are asked or the level of stress experienced can distort what a person remembers. As a result, experiments are commonly used to test these effects, while ethical and practical constraints often prevent studying real-life witnesses directly.

Key factors influencing eyewitness testimony reliability

• Questioning techniques - The wording of questions can shape how events are recalled, potentially introducing bias.
• Stress levels - High anxiety during an event may impair memory formation or focus attention on certain details while ignoring others.

Example: Loftus and Palmer's study on leading questions

• Aim - A classic laboratory experiment by Loftus and Palmer investigated how leading questions - those that suggest a particular answer - affect eyewitness recall.
• Hypothesis - Eyewitness testimony would be less accurate when leading questions are used in interviews.
• Method - Participants watched a film of a car accident and were then asked questions with varying verbs (e.g., "smashed" versus "contacted") to describe the collision. The IV was the verb in the question, and the DV was the estimated speed of the vehicles.
• Results - Participants exposed to stronger verbs like "smashed" estimated higher speeds and were more likely to report seeing broken glass (which wasn't present).
• Conclusions - Leading questions can alter memory, demonstrating that post-event information influences recall.
• Evaluation - The controlled setting provided clear cause-and-effect insights, but the artificial nature (watching a film) may not fully reflect real-life stress.

Such experiments show how subtle influences can compromise testimony reliability.

Field experiments in eyewitness testimony

Field experiments build on laboratory methods but take place in participants' natural environments, such as public spaces, to capture more realistic behaviours. Like lab experiments, they involve a hypothesis, an IV manipulated by the researcher, and a DV that measures the outcome. The key difference is the setting: field experiments aim for ecological validity - meaning the results better reflect real-world situations - while still trying to control variables where possible.

These experiments often involve staging an event for unsuspecting participants to witness, then testing their memory afterwards. Participants are typically debriefed at the end to reveal the study's purpose.

Key features of field experiments

• Natural setting - The experiment occurs in everyday locations, like a street or workplace, rather than a lab.
• Realistic stimuli - Participants observe actual people or events, not videos, which can make findings more applicable to real eyewitness scenarios.
• Variable manipulation - The IV might involve factors like the presence of a weapon or misleading information during questioning.
• Measurement of recall - The DV focuses on the amount or accuracy of details remembered about the staged incident.
• Control efforts - Researchers minimise external influences, though full control is harder than in labs.

This method balances scientific rigour with real-life relevance.

Comparison between laboratory and field experiments

Field experiments are particularly valuable for assessing how factors like weapon focus - where attention on a weapon reduces recall of other details - play out in authentic contexts.

Case studies in understanding criminal behaviour

Case studies involve in-depth investigations of a single individual or small group, often using interviews to gather detailed information. In forensic psychology, they are especially helpful for exploring the origins of criminal behaviour. These studies provide rich, qualitative data that can reveal unique insights not easily captured by experiments.

Unlike experiments, case studies do not manipulate variables but instead document real-life experiences. They are useful for examining rare or extreme cases, such as serious crimes, where creating similar situations ethically would be impossible. However, to be valuable, case studies must ensure validity and reliability.

Applications of case studies in criminal behaviour

• Building case histories - Therapists use detailed personal histories to understand an offender's background, aiding treatment.
• Revealing origins - They can uncover how factors contribute to criminal acts.
• Rich data collection - Methods include long-term interviews, producing comprehensive insights.
• Ethical considerations - Case studies allow study of real events without engineering harmful situations.

Case studies must be reliable and valid for their results to be trustworthy and useful for the development of future research.