Determining boundary conditions of the weapon focus effect

Research Institution / Organisation

Queen Margaret University

In Collaboration With

Pia Pennekamp (QMU), Matthew Gibson (QMU), and other undergraduate and master’s level students

Principal Researcher

Dr Jamal K. Mansour

Level of Research

Professional / Work-based

Project Start Date

September 2015

Research Context

Background
Prior research demonstrates that the presence of weapons can negatively affect an eyewitness’ memory for the perpetrator of a crime (i.e., the weapon focus effect). When a weapon-involved crime occurs, eyewitnesses often provide less detailed descriptions of the perpetrator, than when no weapon was involved. However, much of this research has focused on why the effect occurs (due to the unusualness of a weapon/object vs. the threat it represents). Little work has considered the conditions under which the effect is found. To better apply this work to practice, it is important to understand the variety of conditions under which the weapon focus effect occurs (i.e., boundary conditions).

Aim
To inform considerations of eyewitness evidence when the crime involved a weapon or an object used as a weapon, by examining potential boundary conditions of the weapon focus effect.

Objectives

This project explores 

  1. the types of objects that produce a weapon focus effect (e.g., a Millwall brick)

  2. whether the visibility of an object influences the weapon focus effect (e.g., a gun brandished vs. holstered)

  3. whether how objects are used influences the weapon focus effect (e.g., shooting vs. hitting with a gun)

  4. how witnessing conditions influence the weapon focus effect (e.g., how long the criminal was in view for)

Research Methodology

This project comprises a series of experiments which broadly use the same experimental method and are typically conducted in the lab or online. Participants first view a mock-crime (typically a video). Following the video, they are asked to describe the actor(s) and the event, and then to answer questions about the actor(s) and event. After a delay, they make a lineup decision and indicate how confident they are in their decision. Lineups contain either a guilty suspect or an innocent suspect.

In our first experiment, the mock-crime video depicted a bank robbery. We manipulated the type of object held by an actor (gun, knife, flamingo, or binder) as well as the duration of the mock-crime video (long, short) and how "busy" the background was (lots of eye-catching objects, few eye-catching objects). Memory for the robber and event was poorer when the robber wielded a weapon (gun, knife) or a flamingo (i.e., an unusual object) than when the robber wielded a binder. Furthermore, when the robber wielded a weapon, guilty suspects were less likely to be identified from the lineup than when the robber wielded a flamingo, with both less accurate than when the robber wielded a binder. The duration of the event had a complex effect on performance. You can read more in our published paper.

One experiment, recently concluded, focused specifically on how objects are used. In this experiment, we varied the object held by an actor (newspaper or gun) and how the object was used (in an expected or unexpected way). Analyses of these data are ongoing.

An ongoing experiment is exploring whether the weapon focus effect for a holstered/concealed gun is similar to that for a gun that is brandished/waved.

Interim reports and publications

​Mansour, J. K., Hamilton, C.M., & *Gibson, M. T. (2019). Understanding the weapon focus effect: The role of threat, unusualness, scene complexity, and duration. Applied Cognitive Psychology, 33(6), 99-107. https://doi.org/10.1002/acp.3515
*this paper is freely available at https://eresearch.qmu.ac.uk/handle/20.500.12289/9582

Date due for completion

June 2025
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