A police officer in a reflective jacket standing near two people

We're helping police to better capture evidence by understanding how stress affects memory

 The pioneering work of Professor Lorraine Hope is already having positive impacts in the field

New research from Professor Lorraine Hope, Professor of Applied Cognitive Psychology, is showing how memory performs in dynamic, high-stress situations – and how a psychological approach to interviewing victims, witnesses and suspects can benefit investigations too.

The research, conducted by Professor Hope and her research collaborators over the past 15 years, examines how the memories of those responding to challenging incidents can be impaired.

Professor Hope's research typically uses 'live' high-stress scenarios to study officer's experiences during an operation.

One of these 'live' scenarios saw a physically-exhausted police officer enter a known criminal’s trailer home, where guns and knives were in view. Moments later, the suspect came in from another room, unarmed but shouting.

Researchers found that less than 60 seconds of all-out exertion – as might happen when an officer has chased a suspect or engaged with a resistant criminal – can impair an officer's ability to remember details of the incident. It also impaired their ability to identify the person involved.

Professor Hope said: 'Police officers are often expected to remember, in detail, who said what and the details of a physical struggle. The results of our tests indicate it may be difficult for them to do this.

'As exertion increases to a high level, cognitive resources tend to diminish. The ability to fully shift attention is inhibited, so even potentially relevant information might not be attended to. And ultimately, memory is determined by what we can process and what we pay attention to.'

Police officers are often expected to remember, in detail, who said what and the details of a physical struggle. The results of our tests indicate it may be difficult for them to do this

Professor Lorraine Hope, Professor of Applied Cognitive Psychology 

Professor Hope’s work also examines how victim and witness evidence can be better captured by using evidence-based tools and techniques informed by psychological science.

One such tool is the Self-Administered interview (SAI©). A powerful investigative tool, the SAI© uses a standardised protocol of clear instructions and questions, which allow witnesses to provide their account of what happened in an incident.

Scientific tests and live use of the SAI© by police forces in a number of countries have shown that witnesses who provide an account using SAI© provide more information than if they're simply asked to report what happened.

Completing an SAI© also strengthens witness memory, meaning witnesses are protected against forgetting, and against exposure to potentially distorting post-event information.

Live usage trials with police forces in the UK, Norway and The Netherlands have shown that the SAI© can facilitate an investigation by helping officers obtain critical information quickly and effectively.

The legal system puts great emphasis on witness accounts – particularly those of operational witnesses like police officers – but our research shows how memory can be impaired.

Professor Lorraine Hope, Professor of Applied Cognitive Psychology

Professor Hope and her team have also developed a technique to assist investigators when they're conducting interviews about complex or extended events.

This technique, called the Timeline Technique, moves away from a linear, narrative approach to obtaining witness accounts. Instead, witnesses report their experiences by constructing a 'timeline' of events.

The new technique allows interviewees to organise and report their recollections of the main events across an extended period. They then place events in the order in which they occurred, and identify key people they encountered – and the context in which they encountered them.

As the method is largely self-administered, the interviewee is also less likely to encounter leading or suggestive questions that may influence or distort their account.

Professor Hope said: 'When a witness gives an account in a linear fashion, starting from the beginning, this places a heavy burden on memory. As things come to mind, a witness might try to keep them in mind until the relevant part of the account, rather than reporting them immediately.

'We found that those using the timeline technique gave 47 per cent more correct details when tested immediately. And even after a two-week delay, they provided 32 per cent more correct details.'

Finally, Professor Hope wants the justice system as a whole to understand the implications of this programme of research.

She said: 'Our research shows how memory can be impaired, but it also shows how interviewers can elicit more detailed and accurate information if they have a sound understanding of memory and use tools and techniques informed by psychological science.'