In 1896 Albert Von Schrenk-Notzing testified at the trial of a man accused of murdering three women. Drawing on research into memory and suggestibility he argued that pre-trial publicity meant that witnesses could not distinguish between what they actually saw and what had been reported in the press.

The formal study of eyewitness testimony is usually examined within a framework of cognitive processing, which put simply refers to the different ways in which we make sense of the world around us.

We do this by employing the mental skills at our disposal such as thinking, perception, memory, awareness, reasoning and judgment. Although cognitive processes can only be inferred and cannot be seen directly, they all have very important practical implications within a legal context.

Given that the way we think, perceive, reason and judge can be less than perfect it's easy to understand why the factors influencing these processes are studied by psychologists'; not least because of the grave implications that this imperfection can have within the criminal justice system. As Huff and Rattner note:

the single most important factor contributing to wrongful conviction is eyewitness misidentification.

Stages of eyewitness memory:

Stage 1: Witnessing the incident.

When witnessing an incident, information about the event is entered into memory, however, research has shown that the accuracy of this initial information acquisition can be influenced by a number of factors.

Take the duration of the event being witnessed for instance. In a very simple experiment conducted by Clifford and Richards(1977), participants are instructed to approach a number of police officers and engage in conversation for either 15 or 30 seconds.

Thirty seconds after the conversation ends, the experimenter asks the police officer to recall details of the person they had just been speaking to using a 10-item checklist. The checklist contains items relating to the persons appearance such as hair colour, facial hair etc. The results of the study showed that in the longer 30 second condition, police were significantly more accurate in their recall.

Stage 2: Waiting period before giving evidence.

This stage is concerned with the period of retention between perception i.e., seeing an incident and the subsequent recollection of that incident. Unsurprisingly, research has consistently found that the longer the gap between witnessing an incident and recalling the incident, the less accurate the recollection of that incident becomes.

There have been numerous experiments, usually related to a staged event, that support this contention. Malpass and Devine (1981), for instance, compared the accuracy of witness identifications after 3 days (short retention period) and 5 months (long retention period). The study found no false identifications after 3 days but after 5 months, 35% of identifications were false.

Stage 3: Giving evidence.

The final stage in the eyewitness memory process relates to the ability of the witness to access and retrieve information from memory. In a legal context, the retrieval of information is usually elicited through a process of questioning and it is for this reason that a great deal of research has investigated the impact of types of questioning on eyewitness memory.

The most substantial body of research has concerned leading questions, which has consistently shown that even very subtle changes in the wording of a question can influence subsequent testimony.

One of the most notable researchers in this field is Elizabeth Loftus who has been investigating eyewitness testimony for over thirty years. In one of her classic studies, participants witnessed a film of a car accident and were asked to estimate the speed of the cars involved. One group of witnesses were asked to estimate the speed of the cars when they contacted each other. A second group of witnesses were asked to estimate the speed of the cars when they smashed each other.

On average the first 'contacted' group gave an estimate of 31.8 miles per hour. Whereas, the average speed in the 'second' smashed group was 40.8 miles per hour.

Experimental validity:

In any discussion of eyewitness memory, you'll see the terms, 'experiment', 'participants' and 'staged event' frequently used. This is because the majority of research into eyewitness memory has been conducted within psychology laboratories.

This raises the very important issue of whether it is possible to generalise the findings obtained under these artificial conditions to real life cases.

The simple, if unsatisfactory answer is that it is very difficult to say. Take for instance the work of Yuille and Cutshall, these researchers conducted a case study with witnesses to a real shooting incident, interviewing them just after the event and again 5 months later. They concluded that the performance and accuracy of the witnesses differed in several respects to what would be expected according to the experimental literature.

However, the strength of laboratory based research is that the experimenter is able to exercise a great deal of control over what happens. In the case study reported by Yuille and Cutshall, it was impossible to know the extent to which the witnesses had conferred and how much media coverage of the incident they had seen, and how much influence this had on their testimony.

If you'd like to find out more about eyewitness memory, you can do so by visiting www.all-about-forensic-psychology.com