Factors Affecting Eyewitness Memory

Eyewitness memory plays a pivotal role in many criminal trials.

A substantial body of psychological research on eyewitness memory has developed over the years.

This article covers various types of eyewitness memory, factors affecting eyewitness memory, methods of improving eyewitness memory, and how eyewitness memory is evaluated in the course of investigations and criminal trials.

History of Research on Eyewitness Memory

The advent of psychological research related to the legal system can be traced to 1908, when Alfred Binet demonstrated that a person’s response to questioning could be influenced by the way in which the question was asked.

Although his work did not have a profound influence on the legal system at the time, it was the beginning of empirical research involving witness testimony.

Soon thereafter, William Stern actually applied this research directly to eyewitness testimony.

Eyewitnesses' emotions at the time of the event, can serve to affect the accuracy rate. Hugo Munsterberg released his book, On the Witness Stand, which examined problems associated with eyewitness memory as well as jurors’ inability to accurately assess eyewitness testimony.

Munsterberg’s research was met with quick criticism from John Henry Wigmore, who stated that psychological research was not of a nature that the legal system could use.

He was the first researcher to examine issues related to eyewitness memory in a systematic and scientific manner.

Types of Eyewitness Memory and Factors Affecting Eyewitness Memory

Broadly speaking, eyewitness memory can be divided into two general classes:

• Eyewitness recall
• Eyewitness identification

Eyewitness recall often plays an important role in the investigation of crimes.

When a crime occurs, police officers responding to the crime interview the eyewitnesses regarding their memories associated with the crime, including descriptions of the perpetrator(s) and the crime itself.

The interviewee may be interviewed numerous times throughout the investigation.

Research on eyewitness recall has examined factors that influence the accuracy of eyewitness descriptions, such as levels of stress experienced by the eyewitness or the presence of a weapon.

One of the most widely studied factors, witness questioning, relates to the information that is given to witnesses after they experience the event and the way in which the witnesses are questioned about the event.

In this research, participants who witnessed an event are questioned in a way that induces subsequent reports containing false details.

For example, participant witnesses were asked either “Did you see a broken headlight?” or “Did you see the broken headlight?”

Even though only one word is different between the two conditions, participants who heard the word “the,” rather than the word “a,” were more likely to indicate that they had seen a broken headlight.

The majority of research discussed thus far has involved adults.

However, research has also demonstrated sizeable effects of post-event information on both older adults and children alike.

In fact, children below the age of 3 to 4 and adults over the age of 65 seem to be the groups that are most likely to fall prey to post-event suggestions.

Eyewitness Recognition

Eyewitness identification of perpetrators can play a central role in the investigation of a crime and in resolving the case, whether by trial or through plea bargaining.

Eyewitness identification can occur spontaneously, as is the case when a crime victim encounters her perpetrator in public and calls the police. 

Research on eyewitness identification has examined a large array of factors that are thought to influence identification accuracy.

These factors include the conditions under which the crime occurred, exposure time to the perpetrator, stress experienced by the witness, the presence of a weapon, disguises worn by the perpetrator, and the time between the crime and the identification.

Methods of Improving Eyewitness Memory

The aforementioned distinction between eyewitness recall and identification accuracy is useful for explaining how psychological research has been used to develop methods for improving eyewitness memory.

Practical recommendations from research on eyewitness recall have focused on how to form questions that do not mislead the eyewitness and how to avoid implanting false memories.

Research has also examined whether hypnosis can be used to improve eyewitness recall, but the conclusions from this research are pessimistic

Research on improving eyewitness identification has likewise yielded impressive gains. There are various tests that are used to identify a suspect.

Two of the most common of these tests are the lineup and the show up.

A lineup can be conducted either live (the witness views actual people) or by using a photo spread (the witness views a series of photos).

In general, a lineup usually contains several fillers, people in the lineup that are known to be innocent, and one suspect.

Lineups can contain more than one suspect, but for a variety of reasons, it is not recommended.

Evaluating Eyewitness Memory

In some sense, all estimator variables could be considered predictors of eyewitness accuracy.

Although research has focused on eyewitness recall, testimony, and identification, research on the predictors has almost exclusively been limited to eyewitness identification.

One of the most widely studied predictor variables is eyewitness confidence. This is most likely the case because jurors seem to find confident eyewitnesses extremely persuasive and believable.

This perception of confident eyewitnesses is understandable; intuitively, it seems as though there should be a strong positive relationship between witness confidence and accuracy.

This belief is underscored by the fact that the court has suggested that jurors may employ witness confidence as an indicator of the accuracy of the witness.

Unfortunately, psychological research has found unequivocally and repeatedly that the relationship between confidence and eyewitness accuracy is, at best, a weak one.

Furthermore, this weak relationship deteriorates as the time interval between the event and the confidence statement increases.

The reason for the lack of relationship between confidence and accuracy may be that witnesses often rely on misleading information as the basis for their confidence estimates.

For example, it has been shown that confirmatory feedback increases participants’ confidence in their eyewitness identification.

Simply telling a witness that they have chosen correctly increases the witness’s confidence in the accuracy of his or her identification relative to participants who are not given any feedback. This confidence inflation is especially prominent when the participants are inaccurate.

Eyewitness in Courtroom

Considerable research has addressed how jurors evaluate eyewitness memory and whether their evaluations can be improved.

Using trial simulation methods, research demonstrates that jurors are often insensitive to the factors that are known to influence eyewitness memory: stress experienced by the witness, weapon focus, and the influence of suggestive identification procedures.

Furthermore, jurors tend to rely on factors that are known not to strongly predict identification accuracy.

Witness confidence, for example, has a strong impact on jurors’ evaluations of eyewitness identifications.

In these studies, highly confident witnesses are persuasive, and jurors tend to convict perpetrators on the basis of testimony by highly confident witnesses.