Research News

Mistaken Identity: How Feedback "After the Fact" Influences Eyewitnesses

Eyewitness testimony is a fundamental aspect of the American justice system. Can it be influenced?

Test Your Eyewitness Aptitude
Witness a simulated crime, then try to identify the suspect from a lineup.  For best results, take this test before you read the article. Select "View Video" at right.

New research reveals that giving feedback to eyewitnesses of crimes after they have identified the suspect from a lineup or photospread distorts a witness's memories of both  the original event and the identification decision.  Surprisingly, this "post-identification feedback effect" is not tempered by the passage of time, even when the feedback is delayed by as much as 48 hours.

In a series of NSF-funded experiments led by Dr. Gary L. Wells of Iowa State University, eyewitnesses  viewed a staged crime and were then shown lineups that, unbeknownst  to them, did not contain the culprit. Regardless, all the eyewitnesses  made mistaken identifications. They were then randomly assigned one of several post-identification conditions: they were either given feedback  which confirmed their false identification, told that they had identified someone who was not the culprit, or told nothing.

The figure on the  right shows the results of one of the experiments. Confirming feedback  produced strong, statistically significant differences in eyewitnesses' memories of  key aspects of the witnessing experience, including:

• their confidence level at the time they identified the suspect
• how good a view they had of the event
• their ability to make out facial details
• the ease of identification
• whether they had a good basis (enough information) to make their decision

More often than not, lineups are conducted by police officers who know which person in the lineup is the  suspect. As a result, eyewitnesses often learn, either through direct feedback or confirmatory body language, whether they chose the suspect or not. For this reason, Dr. Wells is a long-time proponent of "double-blind" lineups,  wherein the individual administering the lineup doesn't know the identity of  the suspect, thereby eliminating any chance of informing the witness.  But double-blind lineups are only starting to be introduced in a few  of the over 16,000 independent law enforcement agencies across the United States, primarily because police cannot help but think that to require double-blind lineups is to question their integrity and honesty.

"The need for double-blind  testing is not because we do not trust police," explains Dr. Wells. "It  is necessary because police are human and humans unintentionally (and  commonly without awareness) influence the person they are testing.  Psychologists understand this very well, but outside of psychology,  this is a hard sell."

Whether or not  eyewitnesses exude a high level of confidence about their identifications  of criminal suspects is of immense importance in the courtroom. Judges and juries both rely heavily on witnesses' confidence when making  their own decision about the witnesses' accuracy. The findings demonstrated  by Dr. Wells and his colleagues raise serious concerns about the fallibility  of this system. If feedback can influence the confidence a witness demonstrates in court, then feedback is capable of distorting one of  the most important cues that judges and juries use in making decisions  about witness accuracy.

Effects of Delayed  Feedback
Although the post-identification feedback effect has been well documented  in previous studies by Dr. Wells and others, the current research adds  a new twist by examining delayed feedback. In previous experiments, feedback had  never been given more than 3 minutes after the eyewitnesses made their identifications. In Dr. Wells' new study, he not only tests the effect  of delaying the feedback itself, but he also tests delaying the measures  of witnesses' memories of the original event, and of the identification  experience.

The  unexpected results showed that even delaying feedback by as much as  48 hours did not moderate the post-identification feedback effect; it remained strong and present. This has practical implications for  real-world cases, since there are often cases in which witnesses do not receive immediate feedback from detectives or other authorities  involved with the case but are later told they picked out the perpetrator. Yet even such delayed feedback apparently compromises  the reliability of the witness.

In his efforts to  advance double-blind testing and other measures to ensure eyewitness accuracy, Dr. Wells has presented his findings at hundreds of universities, law-enforcement associations, legal conferences and prestigious professional organizations throughout the United States and Canada over the last 25 years.

"I don't expect  police, prosecutors, judges and others in the legal system to read  the scientific journals," Dr. Wells says. "Therefore, the  only way to give psychology away is to do the hard work of getting  out there and delivering the information to the people who can use  it. Otherwise, the research doesn't get applied."

As to why eyewitnesses  tend to become so much more confident when their identifications are  confirmed, the answer has yet to be discovered, but it probably lies  somewhere in the realm between rational thought and emotion.

"Cold cognitive  mechanisms include the normal tendency for people to recall things  in a manner consistent with present knowledge," Dr. Wells explains. "For  example, if I tell you that the stock market rose dramatically today,  you might recall things consistent with that outcome. In other words,  you "knew it all along" and were confident that you knew  it. We have not been quite as effective in researching the "hot" cognitive processes, like the good feelings that come from confirming feedback, or the ego stroke that makes us boastful."

The results of Well's  research, along with the related work of others, allows a deeper understanding of how eyewitness confidence develops, why it changes and how confidence becomes dissociated  from accuracy. It adds to a body of prior research on eyewitness identification that has had, in some police agencies, a substantial influence on lineup and related identification procedures, making it more likely that the guilty will be caught and the innocent not ensnared.

In related NSF-funded  research, Dr. Wells is studying the issues surrounding mistaken identifications resulting from computer-generated composites.