Although the use of eyewitnesses to solve crimes and identify suspects is a technique as old as criminal justice itself, forensic psychology studies have increasingly questioned the validity of eyewitness testimony. Often people may correctly recall what happened at the scene of a crime, or be able to identify a culprit, but there are many ways eyewitness testimony may be swayed subconsciously, which have important ramifications for criminal cases. At times, false events or elements may be introduced into this testimony without an eyewitness’ awareness.
Ensuring that eyewitness testimony is as reliable as possible is essential for ensuring fair criminal investigations and trials. This is due to the influence such testimony can have over the outcome of a case. Mock jurors have been found to be about 45 percent more likely to convict a defendant when they heard eyewitness testimony. Even if the mock jurors knew the eyewitness had poor eyesight, they were only slightly less likely to issue a guilt verdict.
Studies on memory conducted during the 1970s used participants who viewed a scene involving a car at an intersection, and were asked later to describe the scene. When experimenters introduced the words “stop sign” into their questions about the scene, participants claimed to remember a stop sign being present, when the sign did not actually exist. Cues such as these were sufficient to change how people remembered the scene. These studies have important implications for eyewitness testimony, since they show how leading questions can cause people to change not only their testimony, but their actual memories of an event.
Memories tend to deteriorate over time, leading to incomplete retrieval of events that eyewitnesses have seen. In some cases, eyewitnesses asked to recall events could only describe about 68 percent of the details after a week, and this percentage became lower over time. When false memories were introduced, they were still recalled about one-quarter of the time.
Eyewitnesses may sometimes misidentify individuals in a police lineup, as well. A guide prepared by Iowa State University details how the presentation of a lineup can influence suspect identification. Witnesses tend to compare suspects in a lineup to one another to arrive at a decision on a culprit, instead of comparing each suspect to their memory of the culprit. If the witness receives positive feedback after making their decision, they tend to become more confident that they have selected the right person, even if the individual does not truly resemble the actual perpetrator of the crime. In order to prevent feedback from influencing a witness’ decision, law enforcement agencies recommend having an officer unfamiliar with the identities of individuals in lineup photos be the one to present them.
Although eyewitness testimony is far from perfect, there are steps that can be taken to ensure it is more accurate. One method already mentioned is to avoid giving feedback to witnesses on the information they provide. Another is to present lineup mugshots in a sequential order, rather than all at once, so eyewitnesses are more likely to compare each photo to their own memories, rather than comparing photos to one another. Warning juries of the unreliability of eyewitness testimony is another way to ensure convictions are based on more evidence than just this type of testimony.
Eyewitness testimony can be valuable when collected in a way that reduces errors. Deterioration of memory, the ability to remember nonexistent or false events, and overconfidence in memory can all influence eyewitnesses dramatically, however. Any person involved in the criminal justice system should therefore be aware of the limitations of eyewitness memory to avoid relying on such testimony too heavily.
Allison Gamble has been a curious student of psychology since high school. She brings her understanding of the mind to work in the weird world of internet marketing with forensicpsychology.net.