"Eyewitness testimony is the account a bystander or victim gives in the courtroom, describing what that person observed that occurred during the specific incident under investigation. Ideally this recollection of events is detailed; however, this is not always the case. This recollection is used as evidence to show what happened from a witness' point of view. Memory recall has been considered a credible source in the past, but has recently come under attack as forensics can now support psychologists in their claim that memories and individual perceptions can be unreliable, manipulated, and biased. As a result of this, many countries, and states within the United States, are now attempting to make changes in how eyewitness testimony is presented in court. Eyewitness testimony is a specialized focus within cognitive psychology.
Psychologists have probed the reliability of eyewitness testimony since the beginning of the 20th century. One prominent pioneer was Hugo Münsterberg, whose controversial book On the Witness Stand (1908) demonstrated the fallibility of eyewitness accounts, but met with fierce criticism, particularly in legal circles. His ideas did, however, gain popularity with the public. Decades later, DNA testing would clear individuals convicted on the basis of errant eyewitness testimony. Studies by Scheck, Neufel, and Dwyer showed that many DNA-based exonerations involved eyewitness evidence.
In the 1970s and '80s, Bob Buckhout showed inter alia that eyewitness conditions can, within ethical and other constraints, be simulated on university campuses, and that large numbers of people can be mistaken.
In his study, "Nearly 2,000 witnesses can be wrong", Buckhout performed an experiment with 2,145 at-home viewers of a popular news broadcast. The television network played a 13-second clip of a robbery, produced by Buckhout. In the video, viewers watched a man in a hat run up behind a woman, knock her over, and take her purse. The perpetrator's face was only visible for about 3.5 seconds. The clip was followed by the announcer asking participants at home for cooperation in identifying the man who stole the purse. There was a lineup of six male suspects, each having a number associated with them. The people at home could call a number on their screen to report which suspect they believed was the perpetrator. The perpetrator was suspect number 2. Callers also had the option of reporting if they did not believe the perpetrator was in the lineup. Roughly the same percentage of participants chose suspects 1, 2, and 5, while the largest group of participants, about 25 percent, said they believed the perpetrator was not in the lineup. Even police precincts called in to report the wrong man as the one they believed committed the crime. A key purpose of this experiment was aimed toward proving the need for better systems of getting suspect descriptions from eyewitnesses.
The question at hand is what about an event makes it so easy for eyewitness testimonies to be misremembered. As it pertains to witnessing crime in real time, “uniqueness is overshadowed by the conditions for observations”. The surprise or shock of a crime taking place makes it difficult to accurately pay attention to every detail aside from the sensory experiencing or task an individual is already attending to. Anything that a witness or victim could potentially remember is crowded by a number of factors: time of day, was there enough light to really see the event, number of people surrounding them, what would have made the perpetrator's features stand out in crowd? Potential noises, stress or anxiety induced by the situation, and other distractions all play a huge role in what our mind is perceiving, processing, and remembering.
The mechanisms by which flaws enter eyewitness testimony are varied and can be quite subtle.
One way is a person's memory being influenced by things seen or heard after the crime occurred. This distortion is known as the post-event misinformation effect (Loftus and Palmer, 1974). After a crime occurs and an eyewitness comes forward, law enforcement tries to gather as much information as they can to avoid the influence that may come from the environment, such as the media. Many times when the crime is surrounded by much publicity, an eyewitness may experience source misattribution. Source misattribution occurs when a witness is incorrect about where or when they have the memory from. If a witness cannot correctly identify the source of their retrieved memory, the witness is seen as not reliable.
While some witnesses see the entirety of a crime happen in front of them, some witness only part of a crime. These witnesses are more likely to experience confirmation bias. Witness expectations are to blame for the distortion that may come from confirmation bias. For example, Lindholm and Christianson (1998) found that witnesses of a mock crime who did not witness the whole crime, nevertheless testified to what they expected would have happened. These expectations are normally similar across individuals due to the details of the environment.
Evaluating the credibility of eyewitness testimony falls on all individual jurors when such evidence is offered as testimony in a trial in the United States. Research has shown that mock juries are often unable to distinguish between a false and accurate eyewitness testimony. "Jurors" often appear to correlate the confidence level of the witness with the accuracy of their testimony. An overview of this research by Laub and Bornstein shows this to be an inaccurate gauge of accuracy."
(from Wikipedia)
Report on Eyewitness Identification (Minnesota Supreme Court)