Eye-witnesses are unreliable, Jonah Lehrer notes, because memories change — but there are some ways to improve the process:
Dr. Brewer focused on the police lineup, in which witnesses are asked to pick out a suspect from a collection of similar looking individuals.
Normally, witnesses are encouraged to take their time and carefully consider each possible suspect. But Dr. Brewer knew that strong memory traces are easier to access than weak and mistaken ones, which is why he only gave his witnesses two seconds to make up their minds. He also asked them to estimate how confident they were about the suspects they identified, rather than insisting on a simple yes-no answer.
To test this procedure, Dr. Brewer and his colleagues asked 905 volunteers to watch a series of short films showing such crimes as shoplifting and car theft. The subjects then looked at 12 portraits, only one of which was the actual suspect. According to Dr. Brewer’s data, his version of the lineup led to a large boost in accuracy, with improvements in eyewitness performance ranging from 21% to 66%. Even when subjects were quizzed a week later, those who were forced to choose quickly remained far more trustworthy.
The larger lesson is that, when it comes to human memory, more deliberation is often dangerous. Instead of simply assessing our familiarity with a suspect’s face, we begin searching for clues and guidance. Sometimes this involves picking the person who looks the most suspicious, even if we’ve never seen him before, or being swayed by the subtle hints of police officers and lawyers. As a result, we talk ourselves into having a memory that doesn’t actually exist.