The first psychological issue with witness testimony is "perception" — the question of whether external events are copied into memory accurately. The second is "memory" — the issue of whether initial perceptions, accurate or inaccurate, remain unchanged in the mind.
If human perception is questionable, human memory is at least equally questionable.
The tempting simple assumption is that people have "Flashbulb Memory." That just as a flashbulb fires and imprints an image permanently on film, an event is emblasioned on human memory and remains there unchanged. Alas, that's not the case.
In the first place, people can "remember" things that they could not have possibly seen. One example comes from Daniel Schacter's book Seven Sins of Memory, and concerns the 1992 crash of an El Al cargo plane into an apartment building in the Netherlands.
People throughout the country saw, read, heard, and talked about the catastrophe.
Ten months later a group of Dutch psychologists probed what members of their university communities remembered about the crash. The researchers asked a simple question: "Did you see the television film of the moment the plane hit the apartment building?" Fifty-five percent of respondents said "yes." In a follow-up study, two-thirds of the participants responded affirmatively.
They also recalled details concerning the speed and angle of the plane as it hit the building, whether it was on fire prior to impact, and what happened to the body of the plane right after the collision. These finding are remarkable because there was no television film of the moment when the plane actually crashed.
The psychologists had asked a blatantly suggestive question: they implied that television film of the crash had been shown. Respondents may have viewed television footage of the postcrash scene, and they probably read, imagined, or talked about what might have happened at the moment of impact. Spurred on by the suggestive question.
