We like to think that our memories are something we can rely upon. "I was there" and "I saw it with my own eyes" are phrases taken to express certainty. But how sure can we really be that we are remembering an event exactly as we saw it? But, in fact, the answer should "Not very!"
In 1890, William James, the father of modern psychology, argued that memory was reconstructive, and this theory has since been elaborated on (e.g. by Bartlett in the 1930s). What this means is that rather than memory being like a video tape we can play back whenever we like, and which preserves the details of the memory completely, the context in which we recall something can have an effect on how we recall it.
One of the best known experiments showing how outside influences can affect our memory of an event was carried out by Elizabeth Loftus and John Palmer in 19741. They showed students short videos of a car crash and then asked them to answer some simple questions about what they had seen.
Surprisingly, by altering the wording of the question, they found that the students' judgements of how quickly the car had been travelling could alter dramatically, from 31 mph when the neutral word "contacted" was used, to 40mph when the word used was "smashed".
And in another group, those who had been asked about the speed using a dramatic term were more likely to claim to remember seeing glass smashed on the floor when questioned a week later than those asked the question using a neutral term, despite no glass ever having been present.
These findings suggest that the questions you are asked about an event can have a profound effect on your memory for that event. This is highly relevant to the ways in which the police interview witnesses after a crime, and Elizabeth Loftus's work led to the development of the cognitive interview technique, now used by police forces, which attempts to avoid creating these biases in witnesses by allowing them to recall an event in as much detail as possible with very little prompting.
Memory research is extremely important in criminal matters, as memory researcher Dr Donald Thompson found out in the worst possible way when he was accused of raping a young woman. Dr Thompson was shocked when the woman picked him out of a line up, as he had never met her before.
幸运的是,他有一个十全十美的不在场证明他一直doing a live television interview at the time of the attack, which the woman admitted she had been watching. Her memory of Dr Thompson's face from the TV screen had become conflated with that of the rapist, leading to her false accusation.
This shows just how easily we can confuse in our minds two events that happened at the same time, even when they were completely unrelated. Historically, people were convicted of crimes solely on the basis of eyewitness testimony; but, owing to research done in this area, this is now less common. There have even been several cases of those convicted on this basis being released after DNA evidence proved they could not have committed the crime.
It has also been shown that it is possible to implant false memories in people's minds, without them realising. This time, working with her student Jacqueline Pickrell in 19952, Loftus did just this, convincing people that they had been lost in a shopping centre at the age of 5.
To make the story convincing, they asked relatives for details of a shopping trip that actually occurred (and confirmed that the subject had never actually been lost). They then interspersed the made-up story with these factual details.
When asked, 25% of participants claimed that they remembered this fictitious event occurring. Other studies have found that recall of the false event is higher at a follow up interview than it was the first time the subject was asked about it, suggesting the memory of hearing the story is being taken as a memory of the actual event.
Events can even be implanted that could never possibly have happened. Loftus & colleagues also found that, shown fake advertising for the Disney theme park, people could be made to believe that they had met Bugs Bunny at Disneyland, even though Bugs Bunny is a Warner Brothers' character so would not be at a Disney park3! And the more "evidence" the subjects were exposed to, the more likely they were to claim the event actually happened.
事实上,在这些例子中受试者的relatives claimed that the event happened is very important. People will even accept guilt for a crime they did not commit if they are told that a colleague saw them carrying out the act. This is of paramount importance in the legal system as people may be confused into making a false confession if enough corroborating evidence is supplied4.
This may be due to the fact that hearing people say that you did something causes you to imagine doing it, and if a subject is asked to imagine an event occurring, they often rate it as more likely to have really happened. This is also of importance to therapists, who often ask their patients to imagine childhood events, such as sexual abuse, to try to recover "repressed" memories. There have been several cases where hypnotism and suggestion by therapists have led to accusations of horrific acts of child abuse, which have later been disproven.
What all this reveals is that we cannot be as confident in our memories as we might like. So the next time you are arguing with a friend about what exactly happened at some past event, it may be a good idea to keep in mind that your memory could be playing tricks on you as well...
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