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Okay, maybe that's not convincing. Kids tell stories to themselves; they get confused about the nature of reality. But you're an adult and you know the difference between fantasy and reality. Well, adults get confused, too.

Consider, for instance, the experience of memory researcher Donald Thomson. Thomson appeared on a television show about the unreliability of eyewitness testimony. Not long after the show aired, he was picked up by the police and placed in a lineup. A distraught woman identified him as the rapist who had attacked her.

Thomson had an unshakable alibi--the rape had occurred when he was on the TV show. The victim had been watching Thomson on TV just before the rape, and had confused her memory of Thomson with her memory of the rapist.

Memory researcher Daniel L. Schacter links this case with what he calls "source memory," the ability to recall precisely when and where an event occurred. The rape victim remembered Thomson's face, but misremembered where she had seen it.

People tend to think of memory as being like a tape recorder or a camera, capturing what's out there. That doesn't match with the current thinking of most memory researchers. Their research implies that your memory of an event is something you construct from bits and pieces: from what you saw and heard and experienced and felt at the time; from things people told you afterward; from suggestions and thoughts and implications, all filtered by your attitude, by who you are. Daniel Schacter writes that "memories for individual events resemble jigsaw puzzles that are assembled from many pieces" and suggests that all rememberers normally "knit together the relevant fragments and feelings into a coherent narrative or story."

Elizabeth Loftus discusses this idea in a way that's extremely compelling. Loftus writes about "story-truth" and "happening-truth," terms she borrowed from Tim O'Brien's Vietnam novel, The Things They Carried. Happening-truth is the bare facts--what happened at such and such a time. Story-truth is the story you tell yourself about that truth, the details that you fill in, the Technicolor version that helps you make sense of the world. In story-truth, you may unconsciously fill in a little bit here, adjust things a little bit there--in the same way that a fiction writer consciously edits and recasts a narrative.

Both the authors of this article keep journals--and both of us consult them every now and then. Recently, the Exploratorium needed true stories of personal encounters with weather for a book. Paul dug out his journals to read his entry from the day one of the two ropes of rock climbers that he was leading up Mount Hallett in Colorado had been hit by lightning.

Paul and his partner, Martin Meyer, had reached the summit and had descended to a lower, safer position to wait out an afternoon thunderstorm in a wind shelter. The second rope was still on the cliff when lightning struck the summit. Paul remembers being on the summit after the storm cleared and greeting the second rope of climbers as they arrived. He clearly remembers a smiling but shaken Mike Bolte climbing up the summit gully. Mike had been hit by some of the ground current from the lightning and had a burn mark on his hip to prove it.

When Paul went back to his journal, he was shocked to discover that his recorded account of the event differed from his memory. According to the journal, Paul and Martin had taken turns waiting for the second team on the cold and windy summit, alternating with periods of warming up in the wind shelter. Martin, not Paul, had been at the summit when Mike reached it. Paul first saw Mike when he arrived at the wind shelter. Paul's memory of the event is false. How could that have happened? Well, Paul is a good storyteller. And it makes a much better story to be at the summit greeting the climbers. The story-truth, the way that Paul wanted to remember the event, was stronger than the happening-truth, the bare and unsatisfying facts. But better story or not, Paul was startled to find out that his journal and his memory didn't match.

After reading his journal, Paul was convinced that his memory wasn't always trustworthy. But that doesn't mean that all of his--or your--memories are inaccurate. Most of the details that Paul recalled matched the account in his journal quite closely. Human memory can be, in many circumstances, very accurate. But research has demonstrated that memory can also be prone to distortion and is occasionally untrustworthy, a discovery that many find unsettling.

Elizabeth Loftus writes about some of the reasons that people are disturbed by her research: "Human beings feel attached to their remembered past, for the people, places, and events that we enshrine in memory give structure and definition to the person we think of as our 'self.' " If we accept that memory spills over into dreams and imagination, then how do we know what's real and what's not?

In Total Recall, the psychic mutant asks Arnold Schwarzenegger why he wants to remember. Arnold answers, "To be myself again."

It is easy to think of yourself as the sum of your memories--the end product of all that you've ever experienced. But after doing research into memory, we find that it makes sense to reverse that statement. Your memories are the end product of all you've ever thought and done, filtered through your perceptions and opinions. Who you are is shaped by your memories, and your memories are shaped by who you are.


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