On July 7, 2005, an Islamic suicide bomber detonated an explosive device on a double-decker bus in Tavistock Square, London, killing thirteen people and injuring dozens of others. It was part of a coordinated series of attacks that day that took 52 lives.
Understandably, investigators put a tremendous amount of effort into trying to determine what exactly had happened on that horrible day. They questioned eyewitnesses, and of course the case was all over the news for weeks. Three years later, a man named James Ost, of the University of Portsmouth, became interesting in finding out what impact the event had made on people who lived nearby at the time, and began to interview locals.
A common theme was how traumatizing it had been to watch the CCTV footage of the actual Tavistock explosion. Four out of ten people Ost interviewed had details seared into their brains -- hearing the screams, seeing the debris flying in all directions. One man said he remembered actually seeing someone -- he wasn't sure if it was a passenger or the bomber himself -- blown to bits. More than one said they had felt reluctant to watch it at the time, and afterwards regretted having done so.
All of which is fascinating -- because there is no CCTV footage of the explosion. In fact, no video record of the bombing, of any kind, exists.
Ost's study was not the first to look at the phenomenon of false or invented memory, but it's justifiably one of the most famous. A couple of things that are remarkable about this study are the Ost didn't give much of a prompt to the test subjects about video footage; he simply asked them to recall as much as they could about what they'd seen of the bombing, and the subjects came up with the rest on their own. Second, the memories had astonishing detail, down to the color of clothing some of the people in the imagined video were wearing. And third -- most disturbingly -- was the power of the false memory. Several test subjects, when told there was no footage of the attack, simply refused to believe it.
"But I remember it," was the common refrain.
Our memories are incomplete and inaccurate, filled with lacunae (the psychological term for gaps in recall), and laced through with seemingly sharp details of events that never actually happened. Those details can come from a variety of sources -- what we were told happened, what we imagine happened, what happened to someone else that we later misremembered as happening to us, and outright falsehoods. Oh, sure, some of what we remember is accurate; but how do you know which part that is, when the false and inaccurate memories seem just as vivid, just as real?
The scariest part is how quickly those errors start to form. In the last fifteen seconds, I took a sip of my morning coffee, looked out of the window at a goldfinch on my bird feeder, noticed that my dog had gotten up because I could hear him eating his breakfast in the next room. How in the hell could I be remembering any of that incorrectly, given that it all happened under a minute ago?
Well, a paper that appeared last week in PLOS-One, about a study done at the University of Amsterdam, showed that inaccuracies in our memories increase by 150% in the time between a half-second and three seconds after the event occurs.
The study was simple and elegant. Test subjects were shown words with highlighted letters, and asked to recall two things; which letter was highlighted, and whether the highlighted letter was shown in its normal orientation or else reversed right-to-left. Most people were pretty good at recalling what the highlighted letter was, but because seeing mirror-image letters is not something we expect, recognizing and recalling that took more effort.
And if you wait three seconds, the error rate for remembering whether the letter was reversed climbs from twenty to thirty percent. Evidently, our memory very quickly falls back on "recalling" what it thinks we should have seen, and not what we actually did see.
It's a profoundly unsettling finding. It's almost like our existence is this moving window of reality, and as it slips by, the images it leaves behind begin to degrade almost immediately. "I know it happened that way, I remember it clearly" is, honestly, an absurd statement. None of us remembers the past with any kind of completeness or clarity, however sure we feel about it. Unless you have a video of the events in question, I'd hesitate to trumpet your own certainty too loudly.
And, of course, it also means you have to check to see if the video itself actually exists.