What causes false memories or memory gaps

Correction appended 11/20/13, 10:18 AM

It’s easy enough to explain why we remember things: multiple regions of the brain — particularly the hippocampus — are devoted to the job. It’s easy to understand why we forget stuff too: there’s only so much any busy brain can handle. What’s trickier is what happens in between: when we clearly remember things that simply never happened.

The phenomenon of false memories is common to everybody — the party you’re certain you attended in high school, say, when you were actually home with the flu, but so many people have told you about it over the years that it’s made its way into your own memory cache. False memories can sometimes be a mere curiosity, but other times they have real implications. Innocent people have gone to jail when well-intentioned eyewitnesses testify to events that actually unfolded an entirely different way.

What’s long been a puzzle to memory scientists is whether some people may be more susceptible to false memories than others — and, by extension, whether some people with exceptionally good memories may be immune to them. A new study in the Proceedings of the National Academy of Sciences answers both questions with a decisive no. False memories afflict everyone — even people with the best memories of all.

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To conduct the study, a team led by psychologist Lawrence Patihis of the University of California, Irvine, recruited a sample group of people all of approximately the same age and divided them into two subgroups: those with ordinary memory and those with what is known as highly superior autobiographical memory (HSAM). You’ve met people like that before, and they can be downright eerie. They’re the ones who can tell you the exact date on which particular events happened — whether in their own lives or in the news — as well as all manner of minute additional details surrounding the event that most people would forget the second they happened.

To screen for HSAM, the researchers had all the subjects take a quiz that asked such questions as “[On what date] did an Iraqi journalist hurl two shoes at President Bush?” or “What public event occurred on Oct. 11, 2002?” Those who excelled on that part of the screening would move to a second stage, in which they were given random, computer-generated dates and asked to say the day of the week on which it fell, and to recall both a personal experience that occurred that day and a public event that could be verified with a search engine.

“It was a Monday,” said one person asked about Oct. 19, 1987. “That was the day of the big stock-market crash and the cellist Jacqueline du Pré died that day.” That’s some pretty specific recall. Ultimately, 20 subjects qualified for the HSAM group and another 38 went into the ordinary-memory category. Both groups were then tested for their ability to resist developing false memories during a series of exercises designed to implant them.

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In one, for example, the investigators spoke with the subjects about the Sept. 11 terrorist attacks and mentioned in passing the footage that had been captured of United Flight 93 crashing in Pennsylvania — footage, of course, that does not exist. In both groups — HSAM subjects and those with normal memories — about 1 in 5 people “remembered” seeing this footage when asked about it later.

“It just seemed like something was falling out of the sky,” said one of the HSAM participants. “I was just, you know, kind of stunned by watching it, you know, go down.”

Word recall was also hazy. The scientists showed participants word lists, then removed the lists and tested the subjects on words that had and hadn’t been included. The lists all contained so-called lures — words that would make subjects think of other, related ones. The words pillow, duvet and nap, for example, might lead to a false memory of seeing the word sleep. All of the participants in both groups fell for the lures, with at least eight such errors per person—though some tallied as many as 20. Both groups also performed unreliably when shown photographs and fed lures intended to make them think they’d seen details in the pictures they hadn’t. Here too, the HSAM subjects cooked up as many fake images as the ordinary folks.

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“What I love about the study is how it communicates something that memory-distortion researchers have suspected for some time, that perhaps no one is immune to memory distortion,” said Patihis.

What the study doesn’t do, Patihis admits, is explain why HSAM people exist at all. Their prodigious recall is a matter of scientific fact, and one of the goals of the new work was to see if an innate resistance to manufactured memories might be one of the reasons. But on that score, the researchers came up empty.

“It rules something out,” Patihis said. “[HSAM individuals] probably reconstruct memories in the same way that ordinary people do. So now we have to think about how else we could explain it.” He and others will continue to look for that secret sauce that elevates superior recall over the ordinary kind. But for now, memory still appears to be fragile, malleable and prone to errors — for all of us.

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(An earlier version of this story said that 70% of the subjects had word-lure mistakes. In fact, 100% of them had a minimum of eight mistakes each.)