About ten years ago, some students in my AP Biology class decided to do an experiment on false memory as their final project.
The setup was simple and elegant. One of the students sat behind a small card table on which there were two dozen objects of various types and sizes, initially covered by a cloth. The test subject came in, sat down, and was told (s)he would be given a memory test at the end of three minutes' time to study the objects on the table. The cloth was removed, the timer started.
At a minute and a half in, the other student running the study -- who until then had been offstage -- came in, picked up one of the objects, and walked off with it. Naturally enough, the test subjects focused on which object she'd picked up.
When the three minutes were up, the test subject was read aloud a series of twelve questions about the experience. The answers to only three of them mattered -- the first one and the last two:
- Question 1: What object did the girl in the blue shirt remove from the table?
- Question 11: The girl who came in and removed an object -- what color was her shirt?
- Question 12: How do you know what color her shirt was?
You've probably already guessed that her shirt wasn't blue; in fact, it was brilliant red. But 95% of the fairly sizable number of test subjects answered "blue." Only two test subjects said "red;" several of them said "I don't remember."
But where it got seriously interesting was how the subjects who said "blue" answered question #12. Because the vast majority of them said, "I remember seeing it." Once again, there were only a couple of outliers who said "Because you told me it was blue in question #1," and one or two who said, "I'm not sure." The remainder were convinced they remembered seeing it. When informed that the other member of the scientific team had been wearing a red shirt, several people flat-out didn't believe it and asked that she come back and prove it to them. One of them even accused her of having changed her shirt!
This has always been one of my favorite examples of how plastic and unreliable human memory is. "I know it happened that way, I remember it" is remarkably thin ice. My students' clever experiment is innocuous enough, but think of the role false memories could play in a court of law -- where someone's freedom, perhaps their life, depends on the people on the witness stand remembering what actually happened.
So that's kind of sobering. But a study this week which appeared in Proceedings of the National Academy of Sciences gives us some encouraging news; false memories are easier to eradicate than real memories -- indicating they may be stored differently in the brain, and don't get the same weight as memories of events that we really witnessed.
In "Rich False Memories of Autobiographical Events Can Be Reversed," Aileen Oeberst (University of Hagen), Merle Madita Wachendörfer (Leibniz-Institut für Wissensmedien), Roland Imhoff (Johannes Gutenberg Universität Mainz), and Hartmut Blank (University of Portsmouth) show us a simple protocol by which people can be induced to purge their brains of false or implanted memories. They took a test group of 52 individuals whose parents had also agreed to participate. Without being told what exactly was going on, the test subjects were given a period during which their parents recalled with them a series of childhood memories -- but in each case, two of the "memories" were false and the rest were not. (Examples of false memories implanted were incidents like running away from home, getting lost, or being in a car accident -- more serious and emotion-laden than what shirt someone was wearing!)
As with previous experiments, the test subjects afterward were unable to tell apart the real memories from the false ones; both seemed to exist in their minds with equal intensity. Then the researchers tried two approaches to eradicate the false memories: (1) alerting the test subjects to the possibility that their memories were false, and were due to other sources, such as family narratives; and (2) asking test subjects to describe how they know their memories were true (a little like the "How did you know her shirt was blue?" question my students asked).
Both of them worked, and more interesting still, memories of real events were unaffected when the researchers tried the same strategy on them. Put differently, asking people to slow down and consider their brain's fallibility, and the sources of what they think they recall, had the effect of deleting false memories but not real ones.
Even more interesting was how persistent the effect was. A one-year followup on the test subjects found that the implanted memories were virtually all gone -- asked whether an unreal event had happened in their childhood, almost all the volunteers rejected it."By raising participants' awareness of the possibility of false memories, urging them to critically reflect on their recollections and strengthening their trust in their own perspective, we were able to significantly reduce their false memories. Moreover, and importantly, this did not affect their ability to remember true events," said study senior author Hartmut Blank, in an interview with Science Daily. "We designed our techniques so that they can principally be applied in real-world situations. By empowering people to stay closer to their own truth, rather than rely on other sources, we showed we could help them realize what might be false or misremembered -- something that could be very beneficial in forensic settings."