Thus, “some of the memories in which we play a leading role might in fact have been the experiences of others,” they wrote in the new study, published in the February issue of the research journal Genes, Brain and Behavior.

Many twins have noticed the phenomenon for years. But the researchers, one of whom is a twin herself, say they’re the first to document it scientifically, along with its occurrence among non-twins.

In the new research, the psychologists re-analyzed data from their past studies to try to understand why it occurs. Their finding: although our appropriation of other people’s memories is probably unintentional, it also tends to be self-serving.

People “claim for themselves memories for achievements and suffered misfortunes but are more likely to give away memories of personal wrongdoing,” they wrote. That’s consistent other recent research findings, they added, that have pointed to something obvious to many non-scientists: most of us are often quite selfish.

The scientists started the research “in part because of all of the heat involved in most real world memory errors,” wrote Duke’s David C. Rubin, a member of the team, in an email. 

Controversy has surrounded the accuracy of memories for decades, largely because of how witness recollections affect court cases. A particularly thorny issue has been whether courts should let children sue their parents on grounds that they recently remembered long-suppressed memories of child abuse. Some critics contend these “memories” are often retrieved only with the help of hypnotherapists, who may actually have planted them through the force of suggestion.

Regardless of who is right, researchers have increasingly recognized that memories are highly fallible. And Rubin and colleagues say their findings suggest yet a new way that memories can be distorted.

In their new paper, they quoted as follows a typical conversation between 54-year-old female twins as they participated in one of the studies.

Twin 1: I remember falling over and really hurting my elbow and knee when a wheel came off my roller skate.
Twin 2: Hang on a minute, are you talking about those roller skates we got for our eighth or ninth birthday?
Twin 1: Yeah, so what?
Twin 2: Well that actually happened to me if you don’t mind.
Twin 1: What do you mean, it was me! I was skating with you and [...]
Twin 2: Yeah, with Marie on the old tennis court.
Twin 1: Yeah, but it was me not you, I remember it being really bumpy with grassy bits in it.
Twin 2: I think you’ll find if you think really hard it was me.
Twin 1: Well I remember it so clearly, and you skated home to get mum.
Twin 2: No, you skated home to get mum, because I was hurt and crying and couldn’t move.
Twin1: Oh well, I guess we get confused; it happened so long ago.

The University of Canterbury’s Mercedes Sheen, a member of the research team, wrote in her 2002 Ph.D. thesis: “My own twin and I dispute a memory over a first kiss at summer camp when we were 12. The boy in question was the ‘camp catch,’ and although we both vehemently believe we were the one who was there, the event (one would hope) only happened to one of us.”

Although many twins have noticed the disputed memory phenomenon on their own, the studies found it may happen more often than they think, the researchers wrote. 

A 2001 study involving 20 pairs of same-sex twins uncovered 36 disputed memories, only 15 of which the twins involved already knew to be disputed, the researchers found. The discovery of a memory-ownership question “often seemed to come as a surprise to the participants, and many tried to assert their own right to the memory,” Sheen and colleagues wrote.

The team also interviewed 69 non-twins and found that six reported having experienced a disputed memory. In half the cases, the disagreement was with a sibling; in the other half, a friend. 

In the new study, they analyzed 77 disputed memories gathered in past research. Most cases involved both members of a pair claiming the same memory. But some cases—slightly over one fourth—involved them “giving away” memories, claiming that the other person experienced the remembered event.

Some patterns turned up, the researchers said.

First, “the memories are predominantly bad (wrongdoing or misfortune) rather than good (achievement, gift or daring),” they wrote. Also, most of the disputes in both twins and non-twins occurred among females, they found, probably because “women share memories more than men.” 

A participant was moreover “more likely to claim good memories for herself or himself” than bad ones, they wrote. Participants claimed for themselves 17 out of 18 of the good memories, but only 28 of 43 bad memories.

Also, they wrote: “Of the bad memories, there is a very much stronger tendency to claim misfortunes as one’s own (27 out of 34) than wrongdoings (three of 21).”

Thus, in many ways the memories “could be described as self-serving,” they concluded. 

They also noted that parents usually were unable to resolve memory disputes. That was possibly because the conflicts tended to involve events of middling importance rather than great importance, and the parents themselves couldn’t recall the facts, they said.

The researchers said the apparent self-serving nature of disputed recollections is similar to self-serving tendencies that psychologists have found in other facets of life. 

One interesting parallel is with children’s imaginary friends, they wrote.

Studies have found that “although the preschool children who were reported to have such companions normally appear to interact well with their imaginary friends, they also frequently blame the imaginary playmate when minor things go wrong,” they wrote. And one study indicated that “while imaginary companions are often involved in the child’s behaviour, they are rarely praised for their accomplishments.”

Another intriguing parallel, the researchers said, involves dreams. People sometimes can’t figure out whether they dreamt something or it really happened to them.

“These memories of uncertain origin are likewise rather rare and generally for events of intermediate importance,” they wrote. “Moreover, those who have such memories often try hard to resolve their origin in dreams or reality, just as our disputants expended effort in defending their right to ‘their’ memories.”

Scientists have shown growing interest in self-serving behavior in recent years, and the disputed-memory studies are adding to that research, according to the team.

One 2004 study found that people tend to “attribute their successes to themselves and their failures to external causes,” whereas a study four years earlier “showed that people who were confronted with positive and negative information about themselves later tended to recall the positive information and neglect or forget the negative.”

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