Where were you on 9/11?
Almost any American old enough to remember 2001 has an answer to that question. Classrooms, office parks, living rooms, dorm rooms — wherever you happened to be when you turned on the television or saw the smoke or got a frantic phone call — became imbued with extra meaning. Americans from New York to Fairbanks promised each other they'd never forget where they were when they heard the news.
But research suggests we do forget: not the dead or the importance of the moment, but the details surrounding the day. The emotional, seemingly vivid memory of where you were when 9/11 happened is what's known as a flashbulb memory. Once thought to be seared into the brain permanently, flashbulb memories have turned out to be fallible, just like memories for more ordinary events. [Top 10 Mysteries of the Mind]
The difference is, flashbulb memories don't feel that way, said William Hirst, a psychologist at the New School in New York City who has studied Americans' memories of 9/11.
"People are extremely confident in the accuracy of these not-necessarily-accurate memories," Hirst said. With a nationwide project on memories of 9/11, Hirst and other flashbulb memory researchers are trying to untangle why this is. The answer may have less to do with memory and more to do with how we see ourselves as part of a community and a part of history.
The origin of the flashbulb
The assassination of President John F. Kennedy in 1963 sparked the first scientific description of flashbulb memories. Harvard researchers Roger Brown and James Kulik noticed that people seemed to have particularly vivid memories of where they were when they heard news the president had been shot.
"Indeed," Brown and Kulik wrote in 1977 in the journal Cognition, "it is very like a photograph that indiscriminately preserves the scene in which each of us found himself when the flashbulb was fired."
The researchers did note that certain details disappear from flashbulb memories, like the hairstyle of the teacher who answered the phone and gasped that Kennedy was dead. Nonetheless, they concluded that something was inherently different about flashbulb memories that made them resistant to erosion, likely due to the surprising and personally relevant nature of the event.
But Brown and Kulik had their experimental volunteers respond only once to questions about how well they remembered Kennedy's assassination (as well as other touchstone events such as the death of Martin Luther King, Jr.). Later studies would follow the same people over time, asking them every few months or years to recall their memories of a particular traumatic event, including the Challenger explosion, Princess Diana's death, and eventually, 9/11.
Are 9/11 memories special?
Those studies have found that while people feel very strongly that their flashbulb memories are crystal-clear, the memories actually erode over time just like our memories of birthdays, new car purchases and other life events.
Even as the 9/11 attacks occurred, memory researchers realized they were witnessing a moment that would spawn millions of these seemingly photographic memories. Within days of the 9/11 attacks, psychologists began interviewing and surveying people across the country. On Sept. 12, 2001, Duke University researchers Jennifer Talarico and David Rubin asked 54 Duke undergraduates questions about where they'd been when they heard about the attacks. They also asked the students to provide memories for a few everyday events.
One week, six weeks or 32 weeks later, the students returned to answer the same set of questions. It turned out that the consistency of 9/11 memories was no different than that of mundane memories. In both cases, the number of consistent details about the event dropped from around 12 one day after it happened to about eight consistent details 32 weeks later, while inconsistencies rose. Nonetheless, people felt very confident in their total recall of that moment.
That makes flashbulb memories different from regular memories, Talarico, now at Lafayette College in Pennsylvania, told LiveScience.
"We seem to be willing to admit that we might be forgetting something, or maybe misremembering details of other types of events," she said, but people remain unusually sure of their memories of 9/11 and similar events.
While Talarico and Rubin were querying Duke students on their memories, another group of memory researchers was putting together an ambitious project: a national memory survey on the 9/11 terrorist attacks. Within about a week, memory scientists from New York to Michigan to California (now known as the 9/11 Memory Consortium) were querying people on what they remembered.
The resulting set of data contained responses from more than 3,000 people in seven cities. Following up with those same people one year and three years later, the researchers found a decline in flashbulb memory accuracy that gradually leveled off after year one. In the first year, people's memories were consistent with the initial responses only 63 percent of the time. After that, however, they only lost 4.5 percent of their accuracy per year.
"People began to tell what I would call a canonical story," said Hirst, who was one of the study researchers. "The error they made at 11 months and the error they made at 35 months was the same."
Surprisingly, Hirst said, people tend to be particularly bad at remembering their emotions from the time of the attack. It's hard to look back at an emotional event without coloring it with hindsight, he said.
People "tend to think that the way they felt about it at the time is the same way that they feel about it now," Hirst said. "But their emotions have changed, so they make errors in their memory … You put your present into the past."
Why 9/11 memories feel special
Our memories of 9/11 may feel special for a reason, as some findings suggest that the decay of flashbulb memories over the very long term is slower than for other memories, said Olivier Luminet, a psychologist at the Catholic University of Louvain in Belgium; Luminet pointed to research showing very vivid memories of the German invasion of Denmark during World War II among Danish citizens 50 years later. More research is needed regarding the accuracy of very long-term flashbulb memories, Luminet said. [10 Ways to Keep Your Mind Sharp]
"I will not say these are completely consistent memories, but I would not go the other direction either," Luminet told LiveScience.
But studies have certainly shown that flashbulb memories are subject to contamination. In a 2004 study published in the journal Cognition and Emotion, scientists suggested to Russian study participants that their previously reported flashbulb memories of a 1999 bombing of two Moscow apartment buildings had included visions of a wounded animal. None of the 80 participants had actually reported this, but five were convinced by the suggestion, even creating false memories of bleeding cats and enraged barking dogs. In the case of 9/11, people will sometimes claim to have seen live video of the first plane hitting the North Tower of the World Trade Center, Talarico said, despite the fact that such video was not broadcast until days after the attack.
So why do flashbulb memories feel so special? No one knows for sure, but researchers have a few theories. Elizabeth Phelps, a psychologist at New York University, conducted brain scans of people three years after the 9/11 attacks, asking them to draw upon memories from that day as well as consequential, but nontraumatic memories from around the time of the attacks.
Surprisingly, Phelps told LiveScience, about half the participants didn't rate their memories about the day of 9/11 any differently than they did other important life events from around the same time. The half that did say their 9/11 memories were more vivid were those physically closer to the World Trade Center site when the planes hit. People near Washington Square Park, less than 2 miles (3.2 kilometers) from the attacks, said their memories were more vivid and confidence-inspiring than those about 3 miles (4.8 km) away, at the Empire State Building.
"Those people learned about it on the news," Phelps said. "They didn't see the building fall, they heard about it and then looked at the news like everybody else in the world." In contrast, she said, streets were closed for two weeks around NYU, and some areas near campus were evacuated.
The individuals with the most vivid memories also had unique brain activation patterns when dredging up the memories, Phelps and her colleagues found. The amygdala, an area involved in emotion, was more active, while the posterior parahippocampus, a brain region involved in memory for contextual detail, showed less activity, Phelps said. When something is emotional, people tend to focus on just the emotional stimulus, failing to store broader details in memory.
It's possible that when this happens, you get a few very strong memories that could enhance your confidence about where you were and what you saw, Phelps said. You might then attribute your confidence about those few details to all of your other memories about the day, mistakenly inflating your convictions.
A part of history
Of course, another reason 9/11 memories might seem special is that for Americans, 9/11 is special. Community and sharing reinforce memories and sometimes shape them, said Hirst. He's found that after Michael Moore's movie "Fahrenheit 9/11" came out, people suddenly became much more accurate at remembering where then-President George W. Bush was when the towers were hit. Moore's movie contained a long video of Bush reading to schoolchildren in Florida, seemingly unsure of how to respond to the news of the attacks.
But the national importance of 9/11 also means that someone who didn't remember where they were when it happened would be considered odd — and more importantly, they'd consider themselves odd, Hirst said, comparing finding out about 9/11 to finding out about a parent's death.
"If someone called you and told you your mother had just died in a car accident and later on you were asked to recollect that incident, you personally would believe you would be less of a person if you didn't remember that very vividly," Hirst said. "It's almost a moral requirement."
Events such as 9/11 also inform our identities as citizens, Hirst said. The moment when a spouse or a friend called and said, "Turn on the TV," is one of those rare times that our personal memories intersect with history, he said, quoting memory researcher Ulric Neisser.
"We remember the details of a flashbulb occasion, because those details are the links between our own history and History," Neisser once wrote. "They are the place where we line up our own lives with the course of history itself and say, 'I was there.'"
You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.