Most of us treat memory like a video recording. A century of research says otherwise. Memory is closer to storytelling, and perception itself is shaped by what we expect and what we attend to.

Reconstructive memory

In his 1932 book Remembering, the British psychologist Frederic Bartlett described asking English participants to read and later retell an unfamiliar Native American folk tale, “The War of the Ghosts.” With each retelling the story became shorter and more conventional, and strange details were dropped or changed to fit the participants' own culture. Bartlett concluded that we rebuild memories each time we recall them, using stored fragments plus our expectations and general knowledge. Psychologists call those organized expectations schemas.

The misinformation effect

In 1974 Elizabeth Loftus and John Palmer showed people films of traffic accidents and then asked about them. Some were asked how fast the cars were going when they “hit” each other; others, when they “smashed into” each other. The “smashed” group estimated higher speeds, and a week later they were more likely to report seeing broken glass, though there was none in the film.

This is the misinformation effect: information received after an event can alter the memory of the event itself. Later research by Loftus and colleagues went further. In a 1990s study, after relatives' suggestions, about a quarter of adult participants came to remember, at least in part, a childhood episode of being lost in a shopping mall that had never happened. Memories can be not only distorted but planted.

Confidence is not accuracy

After the space shuttle Challenger exploded in January 1986, the psychologists Ulric Neisser and Nicole Harsch asked students to write down how they had heard the news. About two and a half years later they asked again. Many accounts had changed a great deal, yet people felt confident in their new versions. So-called flashbulb memories of shocking events feel vivid and certain yet can change over time.

This matters in courtrooms. In the United States, mistaken eyewitness identification has been a factor in a large share of convictions later overturned by DNA evidence. The lesson is that a confident, vivid memory can still be wrong. Newer research adds a nuance: a witness's confidence at a first, fairly run lineup carries real information, while confidence that grows later, after feedback and retelling, is much less trustworthy.

Hindsight bias

Hindsight bias is the tendency, after learning an outcome, to believe the outcome was more predictable than it really was, the feeling that we “knew it all along.” In the 1970s Baruch Fischhoff found that people told the outcome of a historical event rated that outcome as more likely than people who were not told. In another study, people who had predicted the results of President Nixon's 1972 trips to China and the Soviet Union later remembered their predictions as more accurate than they had been.

Hindsight bias makes us blame decision makers unfairly for missing what only looks obvious afterward. The remedy is to judge a decision by the information available when it was made.

Seeing what we look for

In a 1999 study by Daniel Simons and Christopher Chabris, viewers counted basketball passes in a short video. About half failed to notice a person in a gorilla suit who walked through the middle of the scene. This inattentional blindness shows that attention is limited, so we can miss obvious things we are not looking for. Expectations also shape what we see: the same ambiguous symbol is read as the letter B among letters and as the number 13 among numbers.

Worked example: interviewing a witness

A small shop is robbed. The clerk, Marcus, saw the robber for a few seconds. Two investigators could approach him in very different ways.

The leading approach. “Was the man wearing a red jacket? Did he have a beard, like the guy who robbed the store down the street? You must have gotten a good look; you were right there.” Each question carries information Marcus may not have had. If he later “remembers” a red jacket or a beard, he may be recalling the questions rather than the robber.

The careful approach. Researchers developed the cognitive interview in the 1980s to avoid such problems. The investigator asks Marcus to describe the event in his own words, without interruption, and to report everything, even details that seem unimportant. Questions are open (“What was he wearing?”), not leading. Marcus is encouraged to say “I don't know” rather than guess.

The lineup. If police show Marcus a lineup, good practice, informed by memory research, includes having it run by an officer who does not know which person is the suspect, telling Marcus the culprit may not be present, and recording his confidence immediately, in his own words, before anyone gives feedback. A first, carefully recorded “I'm fairly sure” is far more meaningful than a later “I'm absolutely certain.”

Hindsight. Afterward, the owner's friends say she should have known her shop was a target. But beforehand nothing marked it out from many others nearby. Judging her by what she knew then avoids hindsight bias and leads to fairer, more useful lessons.