False memories can tarnish justice and even distort history, write Elizabeth Loftus and Maryanne Garry.
Memories are among our most precious possessions. They define who we are as individuals and create a shared past that bonds us with others. Yet a growing body of research in psychological science shows that our memories may not be worthy of such unconditional love and trust.
About 30 years ago, psychologists developed a method for studying memory distortions. People watched a crime or other simulated event. Later they were fed erroneous information about details of the incident, such as the false detail that a vehicle involved in a crime was white instead of blue. These people later claimed that they had seen a white vehicle, not a blue one. Studies such as this reveal the power of leading questions or misinformation to contaminate the memories of witnesses about events they have recently seen.
More recent studies reveal that you can do more than plant a false detail here and there. With the right suggestions, you can make people believe they had childhood experiences they never did, such as getting lost in a shopping mall and being rescued by an elderly woman, being hospitalised overnight with painful earache, spilling punch on the parents of the bride at a family wedding, or surviving a vicious animal attack. How do you plant these false memories? One favourite method is to enlist family members to help persuade their relatives that these key events occurred. Across the many studies, about a quarter of individuals have been induced to report that they had had these childhood experiences. Many gave details and expressed high levels of confidence about their pseudomemories.
Scientists have developed other powerful ways of planting false memories. In one case, "experts" analysed people's dreams, and the bogus analyses produced false memories of being lost or harassed by a bully. In another, scientists doctored people's childhood photos and the bogus photos produced false memories of taking a hot-air balloon ride.
To understand how our autobiographies can be tricked, we must first understand how false memories begin with a seed of suggestion and grow into a full-blown memory-like experience. False memories sprout when a person believes that a made-up event is plausible. They become seedlings when he believes that the event happened. Finally, they take root when he embellishes the belief with the kinds of sensory details that make it feel like a real memory. We can fertilise the memory with a handful of suggestions at any step.
Lest readers take comfort in thinking that if they avoid strong-armed tactics such as doctored photographs, they can trust their memories, other research shows that seemingly innocuous activities can also plant the seed. Getting people to imagine for a minute or two that they broke a window with their hand or found money in a car park inflates their confidence that the events actually happened. You do not even need to imagine, just read. Reading stories and testimonials about witnessing demonic possession raises confidence that this rather implausible event happened.
And if you think you might stop reading and seek refuge in the telly, that may not help. Research shows that false details planted in ads can make you believe you had experiences that you never had. People who reviewed phoney ads showing Bugs Bunny at Disneyland later believed that they had personally met him there. The problem: Bugs does not live at Disneyland; he is a Warner Brothers character. What is next? We need to know when the seeds of suggestion take root, and when they do not. Could we make you believe that you had shaken hands with the purple Tellytubby at Disneyland? How about Posh Spice? Or the Queen? If you are less likely to bind these elements to memory of a childhood trip to a Disney theme park, why? We also need to know whether there are reliable ways to distinguish a true memory from a false one. As of now, there are not, although many behavioural and neuroimaging studies are attempting to find one.
While scientists continue to beaver away at these issues, some wider implications are already clear. Police interrogations that are suggestive or coercive can lead witnesses to faulty memories causing juries to convict innocent people. Psychotherapy methods that are suggestive or coercive can lead patients to false beliefs causing harm to the patients and their extended families. Thousands of families have been affected in this way, another example of a "cure" that is worse than the disease.
More generally, health professionals rely on patient self-report. Even when careful to inquire neutrally, they need to appreciate that their patients' autobiographies may have been distorted even before they walked into the waiting room. For example, research shows that people remember using condoms more often than they really did. Are their exaggerated condom memories the result of exposure to public-service reminders encouraging condom use?
Distortion in the individual mind is one thing, but sometimes distortion affects a family, a culture, or a country. Historians know well that history is not necessarily the same thing as accuracy. They have come to appreciate that the way history is recorded affects the way it is remembered. History textbooks often play down uncomfortable information and play up a rosier perspective. Under some regimes, historical photographs have deleted those who have fallen from political favour. Even recent history is reinterpreted in the "spin room". Are these simply memory distortion techniques applied on a grander scale?
If we have learnt anything from our studies of false memories, it is this: when we hear a memory report, we do not uncritically accept it as true. It is an opinion. It is a hypothesis. And as with many opinions and hypotheses, it is one side of the story.
Elizabeth F. Loftus is professor of psychology at the University of Washington, Seattle, United States. She will speak at the Festival of Science in Glasgow on September 4. Maryanne Garry is senior lecturer in psychology at Victoria University of Wellington, New Zealand.