Our changeable memories:legal and practical implications
ElizabethMARCH 2003 | VOLUME 4 www.nature.com/reviews/neuro
The malleability of memory is becoming increasingly clear. Many influences can cause memories to change or even be created anew, including our imaginations and the leading questions or different recollections of others. The knowledge that we cannot rely on our memories, however compelling they might be, leads to questions about the validity of criminal convictions that are based largely on the testimony of victims or witnesses. Our scientific understanding of memory should be used to help the legal system to navigate this minefield.
Memories are precious. They give us identity. They create a shared past that bonds us with family and friends. They seem fixed, like concrete, so that if you ‘stepped’ on them they would still be there as they always were.
But memories are not fixed. Everyday experience tells us that they can be lost, but they can also be drastically changed or even created. Inaccurate memories can sometimes be as compelling and ‘real’ as an accurate memory. In this article, I discuss the ways in which memories can be reshaped and their implications for the legal system. If we cannot believe our own memories, how can we know whether the memories of a victim or a witness are accurate?
Remaking memories
We are all familiar with temporary memory problems.“I can’t remember the right word,” says a colleague at a cocktail party. “Is it senility?” I reply: “Can you remember the word later?”And the usual answer will be yes, proving that the information was not lost, but only temporarily unavailable. Retrieval problems are common.
However, there are also problems with storing something new. This usually occurs simply because the person concerned is not paying attention. But some people are unable to store new information even if they are paying attention and have the opportunity to repeat the new information over and over again — several hours later, it is gone. Such people, including patients with Alzheimer’s disease, might not even complain about ‘losing their memory’ because they do not realize that anything is missing1.
More insidiously, memories can become scrambled, sometimes in the process of attempting to retrieve something. You might relate a story to a friend but unwittingly include some mistaken details. Later, as you attempt to recall the episode, you might come across your memory of the scrambled recall attempt instead of your original memory. Memory is malleable. It is not, as is commonly thought, like a museum piece sitting in a display case.“Memory is,”as the Uruguayan novelist Eduardo Galeano once said,“born every day, springing from the past, and set against it.”2
Usually the scrambled memory does not matter very much. But if you are an eyewitness to a crime, your scrambled recall could send someone to prison. And, rather than feeling hesitant, you might feel perfectly sure of the truth of your memory. The history of the United States justice system, like those of other countries, is littered with wrongful convictions made on the basis of mistaken memories3 . Huff recently estimated4 that about 7,500 people arrested for serious crimes were wrongly convicted in the United States in 1999. He further noted that the rate is thought to be much lower in Great Britain, Canada, Australia, New Zealand and many other nations, especially those that have established procedures for reviewing cases involving the potential of wrongful conviction.
Ronald Cotton, a North Carolina prisoner who was convicted in 1986 of raping a 22-year-old college student, Jennifer Thompson, puts a human face on these cases. Thompson stood up on the stand, put her hand on the Bible and swore to tell the truth. On the basis of her testimony, Cotton was sentenced to prison for life. Eventually, DNA testing — which began 11 years after Thompson had first identified Cotton — proved his innocence. Another man, Bobby Poole, pleaded guilty to the crime3 .
Faulty memory is not just about picking the wrong person. Memory problems were also evident during the sniper attacks that killed ten people in the Washington DC area in 2002 (see for example, REF. 5). Witnesses reported seeing a white truck or van fleeing several of the crime scenes. It seems that a white vehicle might have been near one of the first shootings and media repetition of this information contaminated the memories of witnesses to later attacks, making them more likely to remember white trucks. When caught, the sniper suspects were driving a blue car. Were we observing unwitting memory contamination on a nationwide scale?
Witnesses can be wrong for several reasons. A key reason is that they pick up information from other sources; they combine bits of memory from different experiences. A growing body of research shows that memory more closely resembles a synthesis of experiences than a replay of a videotape6 . Three decades ago, a method of studying memory distortions was introduced. People watched a simulated crime or accident. Later they were given erroneous information about the details of the event, such as the false detail that a man had curly rather than straight hair. Many of these people later claimed that they had seen a curly-haired person7 . Studies such as this showed how leading questions or other forms of misinformation could contaminate the memories of witnesses about events that they had recently experienced8
In the past decade, the challenges have become greater. Newer studies showed that you could do more than change a detail here and there in someone’s memory. You could actually make people believe that a childhood experience had occurred when in fact it never happened. Examples include being lost in a shopping mall for an extended period of time, being rescued by a lifeguard, or surviving a vicious animal attack9–12. How is this possible? In our studies, we enlist family members to help us to persuade their relatives that the events occurred. This method has led about a quarter of our subjects to believe that they were lost in a shopping mall for an extended period of time, and were ultimately rescued by an elderly person and reunited with their families. In other studies, we engaged people in guided imagination exercises.We asked people to imagine for a minute that as a child they had tripped and broken a window with their hand. Later, many of them became confident that the event had occurred. In other studies, we encouraged people to read stories and testimonials about witnessing demonic possession, and even these raised confidence that this rather implausible event had happened.
One recurring issue for memory distortion research is the question of whether the events being reported after such a manipulation might have actually happened. Perhaps the subject did break a window but had forgotten about it — the imagination exercise might have triggered a true memory rather than planting a false one. To prove that false memories can be insinuated into memory by these suggestive techniques, researchers have tried to plant memories that would be highly implausible or impossible. For example, one set of studies asked people to evaluate advertising copy. They were shown a fake print advertisement that described a visit to Disneyland and how they met and shook hands with Bugs Bunny. Later, 16% of these subjects said that they remembered meeting and shaking hands with Bugs Bunny13. In follow-up research carried out by Grinley in my laboratory, several presentations of fake advertisments involving Bugs Bunny at Disneyland resulted in 25–35% of subjects claiming to have met Bugs Bunny14 . Moreover, when these subjects were subsequently asked to report precisely what they remembered about their encounter with Bugs Bunny, 62% remembered shaking his hand and 46% remembered hugging him. A few people remembered touching his ears or tail. One person remembered that he was holding a carrot. The scenes described in the advertisement never occurred, because Bugs Bunny is a Warner Bros. cartoon character and would not be featured at a Disney property.
Other ‘impossible’ memories have been recently planted in British students15. The false event was “having a nurse remove a skin sample from my little finger.”This medical procedure was not one that was carried out in the United Kingdom, according to extensive investigation of health policy records. After guided imagination, many subjects came to remember the non-existent procedure occurring in their childhood. Some embellished their reported memory with significant detail such as,“There was a nurse and the place smelled horrible.”