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The Certainty of Memory

Scientists have long cautioned that the brain is not a video recorder-storing perfect memory in a way that can be pulled out, rewound, and replayed over and over while remaining intact. Even the simple act of telling a story can modify memory.

This month, the Supreme Court heard its first oral arguments in more than three decades that question the validity of using witness testimony. “Rather than the centerpiece of prosecution, witness testimony should be viewed more like trace evidence, scientists say, with the same fragility and vulnerability to contamination.”

Why is a witness’s account so often unreliable?

Partly because the brain does not have a knack for retaining many specifics and is highly susceptible to suggestion. “Memory is weak in eyewitness situations because it’s overloaded,” said Barbara Tversky, a psychology professor at Columbia University’s Teachers College in New York. “An event happens so fast, and when the police question you, you probably weren’t concentrating on the details they’re asking about.”

Even questioning can lead people astray

Even the process of police questioning and prepping for trial can crystallize a person’s own faulty reconstruction. In 2000, Dr. Tversky published a series of experiments conducted at Stanford University in the journal Cognitive Psychology. In one, volunteers read profiles of fictitious roommates with both charming and annoying habits; they were then asked to write either a letter of recommendation or letter making a case for a replacement.

When later asked to repeat the original description, the volunteers’ recollections were skewed by the type of letter they had written. Their minds had shed qualities that didn’t match the first draft of their own recall and had embellished those that did.

“When we don’t remember, we make inferences,” Dr. Tversky said.

Sometimes we miss details because we weren’t paying attention, but sometimes we are concentrating too hard on something else. Nothing is as obvious as it seems.

Witnesses and the halo effect

In crimes that involve a weapon, Dr. Loftus and other scientists have found that witnesses will fixate on the gun barrel or knife blade but will fail to notice other details as clearly. Yet because they so starkly remember particulars of the weapon and may have the accuracy of parts of their memory affirmed by police officers and prosecutors, witnesses carry an air of assurance into the courtroom.

“Many people think if someone is confident, they must be right,” said Dr. Loftus.

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