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It’s lunch time and you’re sitting around a table, chatting and laughing with your friends as other people pass through the kitchen.

But when one of your coworkers goes to get their lunch from the fridge… it’s gone. Someone took it.

They ask you if you saw anything, to try and get to the bottom of this mystery. But how accurate is your memory of what happened? Whether it’s a missing lunch or something bigger, eyewitness testimony can be really important when it comes to crime.

But our memories aren’t always so great. So there are predictable ways that eyewitness reports can become less accurate, and ways we can prevent that. Psychologists know that our memories aren’t perfect.

We don’t recall every detail, like watching back a YouTube video of what happened. Our brains piece memories back together when we need them, and even the most vivid ones can have missing or wrong information. Like what color is the Pillsbury doughboy’s scarf?

It’s blue, right? No, it’s white. I just put it in your mind that it was blue.

One way memories can become contaminated is when misinformation gets added in, often without you realizing. This can happen because of the way a question gets asked, or by listening to other reports of the event. A classic study published in 1974 by researchers at the University of Washington was one of the first to test how the wording of questions affects eyewitness testimony.

Specifically, they were looking into leading questions. They had 150 undergrads come to a lab, watch a video of a car accident, and then answer questions about it. And one key question affected their responses.

Some participants were asked “How fast were the cars going when they hit each other?” while others were asked “How fast were the cars going when they smashed each other?” Those who heard “smashed” estimated the cars were going a little faster. And a week later, when asked if there was any broken glass, those who heard “smashed” were more likely to say yes when there wasn’t any. So the way this leading question was phrased seemed to affect their memories.

Talking with other witnesses can also muddle things. A study published in 2017 by researchers from California State University had 289 undergrads watch a video of a carjacking in groups of five, then report what they saw one at a time. Two people per group were actually double-agents.

They were trained to say certain things, including the totally false idea that the carjacker had a tattoo on his neck. After talking, there was a delay ranging from 5 minutes to 1 week. Then, participants were told to pick the suspect out of a line-up of pictures.

The longer the delay, the more the misinformation affected them. In some sessions, the suspect wasn’t actually in the line-up of pictures. After the 5 minute delay, about 29% of people chose a photo of a vaguely similar person with a neck tattoo, rather than someone who looked a lot like the suspect.

After just 50 minutes, 48% of people followed the misinformation. And after a week, 60% did. When the suspect was in the line-up, that effect still occurred.

But people were only misled after the week delay and the effect wasn’t as strong. Confidence is pretty important when it comes to accuracy, too. We usually have a good sense of how well we know something.

Like, you’ve probably had a good or bad feeling after taking tests at school. So for eyewitness testimony, if someone is questioned pretty quickly after the event, using good procedures, their confidence can actually help predict their accuracy. But as time goes by, be wary.

The more times you hear something — even if it’s wrong — the more confident you are about it. The good news is that there are ways to protect against misinformation, like by testing your memory right after an event by answering questions, without hearing other perspectives. This improves your ability to accurately recall stuff later… which also works for school, by the way.

Another strategy is to warn people about misinformation. Basically, mentioning that other witnesses or sources like the media get some things wrong, so you should think carefully about where each piece of information in your memory came from. Plus, an easy way to increase how much you can remember is to close your eyes while you try to recall what happened.

It doesn’t help every person all the time, but various studies have shown that blocking out other distractions can help you concentrate. When it comes to telling whether someone is accurate, there are other clues. For instance, people who are good at recognizing faces are more likely to correctly identify a suspect.

And if you quickly point out a suspect, rather than taking a while to  think, you’re more likely to be correct. But it’s important to mention that there’s no way to be 100% sure. Eyewitness testimony can be really useful, even when it comes to things like missing lunches.

But because our memories aren’t perfect, it’s important to take stock of lots of different evidence. Because, honestly, maybe someone just grabbed the wrong lunchbox by accident. It happens.

To me a lot. Thanks for watching this episode of SciShow Psych! If you want to learn more about how our brains store information, check out our video about whether photographic memory actually exists.

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