In the wake of the bombing of the federal building in Oklahoma City in 1995, authorities initially searched for a second bomber working with the perpetrator Timothy McVeigh. The manhunt was triggered when a key eyewitness claimed that another person was with McVeigh when he rented the truck that carried the explosives.
However, authorities eventually discovered that this particular eyewitness had combined two memories. He combined the memory of McVeigh renting the truck with the memory of another person renting a truck the day before; what’s more, this second person just happened to be accompanied by someone who looked a lot like McVeigh.
This case is just one example of how flawed our memories can be, says University of Illinois psychology professor Brian Gonsalves. Our memories are not as sharp as we think.
“Memory is not like pressing ‘play’ on a video recorder and playing back an event in all of its detail,” Gonsalves says. “It’s more dynamic than that. Most often, we only remember bits and pieces of an event, and we’re left to reconstruct the information.”
During the reconstruction of memories, errors are likely to pop up for any number of reasons, such as the brain’s poor encoding of a memory, the attrition of memory over time, or the planting of misinformation. In one Illinois study, for example, Gonsalves found that they were able to plant misinformation and create false memories in subjects roughly one-third of the time when they put them through a memory test.
In the study, researchers showed subjects a series of pictures of people doing random tasks, such as washing laundry or going to a coffee shop. Then they had people read a written summary of what they had just seen, and this is where researchers planted the misinformation. For example, one summary said that Julia went into a coffee shop and picked up oranges, even though it was very clear in the pictures that she picked up bananas.
Researchers followed up with a memory test to find out if the subjects remembered what they actually saw, or if they recalled the misinformation planted in the written summary. According to Gonsalves, subjects had a false memory of the misinformation an average of 32 percent of the time. They remembered the accurate information about 54 percent of the time, and 14 percent of the time they could not remember either the accurate information or the misinformation.
The researchers also monitored subjects with MRI to find out what was going on in the brain when a false memory was being created. They discovered that those who had false memories and those who had accurate memories showed roughly equal activity in regions of the brain that encode the general context of an event, such as that Julia was in a coffee shop. However, subjects who had false memories showed lower activity in the fusiform cortex—a region that is important for encoding specific information, such as that Julia picked up bananas while she was in the shop.
This has implications in many areas, including eyewitness testimony, Gonsalves says. Some people may remember the general context of an event, such as that a robber held up a store, but they may not have encoded memories for specific details about the crime—such as that the robber was a male in his twenties wearing a red sweatshirt.
“Even though you have a general idea of what happened, you might not have been paying attention to the details, which is often the case in eyewitness testimony,” he says. “Our research shows that this is when you are most susceptible to misinformation planted by lawyers or other people. The reconstruction of memories can be very prone to error.”
