New research from psychologists at the University of California, Los Angeles has found that when we repeatedly experience very similar events, our memories of those events can start to blur together—especially if one of them is emotionally charged. This memory “blending” effect was strongest in individuals with higher anxiety and in those who showed stronger physical reactions to emotional events. The study, published in Cognitive, Affective, & Behavioral Neuroscience, offers new insight into how emotional experiences can shape our memories.
Most everyday experiences share many features with each other: your morning commute might look nearly identical from one day to the next, with only subtle differences—like the color of a passing car or the person sitting across from you. Because our brains must keep track of all these similar experiences, they are constantly working to reduce confusion. One strategy the brain seems to use is exaggerating small differences between memories, a phenomenon known as “memory repulsion.” But until now, scientists didn’t know how this process might be affected by emotion, or how it might work differently in people prone to anxiety.
“Our brains are remarkable at storing memories, but they face a major challenge: many of our experiences are very similar. Think about parking at work — if you’ve parked in the same lot hundreds of times, how does your brain keep today’s parking spot from getting mixed up with all the others? The real miracle of memory, then, isn’t just remembering. It’s remembering the right thing at the right time,” said study author David Clewett, assistant Professor at UCLA.
“One way our brains solve this problem is by slightly exaggerating differences between similar memories, a phenomenon known as ‘memory repulsion.’ If two experiences overlap just enough to create interference, our brain subtly distorts them to make them feel more distinct.
“For example, if I parked next to a light red car yesterday and a dark red car today, my brain might make the light car seem even lighter and the dark car even darker. While this creates small inaccuracies, it also helps prevent confusion, ensuring that I remember today’s parking spot correctly.”
“Building on this work, we were interested in how this repulsion process affects emotional memories. Imagine that the dark red car actually damaged your vehicle when they pulled into the parking spot. Is this upsetting event pushed farther away from similar, uneventful memories? This could be useful, particularly for emotional well-being. If our memories blurred together too
much, you might be emotionally triggered by all red cars in the future, which isn’t helpful.”
“Although this example describes something relatively mundane, blurring emotional memories could make it difficult to distinguish between dangerous and safe situations. This could cause fear to spill over into other memories, leading to the development or persistence of emotion disorders.”
The researchers designed an experiment in which participants studied pairs of objects and faces. Sixty-six people participated in the study. Participants were shown pairs of faces associated with different images of everyday objects like blenders or sofas. For each object, there were two versions that were similar in color. For some participants, the two versions were very similar in color, like two shades of red close to each other. For others, the colors were less similar, like a light blue and a darker blue. This color difference was designed to change how much the two memories would interfere with each other – very similar colors should cause more interference.
To bring emotion into the picture, sometimes a loud, startling burst of white noise was played just before participants saw one of the object-face pairs. This noise was designed to create a sense of arousal and mild aversion. The other object-face pairs were preceded by a neutral tone. The researchers used pupil dilation – the widening of the pupils of the eyes – as a measure of how aroused participants were by the sounds.
“People respond in different ways to upsetting things,” explained co-author Erin Morrow, a PhD student in cognitive neuroscience. “One way to measure this difference is by looking at pupil responses to startling noises, like bursts of white noise. Some people might show a larger pupil response, while others might show a smaller response. This is a good way to quantify physiological reactivity, or how distressing individuals found these irritating sounds to be.”
After each round of learning these object-face pairs, participants were tested on their memory. They were shown one of the objects in grayscale and had to use a color wheel to select the color they remembered seeing. This test helped the researchers see if participants’ memories for the colors of the objects had shifted or distorted over time. Participants were also tested on their ability to remember which face was paired with each object. This associative memory test helped measure how much the similar memories were interfering with each other. Finally, participants filled out questionnaires to measure their levels of anxiety and depression.
As expected, the researchers found that people learned to associate the faces with the objects over the course of the experiment, and their color memory for the objects also improved. The loud noise bursts did reliably cause pupil dilation, showing that they did induce physiological arousal in the participants.
However, the results regarding memory distortion were unexpected. Instead of finding memory repulsion – where the remembered colors would be pushed further apart – the researchers found memory attraction. This means that when the object colors were very similar, people tended to remember the colors as being even more alike than they actually were. This effect was stronger for the group who saw very similar colors compared to the group who saw less similar colors.
“Based on prior research, we originally thought that overlapping memories would be pushed away from each other over the course of learning,” Morrow told PsyPost. “This was based on the idea that moderately similar memories stand to benefit the most from separation. However, we actually found the opposite: after repeated opportunities to learn the overlapping events, their memories tended to blend together rather than separate.”
Intriguingly, the amount of arousal a person experienced, as measured by their pupil dilation during the learning phase, was linked to this memory attraction. People who showed greater pupil dilation in response to the sounds were more likely to show memory attraction for the very similar colored objects.
“We found that people who were more physiologically reactive were more likely to remember very similar events as being blurred together,” Morrow explained. “When there was greater blurring between memories, people also tended to confuse other relevant information. This happened after people had been exposed to both events several times.”
Furthermore, the researchers found that people who reported higher levels of trait anxiety – meaning they are generally more anxious people – showed greater memory attraction specifically when one of the similar memories was associated with the aversive sound. This suggests that anxiety might make people more prone to blending together memories, especially when negative emotions are involved.
“We also found that people who reported being more anxious were more likely to experience memory blurring between an upsetting event and a similar, ordinary event,” Morrow said. “Again, this was evident after people had been repeatedly exposed to both events.”
“Whether these memory distortions are helpful or harmful may depend on one’s goals. If you have no reason to keep memories very distinctive and it would be more useful to generalize across situations, then blurring them together might actually make sense! For example, if this memory distortion helps you learn to avoid a situation that looks a lot like a dangerous one, it could help keep you safe in the future. In short, our memories are malleable, and that may not always be a bad thing.”
The researchers noted some limitations of their study. They used simple images of objects and basic colors, which is different from the complex and rich experiences we have in everyday life. It’s important to see if these findings hold up in more realistic scenarios. Also, the memory distortions developed gradually over repeated exposures, suggesting that this blending process takes time. Future research could explore if making it more important for people to distinguish between the similar memories would change the results, perhaps leading to memory repulsion instead of attraction.
“We might be more likely to see memory repulsion if we made it useful to keep these memories separate from one another,” Morrow noted. “Goals matter. We only had time to test participants’ memory for one event at a time. If we had tested memory for the overlapping events simultaneously, people might be more motivated to learn their subtle differences and to exaggerate those differences in their memory.”
The long-term goal is to understand how emotional states reshape memory in everyday life and in mental health.
“Memory distortions might seem undesirable, but they’re a small price to pay for a well-functioning memory system,” Clewett explained. “Our past research has explored how the brain exaggerates differences in sensory details (e.g., colors) to keep similar memories from interfering with each other. But memory doesn’t just stretch details—it also stretches time.”
“In our ongoing work, we’re investigating how the brain subtly warps our sense of time to fit the structure of our experiences. For example, when we move from one location to another, our memories naturally separate those events. But our findings suggest that the brain also goes one step further—it can exaggerate the time gap between them, making them feel like they happened farther apart in time than they actually did.”
“By bending time in this way, the brain isn’t distorting reality for no reason,” Clewett continued. “It is allowing us to remember distinct episodes that can serve us better in the future. Beyond everyday memory function, we’re also interested in studying how different types of memory distortions, especially under emotional circumstances, relate to mental health conditions like post-traumatic stress disorder (PTSD).”
The study, “Distortion of overlapping memories relates to arousal and anxiety,” was published online on October 8, 2024.
