New research is helping us understand why we remember some items from years ago, yet have trouble recalling what we had for dinner last night.
Scientists say our overall perception of the event plays a major role in what we see and what we remember. That is, how much something means to you actually influences how you see it as well as how vividly you can recall it later.
“We’ve discovered that we see things that are emotionally arousing with greater clarity than those that are more mundane,” said researcher and neuroscientist Rebecca Todd, Ph.D.
“Whether they’re positive – for example, a first kiss, the birth of a child, winning an award – or negative, such as traumatic events, breakups, or a painful and humiliating childhood moment that we all carry with us, the effect is the same.”
“What’s more, we found that how vividly we perceive something in the first place predicts how vividly we will remember it later on,” says Todd. “We call this ‘emotionally enhanced vividness’ and it is like the flash of a flashbub that illuminates an event as it’s captured for memory.”
Study findings are published in the Journal of Neuroscience.
Todd and her colleagues studied brain activity and discovered the amygdala is more active when looking at images that are rated as vivid.
The amygdala is the part of the brain responsible for tagging the emotional or motivational importance of things according to one’s own past experience.
Experts believe the increased activation in this area of the brain influences activity in both the visual cortex, enhancing activity linked to seeing objects, and in the posterior insula, a region that integrates sensations from the body.
“The experience of more vivid perception of emotionally important images seems to come from a combination of enhanced seeing and gut feeling driven by amygdala calculations of how emotionally arousing an event is,” said Todd.
The researchers began by measuring the subjective experience of the vividness of perception.
They performed this task by taking pictures of scenes that were emotionally arousing and negative (scenes of violence or mutilation, or sharks and snakes baring their teeth), emotionally arousing and positive (mostly mild erotica), and neutral scenes (such as people on an escalator).
They then overlaid the images with varying amounts of “visual noise,” which looked like the snow one would see on an old television screen.
The pictures were then shown to study participants who were asked to say whether each image had the same, more, or less noise than a standard image with a fixed amount of noise.
“We found that while people were good at rating how much noise was on the picture relative to a standard, they consistently rated pictures that were emotionally arousing as less noisy than neutral pictures regardless of the actual level of noise,” said Todd.
“When a picture was rated as less noisy, then they actually saw the picture underneath more clearly, as if there is more signal relative to noise in the emotionally arousing picture. The subjective meaning of a picture actually influenced how clearly the participants saw it.”
Additional experiments were used to rule out other explanations of their findings, such as how ‘noisy’ a picture seems due to less vibrant colors or a more complex scene. They also used eye-tracking measures to eliminate the possibility that people look at emotionally arousing images differently, causing them to rate some as more vivid.
“We next wanted to see if this finding of emotionally enhanced vividness influenced memory vividness,” said Todd. “So, in two different studies, we measured memory for the images, both right after seeing them in the first place and one week later.”
In the first study, 45 minutes after they did the noise task, participants were asked to write down all the details they could about pictures they remembered seeing. Afterwards, the amount of detail recalled was used as a measure of vividness.
In the second study, participants were shown the pictures again one week later and asked if they remembered them and, if so, how vividly they remembered them from very vague to very detailed.
“Both studies found that pictures that were rated higher in emotionally enhanced vividness were remembered more vividly,” said Todd.
Finally, the researchers used brain imaging measures to look at when the brain responded to emotionally enhanced vividness and what regions of the brain responded.
“We found that the brain indexes vividness pretty quickly – about a 5th of a second after seeing a picture, which suggests it’s about seeing and not just thinking,” Todd said. “Emotion alters activity in the visual cortex, which in turn influences how we see.”
Brain scans in the form of functional magnetic resonance imaging (fMRI) were used to look at what brain regions were more active when people look at things that they perceive as more vivid because they’re emotionally important.
Again, researchers discovered the amygdala, visual cortex, and interoceptive cortex activity went up with increased vividness.
“We know now why people perceive emotional events so vividly – and thus how vividly they will remember them – and what regions of the brain are involved,” Todd said.
“Knowing that there are going to be differences among people as to how strongly they show this emotionally enhanced vividness and the strength of the brain activation patterns underlying them, could be useful in predicting an individual’s vulnerability to trauma, including intrusive memories experienced by people with post-traumatic stress disorder.”
Source: University of Toronto