One of the interesting new researches of psychology says
that there is a link between our emotions and memories. psychologists link
emotion to vividness of perception and creation of vivid memories. Have you
ever wondered why you can remember things from long ago as if they happened
yesterday, yet sometimes can't recall what you ate for dinner last night?
According to a new study led by psychologists at the University of Toronto,
it's because 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," says Rebecca Todd, a postdoctoral fellow in U of T's Department
of Psychology and lead author of the study published recently in the Journal of
Neuroscience. "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."
By studying brain activity, Todd, psychology professor
Adam Anderson and other colleagues at U of T, along with researchers at the
University of Manchester and the University of California, San Diego found that
the part of the brain responsible for tagging the emotional or motivational
importance of things according to one's own past experience -- the amygdala --
is more active when looking at images that are rated as vivid. This increased
activation in turn 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," says Todd.
The researchers began by measuring the subjective
experience of the vividness of perception. 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 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," says 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."
The researchers used additional tests to rule out other
explanations of their findings, such as how 'noisy' a picture seems due to less
vibrant colours 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," says 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. How much detail they remembered was 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,"
says 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. Using electrophysiology (EEG) to measure the
timing of activity in the cortex to see when the brain is sensitive to
vividness, gave them a sense of whether this subjective vividness was more
about seeing vividly, or thinking that it was more vivid when you're
considering it after the fact.
"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," says Todd. "Emotion alters
activity in the visual cortex, which in turn influences how we see."
The investigators also used functional magnetic resonance
imaging (fMRI) 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, they found 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," says Todd. "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."
Funding for the research was provided by the U.S.
National Institute for Mental Health and the Canadian Institutes of Health
Research.
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