老司机直播

Psychologists who overlaid images with visual noise to measure perception found study participants perceived emotionally arousing images more vividly, contributing to sharper memories later. (Image by 老司机直播 News)

How you see it, how you don't

Study examines memory and perception

If you've ever wondered why you can remember some things from long ago yet can鈥檛 recall what you ate for dinner last night, a new study led by psychologists at the University of Toronto may help.

How much something means to you actually influences how you see it - as well as how vividly you can recall it later - the study shows.

鈥淲e鈥檝e discovered that we see things that are emotionally arousing with greater clarity than those that are more mundane,鈥 says Rebecca Todd, a postdoctoral fellow in 老司机直播鈥檚 Department of Psychology and lead author of the study published recently in the Journal of Neuroscience. 鈥淲hether they鈥檙e positive 鈥 for example, a first kiss, the birth of a child, winning an award 鈥 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.鈥

鈥淲hat鈥檚 more, we found that how vividly we perceive something in the first place predicts how vividly we will remember it later on,鈥 says Todd. 鈥淲e call this 鈥榚motionally enhanced vividness鈥 and it is like the flash of a flashbulb that illuminates an event as it鈥檚 captured for memory.鈥

By studying brain activity, Todd, psychology professor Adam Anderson and other colleagues at 老司机直播, 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鈥檚 own past experience 鈥 the amygdala 鈥 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.

鈥淭he 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,鈥 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 鈥渧isual noise,鈥 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.

鈥淲e 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,鈥 says Todd. 鈥淲hen 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.鈥

The researchers used additional tests to rule out other explanations of their findings, such as how 鈥榥oisy鈥 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.

鈥淲e next wanted to see if this finding of emotionally enhanced vividness influenced memory vividness,鈥 says Todd. 鈥淪o, in two different studies, we measured memory for the images, both right after seeing them in the first place and one week later.鈥

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.

鈥淏oth studies found that pictures that were rated higher in emotionally enhanced vividness were remembered more vividly,鈥 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鈥檙e considering it after the fact.

鈥淲e found that the brain indexes vividness pretty quickly 鈥 about a 5th of a second after seeing a picture, which suggests it鈥檚 about seeing and not just thinking,鈥 says Todd. 鈥淓motion alters activity in the visual cortex, which in turn influences how we see.鈥

The investigators also used functional magnetic resonance imaging (fMRI) to look at which brain regions were more active when people look at things that they perceive as more vivid because they鈥檙e emotionally important. Again, they found amygdala, visual cortex, and interoceptive cortex activity went up with increased vividness.

鈥淲e know now why people perceive emotional events so vividly 鈥 and thus how vividly they will remember them 鈥 and what regions of the brain are involved,鈥 says Todd. 鈥淜nowing 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鈥檚 vulnerability to trauma, including intrusive memories experienced by people with post-traumatic stress disorder.鈥

The findings are reported in the paper 鈥淧sychophysical and Neural Evidence for Emotion-Enhanced Perceptual Vividness鈥. 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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