Introducing the brain: perception and memories (Introduction)

by David Turell , Thursday, December 15, 2022, 17:30 (707 days ago) @ David Turell

Scans have worked it out ow the brain handles them:

https://www.quantamagazine.org/how-the-brain-distinguishes-memories-from-perceptions-20...

"...in the 1990s neuroimaging studies revealed that parts of the brain that were thought to be active only during sensory perception are also active during the recall of memories.

“'It started to raise the question of whether a memory representation is actually different from a perceptual representation at all,” said Sam Ling, an associate professor of neuroscience and director of the Visual Neuroscience Lab at Boston University. Could our memory of a beautiful forest glade, for example, be just a re-creation of the neural activity that previously enabled us to see it?

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"...when Favila and her colleagues looked at how perceptions and memories were represented in the various areas of the visual cortex, they discovered major differences.

"As participants recalled the images, the receptive fields in the highest level of visual processing were the same size they had been during perception — but the receptive fields stayed that size down through all the other levels painting the mental image. The remembered image was a large, blurry blob at every stage.

"This suggests that when the memory of the image was stored, only the highest-level representation of it was kept. When the memory was experienced again, all the areas of the visual cortex were activated — but their activity was based on the less precise version as an input.

"So depending on whether information is coming from the retina or from wherever memories are stored, the brain handles and processes it very differently. Some of the precision of the original perception gets lost on its way into memory, and “you can’t magically get it back,” Favila said.

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"But why are memories recalled in this “blurrier” way? To find out, the researchers created a model of the visual cortex that had different levels of neurons with receptive fields of increasing size. They then simulated an evoked memory by sending a signal through the levels in reverse order. As in the brain scans, the spatial blurriness seen in the level with the largest receptive field persisted through all the rest. That suggests that the remembered image forms in this way due to the hierarchical nature of the visual system, Favila said.

"One theory about why the visual system is arranged hierarchically is that it helps with object recognition. If receptive fields were tiny, the brain would need to integrate more information to make sense of what was in view; that could make it hard to recognize something big like the Eiffel Tower, Favila said. The “blurrier” memory image might be the “consequence of having a system that’s been optimized for things like object recognition.”

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"But it’s not clear “whether it’s a feature or a bug,” said Thomas Naselaris, an associate professor at the University of Minnesota. He was not involved in the new study, but he came to a similar conclusion that perception and memory look very different in the brain in a 2020 study. He favors the idea that the difference is advantageous, perhaps in helping to differentiate perceptions from memories. “A person whose mental imagery had all of the detail and precision of their scene imagery could get confused easily,” he said.

"The blurriness could also help to prevent storage of unnecessary information. Maybe the important thing isn’t to remember where each pixel sits in the field of vision, but that the pixels belong to a family member or a friend, Favila said.

“'It’s not like the visual system is incapable of generating highly detailed, vivid and precise imagery,” Naselaris said. People have reported very vivid visual images, for example, when they’re in the “hypnogogic” state between sleep and wakefulness. The brain “just tends not to do it during waking hours.'”

Comment: what I take from this is when we study the brain, se find a every logical design.