A strange phenomenon called visual masking can reveal the time scale of perception, but its underlying mechanisms are not well understood.
Colored plots show neural activity recorded in mouse visual cortex (V1). Each row of tick marks represents the spikes of a different neuron. Although researchers can predict the target side from neural activity with near-perfect accuracy, animal subjects often get incorrect masked trials due to how brain regions downstream of V1 process this information. I am.Image credit: Gail other.
Have you ever wanted to make something invisible? It turns out your brain can do it.
Unfortunately, this is a limited superpower. In visual masking, we do not consciously recognize another image when it appears in rapid succession.
But the timing of those images is important. For masking to work, the first image must flash very quickly, and the second image must follow rapidly (on the order of 50 milliseconds).
Don't get me wrong, the first image doesn't stay in view very long, but it's definitely long enough to be recognizable without the second image or mask.
Scientists discovered this phenomenon in the 19th century, but why and how the human brain does this remains a mystery.
“This is an interesting observation, that your perception doesn't accurately reflect what exists in the world,” said Dr. Sean Olsen, a researcher at the Allen Institute.
“Like other optical illusions, we think this tells us something about how the visual system works and, ultimately, the neural circuits underlying visual perception.”
In a new study, Dr. Olsen and colleagues take a closer look at the science behind this bizarre illusion and show for the first time that it also occurs in mice.
When the mice were trained to report what they saw, they were also able to pinpoint the specific areas of the brain needed for the visual masking illusion to work.
Dr. Christoph Koch, also from the Allen Institute, said, “Our research has narrowed down the region of the brain responsible for perceiving the world around us.''
“What are the steps from the time the photons rain down on your retina to when you actually become consciously aware of what you’re seeing?”
When a rain of photons hits our retina, the information follows a predetermined path from the eyeball through several different areas of the brain and into the highly-processed areas of the cortex, the wrinkled outermost shell of the brain. It ends with
Previous research on visual masking has led scientists to believe that neurons in the early part of the brain in the retina and its pathways are activated even when a person is unaware that they are looking at an image. I know. In other words, your brain sees things without your knowledge.
To explore where unconscious sensations turn into conscious perceptions and actions, scientists first asked 16 mice to move a small mouse in the direction of rapidly flashing images in exchange for a reward if they chose the correct direction. I trained him to spin a Lego wheel.
I then added different masking images on either side of the screen, immediately after the target image.
Adding a mask prevented the animal from performing the task correctly. This means that the animal can no longer recognize the original target image.
Because visual masking had never been tested in mice before, the authors had to create a task for mice, in which the images and the way they were presented were different from those used in previous human studies. I meant that.
To confirm that the optical illusion they showed to rodents was also relevant to us, they tested it on 16 people.
It turns out that human perception (or lack thereof) and mouse perception of this particular visual masking illusion are very similar.
The researchers then used a special technique known as optogenetics, which allowed them to quickly suppress activity in cells or areas throughout the brain with flashes of light.
They targeted this inhibition to the mouse's primary visual cortex, known as the first part of the cortex where visual information from the eyes enters higher cortical areas of the brain.
By turning off the primary visual cortex the moment the masking image appeared, they were able to completely block visual masking after the target image. Even though the masking image was visible, the mouse reverted to accurately locating the first image. the current.
This result implies that conscious perception is occurring in the visual cortex or in higher regions of the cortex downstream.
“This is consistent with the general idea in the field that the cortex is the seat of conscious cognition in mammals, including ourselves,” Dr. Koch said.
Although this study narrowed down the region responsible for conscious perception to the cortex, there are still many regions of the cortex that may be involved.
Further studies will need to silence these other areas to test their effects on visual masking tasks.
“We're starting to put some limits on where masking is occurring,” Dr. Olsen said.
“We think this is a good paradigm to track to track other areas that are listening to the primary visual cortex and essentially fusing the flow of target and mask information in the brain. Masu.”
of findings It was published in the magazine natural neuroscience.
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SD Gale other. Visual cortex is required for posterior masking in mice. nut neurosi, published online on November 13, 2023. doi: 10.1038/s41593-023-01488-0
Source: www.sci.news
