Comment by xg15
1 day ago
>The hole in the retina is sizeable (~9 full moons in the sky), but we don’t notice it because [...] (2) our brain automatically fills in gaps in our visual field by interpolation
I still remember this bit from school and various pop-sci book, but is it actually true? Is there really some group of neurons in the brain somewhere that actively tries to restore the "raw" visual information that was blocked by the blind spot?
Thinking of ANNs, I felt it was more realistic that higher layers in the visual cortex are mostly only using the visual information to find patterns anyway, and that they're robust enough they can still find those patterns without the data from the blind spot locations. (As long as a pattern isn't fully contained within the blind spot regions of course)
An analogy would be a QR code reader that can still parse the encoded information if a part of the QR code is missing - but it won't actually "reconstruct" the missing sections to do this.
But I don't know if it really works like this.
I've read a number of consciousness books and this idea that the brain is inpainting the blind spot. I know Dennett in his "Consciousness Explained" book of 30+ years ago did his best to debunk that idea.
The problem with inpainting is that it suggests there is a generator that knows how to fill in that spot before the "witnessing" part of the visual system then gets to work. This is perhaps best thought about from a more extreme example of dreamining: witnessing visuals with the eyes complete closed. In short, the visual system isn't like a projector screen with the finish fixed-up image that some interior witness views.
I believe that most researchers have a very different model, that of the controlled hallucination. What we experience isn't the photons hitting the array of rods and cones like a 2D array of pixels. Instead, we have an internal model of what we are looking at and visual input is there to provide feedback to keep the model of the world updated. The blind spot isn't experienced because we aren't looking at the 2D grid of pixels -- our model is coherent, and the presence of the blind spot simply means that no corrective feedback comes from that area of that one eye.
One compelling bit of information is there while there are neurons feeding processed visual information forward into the brain, there are more feeding back from that area to the visual system. That is, the the visual system is providing error signals and not the image we are experiencing. When something not predicted appears, the visual system sends forward information guiding the internal model to be updated.
Have you ever had the experience where you have been asked to close your eyes and put into a novel environment before then being allowed to open your eyes? It takes less than a second, but you can feel a moment of disorientation while your brain builds that world model. Another way is via some optical illusions (Necker Cube) or Escher drawings. You can look at a part of the drawing and everything is fine, but then as you change your focus there is a transitory feeling of unease as that world model is in flux as it tries to resolve the new visual input with the model it had been using.
I was going to say the same thing. When we look at a book, we see the book in our minds, not a picture of a book. The processing that happens in our brains works to create the representation, it’s not transforming one image into another.
There’s a significant portion of the population that doesn’t “see” anything in their mind’s eye when reading.
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>(As long as a pattern isn't fully contained within the blind spot regions of course)
There are dedicated optical illusion/explainers that give you the experience of the brain patching over the space with neutral background, even if there's something there, like a symbol or a star.
So if it's something featureless or continuous, like a wall of your room that's a solid color, or a sheet of college ruled paper, the pattern can just be continued.
That said I would stress there's limits to how much of that you can do just by pattern extrapolation as opposed to deriving images from distinct and specific information in a given region of the visual field. You have to know enough about a stretch of visual space to know that it's appropriate to spread a pattern over it, and that's the thing the blind spot doesn't know.
What’s interesting about that is that brain doesn’t actually give you much access to the sensor information directly, but gives an interpretation instead. There is a thing called Saccadic Suppression that blocks visual data processing for 50ms when eyes are moving, and the brain just backfills that missing data from the “next frame”. https://en.wikipedia.org/wiki/Saccadic_masking
Thanks, I had not heard of that one. As a recovering philosophy bro I love cataloging all of these peculiar artifacts of our visual experience. They turn out to matter quite a bit in some of the endless mind versus brain and mind versus matter debates. Off the top of my head:
- Blind spot where the optic nerve exits the eye
- Saccadic Suppression (new to me!)
- Panum's fusional area (how close the overlapping images of your eyes have to be to each other to get merged into a unified image)
- The wagon wheel effect
- trichromatic vision (obvious but important because it easily could have been different)
- The foveial field, the central part of vision that's extremely precise, while things increasingly further away from it are blurry
- specialization in peripheral vision, (eg better sensitivity to starlight, as well as better sensitivity to flickers and motion)
Add those all up and you get a bunch of specific but contingent properties of visual experience. Some people of a certain philosophical frame of mind like to imagine that we inhabit a kind of pure mental experience detached from the physical world, but even if you think you're making no assumptions about the empirical world, all of these contingent facts show up, which make a lot more sense as being the products of biological structure.