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Comment by gmurphy | Hacker News Reader

From the related links in this article, I learned that Visual Snow[1] is not what everyone sees at nighttime or when they close their eyes, as I have, for as long as I can remember. I just figured our eyes cranked their ISO sensitivity up.

[1] https://en.wikipedia.org/wiki/Visual_snow

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There seems to be a range of different experiences.

My eigengrau is not completely uniform: there are subtle variations in monochrome intensity. If I concentrate on the eigengrau, interesting patterns can appear. I have some indirect conscious control over the patterns. For example, if I concentrate and ask for a red spot to appear, usually some shade of dim red will appear forming some pattern, but I don't have control over the details. I lost this ability some number of years ago, then practiced until I got it back.

I can only do this in perfect darkness with a lot of concentration, and I need practice to maintain and improve the ability. I think it's like this article titled "Direct Control of the Visual Field", where you teach yourself to control the Eigengrau: <https://zenodo.org/record/1429102>

The article on Visual Snow shows an actively animated noise field, and I don't see any animation unless I'm really in the groove. The Visual Snow article also implies that it causes distress, and that sufferers seek medical treatment to make it go away. That doesn't apply to me. I have never used hallucinogens, I've never had a migraine, etc. I consider myself creative, so that might be correlated.

Do you have aphantasia? I can't voluntarily experience visualizations of a red spot, or any other imagery, but my understanding is that most people can truly "see" a red spot or a face when they picture it, as if they had an off-screen render buffer.

I can easily create mental images in my mind, like a rotating wireframe cube. I can see these images in my minds eye with my eyes open. I experience these mental images as a separate sensory channel from the eigenbrau, which is much more difficult to perceive and control.

To use your metaphor, my mental images are in an offscreen buffer. My eigenbrau is more like my on-screen buffer, but I can't see eigenbrau with my eyes open, presumably because then my eyes are using that channel.

Wow. I feel like a cliche, but after reading the link I realize that I have the same, and had just assumed that it was something that everyone else also experienced and so never questioned it.

For some reason I’m better at getting triangles to form. I’m also the same as you- no migraines or anything that’d I’d consider a negative symptom.

The other optical-related illusion that someones happens with me is that if I’m focusing on something, occasionally everything else may ‘dim’ and that object will ‘feel’ subjectively closer/zoomed in, but a couple blinks and everything goes back to normal.

Edit: I’ll also add that I consider myself to have a terrible visual imagination. If I try and imagine a face (even my parents) I basically don’t get anything. If I concentrate very hard I can imagine something basic - like the wireframe of a cube - but requires a lot of effort to maintain.

I experience the same thing, although I cannot even visualize a fleeting triangle unless I am at the edge of falling asleep. I would describe the focus effect as similar to looking through a pair of binoculars, making the target occupy the entire field of view with an exaggerated sense of depth. I associate it with flow and consciously noticing the effect usually interrupts my focus enough to make it dissipate. I've never found a name for this phenomenon.

If I understand correctly, eigengrau is what everyone sees at low light intensities; visual snow includes that but also daytime noise, floaters, streaks, afterimages.

I see wonky shit all the time, and have just put it down to individual differences in retina & processing sensitivity. But, I have the occasional migraine with aura, AND have used hallucinogens in the past.

So now I wonder how much my visual perception is caused by heredity, and how much by external influences...

Floaters are particles floating around in your eye's vitreous fluid. I have them, but I only see them in rare circumstances when sunlight is shining into my eyes at exactly the right angle.

There is also a disfunction of your cornea, "Fuchs' corneal dystrophy", which can cause glare, halos and streaks, especially at night. I just found this by googling.

Wikipedia defines visual snow as a neurological condition, and I don't wish to conflate that with floaters or corneal problems.

I can experience afterimages if I look at a strong coloured light for a while, then immediately look at a white piece of paper. I'll see an after image in the complementary colour, because the image is temporarily "burned in" to my photoreceptors. I understand that this is a universal experience.

What I'm looking for is different names for each of these distinct visual experiences, if they have different underlying mechanisms.

There is also HPPD (Hallucinogen persisting perception disorder) [using the same gif to visualize even]

https://en.m.wikipedia.org/wiki/Hallucinogen_persisting_perc...

I always thought this is the way human see the world. But no it's just me and some other unfortunate people it seems. I too always assumed it's associated to migraines. Thanks for the visual snow hint!

Wow, I also assumed this was just something everyone had but never talked about. Visual snow, floaters and strong afterimages as long as I remember. Later migraines with aura since 20s.

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