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The limits to what I can visualise? Well, I'd put it this way - there definitely are limits, but what they are is a matter of training. There are traditions of mental training that challenge the practitioner to visualise increasingly complex things, so I've run into them.

A standard example of such visualisation is 'in bluish-white light on a dark background, imagine a line. from the same light, imagine drawing a circle using the line as a diameter. Now draw an equilateral triangle touching the boundary of the circle. Then a square around the triangle. Finally, draw another circle around the square, and hold the resulting image stable in your mind' (yes, this shape probably inspired Rowling's description of the deathly Hallows. It's a very old exercise).

I can visualise the line and the first circle easily. I can add the triangle, but at this point it already takes some effort, I can't do it if I'm even a little distracted. Typically, adding the square makes me 'lose' an earlier detail, usually the line, from my visualization.

That's probably not very informative to your question though, because visualization doesn't have the same sorts of rules around complexity a graphics screen does, the brain definitely uses some form of internal shorthand. I can picture a particular celebrity as easily as I can picture a circle, and picturing her holding an item from my grocery list in each hand is if anything somewhat easier than picturing two other elementary shapes connected to the circle. Maybe because humans are used to imagining other humans holding things, I'm not sure.

In any case, there are definitely limits to what a person can visualize, and they're pretty modest for the untrained mind, but it's quite unlike a graphics program where one could simply count the number of pixels required. Not sure if that helps or not...

> A standard example of such visualisation is 'in bluish-white light on a dark background, imagine a line. from the same light, imagine drawing a circle using the line as a diameter. Now draw an equilateral triangle touching the boundary of the circle. Then a square around the triangle. Finally, draw another circle around the square, and hold the resulting image stable in your mind' (yes, this shape probably inspired Rowling's description of the deathly Hallows. It's a very old exercise).

I can't even visualise the dark background or the light.

When you look at a photograph and then look away but try to recall details, how is your memory of it encoded? Do you immediately have a verbal description of it in your head?

I can’t see the light in your example either. If I shut my eyes, and try to see it, I just see blackness though I have no problems with the concept of a blue light (or even the entire scene) - I just don’t see it. To answer the photo question, I don’t have a verbal definition of a photo, I have a relational one. I can still describe the photo reasonably well, but I don’t “see” anything.

I’ve thought quite a bit on how my mind works once I discovered that “the mind’s eye” wasn’t just a euphemism for other people. I think my mind works with rules rather than visuals, and it constructs/deconstructs a lot of them as needed to describe something it can work with.

I’m a software engineer, an ICT5, working at Apple. I tell people my primary skill is “solving problems”, and that’s accurate as a 10k-foot view. I’m good at mentally modeling the intricacies of how a system works, what the dependencies are, what the interactions are between sub-parts, how that effects corner-cases. I can “run” this mental simulation in my head forwards and backwards a bit (not too far) and get a grasp of how it fits together. But there’s no visual to any of this, whether I’m thinking about a bicycle or server-side cryptographic mail storage and transport. It’s all just interacting rules. I’m often the one to point out a flaw in a systems model well before we get to implementation, and I’m good at “breaking new ground” when it comes to implementing something, even for a different group - I get “loaned out” a fair bit.

So I think there are upsides to not having a mind’s eye - I chose physics at college, and found it easier than most I think; equally there are upsides to having the ability to visualise things, I expect. It’s probably a species-optimization to have the capacity for both…

This fits me very well as well. It did not connect with me that people weren't talking figuratively when talking about seeing stuff until I read an article saying some people didn't, and I realised I was the outlier.

If I were to try to remember code, or try to remember a photograph, or try to remember how to get to the closest Super-Market, it's all structured in my mind in the same way. I might remember details, but only if I have paid attention to those details and understand why those things are important to remember. If those details happened to be based on visual details, I would use that, but it is no way close to the same amount of details of a photograph.

I think the best way to answer this might be for you to imagine what a blind person imagines when they take a trip.

I don't know how it is encoded, but I certainly can verbally describe things relatively easily, but I also tends to have a mental spatial understanding of what I see, so I can move through a model of what I've seen and describe element by element on the basis of e.g. that I know how elements of what I've seen is connected.

I'm fairly sure I fall on the aphantasia side of things (or at least mostly - I've had what I'd consider "flashes" occasionally over a couple decades, which serve as a contrast to what I normally experience), but I don't really have any trouble "knowing" what a triangle-in-a-circle-in-a-square-in-a-circle looks like. I can even draw intersections and segments in isolation, or rotate the thing (or the square and circle in opposite directions) and basically immediately tell you how the edges / corners will align with each other.

But I don't "see" any of that. In any way. You tell me it's drawn in a blue light, or the square is an inch thick piece of plaid: sure. now it's plaid. I already have colors picked out and I'm remembering how the threads in the fabric produce patterns when viewed up close, especially where the stripes overlap. I'm not seeing anything though.

It's closer to how I deal with math - 5x7 is 35 because I know it is. I memorized single-digit multiplication long ago, and if I ever want to reassure myself I can just do repeated addition. It's not accompanied by literally any metaphor or mnemonic or whatever, it's just equal to thirty five, and 35 is 三十五 is ٣٥ regardless of where it comes from. Similarly, rotating the deathly hallows by 90 degrees is just a rotated deathly hallows - the line is now sideways, the triangle has a vertical edge on the left, the green stripes in the plaid are now sideways and the diagonal-hashed intersections at the overlaps are in the opposite direction, etc.

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Maybe also oddly, I have a very good visual memory in practical terms. I disassemble and reassemble stuff with no trouble, and when I'm looking for a phrase in a book I read a year ago I can generally find it within an inch of where I remember it on a page (but not usually what page it is). When I'm looking for things I lost, I generally hunt by looking for colors or textures that were adjacent to where I last remember it. I'd never describe how I remember that or how I look for it as seeing though - there's just a wadded up blanket near it with a big fold that tangents with the far right corner of my phone, so I go looking for wadded up blankets.

I feel like this is probably mostly a sensory-qualia thing, almost totally orthogonal to what is being thought about / done. People who can see things in their mind's eye can't necessarily do anything with it beyond having the experience, and people who are totally internally blind can do things that seem to be based on sight. And to some degree both of those are train-able.

The instability and detail-injection has been a fairly big question-mark for me as well. I can completely believe people "see" things at will, and many I've run across claim it's "as real as real-life", but then they immediately fail to answer any simple questions about it. Like if the seat on their visualized bicycle is in front of or behind the rear wheel. Even ignoring if their answer makes physical sense, most of the time there's a significant pause while they try to decide, and something like half of the time they change their mind later.

I suspect it's more like dreaming of a thing than a photograph-like construct, at least in a significant number of cases. It'd also explain why it seems so dream-like when you get into specifics, where the pieces may make sense but they do not even remotely add up to a coherent whole - context or something is lost each time it's visualized. The main important part is that it feels like seeing a thing, which is both 1) something not everyone can do/achieve, and 2) more than sufficient for individual use or broad concepts.

And it can probably be trained to be more stable and detailed, and there are rare outliers where it's significantly better - there do seem to be people capable of maintaining a stable "thing" from inception through real-world construction.

When I try to visualize an apple, it’s amorphous. One minute it might be red, the next green, the next it’s a cartoon. I can’t “hold” the image in my head, and focusing on specific details is easier than the whole apple at once.

What are the limits of what you can dream about?

I have aphantasia (when I'm awake) and visual imagery in my dreams that is sharper and more detailed than real life. I'm also able to lucidly dream although I try not to as it messes with my long term memory.

I would say that we can dream about most things but there are a few obvious limits as there are types of thoughts that will make you wake up:

* Reading is difficult and typically books in dreams don't have words in them.

* "Pushing" (there is no good word for this) the direction of a dream in a particular way too hard will wake you up. It has to be done very gently.

* Abstract reasoning / logic is difficult in dreams, it causes you to concentrate too hard and then you wake up.

In general the limits are to do with the two dominant modes of thought: spontaneous unquestioning creation of ideas is very compatible with dreaming and you can float easily between multiple "perspectives" or versions without any problem. Analytical / questioning / critical thinking is incompatible with dreaming and causes you to wake up. Lucid dreaming is typically learning how to float in the sweet spot between the two modes.

> I have aphantasia (when I'm awake) and visual imagery in my dreams that is sharper and more detailed than real life.

I'm not being snarky, but... how do you know? I mean, if you can't visualize when you are awake, how do you even know what you see/saw when you were dreaming?

I'm guessing they can remember having seen things in the dream in the same way that they can remember having seen things in waking life, but cannot voluntarily conjure arbitrary images while awake.

I think the range of abilities and experiences around visualization, perceptual memory, and so forth, suggests that seeing and remembering are pretty complicated collections of multiple simultaneous processes that are a little differently expressed in different people, and that are not necessarily perfectly coordinated.

More generally, I think we tend to think of ourselves as singular, but we have pretty good reasons to think that a person isn't actually a singular thing, but is instead a collection of many processes that are only more or less coordinated and cooperating.

I don't really understand your question - do you experience dreaming in a different way? I can remember what I saw in a dream, but I cannot visualize it. This is the same as waking memories - I can remember what I saw but I cannot see it again.

The only exception would be the hypnogogic state when I have visual imagery but I'm not entirely present to process it.

Why would you need to be visualize when you were awake to remember what you saw when you were dreaming? As someone who has Aphantasia but does see when they dream this question in really puzzling.

I wouldn't know... I have aphantasia and sometimes I'm not even convinced that I even dream (I'm being facetious but at the same time I'm really not). Many others with aphantasia report similarly that they do not have recollections of their dreams.

I think that I know that I dream, deep down, because of things that former roommates and my wife have told me, but... I am trusting them at their word. And I know they're not lying to me, because why would they, but... I don't know it myself because I haven't experienced it.

Dreams are different from imagining things. When I dream, I'm seeing the dream out of my 'eyes', but its more floaty and out of body.

But when I wake up, I'm remembering what I experienced and it's like a fuzzy movie playing in my head. Imagining things, I think, is very closely tied to remembering and manipulating visual input.

different person, also have aphantasia. My dreams are completely devoid of sensory content except sometimes the entire dream is music.

I sound pretty far down a different path - my dreams are nearly always entirely audio-free in any form, but I can read just fine in them, which I've heard described as "impossible" many, many times.

Your comment really caught my eye. Would you mind saying a few words about what a dream that's devoid of sensory content is like (i.e. what is it that remains that makes it a dream)?

> sometimes the entire dream is music

What does this mean?

How are we to convince a blind man that we can see?

You could convince a blind man that you could see quite easily, by doing things that require vision and that blind people couldn't reproduce. Since the alleged visualizers don't seem to be able to do anything aphantasia-people can't - it makes me think visualization isn't real.

I remember hearing about a study on mental rotation. The time it takes most people to determine whether two shapes are identical (but rotated) is roughly proportional to the angle of rotation between those two shapes. That seems to be close to what you're asking for.

Whenever I have to mentally rotate shapes (only on tests of mental rotation / IQ) I do it by just comparing the features of the original shape to each of the candidates and ruling out options. e.g. noticing that one option has too many vertices or not enough. It's tedious but pretty reliable.

Your comment made me Google "aphantasia mental rotation" and the summary of the first result I got makes me think I'm probably right. As I read the summary, aphantasia people were slower but more accurate. In other words, the aphantasians know they don't have visual imagery and therefore do the slow but steady thing whereas the visualizers think they have visual imagery and are fast but wrong.

Granted, I haven't read the paper, but at first glance I'm counting it as evidence for me.

https://jov.arvojournals.org/article.aspx?articleid=2700106

Or we've spent a whole lifetime training spatial recall, and so we can do that part better. I can spatially "manipulate" scenes I remember well with great precision, and I don't visualise anything. As such I don't think you can reasonably say anything at all about the ability to visualise based on this.

But why would it take visualizers longer to just pretend to rotate a shape over a greater angle? I think the best explanation is that something is really being rotated, however inaccurate, simplistic, or vague.

So here is one potential discriminator. A person that can visualize sees something traumatizing. For example, witnessing someone being killed, or a gruesome accident on the highway. That person will repeatedly have flashbacks re-playing those images again and again. It's horrific.

How do you distinguish that from normal memory recall?

> it makes me think visualization isn't real.

It is. The problem is that it's not a pixel-perfect reproduction of things on a screen. It's not a movie theater, or a computer screen.

The brain is a powerful pattern-recognition machine that gets exceedingly more complex with age and experience. So:

If you ask the person visualize a bicycle, the person will visualize an amalgamation of bicycles that roughly has two wheels, a saddle, and a handlebar. And this will differ from person to person.

A kid will vividly imagine the bicycle he/she has, or the bicycle he/she wants. Same is likely for avid cyclers. For most people it will probably be a superimposed image of many bikes they've seen over the course of their lives blurring together.

The reason is probably because recollection of details is costly, and usually not that important for our very ancient very lizard brain whose primary reaction to things is still fight or fight :)

But then if you ask a person to visualize "a yellow bycice with red tyres", the visualization will become clearer, but still fuzzy and different for different people. If you've seen such a bicycle (esp. recently), you will visualize that, with high degree of fidelity. If not, your brain will once again create an amalgamation of bicycles, and create an overlay of yellow and red that may or may not be of high fidelity (I can't imagine red tyres on a bike for some reason, but I can imagine red rims on a bike, go figure).

Kids are better at visualising and imagining things because they have fewer sources to draw from, and they don't interfere with each other.

For adults it's more like a combination of camera obscura and long exposure:

- You visualize certain details in a sea of recognizable fuzziness. Example: "vizualize a street vendor" can be something similar to this (long exposure): https://lh3.googleusercontent.com/proxy/kIDQANDGRgVD91zdzZpg...

- You visualize a regonizable pattern without specific details. Example: "visualize a passage" can be similar to this (camera obscura): https://i.shgcdn.com/dea29cf1-c27d-4f55-a029-9443222c0a0b/-/...

It definitely is real for 95% of people, you just don't have it. I doubt you could draw well from imagination even with artistic training, so there's that. Everything else is just pure cope.