Previously: Generalizing From One Example

There was a debate, in the late 1800s, about whether "imagination" was simply a turn of phrase or a real phenomenon. That is, can people actually create images in their minds which they see vividly, or do they simply say "I saw it in my mind" as a metaphor for considering what it looked like?

Upon hearing this, my response was "How the stars was this actually a real debate? Of course we have mental imagery. Anyone who doesn't think we have mental imagery is either such a fanatical Behaviorist that she doubts the evidence of her own senses, or simply insane." Unfortunately, the professor was able to parade a long list of famous people who denied mental imagery, including some leading scientists of the era. And this was all before Behaviorism even existed.

The debate was resolved by Francis Galton, a fascinating man who among other achievements invented eugenics, the "wisdom of crowds", and standard deviation. Galton gave people some very detailed surveys, and found that some people did have mental imagery and others didn't. The ones who did had simply assumed everyone did, and the ones who didn't had simply assumed everyone didn't, to the point of coming up with absurd justifications for why they were lying or misunderstanding the question. There was a wide spectrum of imaging ability, from about five percent of people with perfect eidetic imagery to three percent of people completely unable to form mental images.

Summary: I do not have visual mental imagery. I want it. How do I get it? What exercises, if any, will help?

In further detail... Here's Francis Galton's Statistics of Mental Imagery paper. I'm not quite at the 3% level of completely unable to form mental images, but I'm close. In particular there are three times I have vivid, sharp mental imagery, and the existence of such times tells me I have the brain hardware to visualize. It's enough to let me know that I want it all the time. Unfortunately I don't know how to get it. And searching online has proven difficult and frustrating... for example this article is first of all about a different meaning of "visualize", it's talking about some kind of self-help motivational thingy, and second of all it starts by saying "How to Visualize: I want you to relax and close your eyes. Picture a hot, sunny day at the beach."

Full Stop. Halt, Catch Fire and Burn.

That's already too far. For those of us who don't visualize, practice definitely does not consist of pulling up mental images, playing with them in new ways, and expanding our imagination. I'm very good at imagination in some ways, but I lack that first ability to pull up a mental image. That's what I want to learn how to have!

Here is a description of what I can do, what I have tried, what I have learned, etc.

I see vivid visual mental imagery in 3 situations:

While dreaming. My recollection of dreams has that I see fairly vivid, sharp, whole-scene imagery.
Just before sleep. When I am in a certain almost-sleeping state, I can tell my mind to picture something - like an apple, or a horse - and I will often be able to see that thing vividly, briefly, and then it morphs into a scene. A beach with an ocean, or a pleasant clearing in a forest. If I try to alter the scene, like putting a beach towel and umbrella on the beach, the scene changes and morphs in some way but seemingly without regard to the changes I requested. Maybe my POV starts moving forward down a newly created path in the forest, for example.
During meditation. Sometimes I feel like I'm in exactly the same mental state during meditation as I am just before sleep, except without the tiredness. The imagery has the same characteristics in both situations.

I have tried 3 classes of practice:

Staying in visualization situations. When I find myself in the just before sleep or meditation state, I stay there for a while and play with imagery. This is fun but I have seen no increase in control over what I visualize and no increase in the range of states in which I can visualize.
Explicit imagery practice. I have found or drawn simple shapes, like a square or a ball, then stared at the shape, closed my eyes, seen the shape for as long as it stayed visualizable, opened my eyes to refresh, repeat. This straight up hasn't worked at all. I don't visualize it, only have the afterimage, and need to refresh within about a second.
Object drawing. I have had 3D constructions of blocks and tried drawing them from different angles on paper. This is an exercise I did while growing up during summers. Unfortunately there was no actual imagery or mental rotation involved, I just logic'd out where lines must surely go and drew like that.

Here is what my mental imagery looks like, per Francis Galton's questions.

Picturing breakfast. The image is extraordinarily dim, extraordinarily ill-defined (at most an edge or two changing the black-purple-brown background static texture), and not at all natural colors.
Vividness of Mental Imagery scale. This is a sequence of 100 descriptions of imagery, organized approximately in order from most vivid to least vivid. Of the given responses I identify most strongly with 94, 95, 96, 97, 98, and 99.

Here are my results on Marks' Vividness of Visual Imagery Questionnaire: 4s on everything except 5s on 4, 6, 9, 11, 14. Results suspect since I had exactly one 5 on every section. Marks suspects, unofficially, that those without visual mental imagery may actually have it but be unable to consciously notice/report that they have it.

I read through the Stanford Encyclopedia of Philosophy's entry on Mental Imagery, following links to places or ideas that looked promising. I have many forms of mental imagery: good aural, very good verbal, very good analytic, good motor, poor yet extant haptic. But not visual.

Eric Schwitzgebel questions our introspection about mental imagery in general based on the lack of correlation between scores on Marks' VVIQ and subjects' ability to perform certain tasks that "psychologists have often supposed to require visual imagery". Such tasks include mental rotation and visual memory, both of which I can perform easily. I find it blindingly obvious that actual visual mental imagery is not required for these tasks. Here is my own introspection about mental imagery: what I call Imagination is sufficient for all the tasks that supposedly require visual imagery.

Does anyone know of (tested?) exercises for developing visual mental imagery from scratch?

Does anyone know that developing visual mental imagery from scratch is likely impossible?