On the other hand I have a hard time believing people actually fully see visual information in their head.
No dudes, we can see the Mona Lisa just by thinking about it. Quite literally. I can see Luke and Obi Wan sitting in the hut discussing the Force, and that blue hologram of Carrie Fisher, in detail. And of course there’s audio, now the Cerveza Cristal theme is rattling around my head.
The “screen” even has a location, it’s behind my eyes, maybe an inch above and ahead of my ears. Someone else in this thread said something about “closing your eyes, if you just see light…” no, that’s wrong, the picture is in a different place entirely.
(I’m probably a two or one on that “red star” test.)
I can superimpose things from it on normal reality too though, wherever I want them. They're in all three dimensions, like I can walk around them, or just copy the entire scene wholesale to my inside mind and move it about while I stay still.
It wasn't until I learned about aphantasia that I discovered I'm on an extreme end even of the hyperphantasia end of the spectrum, but it made sense of the fact that as a child, I had a lot of trouble recognizing when I was awake vs. dreaming. I was pulling things into "reality" from my imaginary space as easily awake as most people do while dreaming.
When I was 5 years old, a child psychologist gave me a standard-face watch and told me to practice looking at it whenever I wasn't sure whether I was awake. When I was awake, I would be able to read it. When I was dreaming, I wouldn't be able to. It worked!
I still remember the night in my late 20s when I was absolutely sure I was dreaming (I'm usually a lucid dreamer). By this time I had long since stopped relying on the watch to tell when I was dreaming, because years of life experience had made it much easier to tell, but I still wore a standard-face watch due to years of habit. That night I dreamt I was standing in a pool, pouring water back and forth between my hands. I looked down at my watch and it was 11:37.
When I woke up, I kid you not, the watch on my bedside table's battery had died and it was stopped at 11:37. I've been able to read books and clocks while sleeping ever since.
The only other people I've talked to/heard of who experience something similar also have one or more kinds of synesthesia, which I don't have. I can pull anything from my inner world into the outer one and vice versa, but the things are only themselves. Numbers and letters don't have colors, smells, or personalities. Music notes aren't tactile. Nothing like that.
But it's not static either. I can manipulate it at will. I can move around the space, or move the space around me. There will be more details if it's a space I know well, because more things will have entered my awareness over time, but I can also make educated guesses, like assuming the legs on the back of a table probably match the ones on the front even if I haven't seen the back.
I was actually an adult before I realized not everyone has this. Even then, at first I thought only people who had aphantasia didn't have it. I thought it was totally normal to have an inner world as detailed as the outer one. Now I kinda just think everybody else is missing out!
For what it's worth, I can also hear them. I carry on conversations with people who aren't physically in the room all the time. For example. (My doc assures me that this is fine as long as I know they're not in the room and I don't trust what they say without verifying!) It's extremely useful for bouncing ideas around, even if it's really only an elaborate way of thinking about something by myself in several ways. I find it intuitively easier to discuss something with another person than just to sit and think about it.
I will say it's not much of a tactile sense, though. I can use my hands to manipulate things if I want, but I don't feel them nearly as clearly as I can see and hear them. I guess I also just don't do this as often, because how something physically feels isn't usually terribly important to me. Same reason I look at and listen to a lot more things for information in the outside plane than I touch.