The name is aphantasia.
In the blog post where I talked about the failed covers of The Bright Black Sea, I mentioned that I could not picture peoples' faces in my head, or indeed, as I explored my mind more, that I could not picture anything clearly in my head. At best I'd “see” a vague impression, from which I might be able to piece by piece reconstruct an image. For example, I can probably draw a good picture of my house without looking at it, because I “know” what it looks like without actually “seeing” it in my mind, at least not as a complete image.
The reason why I mentioned this in the post was because I had considered a cover with characters on it, and rejected it for two reasons. The first was that I had no clear mental images of my characters. In my writing, you'll find few references to how they look, most are vague and you're free to ignore them, which reflects the fact that I don't have pictures of real people, people I see everyday and/or have known all my life, much less make believe ones. I could, I suppose, make a spread sheet of each character's physical characteristics, tall,/short, blond/black/brown/red hair, etc. and then just plug those features in when writing about that character, but since there appearance isn't important to me, I'd probably never think about doing it anyways.
The upside is that rather than try to compensate for this imaginative gap with a cheat sheet, I just outsource the job to you, my readers. You're free to imagine them anyway you like. Anyway they appear in your mind while reading about them goes. And that being the case, I didn't want to give them any physical appearance on a cover or interior art. They're yours to image.
A few weeks after that post, I came across an article that describes this condition of not being able to see images in one's mind, a condition called aphantasia.
The BBC article is here: http://www.bbc.com/news/health-34039054
I suppose there are degrees in every condition. I have no trouble finding my car in a parking lot, and I don't think I would even if it wasn't bright green. (My wife's choice.) I still can find my way around places I've visited in many years. And strangely enough, I'm pretty certain that I dream in fairly images, though that's a bit hard to say, because while I retain the impression of images, I can't recall more than an impression of those images – the condition reasserts itself in my waking mind.
I found this interesting. I had realized long before this article that other people could recall events much more vividly in mind than I could, so the condition itself was no surprise, only that it was a diagnosed condition. I don't see it as any sort of handicap. I'm a painter, after all, and most of my paintings are strictly from “imagination”. While my later acrylics are often impressionistic, my earlier work is much more realistic. (There are a few samples of this style on my DeviantArt site.) In all of them, I wasn't painting from what I could “see” in my mind, so much as taking an impression of a place,/time/mood and then engineering something like it onto the paper or board – and as often as not, into something different than what I set out to paint.
The one downside is that I don't get my money's worth as a tourist. I know I was there, but the only way to relive it, is to look at the photos taken. I can not replay the sights and sounds in my mind over and over again, like other people can. Seeing that I hate to travel, that's no big deal, though I wonder if this inability to relive the experience has something to do with my disinclination to travel. What's the cart, what's the horse? And since I can easily find plenty of photos of everywhere, and view many places on street view, going so place to take pictures, and putting up with all the wear and tear and stress of travel is not worth it.