I think in images a lot. It's damned useful for an organic chemist to be able to visualize a molecule in three dimensions without having to resort to models. Stereochemistry has always been easy for me. It's also terribly handy to be able to visualize a map in one's mind when one is trying to navigate an unfamiliar area. I'm good at doing visual art things (despite my total lack of ability to draw) because I can visualize the effect I'm going for before I actually start building the image1.
The thing that's frustrating about it is that I often have problems expressing those images in words. I've imagined scenes and sequences for stories in my mind, but when I sit down and attempt to put those scenes into words as a piece of fiction I have a very hard time doing it. The reverse is also true. When I read, the characters are often faceless, and they are walking through an ill-defined (in my mind) space where stuff happens. I can eventually get a feel for locations and descriptions, but it's difficult, and often requires lots of rereading. Maps are good, too. (One big frustration I have with The Silmarillion is that the large map that comes with it is both awkward to use and is missing half the notations that the tiny map that is part of the text has.) There are exceptions to this, but it's usually due to the object or person being truly distinctive in some way, like the Moties in The Mote in God's Eye, and it's rare.
It's not that I'm bad with words. I'm good with words, and I do think in words as much as images. I love playing with words and making puns and writing things that rhyme. It's just that in my mind the image space seems to be completely separate from the word space, and there is very little communication between the two. My daydreams are either detailed visual images with few words, or imaginary conversations with people in some nebulous setting, often wherever it is I happen to be in real life at the time. (Notice that almost all of my stuff in Sang Sacre is conversations between me and Phred. It's just so much easier for me to do it that way. I used to write essays as conversations, too.)
It's possible that I'm just lazy, and that I could write those scenes if I worked harder at it. I have done it, I'm just rarely satisfied with the results. The same holds for reading. If I work hard enough at it, I can usually get a picture. (Except for Helm's Deep. Would it have killed Tolkein to put a map in there?)
There is a movement space in my mind as well, although that tends to be pretty closely aligned to the image space. When playing softball I got to a point where could feel the difference in swinging a 28 ounce bat and a 26 ounce bat in batting practice before a game, and figure out which one to use during the game by the way my swing moved and how the ball felt coming off the bat. There was no detailed analysis of the mechanics of the swing, or the components of it like the wrist roll or the follow through. I was blessed with good natural mechanics, so I never paid much attention to all the little things that go into it. I just knew how to do it. The only thing I worried about was whether or not the swing felt right. If it didn't, I grabbed the other bat. It's another thing that I would be hard-pressed to describe in words.
I'm not sure there's a point to all this. It's just something I'd never really thought about in detail before.
1. My inability to draw has had a marked effect on my software choices for doing image creation. Since I can't draw, when I wanted to create images pre-computer, I had to do collage. When I started working on the computer I discovered that I had a much easier time using Altamira Composer (or even PageMaker), than using PhotoShop or Illustrator, because Composer builds images in the same way one builds a collage, moving and layering many smaller pieces into one final piece. PhotoShop wasn't able to do this until much later in the game, and it still doesn't do it as well.