Sometimes when I am reading, I let my eyes blur to rest them for a moment. In that blurred vision, the spaces in between the words become more pronounced, sometimes falling into arrangements that suggest shapes and figures. I see all different kinds of things in these shapes made by the spaces. People. Animals. All kinds of things. Anyone else?
Not so much with words, but definitely with leaves blowing on large trees blowing in the wind, or knots on wooden boards.
I look at the negative space in the real world, especially if I'm composing a photograph or planning a painting. I don't do it with the whitespace in books, though.
I do that with carpets all the time, and my floor at night. My room's so messy that all sorts of monsters start popping out once the lights go down.
If I did that, Wrey, I would never see anything else again. hahaha Seriously, I do know what you mean, though. I used to do that all the time when I was working on my last manuscript. I think the weirdest thing I ever saw was a horrible face. I turned off the computer and went to bed.
I imagine most folks do something analogous to what you're suggesting. Might not be the white space between words, but it could be the shape of the letters or the sound of the language or (in my case) I sometimes read a story from the end toward the beginning, maybe after I've read it from beginning to end (or not). I don't necessarily "see" things that way (meaning visual), but doing that with words and stories is part of what prompts my imagination to take hold, or (in the case of reading a story from end to beginning) gives me a different understanding of what the writer was actually doing (I think, because I'm processing the story in a different way). I think everyone has unique ways of "seeing" beyond what their eyes permit them to actually see. So, if you're trying to be sure you're not just crazy, you can either accept that you're not, or that everyone else probably is, too. Your call.