I do not know what is happening when I read a fiction novel, I've never tried to watch my thoughts as I was reading fiction and memory is bad. I'm in the middle of one, I'll check tonight. I definitely don't Mental Image scenes or characters, that's something I'd have noticed.

Edit: I read a chapter. I know I didn't Mental Image and I didn't notice the thing I call Imagining. I paid attention to my reading speed, which is normally very high. Passages on description of physical scenery I skipped over faster than I thought I could possibly read them - going back and reading deliberately, I found that whatever heuristic or background process let me skip them correctly identified that there was nothing there for me. Passages on characters' inner thoughts or conversations aloud or on action occurring I never skip-skimmed.

It's not "just" words on a page... but there's no visual involved beyond the symbol.