How inner monologues work and who has them(psychologytoday.com)
psychologytoday.com
How inner monologues work and who has them
https://www.psychologytoday.com/us/blog/intersections/202304/inner-monologues-what-are-they-and-whos-having-them
https://www.psychologytoday.com/us/blog/intersections/202304/inner-monologues-what-are-they-and-whos-having-them
One point though: It is not necessarily the case that visual imagery is the only alternative to an inner dialogue. In both cases, that dialogue, or those images, are things you are aware of. There is something going on behind the scenes to generate those experiences. An alternative to dialog/images is just nothing being generated. I.e., there is something going on subconsciously, but there is nothing related to that activity that breaks through to awareness.
We all experience this, in which some "inspired" breakthrough just suddenly appears in your mind. That breakthrough must have come from somewhere in your subconscious mind.
Anecdotally, this is a conversation that my wife and I have occasionally, about our different mental landscapes. She is a very organized person, with lots of lists and internal (and sometimes external) dialog. I need to let problems just simmer in my mind, without paying attention to them, and I eventually get an answer. She believes that my mind is usually empty. My view is that both of us think subconsciously, but the different is that she has some mental dialog/imagery accompanying her subconscious thinking.
More generally, maybe the real thinking is always subconscious, and what we call thinking (the awareness of reasoning) is just accompanying imagery.