Being in that situation, two things that stand out are: when thinking about a topic, I do sometimes formulate my questions or hypotheses in internal words, but the "answers" come back in non verbal form: for instance I suddenly just "know" where the flaw in the argument is, or what (counter)example I need to think more about. The other striking fact is that when I am very emotional (eg angry), the internal monologue is suddenly very vivid :)