I went on vacation during this discussion, and completely lost track of it in the process - oops. It's an interesting question, though. Let me try to answer.

First off, using a sensory modality for the purpose of thinking. That's something I do, sure enough; for instance, right now I'm "hearing" what I'm saying at the same time as I'm writing it. Occasionally, if I'm unsure of how to phrase something, I'll quickly loop through a few options; more often, I'll do that without bothering with the "hearing" part.

When thinking about physical objects, sometimes I'll imagine them visually. Sometimes I won't bother.

For planning, etc. I never bother - there's no modality that seems useful.

That's not to say I don't have an experience of thinking. I'm going to explain this in terms of a model of thought[1] that's been handy for me (because it seems to fit me internally, and also because it's handy for models in fiction-writing where I'm modifying human minds), but keep in mind that there is a very good chance it's completely wrong. You might still be able to translate it to something that makes sense to you.

..basically, the workspace model of consciousness combined with a semi-modular brain architecture. That is to say, where the human mind consists of a large number of semi-independent modules, and consciousness is what happens when those modules are all talking to each other using a central workspace. They can also go off and do their own thing, in which case they're subconscious.

Now, some of the major modules here are sensory. For good reason; being aware of your environment is important. It's not terribly surprising, then, that the ability to loop information back - feeding internal data into the sensory modules, using their (massive) computational power to massage it - is useful, though it also involves what would be hallucinations if I wasn't fully aware it's not real. It's sufficiently useful that, well, it seems like a lot of people don't notice there's anything else going on.

Non-sensory modes of thought, now... sensory modes are frequently useful, but not always. When they aren't, they're noise. In that case - and I didn't quite realise that was going on until now - I'm not just not hallucinating an internal monologue, but in fact entirely disconnecting my senses from my conscious experience. It's a bit hard to tell, since they're naturally right there if I check, but I can be extremely easy to surprise at times.

Instead, I have an experience of... everything else. All the modules normally involved with thinking, except the sensory ones. Well, probably not all of them at once, but missing the sensory modules appears to be a sufficiently large outlier that the normal churn becomes insignificant...

Did that help? Hm. Maybe if you think about said "churn"; it's not like you always use every possible method of thought you're capable of, at the same time. I'm just including sensory modalities in the list of hot-swappable ones?

...

This is hard.

One more example, I suppose. I mentioned that, while I was writing this, I hallucinated my voice reading it; this appears to be necessary to actually writing. Not for deciding on the meaning I'm trying to get across, but in order to serialise it as English. Not quite sure what's going on there, since I don't seem to be doing it ahead of time - I'm doing it word by word.

1: https://docs.google.com/document/d/1yArXzSQUqkSr_eBd6JhIECdUKQoWyUaPHh_qz7S9n54/edit#heading=h.ug167zx6z472 may or may not be useful in figuring out what I'm talking about; it's a somewhat more long-winded use of the model. It also has enormous macroplot spoilers for the Death Game SAO fanfic, which.. you probably don't care about.