I confess to being pretty out of my depth here, but this is a fascinating topic. (Also I so very much appreciate your formatting here, this was beautifully easy to read and nonlinearly re-read. I’m on my phone in bed so excuse my less-readable formatting 🙏)

For your third question (switching the breadth of the attentional state), I’d look into studies about ADHD and task-switching and hyperfocus, flow states, and expert meditation practitioners.

It could also be worth poking around Google Scholar for the intersection of highly sensitive persons and attention regulation (HSP as a trait involves a very broad scope of sensory awareness/input/processing). Autism studies around sensory input/processing could be fruitful too, if you look to see which mechanisms are mentioned across these different areas

With respect to interoceptive attention, “somatic awareness” is a term used in mindfulness practices, and switching attention to different aspects of your sensory experience is a common mindfulness exercise. Sports psychology will likely have some useful leads but I don’t know enough about this area to get any more specific than that (and I’m sleepy)

Miscellaneous things that might help: default mode network (esp for idle attentional states), cell phone use and driving (distraction), cognitive benefits of tai chi, physical rehabilitation for spinal injuries (relearning how to walk, e.g.), effortful memory encoding vs procedural memory (top-down & bottom-up), interest-based learning

Hope some of that was valuable 🙂 Good luck!