"avoid visual imagery as you literally can't see while you're imagining something visual."

I guess depends to the person in question. I am imagining a road, a car on it, me driving it, as i am writing this post, looking at the screen, watching the letters come in and correcting a few typos. When i am really bored out of my mind I imagine silly HUD overlay. The interference is comparable of that from verbal monologue while you listen to someone.