>for some people it could be something you've heard enough to memorize and can predict perfectly.

Totally agree with this. For me there's a particular recording of an instrumental concert (Casiopea vs T-Square, if you're curious) that is incredibly enjoyable if I'm paying attention, but I have it basically memorized at this point. Listening to it helps me get into a working rhythm, and then I'll blink and realize I was deeply focused for over an hour (based on the point in the recording when I actively notice it again).