My wife has to have something occupy one thought stream on a sensory channel in order to focus on the something she really wants to focus on on a separate channel. She usually runs three or four.

A friend knows how to fork and merge parallel streams at will, but can get bored. The mental intensity he can achieve when all of his streams merge is much greater than typical. He tells me he’d run podcasts at 4x or something while he works on other stuff.