Some people do zone out into their music and do not notice anything else. Some people also crank up their music so that they can't hear anything else.

Honestly hasn't everyone at one time or another while on the bike on a long boring road starting thinking about something and then all of a sudden got startled by someone coming up along side of you and the last time you checked there wasn't anyone within amile behind you? It doesn't take music to get zoned out and not hear something.

By the way I usually listen to books on my mp3 when riding on my own. Mostly financial or business books to give me ideas and help with my business.