Q: This has been a question that has been nagging me. Is there such thing as
"peripheral hearing"?

A:  I’ve not heard of anything like that.  There is a phenomenon called auditory exclusion that is found in combat.  Some people report that their gunfire sounded distant and quiet during a shootout.  Other people have totally been unable to hear shouted instructions or warnings during a fight.  This could have disastrous consequences if you are fighting multiple opponents and you can’t hear the other attackers as you focus on the main threat. 

For a really good article on the types of physiological changes you can expect to encounter in a fight, check out the article by Darren Laur, Personal Protection Systems Inc., regarding the real physical effects of fear and why you will react in a certain way.  It's called The Anatomy of Fear and How It Relates To Survival Skills Training