Getting talkative people to remain quiet & vice versa

Interestingly enough, both the over-talker and the under-talker suffer from the same root issue: no one is truly listening to them. One wears out a perfectly good set of lips trying to get their point across, while the other is silently thinking, "No one is listening or will care anyway, so why bother?" I've read numerous tips on how to shut down a talker or open up a quiet person in small groups, but no one examines the other end of the relationship to see if something's awry and contributing to the other person's ungroup-like behavior.