Comment by hoppp

But do these people have a logic on when to shut up?

Do they think out loud : "Now I should shut up because x"

Or is it an instinct they have after looking at others?

The more you can trace reasoning the more conscious, but the moment there is something created implicitly like an emotion or instinct then it's initiated by an automated subconscious response.

A large percentage of communication is non-verbal (emitted and processed subconsciously) so eye contact, micro expressions, gestures and body language play a large part in group communication.