In my opinion the answer is.."wait time." As a strong leader, I often find myself asking questions and then giving the answer before the audience even has a chance to think. This eventually shuts down discussion, because the attendees know they don't have to participate, because the leader will eventually do all the talking.
In a recent inservice, our presenter told us to wait a minimum of 8 seconds before talking after asking a question. I have been doing that...and it is amazing how many people pipe up at that magical 8 second point.