Looking back at this, it occurs to me that I may have misunderstood your question and thus answered a different one that you meant to ask. There are things that I take as real-time indications that what I've said has registered -- for example, being able to answer questions or to ask sensible ones -- and things that I take as indicators that it hasn't, such as asking questions I've already answered. When I'm talking to groups I often get neither, unless I've done enough prep to create exercises specifically intended to obtain them,