Hi John
Line sag and line slag, means the caster searches for the "feel" of line tension on the rod tip often means the caster falls into the trap of using the wrist/elbow to gain control. The caster reverts to reinforcing an arm centric technique when a body centric technique is the instructional objective..
The only time I see this is at the start of the lesson with self taught casters who are trying to "feel" their back cast, instead of looking at it. Then as mentioned earlier, Old way/New Way takes care of that.
But they not always delighted, are they?
I cannot think of any example of anyone that is achieving their casting objective with room to spare being in any way upset. What problems have you observed?
In your studies of the research available, have you seen an external cue that a caster/thrower can use for the cognitive stage of learning the stretch and release mechanism used in throwing sports?
Like Mark, I am not sure what it is. Initially, it was presented as extended layback but that seems to have gone by the board. I'm fairly sure that you have said that it's not the stretch release cycle and I suggested the hip cocking that you get from stepping but I don't recall getting an answer. That said, I would be surprised to see individual muscle groups being given much coaching attention in a dynamic activity in the cognitive stage. It would be like considering your quads when learning to ride a bike or using nymphs to catch trout.
regards
Vince