George S. Ledyard
This goes beyond the simple idea of negative reinforcement... it hurts if I stand still so I will move.... The pain involved with taking a hit of this type actually stimulates the nerves and begins to develop a body based sensitivity that allows one to feel a blow coming before it arrives. Since most of us in Aikido do not actually strike our partner's when they are unresponsive, it is more difficult to develop this type of sensitivity. I have seen Ushiro Sensei totally let an uke off the hook rather than hurt him and then the uke went away thinking that Ushiro Sensei hadn't been able to do anything to him. Everyone watching could see that the fellow was simply too full of tension, mental and physical, to perceive what Ushiro was putting out. The only option was to hit the guy and Ushiro chose not to.
This is a general statement and not aimed at Abe Sensei or any of the other folks already referenced in this thread...
The danger with this kind of 'shaping' training is it can lead to the kind of stuff you see with Dillman and the Kombat Ki folks, where their students have been hit so many times at critical places that pantomiming these impacts can result in real physical reactions (like passing out). Unfortunately, those kinds of real and dramatic results are only possible with those students who have been properly shaped for these demonstrations to work. In my opinion, that becomes the realm of the parlor trick. Yes there are dense people out there, who have trained out many of their natural self-preservation responses, but there are also those people out there who have trained *in* vulnerabilities and responses that did not exist before. If we're to study budo, then even if we're going to go along with the throw (something we all do for safety in some situations) then we still have to go into that with both sides of the encounter fully aware that we are making those compensations/assumptions AND be careful not to train those vulnerabilities to the point that they become detriments to our own martial ability.