It is never used, as it is illegal and unethical. None of the above. The agent must devote a great deal of attention on the process. The agent feels empowered and in control. The agent experiences negative reinforcement when punishment works.
Punishment becomes less effective as it is delivered more and more often.
Presenting an aversive stimulus contingent on occurrence of a target response. A response cost approach. The Premack Principle. Responses are likely to occur in bursts early in the process. The effects occur faster than punishment approaches, other things equal.