Answer:
shaping
Explanation:
In most cases of operant conditioning, the desired behavior is too complex to emit without first being modeled by the environment. "Shaping" is the procedure in which the experimenter or environment first rewards rough approximations of behavior, then finer approaches, and finally the desired behavior itself.
When the environment or experimenter decides to reward successive approaches toward target behavior, what is happening is the modeling process, so the correct answer to this question is "shaping."
