Answer:
HABITUATION
Step-by-step explanation:
Habituation is considered a form of learning that is experienced when an animal no longer responds to a cue or stimulus following a period in which the cue and stimulus were repeatedly used. It falls under non-associative learning, which implies that the stimulus is not connected to any reward or punishment. Sadie in this case would always bark when the letter carrier dropped off packages, but because this behavior was not rewarded nor punished, the behavior was stopped.