Pavlov noticed that dogs began salivating at the mere sight of the person who regularly brought food to them. For the dogs, the sight of this person had become a(n) stimulus.

conditioned stimulus

Explanation: Ivan Pavlov first discovered the process of classical conditioning in his experiments on the digestive response of dogs. He noticed that the dogs naturally salivated in response to food, but that the animals also began to drool whenever they saw the white coat of the lab assistant who delivered the food. According to Pavlov conditioned stimulus are responsible for the action.

answer; delirium is a common adverse reaction seen when elderly patients take diphenhydramine;