Rachel is training her dog, Duke, to bark every time someone knocks on the door. She already knows that seeing the family cat will make Duke bark; so she decides to knock on the door and then open the door to reveal the cat in an effort to condition Duke to bark. What is serving as the unconditioned stimulus?

A. Rachel

B. Duke's bark

C. The cat

D. The knock

Answer: The cat is the Unconditioned Stimulus

Explanation:An Unconditioned stimulus is me that sparks or triggers an unconditioned response;

For example, the cat is the unconditioned stimulus for the dog's reaction which in turn is an unconditioned response to the cat. We can also say that an Unconditioned Stimulus is any stimulus that causes or triggers an unlearnt/Unconditioned response. Another example of Unconditioned stimulus is Hunger, and we respond to it by eating.