Which term refers to a stimulus that naturally triggers a response without prior learning?

• A. Neutral Stimulus (NS)
• B. Unconditioned Stimulus (UCS)
• C. Conditioned Stimulus (CS)
• D. Unconditioned Response (UCR)

Answer: (B)

In classical conditioning, a stimulus that naturally triggers a response without any prior learning is called an unconditioned stimulus. It naturally brings about an unlearned, automatic reaction. For example, presenting food to a hungry animal causes salivation without training; that salivation is the unconditioned response. A neutral stimulus, like a bell, doesn’t cause salivation on its own. After repeatedly pairing the bell with food, the bell becomes a conditioned stimulus that can trigger salivation as a learned response. The key idea is that the unconditioned stimulus elicits the response without learning, which is why it’s the correct term here.