What is an unconditioned stimulus?

• A. A stimulus that is learned through association with a reward.
• B. A neutral stimulus that does not influence behavior.
• C. A stimulus that naturally and automatically triggers a response.
• D. A stimulus that predicts reinforcement.

Answer: (C)

Unconditioned stimulus is a stimulus that naturally and automatically triggers a response. In classical conditioning, this is something that does not require learning to produce a reflexive reaction. For example, in a training scenario, food presented to a hungry dog naturally causes the dog to salivate or show interest—the response happens without prior learning, and the food is the unconditioned stimulus. The reflexive reaction to the stimulus is called the unconditioned response.

This stands in contrast to a conditioned stimulus, which starts as a neutral cue and only elicits a response after it has been paired with the unconditioned stimulus. A neutral stimulus is simply something that initially does not influence behavior, and a stimulus that predicts reinforcement is a cue signaling that a reward is available, which becomes a conditioned stimulus or discriminative cue through learning.