In Pavlov's experiment, what was the unconditioned stimulus?

In Pavlov's classic conditioning experiment, the unconditioned stimulus is the stimulus that naturally and automatically triggers a response without prior conditioning. In this case, the meat powder served as the unconditioned stimulus because it naturally elicited a salivary response from the dogs. The dogs do not need to be trained or conditioned to salivate in response to the meat powder; this is an innate biological response.

In contrast, the bell was originally a neutral stimulus that became the conditioned stimulus after being paired with the meat powder. Salivation itself is the conditioned response to the bell after the conditioning phase. The sound represents the same concept as the bell, being a neutral stimulus before conditioning and not an unconditioned stimulus. Thus, meat powder is clearly identified as the unconditioned stimulus since it precedes conditioning and produces an unlearned response.