Explanation:

- Classical conditioning is a form of learning where a neutral stimulus comes to elicit a response after being paired with a stimulus that naturally brings about that response.

- The earliest experiments in classical conditioning were performed by Ivan Pavlov.

- Pavlov used dogs to show how a bell (neutral stimulus) could cause salivation after being paired with food (unconditioned stimulus).

- Option 1: K. Young – Not known for classical conditioning work.

- Option 2: Erickson – Known for psychosocial development theory, not behaviorism or conditioning.

- Option 3: Piaget – Famous for cognitive development studies, not conditioning.

- Option 4: Ivan Pavlov – Correct. He is the pioneer of classical conditioning research.