Final answer:
Ivan Pavlov, John B. Watson, and B.F. Skinner are considered the three pioneers of the Early Behaviorism phase, with their respective work on classical and operant conditioning shaping the foundation of behaviorist psychology.
Step-by-step explanation:
The three pioneers of the Early Behaviorism phase were Ivan Pavlov, John B. Watson, and B. F. Skinner. These psychologists laid the groundwork for the behaviorist movement by focusing on observable behaviors rather than internal mental processes.
Pavlov is known for his work with classical conditioning, demonstrating how reflexive behaviors could be triggered by associated stimuli. John B. Watson, often credited as the father of behaviorism, championed an objective approach to the study of psychology, emphasizing the importance of observable behavior. B.F. Skinner further developed this discipline with his research on operant conditioning, showing how consequences shape behavior.