Final answer:
John B. Watson and Ivan Pavlov's contributions to early behaviorism were foundational, emphasizing the study of observable behavior and stimulus-response reactions, which steered psychology towards behaviorism in the early 20th century.
Step-by-step explanation:
The contribution of behaviorists like John B. Watson to early behaviorism was to shift the focus of psychology from internal mental processes, which can't be objectively measured, to directly observable behavior. Watson, along with Ivan Pavlov, laid the groundwork for what would become known as behaviorism, emphasizing stimulus-response reactions as a means of studying behavior. Watson's methodology involved controlling and predicting behavior, signifying a major paradigm shift away from the study of consciousness and towards observable actions. This perspective formed the basis of behaviorism, which contributed significantly to psychology in the early 20th century.