Final answer:
John B. Watson was the key figure in behaviorism during the 20th century, emphasizing observable behaviors over internal mental processes.
Explanation:
John B. Watson was the major proponent of behaviorism during much of the 20th century. Behaviorism is a school of thought in psychology that focuses on observable behaviors and rejects the study of internal mental processes. Watson's work shifted psychology's focus from the mind to behavior, influencing the field significantly.
Learn more about Behaviorism here:
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