Gustav Fechner
Fechner, along with Wilhelm Wundt and Hermann von Helmholtz, is recognized as one of the founders of modern experimental psychology. His clearest contribution was the demonstration that because the mind was susceptible to measurement and mathematical treatment, psychology had the potential to become a quantified science. Theorists such as Immanuel Kant had long stated that this was impossible, and that therefore, a science of psychology was also impossible.
John B. Watson
John Broadus Watson (January 9, 1878 – September 25, 1958) was an American psychologist who established the psychological school of behaviorism. Watson promoted a change in psychology through his address "Psychology as the Behaviorist Views it", which was given at Columbia University in 1913. Through his behaviorist approach, Watson conducted research on animal behavior, child rearing, and advertising. In addition, he conducted the controversial "Little Albert" experiment and the Kerplunk experiment. Watson popularized the use of the scientific theory with behaviorism. He was also editor of "Psychological Review" from 1910 to 1915. A "Review of General Psychology" survey, published in 2002, ranked Watson as the 17th most cited psychologist of the 20th century.