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.
Kenneth Spence
Kenneth Wartinbee Spence (May 6, 1907 – January 12, 1967) was a prominent American psychologist known for both his theoretical and experimental contributions to learning theory and motivation. As one of the leading theorists of his time, Spence was the most cited psychologist in the 14 most influential psychology journals in the last six years of his life (1962 – 1967). A "Review of General Psychology" survey, published in 2002, ranked Spence as the 62nd most cited psychologist of the 20th century.