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.
Juan Luis Vives
Vives is considered the first scholar to analyze the psyche directly. He did extensive interviews with people, and noted the relation between their exhibition of affect and the particular words they used and the issues they were discussing. While it is unknown if Freud was familiar with Vives's work, historian of psychiatry Gregory Zilboorg considered Vives a godfather of psychoanalysis. ("A History of Medical Psychology", 1941) and the father of modern psychology by Foster Watson (1915.)
Vives taught monarchs. His idea of a diverse and concrete children's education long preceded Jean Jacques Rousseau, and may have indirectly influenced Rousseau through Montaigne.