Wolfgang Köhler
In 1910–13, he worked with fellow psychologists Max Wertheimer and Kurt Koffka. He and Koffka were subjects for Wertheimer’s  studies, which led them to conclusions about the nature of vision. They collaborated on the founding of a new holistic attitude toward psychology called Gestalt theory, from the German word for “whole". This was influenced by some earlier work of Carl Stumpf (Köhler’s teacher) and Christian von Ehrenfels. Wertheimer had attended Ehrenfels' lectures at the University of Prague.