In 1941, with the collaboration of Marc Lambercier, Piaget launched an experimental psychology program that lasted two decades. The challenge was to demonstrate that perception also depends on development and that it is based in part on the organization of action. With about fifty articles written by Piaget and more than thirty collaborators, this “Research on the Development of Perceptions”, published between 1942 and 1960 in the Archives of Psychology, led to the book The mechanisms of perception, in 1961.