Karl Spencer Lashley was an American psychologist who conducted quantitative studies of the relationship between brain mass and learning ability. In studies on intelligence and the role of the frontal lobes Shepherd collaborated with J. Franz. He challenged the ongoing concept of cortical localization. The debate between localization and the holistic emphasis on brain function was brought into focus by Lashley. He died on 7 August 1958 at the age of 68.