Karl Duncker

[1] Until 1935 he was a student and assistant of the founders of Gestalt psychology in Berlin: Max Wertheimer, Wolfgang Köhler and Kurt Koffka.

In 1935, exiled by the Nazis, he got an assistantship in Cambridge with Frederic Charles Bartlett and later immigrated to the US, where he was again an assistant of Wolfgang Köhler's at Swarthmore College.

His younger brother Wolfgang Duncker (1909–1942), a communist in exile in Moscow, was arrested in 1938 during the Great Purges and died in the Gulag.

Duncker coined the term functional fixedness for describing the difficulties in visual perception and in problem solving that arise from the fact that one element of a whole situation already has a (fixed) function which has to be changed for making the correct perception or for finding the solution to the problem.

The difficulty of this problem arises from the functional fixedness of the box, which originally contained thumb-tacks.