January 21, 1887–June 11, 1967

BY ULRIC NEISSER

WOLFGANG KÖHLER, distinguished psychologist and cofounder of Gestalt psychology, made many important contributions to science. Although he is probably best known for his empirical studies of chimpanzee problem solving (The Mentality of Apes [1925]), Köhler’s deepest commitments were theoretical and philosophical. Perhaps his most fundamental commitment was to the principle of psychophysical isomorphism: Because brain and mind are identical, the structure of conscious experience during perception or memory or problem solving necessarily mirrors the physical structure of activity in the brain. “Experienced order in space,” for example, “is always structurally identical with a functional order in the distribution of underlying brain processes” (1947, p. 61). In Köhler’s view those underlying processes were trans-neuronal electrical currents flowing in well-defined regions of the brain. Isomorphism in this sense was one of the founding assumptions of Gestalt psychology, one that Köhler did more than anyone else to explore both empirically and theoretically.

In psychology the first half of the twentieth century was a time of competing schools: Titchener’s structuralism, Freud’s psychoanalysis, the behaviorism of Watson and Skinner, the functionalism of many American experimen-