Karl Lashley


A student of Watson at Johns Hopkins, Karl Lashley more physiologist than psychologist. Best known for his doctrine of “mass action,” Lashley showed that the “brain fields” proposed by Gestalt psychology did not exist. Kohler had held that the brain functions by electrical fields; Lashley short-circuited the “field” by putting silver foil on the cortex and yet the behavior still occurred.

In another animal study, Lashley showed that when brain portions are damaged (i.e., surgically removed), rats don’t lose the ability to make light-dark discriminations. Although limited in scope, other parts of the brain take over functions when the brain is incapacitated. Similarly, when cats and monkeys were taught to escape, and portions of the cortex are removed (“extirpation”), the animals could not initially perform the task but were able to relearn it. Technically called “equipotentiality,” Lashley maintained that each part of the brain was equally important.


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