Gestalt Psychology Started With Max Wertheimer Watching Lights Move on a Train

In 1910, Max Wertheimer was riding a train from Vienna toward the German Rhineland on holiday, watching railroad-crossing lights flash one after the other through the window. The lights were stationary; what he saw was movement. The illusion is so familiar to anyone who's stood at a level crossing that no one before him had thought to ask whether it should be familiar. Wertheimer got off at Frankfurt, called on the psychologist Friedrich Schumann, and set up an experiment with a tachistoscope that flashed two parallel slits of light at adjustable intervals. At intervals between roughly 30 and 100 milliseconds, the two stationary slits produced not two flashes but the visual experience of a single light moving smoothly between them. He published the result in 1912 as the phi phenomenon.

The argument the paper carried was bigger than the demonstration. Mainstream perceptual psychology of the period assumed that what you saw was assembled from elementary sensations — points, edges, colors — added together by the brain. The phi phenomenon was a counterexample. The experience of continuous motion was not present in either of the two flashes individually. Whatever it was, it emerged at the level of the whole.

That insight became the founding move of Gestalt psychology, which Wertheimer developed in Frankfurt and Berlin with Kurt Koffka and Wolfgang Köhler through the next two decades. The famous slogan — "the whole is different from the sum of its parts" — comes directly out of it. Wertheimer fled Nazi Germany in 1933 for the New School in New York, where he spent his last decade. He befriended Einstein in Berlin during the war years and spent considerable time, in conversation and in his unfinished book Productive Thinking, trying to model how Einstein had arrived at relativity.