Story of Psychology - Morton Hunt [184]
The phenomenon, known for decades, had never been satisfactorily explained. Thomas Edison and others who had developed motion pictures in the 1890s were content to achieve the effect without understanding what caused it. But on the train that day Wertheimer had a sudden intuition about the answer. He had taken his doctorate at Würzburg, where, in defiance of Wundtian principles, a handful of psychologists had been using introspection to explore conscious thinking. It now occurred to him that the illusion of motion might be due to something happening not in the retina, as many psychologists thought, but in the mind, where some higher-level mental process supplied transitions between the successive pictures, thereby creating the perception of movement. He promptly lost interest in the problem of the moving landscape and never returned to it.
At the time, Wertheimer, who had been doing research at the University of Vienna on the inability to read, was on his way to the Rhineland for a vacation. But his idea so excited him that he got off the train at Frankfurt to consult Professor Friedrich Schumann, an expert on perception with whom he had studied at the University of Berlin before going to Würzburg, and who had recently moved to the University of Frankfurt.
In town, Wertheimer bought a stroboscope at a toy store and spent the evening working with it in his hotel room. (A stroboscope is a scientific instrument for seeing moving parts, as in machinery, slowed down or stationary, but in the nineteenth century and early in the twentieth the term referred to a popular toy that created the impression of motion.) The stroboscope came with pictures of a horse and boy; at the right speed of operation the horse appeared to trot and the boy to walk. Wertheimer replaced the pictures with pieces of paper on which he alternately drew lines in two locations, parallel to each other. He found that at one speed of operation he saw first one line and then the other in their different places; at another, both lines side by side; and at yet another, a single line moving from one position to another. He had a historic experiment and a theory of psychology in the making.
The next day Wertheimer called on Schumann at the university, told him what he had observed and what he guessed was the explanation, and asked his opinion. Schumann could cast no light on the matter but offered Wertheimer the use of his laboratory and equipment, including a new tachistoscope of his own design. With it a researcher, by regulating the speed of rotation of a wheel with slits in it, could expose a visual stimulus to the viewer for brief durations, and by using wheels with differently located slits and a prism could present the viewer with alternating images. The tachistoscope did with precision and control what the stroboscope did crudely.
Because Wertheimer would need volunteers to serve as experimental subjects, Schumann introduced him to one of his two assistants, Wolfgang Köhler, who shortly brought in the other assistant, Kurt Koffka.2They were somewhat younger than Wertheimer (he was thirty, Köhler twenty-two, and Koffka twenty-four), but all three were interested in the higher-level mental phenomena that the New Psychology of the physiologists and the followers of Wundt ignored, and they hit it off at once. They were to be friends and co-workers for their entire lives.
Wertheimer, single and possessed of an independent income—his father had been director of a successful commercial school in Prague— could do as he pleased; what he pleased was to abandon his vacation plans and remain in Frankfurt for nearly half a year conducting a series of experiments, with Köhler, Koffka, and Koffka’s wife serving as his subjects.
In his basic experiment, adapted from the