G EST AL T PSYCHOLOGY was conceived, according to the legend, on a train somewhere between Hannover and Frankfurtam-Main, in 1910 (the exact date and hour could no doubt be reconstructed), when the psychologist Max Wertheimer fell to musing on the optical behavior of the lines and poles of the telegraph system running alongside the tracks (M. M. Wertheimer, 1964). Accordingly as the train sped up or slowed down, the poles would appear to be first of all what they were (Le., separate poles, in series), then a single pole, looming forward and back in undulating motion, and then again a single pole frozen at a particular spot outside the window, while the wires themselves might take on the appearance of a stationary wire, only waving up and down. Still according to legend, Wertheimer left the train at Frankfurt,
entered a toy shop, and purchased a child's stroboscopic device, the better to study these familiar yet peculiar effects, which did not seem at all well accounted for under the prevailing reflex or Associationist school of psychological thought. The result, two years later, was a paper, "Experimentelle Studien ueber das Sehen von Bewegungen" ("Experimental Studies in the Perception of Motion," M. Wertheimer, 1912), in which he propounded the concept of a "Phi" factor, or integrative principle, by which the organism translated individual, serial sense impressions into a unified perception of continuous motion; thus the Gestalt school was born.