In 1935, Hans Wallach published a comprehensive series of experiments related to this topic, but since the article was in German it was not immediately known to English-speaking researchers. An English summary of the research was published in 1976Wallach, H. (1976). On perception. Quadrangle/New York Times Book Company. chap. IX.1 and a complete English translation of the 1935 paper was published in 1996.Wuerger, S., Shapley, R., & Rubin, N. (1996). "'On the visually perceived direction of motion' by Hans Wallach: 60 years later." Perception-London, 25: 1317–1368. Wallach's analysis focused on the interaction between the terminal points of the diagonal lines and the implicit aperture created by the edges of the pole.
