Mario Ponzo and the Age of Visual Illusions

Vision had long been investigated by Italian artists and scientists such as Brunelleschi, Alberti, Leonardo, and Galileo, and all of them had been concerned with illusions. The pace of experimental studies of a subset of illusions quickened in the second half of the 19th century, but the investigation of such geometrical optical illusions started rather late in Turin. It was stimulated by the arrival of Kiesow from Wundt’s laboratory in Leipzig. Botti initiated experiments on spatial illusions, followed by Ponzo, who wrote two articles in 1912 that indelibly linked his name to a simple configuration of equal circles or lines contained with converging lines—the Ponzo illusion. This happened despite the publication of essentially the same figures over a decade earlier by Thiéry and Sanford.