During the mid-1950s, Jean-Pierre Vasarely, who worked under the name Yvaral, began to experiment with the illusion of warping patterns. Unlike his father, the Op artist Victor Vasarely, Yvaral extended his practice into the realm of sculpture, creating works in which simple visual motifs are only activated by the viewer’s perception. In Acceleration #15, Series B, he suspended vinyl cords in front of a black and white striped background, and the kinetic relief may appear to vibrate or shimmer. This unexpected result is referred to as a “moiré effect,” which occurs when one repetitive design is superimposed over another to create an altogether new image. In 1960, Yvaral cofounded the Groupe de Recherche d’Art Visuel (GRAV) with Julio Le Parc, Francesco Sobrino, Jesús Rafaël Soto, Horacio Garcia Rossi, François Morellet, and Joël Stein (French, 1926–2012).