Real movement had been incorporated into works of art by the 1920s, notably through the Constructivists (Naum Gabo was the first to use the word kinetic in relation to art) and then through Alexander Calder and his mobiles in the 1930s. A revival of kinetic art was to occur toward the middle of the 1950s. The exhibition "Le Mouvement" at the Galerie Denise René Gallery in Paris in 1955 and then "Bewogen Beweging" at the Stedelijk Museum in Amsterdam in 1961 contributed to the recognition of kinetic art. There are different forms of kinetic art, including machines and mobiles, as well as lumino-kinetic works involving light and movement. In the broadest sense, certain works of Op art creating effects of optical movement could also be considered kinetic art. Machines with motors appeared around 1950. With works such as the Tour spatiodynamique (Spatiodynamic tower, 1961), Nicolas Schöffer was to integrate the discoveries of electronics and cybernetics within structures appealing to multiple senses. The poetics of the machine comes through in the playfully eccentric works of Jean Tingueley and the slowness of those of Pol Bury. Lumino-kinetic art underwent a revival around 1950, notably with the Tableaux mobiles (Moving paintings) of F. J. Malina. Schöffer developed walls of light, prisms, and video circuits. Gyula Kocise, Martial Raysse, and Piotr Kowalski used neon for their works. Exhibits such as "Kunst-Licht-Kunst" at the Stedelijk Van Abbemuseum in Eindhoven in 1966 or "Lumière et mouvement" at the Musée d'Art Moderne de la Ville de Paris in 1967 helped to make this current of kinetic art better known. The works of François Morellet, Julio Le Parc, and Yaakov Agam revealed an art linking light and the environment. The Museum of Modern Art's 1965 exhibition "The Responsive Eye" brought together the main figures of what was to be called Op Art. Here, the movement was virtual rather than real; based on physiological phenomena, it was an outgrowth of experiments in painting at the beginning of the century. Among the best-known artists in this area are Victor Vasarely, Jésus-Raphaël Soto, Yaakov Agam, Carlos Cruz-Diez, Nicolas Schöffer, and the members of the Paris-based group known as GRAV (Groupe de Recherche d'Art Visuel, 1960-1968).