the work. Virtual movement By the 1940s, new styles of mobiles, as well as many types of sculpture and paintings, incorporated the control of the spectator. Artists such as Calder, Tatlin, and Rodchenko produced more art through the 1960s, but they were also competing against other artists who appealed to different audiences. When artists such as Victor Vasarely developed a number of the first features of virtual movement in their art, kinetic art faced heavy criticism. This criticism lingered for years until the 1960s, when kinetic art was in a dormant period. Materials and electricity Vasarely created many works that were considered to be interactive in the 1940s. One of his works Gordes/Cristal (1946) is a series of cubic figures that are also electrically powered. When he first showed these figures at fairs and art exhibitions, he invited people up to the cubic shapes to press the switch and start the color and light show. Virtual movement is a style of kinetic art that can be associated with mobiles, but from this style of movement there are two more specific distinctions of kinetic art. Apparent movement and op art Apparent movement is a term ascribed to kinetic art that evolved only in the 1950s. Art historians believed that any type of kinetic art that was mobile independent of the viewer has apparent movement. This style includes works that range from Pollock's drip technique all the way to Tatlin's first mobile. By the 1960s, other art historians developed the phrase "op art" to refer to optical illusions and all optically stimulating art that was on canvas or stationary. This phrase often clashes with certain aspects of kinetic art that include mobiles that are generally stationary. In 1955, for the exhibition Mouvements at the Denise René gallery in Paris, Victor Vasarely and Pontus Hulten promoted in their "Yellow manifesto" some new kinetic expressions based on optical and luminous phenomenon as well as painting illusionism. The expression "kinetic art" in this modern form first appeared at the Museum für Gestaltung of Zürich in 1960, and found its major developments in the 1960s. In most European countries, it generally included the form of optical art that mainly makes use of optical illusions, such as op art, represented by Bridget Riley, as well as art based on movement represented by Yacov Agam, Carlos Cruz-Diez, Jesús Rafael Soto, Gregorio Vardanega, Martha Boto or Nicolas Schöffer. From