Kinetic art 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, or Nicolas Schöffer. From 1961 to 1968, GRAV ("Groupe de Recherche d’Art Visuel") founded by François
Optical illusion from pathological changes in the physiological visual perception mechanisms causing the aforementioned types of illusions; they are discussed e.g. under visual hallucinations. A familiar phenomenon an example for a physical visual illusion are when mountains appear to be much nearer in clear weather with low humidity (Foehn) than they are. This is because haze is a cue for depth perception for far-away objects (Aerial perspective). The classical example of a physical illusion is when a stick that is half immersed in water appears bent. This phenomenon has already been discussed by Ptolemy (ca. 150) and was often a prototypical example