Vasarely’s work came to international attention in 1965 in The Responsive Eye, a landmark exhibition held at the Museum of Modern Art in New York that introduced “perceptual abstraction” – or Op art – to North American audiences. This painting dates from the following year, when the movement’s popularity was at its height. Limited to just two colours (grey and yellow) and two geometric forms (the circle and the square, equal in size), the work emphasizes perception and movement through the sequence and interaction of the shades and shapes, a play involving both the eye and the mind. Such optical effects catch the eye of the viewer, who is a full participant in this animated art form. Despite the deliberately democratic overtones of Op art, the polar sensations of order and instability that create a dynamic tension were linked to the then current research in physics and optics, and to earlier developments in Gestalt and experimental psychology.