Bridget Riley is one of Britain’s best-known artists whose career has spanned over 50 years. She first came to notice in the early 1960s with monochrome paintings that explored the dynamics of optical effects. “In my earlier paintings, I wanted the space between the picture plane and the spectator to be active. It was in that space, paradoxically, the painting 'took place…then, little by little, and, to some extent deliberately, I made it go the other way, opening up an interior space, as it…