This role of cognition in vision was explored by Rene Descartes, whose epistemological investigations contributed much to both art and science. In La Dioptrique, published in 1637, Descartes concerned himself with the study of light and optics, arguing that our conception of ‘very perfect images’ received by the retina could only be realised in the mind. According to Descartes, our knowledge of the world was completely untrustworthy, a mental representation constructed through what he called ‘sense datum’ that may (or may not) look like the actual thing we see. This stored data is, he argued, what we reference when we dream or hallucinate, like a vast library of visual knowledge full of things we classify as 'familiar'. After Descartes, knowing could never again be separated from seeing.