 Helmholtz argues that perceived properties such as separation in space are well-founded inferences from two sources of knowledge: our experience, and the properties of our sense organs. For Helmholtz, knowledge of the way our physiology works in perception is essential to any epistemological account of spatial properties. Helmholtz argues that the more we know about the physiology of perception, the more accurate our inferences about our experience will be. In the case of a person grasping a pen or touching a grain of sand, Helmholtz argues that we become aware that the object touched is a single object by studying the position of our sense organs: the nerve endings in our fingers, in this case. Our awareness of distinction of spatial position, necessary for depth perception and perception of distance, is learned and not innate. Lenoir (2006) is a rich history of Helmholtz’s influences on this score, including Johann Herbart, Wilhelm Wundt, Carl Friedrich Gauss, and an analysis of Helmholtz’s theory of perception as “operationalizing” the Kantian view.