“The so-called extramission theory of vision has its origin, for western thinkers at least, in Plato’s explanation of color as the mixing in air of two beams of fire, one issuing from the viewer’s eyes and one from the object being viewed. Aristotle argued that color was carried in one direction only, on light reflected off objects, but versions of Plato’s extramission theory commanded the assent of Cicero, Euclid, Ptolemy, and Al-Kindi and were not refuted to the satisfaction of most serious thinkers until the optical experiments of Kepler, Descartes, Huygens, and Newton in the later seventeenth century. . . . Plato’s theory actually does make sense of what vision feels like. We experience vision as being directed at or to something: we decide (or so we think) where to cast our gaze.”

—Bruce R. Smith, The Key of Green, 2009.