shb@oravax.UUCP (Stephen H. Brackin) (12/03/88)
Under optimal conditions, a rod in the human eye can respond to a single photon; as few as 5 to 8 such responses can give rise to the perception of light. This is one of the clearest and most impressive examples of "gooey-ware" performance in a biological system. The sensitivity of the eye was established by Selig Hecht, Simon Shlaer and Maurice Henri Pirenne in "Energy, Quanta, and Vision", Journal of General Physiology, Vol. 25, No. 6 (July 20, 1942), pp. 819-840. The paper is reprinted in "Cellular Neurophysiology", edited by Ian Cooke and Mack Lipkin Jr., Holt, Rinehart and Winston, 1972, pp. 796-817, which also contains several more recent articles on visual perception. Hecht, Shlaer and Pirenne show that under extreme conditions the main source of variation in whether light is seen is how many photons are absorbed by imperfectly transparent material in the eye itself. Stephen H. Brackin Odyssey Research Associates, Inc.