🚀 go-pugleaf

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.