Wald and his teacher Hecht contributed to a tradition that goes back to the 1870’s. It is worthwhile to both address the history of the scientific understanding of vision that preceded these two as well as review the basics of visual physiology, as we understand it today.
All of the scientific work explored in this exposition falls within what is sometimes called “the duplicity theory of vision.” This is a research tradition in ocular physiology that holds that light sensitivity is processed by more than one substance in the eye. That is to say that the eye contains different structures that are specially designed to react only to certain kinds of light: cones, which react to daylight, and rods, which react to low (night time like) light levels (Schultze 1866; Stabell and Stabell 2009). What follows is an incremental history of the understanding of the different mechanisms of light and dark vision, cones and rods respectively, and the molecular basis of their photochemical activity.
An interlude on human visual physiology
In the human retina there are about 130 million receptor cells; of them, only four million are cones, the other 126 million are rods. Cones and rods are transducing photoreceptor cells in the retina. A transducing cell take sensory input, say photons hitting the retina, and translates that into an output that is a representation of that input in a form usable by other systems of the body and brain. Cone cells are highly concentrated in an area at the back of the eye called the fovea, or fovea centralis. Human visual acuity is at its best in daylight and at the dead center of the visual field because of the mass of cones in the fovea. As you move away from the fovea the number of cones dramatically drops, and the number of rods increases until in the peripheral field of the retina there are only rods and no cones. The rods handle lowlight and peripheral vision, and are achromatic (i.e. they do not detect color).
An interlude on the history of the understanding of the photochemistry of vision
Vision cognition is handled in steps: first in the eye, with the lens and cornea focusing light onto the photoreceptors of the retina (called ‘retinal phototransduction’); then in the neural tissue behind the retina that transports the received signals from retinal photoreceptors to the brain; and then the finishing touches (the cognitive aspects of the visual process) are applied in the brain proper (Marr 1982; or for an approachable overview of visual psychology generally, see Gregory 1990).
Wilhelm Kühne (Heidelberg University, in Heidelberg, Germany) and Franz Boll (University of Genoa, in Genoa, Italy) discovered that retinal phototransduction involved photochemistry in the mid 1870’s (Stabell and Stabell 2009). In 1877, Boll extracted a substance from the retina of frogs that he called “visual purple” (what we now call “rhodopsin”), and showed that it bleached out when exposed to light and regenerated when left in the dark (Boll 1877). Boll thought this substance was involved in color vision (Boll 1878), but Kühne rejected this hypothesis because he didn’t find any visual purple in the fovea, where, as we’ve already said, human color vision is best. Instead, Kühne hypothesized that visual purple was a Sehstoff—a substance that allowed vision generally, and showed that visual purple wasn’t the only such substance (Kühne 1877-1878; Kühne 1880).
Note: There is no science without a scientist, and so the author has attempted to maintain the essential truth of that—namely that at each stage of the scientific process there is a person looking at evidence and making judgments. However there is almost no personal biography, and much of the professional biography of each author has been abridged dramatically. In spite of this, the reader should keep in mind that each of these individuals were complicated people who share at least a job description. George Wald once said, “A scientist should be the happiest of men. Not that science isn't serious; but as everyone knows, being serious is one way of being happy, just as being gay is one way of being unhappy”. Each of these individuals had a scientific ethic, as well as a body of scientific work, and where possible, the author of each section has attempted to not forget the romanticism of the spirit of investigation, or the fact that many of these people were excited by a simple truth—after all, they were seeing things no one else had seen before. That majesty can be easy to forget if you are an outsider new to the complexities of visual physiology, but these scientists never forgot it.
Universalizing Photochemical Theories of Vision: Hecht, Wald, and the Marine Biological Laboratory
- Applebury, Meredith. "Establishing the Molecular Basis of Vision: Hecht and Wald." In The Biological Century, by Robert Barlow, John Dowling and Gerald Weissmann, 175-202. Cambridge, Massachusetts: Harvard University Press, 1993.
- In The Biological Century, by Robert Barlow, John Dowling and Gerald Weissmann. Woods Hole, Massachusetts: The Marine Biological Laboratory, 1993.
- Boll, Franz. "Zur Anatomie und Physiologie der Retina (on the anatomy and physiology of the retina)." Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin, Akademie der Wissenschaften (Monthly reports of the Royal Prussian Academy of Sciences in Berlin), 1877: 783-788.
- Boll, Franz. "Zur Physiologie des Sehens und der Farbenempfindung (the physiology of vision and color perception)." Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin (Monthly reports of the Royal Prussian Academy of Sciences, 1878: 2-7.
- Dowling, John. "George Wald 1906-1997, A Biographical Memoir." National Academy of Sciences 78, no. Biographical Memoirs (2000).
- Gregory, Richard L. Eye and Brain: the psychology of seeing. Fourth Edition. Princeton, New Jersey: Princeton University Press, 1990.
- Hecht, Selig. "Intensity and the process of photoreception." Journal of General Physiology 2 (1919/1920): 337-347.
- Hecht, Selig. "Rods, cones, and the chemical basis of vision." Physiological Review 17 (1937): 239-290.
- Hecht, Selig. "The dark adaptation of the human eye." Journal of General Physiology 2 (1919/1920): 499-517.
- Hecht, Selig. "The nature of foveal dark adaptation." Journal of General Physiology 4 (1921/1922): 113-139.
- Hecht, Selig. "The photochemical nature of the photosensory process." Journal of General Physiology, 2 (1919/1920): 229-246.
- Hecht, Selig, C. Haig, and George Wald. "The dark adaptation of retinal fields of different size and location." Journal of General Physiology 19 (1935/1936): 321-337.
- Helmholtz, Hermann von. Handbuch der Physiologischen Optik (handbook of physiological optics. Leipzig: Voss, 1867.
- Kühne, Wilhelm. "Chemische Vorgänge in der Netzhaut (Chemical Processes in the Retina)." In Handbuch der Physiologie (Handbook of Physiology), 235-342. Leipzig: F.C.W. Vogel, 1880.
- —. Ueber den Sehpurpur (about the visual purple). Heidelberg: Untersuehungen aus dem physiologischen institute der universität Heidelberg (from the physiological institute of the univeristy of Heidelberg)., 1877-1878.
- Müller, George Ellias. "Über die Farbenempfindungen (about color sensations)." Zeitschrift für Psychologie und Physiologie der Sinnesorgane (journal of psychology and physiology of the sense organs) Ergänzungsband (supplement) (1930): 1-434.
- Müller, George Ellias. "Zur Psychophysik der Gesichtsempfindungen (Towards a psychophysics of visual sensations)." Zeitschrift für Psychologie und Physiologie der Sinnesorgane (Journal of psychology and physiology of the sense organs, 1896: 321-413.
- Marr, David. Vision. New York, NY: W.H. Freeman and Company , 1982.
- Schultze, Max Johann Sigismund. "Zur Anatomie und Physiologie der Retina (The Anatomy and Physiology of the Retina)." Archiv für mikroskopische Anatomie (Archive for microscopic anatomy). 2 (1866): 175-286.
- Stabell, Bjørn, and Ulf Stabell. Duplicity Theory of Vision. Cambridge, Massachusetts: Cambridge University Press, 2009.
- Wald, George. "Selig Hecht 1892-1947." National Academy of Science, 1991.
- Wald, George. "The molecular basis of visual excitation." Nobel Lecture, December 1967.
- Wald, George. "The photochemistry of vision." Documenta Ophthalmologica 3 (1949): 94-137.
- Wald, George. "The porphyropsin visual system." Journal of General Physiology 22 (1938/1939): 775-794.
- Wald, George. "Visual purple system in fresh-water fishes." Nature 139 (1937): 1017-1018.
- Wald, George. "Vitamin A in the retina." Nature, no. 132 (1933): 316-317.
- Wald, George. "On the mechanism of the visual threshold and visual adaptation." Science 119 (1954): 887-892.
- Young, Thomas. "The Bakerian Lecture: On the theory of light and colours." Philosophical Transactions of the Royal Society of London 92 (1802): 12-48.
Haldan Keffer Hartline, a Prize, and Two Accidents
- Bang, Frederick. "A bacterial disease of limulus polyphemus." The Marine Biological Laboratories, Woods Hole, Massachusetts, and the Department of Pathobiology, School of Hygiene and Public Health, The Johns Hopkins University, 1955.
- Barlow, Robert. "From string galvanometer to computer: Haldan Keffer Hartline (1903–1983)." Trends in Neuroscience 9 (1986).
- Graham, C.H., and Haldan Keffer Hartline. "The response of single visual sense cells to lights of different wave lengths." Journal of General Physiology, 1935: 917-931.
- Grant, R, and F Ratliff. "Haldan Keffer Hartline." Biographical Memoirs of Fellows of the Royal Society (The Royal Society) 31 (Nov 1985): 262-292.
- Hartline, Haldan Keffer. "Influence of light of very low intensity on phototropic reactions of animals." Journal of General Physiology 6, no. 2 (1923): 137-152.
- Hartline, Haldan Keffer. "Inhbition in the eye of limulus." Journal of General Physiology 39, no. 5 (1956).
- Hartline, Haldan Keffer. "intensity and duration in the excitation of single photoreceptor units." Journal of Cellular and Comparative Physiology, 1934: 229-247.
- Hartline, Haldan Keffer. "The dark adaptation of the eye of Limulus, as manifested by its electric response to illumination." Journal of General Physiology 13, no. 3 (1930).
- Hartline, Haldan Keffer. "Visual receptors and the retinal interaction." Nobel Lecture, December 1967.
- Hartline, Haldan Keffer, and Floyd Ratliff. "Inhibitory interaction of receptor units in the eye of Limulus." Journal of General Physiology, 1957: 357-376.
- Hartline, Haldan Keffer, and Floyd Ratliff. "Spatial summation of inhibitory influences in the eye of Limulus, and the mutual interaction of receptor units." Journal of General Physiology, May 1958: 1049-1066.
- Madrigal, Alexis. "The Blood Harvest." The Atlantic, Feb 26, 2014.
- Nobelprize.org. Haldan K. Hartline - Biographical. Nobel Media AB 2014. 1967. http://www.nobelprize.org/nobel_prizes/medicine/laureates/1967/hartline-bio.html (accessed 2015 14, 2015).
- Ratliff, Floyd. "Haldan Keffer Hartline 1903-1983." National Academy of Sciences, 1990.
- Shuster, Carl N, Robert B Barlow, and H Jane Brockmann. The American Horseshoe Crab. Cambridge, Massachusetts: Harvard University Press, 2003.
Roger Hanlon, Universal Camouflage, and Studying Vision at the MBL in the 21st Century
- Allen, J.J., L.M. Mäthger, A. Barbosa, and R.T. Hanlon. "Cuttlefish use visual cues to control 3-dimensional skin papillae for camouflage." Journal of Comparative Physiology, 2009: 547-555.
- Chiaoa, Chuan-Chin, J. Kenneth Wickiser, Justine J. Allen, Brock Genter, and Roger T. Hanlon. "Hyperspectral imaging of cuttlefish camouflage indicates good color match in the eyes of fish predators." PNAS 108, no. 22 (May 2011): 9148-9153.
- Hanlon, Roger. "Cephalopod dynamic camouflage." Current biology , 2007: 400-404.
- Hanlon, Roger. Rapid adaptive camouflage and signaling in cephalopods. PART I: Concepts and questions. Performed by Roger Hanlon. iBiology.org. 2011.
- MBL. Hanlon lab - overview. 2011. http://www.mbl.edu/bell/current-faculty/hanlon/.
- Ulmer, K.M., K.C. Buresch, M.M. Kossodo, L.M. Mäthger, L.A. Siemann, and R.T. Hanlon. " Vertical Visual Features Have a Strong Influence on Cuttlefish Camouflage ." Biological Bulletin 224, no. 2 (2013): 110-118.
- Zimmer, Carl. "Cuttlefish camouflage." New York Times, February 13, 2008: http://www.nytimes.com/video/science/1194817111131/cuttlefish-camouflage.html.