Universalizing Photochemical Theories of Vision: Hecht, Wald, and the Marine Biological Laboratory - Selig Hecht and Building Photochemical Theory at the Marine Biological Laboratory

Our story of photochemical research at the MBL starts with Selig Hecht. In the Summer of 1918, Hecht, at the behest of his graduate school advisor, George Howard Parker, came to the MBL, in Woods Hole, MA, for the first time. Parker had made the long voyage to Woods Hole from the Oceanographic Institute of La Jolla, California, regularly since it opened in 1888, and in 1918, moved his laboratory there full time. Hecht, then twenty-six, newly married, and with a freshly minted PhD from Harvard and a teaching position at a Jesuit school in Omaha, Nebraska, started his traditional summer escapes to Woods Hole; there he continued to develop the research program he had begun at the Oceanographic Institute of La Jolla, California, in 1917. At La Jolla, Hecht had investigated light sensitivity in Ciona, a colonial sea squirt, or ascidian, and he brought his interest in light sensitivity in invertebrates to the MBL. It was at the MBL that he expanded his research program to Mya arenaria, the North-Atlantic long-necked saltwater clam (Barlow, Dowling and Weissmann 1993; Wald 1991).

Over the next several years Hecht applied his theories of the chemistry and physiology of photoreception to human visual systems, particularly working in the lab of Edward Charles Cyril Baly in Liverpool, England, for a year as a National Research Council fellow. Hecht was interested in extending his work on photoreception to the problem of light and dark adaptation. He spent the last two years of his National Research Council fellowship at Harvard Medical School and at the MBL. It was during this time that Hecht contributed significantly to Maxwell Schultze’s (1866) duplicity theory of human vision by demonstrating that low and high intensity light discrimination are handled by different kinds of cells: low light in humans, Hecht showed, was processed by rod cells, whereas high intensity light was processed by cone cells.

Duplicity theory understands different visual processes as being handled by two different systems: night vision by one system (now known to be the rod system, which is achromatic) and day vision by another (now known to be the cone system, which is chromatic) (Stabell and Stabell 2009). It is now known that in the human eye these light transducing cells (rods and cones) allow the retina, a light-sensitive layer of tissue within the eye, to act as a kind of infinitely exposable ‘photographic film,’ translating the light that hits it into a representation of the incoming visual image in electrical form. That is, the retina translates the stimulus into a signal that the rest of the brain/mind can use to guide thought and action. Hecht wanted to know how the retina could be infinitely exposable, and so he studied various animals’ ability to adapt to different levels of light exposure, i.e., he studied light and dark adaptation. There are a number of reasons to study vision from this angle: the most obvious being that if the duplicity theory is accurate then understanding light and dark adaptation will allow investigators to understand the conditions under which both systems start and stop.

Hecht, using his studies of light and dark adaptation, proposed an abstract formalism for all photochemical vision, in all animals. Hecht said that light acted on a substance, S, and so broke it into two products, P and A, which were also the precursors for S. That is, during the process of dark adaptation two basic substances, P and A, could create S; and conversely during light adaptation, S, when exposed to light, would create P and A. Hecht argued that this was the process Boll and Kühne had observed in visual purple. This was a theoretical solution to the problem of infinite exposure.

Hecht’s experimental work was on Mya. He would shine a light on the clam when its syphon was extended and measure how quickly the syphon was withdrawn. Hecht noticed that the reaction time of the clams followed well-known photochemical principles, like the Bunsen-Roscoe reciprocity law; i.e., a long low intensity exposure would produce the same effects as a short high intensity exposure, if the proportions were identical.  In 1929 Hecht proposed that his photochemical theory of vision could explain how three types of cones cells could be used to account for the trichromatic, or Young-Helmholtz (Helmholtz 1867; Young 1802), theory of human color vision.

Hecht spent 1924 in Naples, Italy, and 1925 in Cambridge, England, with his wife, Celia Hübschman and their young daughter, Maressa. In September of 1926, Hecht moved his family back to America and took up a professorship in biophysics at Columbia University. Hecht held this position for the next 23 years, until his death in 1947 (Barlow, Dowling and Weissmann 1993; Wald 1991).

Hecht’s lab at Cambridge was enormously productive, not only in terms of theories of visual perception, but also in technologies of investigation and practical application. In the late years of WWII, Hecht and his close collaborator, Simon Shlaer, developed an adaptrometer that could determine the efficiency of dark adaptation in the human eye, which was used extensively by the allied forces. He also served on several military and governmental councils that dealt specifically with technical problems in vision: for example, the National Research Council Committee on Visual Problems and the Army-Navy Office of Science Research and Development Vision Committee. His lab is also notable for the many students who worked there, including, George Wald.