Image by Ludwig Knaus, 1881
Hermann Ludwig von Helmholtz was born on August 31, 1821, in Potsdam near Berlin, Germany, into a well-educated family. His father, an educator, taught him the classical languages and introduced him to philosophy. Helmholtz studied medicine in Berlin under physiologist Johannes Müller, at the same time attending lectures in physics and mathematics. Müller was an adherent of the then broadly accepted philosophical nativism. Helmholtz spent much of his life finding objective arguments against nativism and in favor of empiricism. After spending several years in military service in Potsdam and a stint as associate professor of physiology at the Prussian University, he became a full professor of anatomy and physiology in Bonn. Three years later, he moved to the University of Heidelberg and in 1871 became the professor of physics at the University of Berlin, where he remained until his retirement. Helmholtz had a broad range of interests, from astronomy to physics, physiology, and the relationship between the physical world and human sensory perception. In 1847, he wrote an important article on the conservation of physical force [1]. In 1850, Helmholtz invented the ophthalmoscope for inspecting the interior of eyes for medical purposes and revolutionized the practice of ophthalmology [2]. Among Helmholtz’s many students were H. R. Hertz, M. Planck, A. A. Michelson, W. Wundt, and W. Kohlrausch (the co-discoverer of the Helmholtz–Kohlrausch effect). Helmholtz died on September 8, 1894, in Berlin.
39.1 Trichromatic Theory of Color Vision
In sensory perception, he specifically covered hearing and, most extensively, vision. His most important publication is Handbuch der physiologischen Optik (Treatise on physiological optics), a 900 + page work whose first edition was published in 1867 when he was in Heidelberg [3]. The book’s main sections are (1) Anatomical description of the eye, (2) Physiological Optics, (3) Dioptrics of the eye, (4) Sensations of vision, including Simple colors and Compound colors, (5) Intensity and duration of the sensation of light, (6) Contrast (including colored shadows), and 7. Duplicity theory [4]. A second edition authored by Helmholtz was published posthumously in 1896, supervised by Helmholtz’s assistant Arthur König who also added over 7800 literature references [5]. A third edition was published in 1909, consisting of the second edition, with contributions by A. Gullstrand, J. von Kries, and W. Nagel [6]. It was translated into English by J. P. C. Southhall and published with an additional contribution by the Optical Society of America [7].
Chromaticity diagram based on König and Dieterici’s fundamental color sensitivity functions determined in Helmholtz’s laboratory. Loci of spectral color stimuli are on the curved solid line. Letters indicate loci of Fraunhofer lines in the spectrum [5]
While Helmholtz developed an experimentally supported general psychophysical theory of vision, he was also concerned about and experimented with many additional phenomena of the human visual system. He is the first to mention color constancy, saying that “we always start out forming a judgment about the colours of bodies, eliminating the difference of illumination by which the body is revealed to us.” [6] The color vision theory of Helmholtz, based on Young’s conjecture of three sensor types, is known as the Young–Helmholtz theory of trichromatic color vision.
Helmholtz’s rival Ewald Hering developed a theory of color vision essentially based on psychology to which he gave a presumed physiological basis. Both views attracted followers [8]. Today, the controversy has been narrowed but still remains. Interestingly, their expressed epistemological views were not as might be expected: Helmholtz viewed lights and colors as symbols. In 1852, he said “Light and color percepts are only symbols for the relations of reality; with the latter they have as little and as much similarity or relationship as the name of a person or its written form with the person itself.” Hering, on the other hand, believed that, in perception, our access to real objects is a direct one.