Copyright © 1999 Massachusetts Institute of Technology
Hermann Ludwig Ferdinand von Helmholtz (1821-1894) was born on August 31, 1821, in Potsdam. His father, Ferdinand Helmholtz, was a respected teacher of philology and philosophy at the gymnasium. His mother was the daughter of a Hanoverian artillery officer with the surname Penne, descended from the Quaker William Penn, founder of Pennsylvania.
After serving as an army surgeon, Helmholtz held a succession of academic positions -- lecturer at the Berlin Anatomy Museum, professor of physiology at Konigsberg, professor of physiology at Bonn, professor of physiology at Heidelberg, professor of physics at the Military Institute for Medicine and Surgery in Berlin, first president of the Imperial Physico-Technical Institute in Berlin. He married and had two children, his son Richard becoming a physical chemist. During his extremely distinguished life he was ennobled by the emperor: hence the "von" in his name.
Helmholtz was no less than a hero of nineteenth-century science, making major contributions to physics and the foundations of geometry, and founding the modern science of visual and auditory perception. He formulated the principle of conservation of energy in 1847, and made significant contributions to the philosophy of non-Euclidean geometry. This fueled his rejection of the prevailing Kantian philosophy in favor of a thoroughly empirical approach to the natural and biological sciences. He was the last scholar to combine both in depth.
Helmholtz was the first to see a living human RETINA. The wonderful memory of doing so remained with him for the rest of his life. His discovery was made with the extraordinarily useful instrument, the ophthalmoscope, which he invented in 1851. He explained why the pupil is black -- the observing eye and head gets in the way of light reaching the observed retina -- so he introduced light onto the retina with a part-reflecting 45° mirror, using thin microscope slides for part-reflecting mirrors, and also a concave lens. Although Helmholtz immediately saw its general medical significance, doctors were slow to adopt it. It became his most famous invention, which set him up as a scientist commanding support for any future work he chose to undertake.
A guiding principle for Helmholtz's physiological psychology was his teacher Johannes Muller's law of specific energies (perhaps better called law of specific qualities): "In whatever way a terminal organ of sense may be stimulated, the result in CONSCIOUSNESS is always of the same kind." Various SENSATIONS are given not by different nerve signals but according to which part of the "sensory" brain is stimulated. The eyes, ears, and the other organs of sense convert patterns of various kinds of physical energies into the same neural coding, now known to be trains of minute electrical impulses called action potentials, varying in frequency according to strength of stimulation. It was Helmholtz who first measured the rate of conduction of nerve, and recorded reaction times to unexpected events. His teacher Johannes Muller thought the speed must be too great to measure, probably greater than the speed of light; but Helmholtz showed him to be wrong with a very simple technique. For noninvasive measures on humans, he touched the shoulder or the wrist and noted the difference in reaction times. Knowing the difference in length of nerve between shoulder and wrist, it was easy to calculate the conduction rate, and also to find the brain's processing delay time. For a long time Muller could not believe that nerve conduction rate is slower than sound!
Helmholtz followed the English philosopher John Locke (1632-1704) in holding that sensations are symbols for external objects, no more like external objects than words used to describe them. Thus the physical world is separated from experience, and perception is only indirectly related to external events or objects. This, and Muller's law of specific energies, are basic to his theory that visual perceptions are unconscious inferences. This was a generation before Freud's unconscious mind, which also evoked much criticism as it challenged the right to blame, or indeed praise, actions that are unconscious. Yet studying unconscious processes has proved vital for investigating brain and mind, perhaps ultimately to understanding consciousness. For Helmholtz phenomena of ILLUSIONS are important evidence for understanding perceptions as inferences, depending on assumptions that may be wrong. His basic principle was: "We always think we see such objects before us as would have to be present in order to bring about the same retinal images under normal conditions of observation." So after-images and even crude pictures are seen as objects.
Apart from the mathematical and experimental sciences as well as philosophy, he was talented in languages and in music, playing the piano. He conveyed science and something of the arts to the public with notable popular lectures that remain interesting to read. Remarkably active throughout his life, he suffered occasional migraines, which interrupted his work, and hay fever, which spoiled his holidays. He traveled widely, often to the British Isles, and was a particular friend of the physicist Lord Kelvin, meeting in Glasgow, Scotland. He attributed his success to the unusual range of his knowledge, which indeed was exceptional.
Helmholtz's death on September 8, 1894, a few days after his seventy-third birthday, resulted from an accidental fall while on a ship bound for America, which, sadly, he never visited. Neither of his biographies mentions his account of perception as unconscious inference, which after a long delay is now seen as centrally important in current cognitive psychology. There should be a fuller and more readable life of this major scientist and philosopher, who gave psychology a scientific basis that is still not fully appreciated, and championed thoroughgoing empiricism for understanding physics and biology, and even the misleading yet highly suggestive phenomena of illusions.
Helmholtz, H. von. (1866). Treatise on Physiological Optics. vol. 3. 3rd ed. Trans. by J. P. C. Southall. New York: Opt. Soc. Amer., 1924. Dover reprint, 1962.
Helmholtz, H. von. (1881). Popular Lectures. London: Longmans Green. Dover reprint, 1962.
Koenigsberger, Leo. (1906). Hermann von Helmholtz. Oxford: Oxford University Press. Dover reprint, 1965.
M'Kendrick, John. (1899). Hermann von Helmholtz. London: Fisher Unwin .
Copyright © 1999 Massachusetts Institute of Technology