After gaining his MD, Hering stayed in Leipzig for several years, and before he was 30 had written a series of short monographs on visual space and eye movement. They are slightly querulous in tone and do not now make the same impact as his contribution during the following decades, but they obviously marked the author as a rising young scientist of significance. His first major academic post, as physiology lecturer in the Vienna military medical academy (the Josephinum), brought him into contact with Josef Breuer, who was later to work with Sigmund Freud on the foundation of psychoanalysis. Together Hering and Breuer showed that respiration was in part controlled by receptors in the lung, which signal excessive distension and cause cessation of inspiration: the Hering–Breuer reflex. The Josephinum was about to be dissolved, and in 1870 Hering accepted a call to be professor of physiology at the Charles University in Prague, where he stayed for 25 years, until returning to Leipzig as head of the physiology department in 1895.
In his physiological researches Hering sought a synthesis of physics and psychology. He epitomized his attitude to purely physical analysis in sensory physiology in his analogy of those who might understand a timepiece by dissecting it into component gears: would not a glance at its face and hands yield an indispensable insight into its function? Accordingly, Hering made the subjective phenomena of sensation fully fledged ingredients when assembling the bases for a physiological theory, most successfully in his theories of brightness perception and colour vision. In this he broke ranks with almost the entire materialist natural philosophy of his time, except indeed with Mach, a colleague in Prague. Hering did not follow Fechner, who stressed a rather simple form of psychophysical parallelism. Nor was he entirely in the tradition of Goethe and Schopenhauer, who, while sponsoring opponent theories of colour vision, placed almost all the emphasis on the subjective elements. Hering's theories of light and colour postulated substances and neural processes that could go in two directions from their neutral point — anabolic and catabolic. To arrive at these formulations, he used not only the available data on colour mixture that had been basic to previous theories, but also the observations that subjectively yellow did not appear to be a mixture of green and red, that yellow was a stable hue with changes in intensity, and that after-images and complementary colours fitted best into an opponent-colour scheme. It took 75 years before electrophysiologists demonstrated the existence at the cellular level of Hering's mechanisms: centre-surround organization of retinal ganglion cells, and opponent, i.e. excitatory and inhibitory, coding of colour. However, Hering was still very much a creature of the science of the middle of the 19th century. His postulated sensory and neural processing may have been more advanced and more encompassing than that of his contemporaries, yet he also believed it to reside in the cells of the organism. Its universality and presence at an early stage of development (in the case of perfect conjugacy of the eye movements even at or shortly after birth) led him to conclude that the mechanism for this kind of processing (i.e. of eye movements, of colour and brightness detection) was inborn.
In his most widely read essay (1870), Hering dealt with 'Memory as a general function of organized matter'. Because memory survives periods of unconsciousness (see memory: experimental approaches) and sleep, it cannot be merely associated with our consciousness but must be regarded as a capacity inherent in brain substance and hence must follow the rules of purely material processes.
Hering's acceptance of compelling perceptual impressions as pointers of how the organism processes sensory inputs, and his willingness to postulate for them physiological, i.e. to him material, channels, at one time had great influence. A whole generation of researchers in perception followed Hering's lead by basing their theories on rules derived from (to them) persuasive sensory judgements: Gestalt psychology was a major force until well into the 1930s. While never popular with the physicalist researchers who have dominated sensory physiology and psychology from the 1930s to this day, Hering's theories had more unity of design and less of a dualistic component than those of, say, Helmholtz. The latter relegated certain visual phenomena, such as apparent contrast, to 'errors of judgement', whereas Hering looked at them as inevitable concomitants of the physiological organization that gives us good discrimination of colour or contrast or space. As the diversity and richness of neural connectivity of the mammalian brain are being displayed by modern neuroanatomy and neurophysiology, and the untold variety of possible pathways becomes evident, many scientists are turning again to Hering and his characteristically synthetic way of making theories.
(Published 1987)
— Gerald Westheimer
