Editing Ewald Hering (section)

==Research==

===Binocular vision===
[[File:Heringvisualdirection.png|thumb|Hering's demonstration of his law of visual direction]]

Hering studied a broad range of subjects in vision, among them his outstanding studies on binocular vision.
<ref>{{cite book | author=Hering, Ewald |title =Die Lehre vom binokularem Sehen | location=Leipzig | year=1868}}</ref><ref>{{cite book |author=Hering, Ewald |title=The theory of binocular vision: Ewald Hering (1868); edited by Bruce Bridgeman and Lawrence Stark; translation and introduction by Bruce Bridgeman; commentary by Lawrence Stark |publisher=Plenum Press |location=New York |year= 1977 |isbn=978-0306310164  }}</ref> He derived, almost simultaneously with Helmholtz, the theoretical shape of the horopter. Despite identical results, Hering's derivation was far more modern and elegant, using recently developed projective geometry. Indeed, Helmholtz himself qualified Hering's approach as "very elegant, comprehensive and complete". Subsequently, Hering empirically estimated the shape of the horopter. Alongside with [[Helmholtz]] and [[Hillebrand]], he noticed that the empirical horopter does not match the theoretical horopter, a phenomenon now named the [[Hering–Hillebrand deviation]].

Hering is also well known for his [[Hering's law of visual direction|Law of Visual Direction]] which describes the perceived egocentric direction of an object from an observer. Unbeknownst to Hering and other visual scientists of the time, a similar law had been proposed by [[Alhazen]] (1021) <ref>{{cite book|last1=Smith|first1=A. Mark|title=Alhacen's theory of visual perception. Volume Two, English Translation.|date=2001|publisher=American Philosophical Society|location=Philadelphia}}</ref> and [[William Charles Wells|Wells]] (1792) <ref>{{cite book|last1=Wells|first1=W. C.|title=An Essay upon Single Vision with Two Eyes: Together with Experiments and Observations on Several Other Subjects in Optics|url=https://archive.org/details/essayuponsinglev00well|date=1792|publisher=Cadell|location=London}}</ref> 
although both their laws were different.

=== Hyperacuity ===

[[File:Ewald Hering (1899) Fig 2.pdf|thumb|right|240px|Ewald Hering's model of how a Vernier acuity stimulus is coded by a receptor array. Receptors marked ''c'' signal a different position code along the horizontal direction from either the position ''a'' code or the position ''b'' code.<ref name="Strasburger-2018" />]]Hering did seminal work on what we now<ref>following [[Gerald Westheimer|G. Westheimer]]</ref><ref>{{cite journal | last = Westheimer | first = Gerald | title = Visual acuity and hyperacuity | journal = Investigative Ophthalmology and Visual Science | volume = 14 | pages = 570–572| year = 1975| issue = 8 | pmid = 1150397 }}</ref><ref>[https://iovs.arvojournals.org/article.aspx?articleid=2175231 Link to Westheimer (1975)]</ref> call [[hyperacuity]]: spatial resolution in certain visual tasks that exceeds [[visual acuity]] by about an order of magnitude. In his famous 1899 treatise "On the Limits of Visual Acuity"<ref name="Strasburger-2018">{{cite journal | last1 = Strasburger | first1 = Hans | last2 = Huber | first2 = Jörg | last3 = Rose | first3 = David | title = Ewald Hering (1899) On the Limits of Visual Acuity: A Translation and Commentary. With a Supplement on Alfred Volkmann (1863) Physiological Investigations in the Field of Optics | journal = i-Perception| volume = 9 | issue = 3 | pages = 204166951876367 | year = 2018 | doi = 10.1177/2041669518763675 | pmid = 29899967 | pmc = 5990881 }}</ref> he summarized empirical data published 1863 by [[Alfred Wilhelm Volkmann]]<ref>{{cite journal | last1=Strasburger|first1= Hans|last2= Rose| first2=David |year=2018| title=Alfred Volkmann (1863). Physiological Investigations in the Field of Optics (Physiologische Untersuchungen im Gebiete der Optik). Partial translation and Commentary; Supplement to Strasburger, H.; Huber, J.; Rose, D. (2018). "Ewald Hering (1899) On the Limits of Visual Acuity|journal= i-Perception| volume=9 |issue=3| pages=204166951876367 |doi= 10.1177/2041669518763675|pmid= 29899967|pmc= 5990881}}</ref><ref>{{cite book | last= Volkmann|first= Alfred|year= 1863| title= Physiological Investigations in the Field of Optics (Physiologische Untersuchungen im Gebiete der Optik) | location=Leipzig|publisher= Breitkopf und Härtel |url= https://archive.org/details/b22328221}}</ref> and Ernst Anton Wülfing 1892<ref>{{cite journal | last = Wülfing | first = Ernst Anton | title = Ueber den kleinsten Gesichtswinkel [On the smallest visual angle]| journal = Zeitschrift für Biologie |series=Neue Folge | volume = 11 | pages = 199–202| year = 1892 | url =  https://archive.org/details/zeitschriftfrbi53unkngoog}}</ref> who found that there are visual tasks in which  spatial resolution goes well below the size of [[cone cells|receptor cells]] in the central retina.<ref>"In the year 1892, Wülfing showed that one can recognise differences in position that correspond to a visual angle of 12–10'' or even less" (translated from Hering 1899)</ref> In an explanatory model, Hering superimposed a [[Vernier acuity]] stimulus – a disalignment among two line segments – onto an idealized receptor array. He argued that, by a mechanism of integration across [[Microsaccade|small eye movements]], the location information signalled by the involved receptors is coded to a much higher precision than would be possible by a single receptor, an explanation that still holds up today.<ref name="Strasburger-2018" /><ref>{{cite journal | last1 = Westheimer | first1 = Gerald| title = Hering Hermeneutics: Supplement to Translation and Commentary of Hering (1899) by Strasburger et al. | journal = i-Perception| volume = 9 | issue = 6 | pages = 204166951881592 | year = 2018 | doi = 10.1177/2041669518815921| pmid = 30559959| pmc = 6291878}}</ref><ref>{{cite journal | last1 = Jiang | first1 = H. | last2 = Cottaris | first2 = N. | last3 = Golden | first3 = J. | last4 = Brainard | first4 = D. | last5 = Farrell | first5 = J. E. | last6 = Wandell | first6 = B. A. | title = Simulating retinal encoding: Factors influencing Vernier acuity | journal = Human Vision and Electronic Imaging | volume = 2017 | issue = 14 | pages = 177–181 | year = 2017 | url =  https://www.biorxiv.org/content/early/2017/02/17/109405| doi = 10.2352/ISSN.2470-1173.2017.14.HVEI-140 }}</ref><ref>{{cite journal | last1 = Rucci | first1 = M. | last2 = Lovin | first2 = R. | last3 = Poletti | first3 = M. | last4 = Santini | first4 = F. | title = Miniature eye movements enhance fine spatial detail | journal = Nature | volume = 447 | issue = 7146 | pages = 851–854 | year = 2007 | url =  https://open.bu.edu/bitstream/handle/2144/2052/06.010.pdf?sequence=1| doi = 10.1038/nature05866 | pmid = 17568745 | bibcode = 2007Natur.447..852R | s2cid = 4416740 }}</ref>

===Eye movements===
[[File:Mullerstimulus.gif|thumb|Depiction of predictions for refoveating Muller's stimulus with eyes moving independently or eyes following Hering's law of equal innervation]]

Hering further studied eye movements. He developed the [[Hering's law of equal innervation]] to describe the conjugacy of eye movements in animals. According to this law eye movements are always equal in intensity in the two eyes but not in direction. Eye movements can therefore be either conjugate (in the same direction such as [[saccades]] or [[smooth pursuit]]) or disjunctive (such as [[vergence]] eye movements). Hering's law of equal innervation is best described by Müller's stimulus where the fixation point changes position in 1 eye but not the other eye. Simplicity conducts that only the misaligned eye should move to refoveate. Hering's law predicts that because the eyes must always move by equal amounts, both eyes should move in the new binocular direction of the target (see Hering's law of visual direction above), then move in opposite direction to adjust vergence to that of the target. In other words, the eye in which the target did not move will move away and then back at the target. This prediction was experimentally confirmed by Yarbus in his seminal work on eye movements. However it is now known that strong deviations from Hering's law exist.

===Color theory===

Hering disagreed with the leading theory developed primarily by [[Thomas Young (scientist)|Thomas Young]], [[James Clerk Maxwell]] and [[Hermann von Helmholtz]].<ref name="Turner, R. M.-1994">{{cite book |author=Turner, R. M. |title=In the eye's mind: vision and the Helmholtz-Hering controversy |publisher=Princeton University Press |location=Princeton, N.J |year=1994 |isbn=978-0-691-03397-6 }}</ref> 
Young proposed that color vision is based on three [[primary color]]s: red, green, and blue. Maxwell demonstrated that any color can be matched by a mixture of three primary colors. This was interpreted by Helmholtz as proof that humans perceive colors through three types of receptors, while white and black would reflect the amount of light.

Hering instead held that the visual system works based on a system of [[Opponent process|color opponency]]. His evidence stemmed from color-adaptation experiments and the linguistic observation that certain color names cannot be combined into one. In this model, colors are perceived through mechanisms sensitive to three pairs of opponent colors: red-green, yellow-blue and white-black.

[[Johannes von Kries]] published in 1905 the ''[[zone theory]]'' that synthesizes both descriptions as one, where the Young-Helmholtz theory describes the interaction of light with receptors and Hering the image processing stage.<ref name="Moore-1992">{{Citation|url=https://books.google.com/books?id=m-YF1glKWLoC&pg=PA128|last=Moore|first=Walter John|title=Schrödinger: Life and Thought|isbn=9780521437677|date=29 May 1992|publisher=Cambridge University Press }}</ref>
Later, in 1925, [[Erwin Schrödinger]] published a paper inspired by von Kries, titled ''On the relation of the four color to the three color theory''. There he probes a formal relationship between the two color theories.<ref name="Moore-1992"/>

Both theories have solid empirical evidence. The conundrum was resolved by the discovery of color-opponent ganglion cells in the [[retina]] and [[lateral geniculate nucleus]]. We now know that the human eye possesses three types of color-sensitive receptors (as proposed by Young, Maxwell, and Helmholtz) which then combine their signals in three color-opponent channels as proposed by Hering. Thus, both the Hering and Young-Helmholtz theories are correct.{{dubious|date=February 2025}}

===Physiology===

Hering made significant contributions to the field of physiology as well as psychology. In particular he demonstrated with his student Breuer the [[Hering–Breuer reflex]], or that artificially inflating the lungs triggers an automatic signal triggering expiration. Then deflating the lungs in turns triggers a new signal inducing respiration. That is, inspirations and expirations are an endless reflex loop triggering each other. He also showed the [[Traube-Hering]] reflex, or that inflating the lungs triggers an acceleration of the heart.

===Other research===
[[Image:Hering illusion.svg|thumb|right|upright|The Hering illusion]]
In 1861, Hering described an [[optical illusion]] which now bears his name – the [[Hering illusion]]. When two straight and parallel lines are presented in front of radial background (similar to the spokes of a bicycle), the lines appear as if they were bowed outwards. The [[Orbison illusion]] is one of its variants, while the [[Wundt illusion]] produces a similar, but inverted effect.

Hering first suggested the idea of [[organic memory]] in an 1870 lecture for the Imperial Academy of Science in [[Vienna]]. Hering took influence from the idea of [[inheritance of acquired characteristics]] and suggested that memories could be passed on through generations by [[germ cell]]s.<ref>Stanley, Finger. (1994). ''Origins of Neuroscience: A History of Explorations Into Brain Function''. Oxford University Press. p. 338. {{ISBN|978-0-262-01704-6}}</ref>