View source for Joseph Delboeuf

[[File:Delboeuf 1891.JPG|right|thumb|{{center|Joseph Delboeuf (1891)}}]]
'''Joseph Rémi Léopold Delbœuf''' (30 September 1831, [[Liège]], [[Belgium]] – 14 August 1896, [[Bonn, Germany]]) was a Belgian [[experimental psychologist]]<ref name="zusne_Bio">{{cite book |first=Leonard |last=Zusne |date=1984 |url=https://archive.org/details/biographicaldict00zusn |url-access=registration |title=Biographical Dictionary of Psychology |via=Internet Archive |access-date=2015-06-28 |publisher=Greenwood Press |isbn=9780313240270 |edition=revised}}</ref> who studied visual illusions including his work on the [[Delboeuf illusion]].<ref name=":43" /> He studied and taught [[philosophy]], [[mathematics]], and [[psychophysics]].<ref name="zusne_Bio" /> He published works across a diverse range of subjects including the curative effects of [[hypnotism]].<ref name=":2" />

== Early life and education ==
Joseph Delboeuf was born in the French speaking town of Liège, Belgium.<ref name=":1">{{Cite journal|last1=Nicolas|first1=Serge|last2=Murray|first2=David J|last3=Farahmand|first3=Bahar|date=1997|title=The Psychophysics of J-R-L Delboeuf (1831–1896)|journal=Perception|language=en-US|volume=26|issue=10|pages=1297–1315|doi=10.1068/p261297|pmid=9604065|s2cid=12935952|issn=0301-0066}}</ref> His father, a pewter craftsman, died early in Delboeuf’s life.<ref name=":1" /> He studied at the [[University of Liège]], earning his PhD in philosophy in 1855, followed by physics and mathematics in 1858.<ref name=":3">{{Cite book|title=Encyclopedia of the History of Psychological Theories|date=2012|publisher=Springer US|isbn=9781441904256|editor-last=Rieber|editor-first=Robert W.|location=New York, NY|doi = 10.1007/978-1-4419-0463-8 }}</ref><ref name=":43">{{Cite journal|last=Nicolas|first=Serge|date=1995|title=Joseph Delboeuf on Visual Illusions: A Historical Sketch|journal=The American Journal of Psychology|volume=108|issue=4|pages=563–574|doi=10.2307/1423073|jstor=1423073|pmid=8585601}}</ref>  He received a scholarship from the [[University of Bonn]] and continued his postdoctoral research under philosopher and mathematician [[Friedrich Ueberweg]].<ref name=":1" /> In 1860, he began teaching Greek at l’Ecole Normale des Humanités de Liège.<ref name=":1" /> In 1863, he was given the post of [[Maître de conférences|Maitre de Conférences]], which he only held for a few months before being appointed Chair of Philosophy at [[Ghent University|University of Ghent]], leaving his research in mathematics.<ref name=":3" /><ref name=":1" /> There, he met [[Joseph Plateau]], who helped him publish his first two notes on optical illusions in the Bulletin of the [[Royal Academy of Belgium]].<ref name=":43"/> He then began his research in [[psychophysics]] with [[Gustav Fechner]] in 1865.<ref name=":1" />

==Work==
Delboeuf began his psychophysical experimentation on [[brightness]] in 1865 with [[Gustav Fechner]]. Delboeuf introduced the concept of sense distance (''contraste sensible'').<ref name=":12">{{Cite journal|last1=Nicolas|first1=Serge|last2=Murray|first2=David J|last3=Farahmand|first3=Bahar|date=1997|title=The Psychophysics of J-R-L Delboeuf (1831–1896)|journal=Perception|language=en-US|volume=26|issue=10|pages=1297–1315|doi=10.1068/p261297|pmid=9604065|s2cid=12935952|issn=0301-0066}}</ref>

Delboeuf is known for his description of the [[Delboeuf illusion]] in 1893.<ref name=":43" /> Many experiments have been performed on this illusion since that time.

=== Hypnotism ===
After completing work on sleep and dreams, Delboeuf started researching [[magnetism]] and [[Hypnosis|hypnotism]].<ref name=":5">{{Cite journal|last=Wils|first=Kaat|date=2017-03-15|title=From transnational to regional magnetic fevers: The making of a law on hypnotism in late nineteenth-century Belgium|journal=Notes and Records |volume=71|issue=2|pages=179–196|doi=10.1098/rsnr.2017.0007|pmid=30125058|pmc=5554305|issn=0035-9149}}</ref> At the First International Congress on scientific and experimental hypnotism (1889), a motion was put forward to ban non-medical practitioners from using hypnosis.<ref name=":6">{{Cite journal|last=Shamdasani|first=Sonu|date=2005|title='Psychotherapy': the invention of a word|journal=History of the Human Sciences|volume=18|issue=1|pages=1–22|doi=10.1177/0952695105051123|s2cid=146593953|issn=0952-6951}}</ref> However, Delboeuf argued that a medical degree was not required to practice hypnotism; rather, it should be used freely, yet with caution.<ref name=":6" /> Along with a group of magnetizers in Verviers, he argued that hypnotists had specific personal skills that could not be acquired by all doctors.<ref name=":5" /> Thus, the clinical technique of hypnotism was proposed as an alternative to [[Traditional medicine|traditional medical]] therapies.<ref name=":5" />

==== Curative effects ====
Most of the work Delboeuf published was on the curative effects of hypnotism. However, his hypotheses were often difficult to test and falsify.<ref name=":7">{{Cite journal|last=T. W.|date=1888|journal=Mind|volume=os-XIII|issue=49|pages=148–152|doi=10.1093/mind/os-xiii.49.148|issn=0026-4423|title=Prof. Delboeuf on the Curative Effects of Hypnotism|url=https://zenodo.org/record/2064829}}</ref> To test his hypotheses, he suggested that he would need two identical patients to be treated with different approaches. Instead, he used the [[symmetry]] of the opposite sides of the body.<ref name=":7" /> He would make two identical lesions on two parts of the body (e.g., arms) and would apply hypnotism to one area while leaving the other alone for nature to act upon.<ref name=":7" /> He found that not only can the consequences of [[pain]] be avoided from hypnotic suggestion (i.e., no pain experienced), but that over the course of the injury or disease, the actual effects of the operation could be halted over time.<ref name=":7" /> Hypnotism's mode of action, concluded Delboeuf, is like pain, in that it "hypnotizes" by calling attention to itself.<ref name=":7" /> Thus, hypnotic suggestion prevents the effects of pain by withdrawing attention from it.

==== Post hypnotic suggestion ====
Delboeuf, with [[Hippolyte Bernheim]] in 1885, introduced a new solution to the problem of post hypnotic suggestion.<ref name=":2">{{Cite journal|last=LeBlanc|first=André|date=2004|title=Thirteen days: Joseph Delboeuf versus Pierre Janet on the nature of hypnotic suggestion|journal=Journal of the History of the Behavioral Sciences|language=en|volume=40|issue=2|pages=123–147|doi=10.1002/jhbs.20000|pmid=15048665|issn=0022-5061|doi-access=free}}</ref> They argued that subjects drifted into a dream-like state in which they became aware of the [[suggestion]] and time remaining in this state. Their idea was very similar to a ''[[double consciousness]] theory'' suggested by [[Pierre Janet]]. They highlighted that subjects are unable to remember the suggestion when they wake because the memory is only available in the dream-like or hypnotic state.<ref name=":2" /> In other words, they describe the memory being in a “dormant” state that returns during the hypnotic state. Delboeuf argued that the amnesia from waking from hypnotic sleep was similar to that from waking up from regular sleep. We tend not to remember our dreams because we are unable to establish a connection between the waking and dream state. We do, however, tend to remember dreams when we wake up in the middle of a dream because our waking and dreaming state bridge together. Therefore, Delboeuf predicted that subjects should be able to recall their hypnotic sleep if they were awakened in the middle of it. He tested his predictions in an experiment with [[Marie Wittman]], who was awakened in the middle of a hypnotic hallucination and remembered everything. Delboeuf repeated his experiment with other subjects with similar results. His experiments convinced him of the similarity between normal dreams and hypnotic states.<ref name=":2" />

=== Mathematics ===
During his time at the [[University of Bonn]], Delboeuf published ''Prolégomènes philosophiques à la géométrie'' (1860), disputing his mentor Ueberweg’s concept of Euclidean space and earning the praise of [[Bertrand Russell]].<ref name=":13">{{Cite journal|last1=Nicolas|first1=Serge|last2=Murray|first2=David J|last3=Farahmand|first3=Bahar|date=1997|title=The Psychophysics of J-R-L Delboeuf (1831–1896)|journal=Perception|language=en-US|volume=26|issue=10|pages=1297–1315|doi=10.1068/p261297|pmid=9604065|s2cid=12935952|issn=0301-0066}}</ref> He argued that,  in order to use geometry to find the fundamental qualities of “determinations of space,” we must first understand the concepts of both “determination” and “space.” In this paper, he independently discovered Euclidean postulate 5.<ref>{{Citation|last=Torretti|first=Roberto|chapter=Foundations|date=1984|pages=153–253|publisher=Springer Netherlands|isbn=9789027718372|doi=10.1007/978-94-009-9909-1_3|title=Philosophy of Geometry from Riemann to Poincaré}}</ref> Postulate 5 states that, if a line intersects two straight lines that together form two interior angles on the same side that sum to less than 180 degrees, then the two straight lines must meet on that side.<ref>{{Cite journal|last=BEESON|first=MICHAEL|date=2016|journal=The Bulletin of Symbolic Logic|volume=22|issue=1|pages=1–104|issn=1079-8986|jstor=43740450|title=Constructive Geometry and the Parallel Postulate|doi=10.1017/bsl.2015.41|arxiv=1407.4398|s2cid=119309574}}</ref>

==== Psychophysics ====
Delboeuf first conducted psychophysics experiments at the University of Gand (1855-1866).<ref name=":14">{{Cite journal|last1=Nicolas|first1=Serge|last2=Murray|first2=David J|last3=Farahmand|first3=Bahar|date=1997|title=The Psychophysics of J-R-L Delboeuf (1831–1896)|journal=Perception|language=en-US|volume=26|issue=10|pages=1297–1315|doi=10.1068/p261297|pmid=9604065|s2cid=12935952|issn=0301-0066}}</ref> He primarily worked on [[Weber–Fechner law|Weber's Law]] (proposed by [[Gustav Fechner|Fechner]]):<ref name=":8">{{cite journal|id={{ProQuest|816391645}}|doi=10.1037/a0021640|title=Gustav Fechner: 150 years of Elemente der Psychophysik|year=2010|last1=Robinson|first1=David K.|journal=History of Psychology|volume=13|issue=4|pages=409–410}}</ref>

<math display="block">S = K \log I</math>

Where ''S'' stands for the strength of a sensation, ''I'' stands for the intensity of an external stimulus, and ''K'' is a constant.<ref name=":8" />

Delboeuf proposed two main changes to Fechner's formula.<ref name=":14" /> The first change was related to mathematical aspects.<ref name=":14" />  Delboeuf argued that, in some cases, Fechner's formula would result in negative values for S.<ref name=":14" />  For example if <math>I = 0</math>, then <math>S < 0</math>.<ref name=":14" />  Delboeuf proposed that, because a negative value of ''S'' did not make sense, the formula could not be applicable to all cases.<ref name=":14" /> For example, in cases where the strength of a sensation may lead to inability to view an external stimulus (for instance due to glare), the formula would not be applicable.<ref name=":14" /> To address this issue, Delbeouf added a term to the end of Fechner's equation:<ref name=":14" />

<math display="block">S = K \log \frac{I + c}{c}</math>

Where ''c'' stands for the baseline physiological level of excitation within the senses.<ref name=":14" />

Delboeuf's second change to Fechner's formula was the addition of a supplementary equation:<ref name=":14" />

<math display="block">f = \log \frac{m}{m - I'}</math>

Where ''f'' stands for the amount of fatigue from effort of the sense organ given a stimulus, ''m'' stands for the amount of available sensitivity of the organ, and ''I''' stands for the intensity of the stimulus.<ref name=":14" /> This supplementary equation would account for the change that a sense organ experiences due to the magnitude of excitation from an external stimulus.<ref name=":14" /> By adding this equation, Delboeuf accounted for fatiguing effects that sensations have on sense organs.<ref name=":14" />

==== General Theory of Sensitivity ====
Delboeuf investigated the laws of nature and [[Sensation (psychology)|sensation]] in his paper "General Theory of Sensitivity."<ref name=":15">{{Cite journal|last1=Nicolas|first1=Serge|last2=Murray|first2=David J|last3=Farahmand|first3=Bahar|date=1997|title=The Psychophysics of J-R-L Delboeuf (1831–1896)|journal=Perception|language=en-US|volume=26|issue=10|pages=1297–1315|doi=10.1068/p261297|pmid=9604065|s2cid=12935952|issn=0301-0066}}</ref> Delboeuf proposed that a sensation consists of two aspects: (1) formation of the sensation and (2) how sense organs function.<ref name=":15" /> Delboeuf further proposed three laws that can be applied to determine sensation strength:<ref name=":15" />

1. Law of Degradation: as soon as a sensation occurs, the strength of a sensation begins to degrade.<ref name=":15" />

2. Law of Intensity: in order for a sensation to increase in strength, it must be stimulated by excitations that are also increasing in magnitude.<ref name=":15" />

3. Law of Tension: as the strength of a sensation increases, the level of tension also increases.<ref name=":15" /> Tension is associated with unpleasantness, pain, fatigue and even the destruction of the sensation itself.<ref name=":15" />

=== Visual illusions ===
[[File:Delboeuf_illusion.svg|thumb|Delboeuf illusion (1865)]]
Delboeuf started researching [[perception]] after meeting [[Joseph Plateau]] (1801-1883), a physicist known for his work on vision.<ref name=":43"/> After this encounter, Delboeuf changed his focus from [[Fechnerian Psychophysics|Fechnerian psychophysics]] to the psychology of perception.<ref name=":43" /> His first work on [[illusion]]s was a discussion of [[Zöllner illusion|Zollner]]'s Pseudoscopy (1865) in which he proposes a theory that all [[optical illusion]]s could be explained by the muscular strength and structure of the eye.<ref name=":43" /> He went on to publish a work on Optico-Geometric Illusions, in which he reinforces his proposed theory.<ref name=":43" /> These works led Delboeuf to develop an experiment on an optico-geometric illusion that later became known as the [[Delboeuf illusion]] (1865).<ref name=":43" /> This illusion is based on the idea that stimuli can be perceived as larger or smaller based on their illumination and surroundings.<ref>{{Cite journal|last1=Surkys|first1=Tadas|last2=Bertulis|first2=Algis|last3=Bulatov|first3=Aleksandr|date=2006|title=Delboeuf illusion study|journal=Medicina (Kaunas)|volume=42|issue=8|pages=663–681|pmid=16963835}}</ref> Delboeuf is well known for his work on this illusion.<ref name=":43" /> Later in his career, he published an explanation of the [[Müller-Lyer illusion|Muller-Lyer Illusion]] in terms of eye movements instead of the mis-estimation of angles theory [[Franz Brentano|Brentano]] had published.<ref name=":43" /> Many studies have been conducted on the Delboeuf illusion (1865) since the publication of his original study, and many explanations for this illusion have been put forth.<ref name=":43" />

== Works ==
{{wikisource author}}{{div col}}
* ''De la moralité en littérature'' (1861)
* ''De la psychologie comme science naturelle, son présent et son avenir'' (1875)
* ''Le sommeil et les rêves'' (1885)
* La mémoire chez les hypnotisés (1886)
* De l'influence de l'éducation et de l'imitation (1886)
* Une Visite à la Salpêtrière (1886)
* De la prétendue veille somnambulique (1887)
* Magnétisme: À propos d'une Visite À L'Écold de Nancy (1889)
* comme Quoi il n'y a pas d'hypnoitisme (1891)
* Quelques Considérations sur la Psychologie de l'Hypnotisme (1892)
* Note sur certaines illusions d'optique; essai d'une theorie psychophysique de la maniere dont l'oeil apprecie les distances et les angles (1865)
* Seconde note sur de nouvelles illusions d'optique: Essai d'une theorie psychophysique de la maniere dont l'oeil apprecie les grandeurs (1865)
* Etude psychophysique. Recherches theoriques et experimentales sur la mesure des sensations et specialement des sensations de lumiere et de fatigue Memoires couronnes et autres memoires publies par l'Academie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique (1873)
* La mesure des sensations (I): Reponses a propos du logarithme des sensations (1875)
* Analyse du memoire: Theorie generale de la sensibilite (1875)
* Theorie generale de la sensibilite Memoires couronnes et autres memoires publies par l'Academie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique (1876)
* La psychologie comme science naturelle: Son present et son avenir (1876)
* La loi psycho-physique: Hering contre Fechner (1877)
* La loi psychophysique et le nouveau livre de Fechner (1878)
* Elements de psychophysique generale et speciale (1883)
* Examen critique de la loi psychophysique: Sa base et sa signification (1883)
{{div col end}}

=== Articles in ''[[Popular Science Monthly]]'' ===
* {{Cite PSM|Dwarfs and Giants|volume=22|month-and-year=April 1883}}
* {{Cite PSM|What May Animals Be Taught?|volume=29|month-and-year=June 1886}}
* {{Cite PSM|The Psychology of Lizards|volume=43|month-and-year=September 1893}}
* {{Cite PSM|Affections and Jealousies of Lizards|volume=50|month-and-year=January 1897}}
* {{Cite PSM|In a World Half as Large|volume=52|month-and-year=March 1898}}

==See also==
* [[The Salpêtrière School of Hypnosis]]

== References ==
<references />

== Further reading ==

*François Duyckaerts, (1992). Joseph Delbœuf philosophe et hypnotiseur,
* LeBlanc, A. (2004). Thirteen Days: Joseph Delboeuf versus Pierre Janet on the Nature of Hypnotic Suggestion, Journal of the History of the Behavioral Sciences, 40, 123-147.

==External links==
* {{Internet Archive author |sname=Joseph Delboeuf}}

{{Authority control}}

{{DEFAULTSORT:Delboeuf, Joseph}}
[[Category:Belgian psychologists]]
[[Category:Belgian mathematicians]]
[[Category:Belgian philosophers]]
[[Category:Experimental psychologists]]
[[Category:Belgian hypnotists]]
[[Category:1831 births]]
[[Category:1896 deaths]]