Cites 'Proceedings of the Physiological Society', Journal of Physiology 20 (Supplement) (1896), pp. xi-xxii.
Description:

'Photograms were taken from the disc (several separate specimens of the disc were made and photographed) in rotation. No difference between the two bands was discernible in the photograms [note: 'The photograms and the discs were demonstrated before the Physiological Society, November 14th of last year, cp. Proc. Physiol. Soc. p. xviii. This Journal, vol. xx.']' (39)

Cites A. Charpentier, 'Recherches sur la persistence des impressions rétiniennes et sur les excitations lumineuses de courte durée', Archives d'Opthalmologie 10 (1890), pp. 10, 108-135, 212-230, 340-356, 406-429 and 522-537.
Description:

'Charpentier [note: 'Archives d'Opthalmologie, 1890.'] has found the duration [of stimulus reqired to induce light sensation] less for retinal points corresponding with the peripheral part than for those corresponding with the central part of the field of vision.' (35)

Cites A. Fick, 'Ueber den zeitlichen Verlauf der Erregung in der Netzhaut', Archiv für Anatomie, Physiologie und wissenschaftliche Medicin (1863), pp. 739-764.
Description:

'Fick [note: 'Arch. f. Anat. u. Physiol. 1863.'] has shown that a more intense light sensation developes more speedily than does a less intense.' (35)

Cites A.D. Waller, 'A New Colour-Contrast Experiment', The Journal of Physiology 12 (4) (1891), pp. xliv-xlix.
Description:

'I for my part do not at all deny to "judgment" a rôle in many examples of simultaneous contrast. In Waller's contrast experiment [note: 'Proc. Physiol. Soc. 1891, p. xliv. This Journal, xii.'] it certainly is active... But to explain the fact that the contrast effect upon Bl' does not make the honmogeneous steel-grey Bl' Bk more blue than Bl Bk' "judgment" need not be invoked.' (43)

 

Relevant passage from Waller:

'Meyer's experiment on colour-contrast, Helmholtz's interpretation of the experiment, and Hering's recent criticism of the interpretation are presumably within the recollection of all physiologists, most of whom will probably have admitted that the particular interpretation offered by Helmholtz has been fully disproved.

The following modification of the experiment seems to me however almost demonstrative of the influence of judgment in the determination of a contrast effect-I do not say however of its exclu sive influence.

A narrow strip of grey paper on a white card; two rectangular pieces of coloured paper abutting upon the middle third of the grey strip; a tissue-paper cover; a point of fixation to obviate wandering of the eye and successive contrast; two pins or wires stuck in a cork at a distance equal to the length of the middle third of the grey strip. According to the dimnensions of the various parts and the intensity of illumination, the. grey strip seen through the tissue-paper appears of uniform tone in its whole length, or it may be slightly tinged by the complementary tone, especially in the middle. But if the pins are brought across the grey slip so as to limit the middle from the upper and lower thirds, that portion very evidently takes the complementary tone, while the tone of the upper and lower thirds less evidently approximates towards that of the inducing colour. The main effect is this very evident change of the middle third on the introduction of the demarcation lines formed by the two pins; lines of any kind on the tissue-paper answer equally well, but the pins are convenient for putting the demarcation on and off; the complementary effect "springs up" into evidence with the demarcation, and " melts away" with its removal; the secondary complementary effect in the upper and lower thirds of the grey slip comes and goes in a similar manner but is much less obvious. Many observers fail to see it at all, although they may be able to recognise that there is a difference of brightness [note: 'I have not yet succeeded in bringing the after-image under observation with sufficient clearness and accuracy to be able to say anything definite as to a difference in the simultaneous after-effects with and without demarcation lines.'].

It need hardly be said that this is an entirely different change from that mentioned by Helmholtz as resulting from the marking out of the limits of a grey patch on coloured ground under thin paper. In this case the comnplementary tint of the patch is diminished, in the case above described the complementary effect is brought out.

The simplest verbal explanation of the effect seems to be that whereas without the demarcation lines the evident continuity of the grey slip is an item of sensory information against the complementary effect, with these lines this informing item is weakened or lost. This is an interpretation in "psychological" terms; whether or no it is convertible into " physiological" terms, is more a question of dialectics than of fact.

The ambiguous connotations of the expression " misdirection of judgment" (urtheilstiiuschung) play a very large part in contrast controversies [note: 'Cf. Pfülger's Archiv, xxxvii. p. 520; xxx. p. 159; xi. p. 323; xuI. p. 91.']. I have used the term, as is usual, in an almost meaningless sense, that is to say without wishing to imply adhesion to a psychological or to a physiological theory. Judgment or inference is the resultant of compared sensations; all sensations have presumably the material alteration of an unknown substance as their cause, and the use of psychological terms does not imply that these hypothetical physical changes are ignored or denied. It is well however to use such terms sparingly and carefully, and to think as far as possible in terms of physical changes. But there are many psychical phenomena which can be placed and studied under experimental conditions, and which for translation into the terms of a physical hypothesis make denmands upon the imagination in excess of what may legitimately be granted in our present state of positive knowledge. Phenomena of this character are more simply described in psychological terms, than prematurely forced into the verbal patterns of any material theory. But I think it necessary expressly to state that I use such terms in no anti-physical sense, but in a literally meta-physical sense-meaning by metaphysical as applied to any phenomenon, that its physical ratio has not yet been discovered, and not implying any assertion that such ratiQ will or will not be proved to exist.

This is no digression but an essential explanation of my meaning, which is that the experiment above described fits better into the verbal form of Helmholtz's "psychological" theory than into that of Hering's "(physiological " theory. I have therefore preferred to interpret it provisionally in meta-physical terms; but I am quite prepared to admit that in this particular case, as in many others, the " meta" may be wiped out by a more exact analysis in terms of material change.

Whenever ground is entered upon entailing a comparison between the views of Helmholtz and of Hering, the overlapping of psychological and physiological interpretations, the equivalence of many terms and descriptions given in the two languages, the arbitrary character of the distinction drawn between the two classes of phenomena, press themselves upon our attention and almost create the impression that there is little real difference, that the two views exhibit the phenomena in complementary aspects. There are however very fundamental differences of doctrine. Helmholtz draws a line between simultaneous and s'uccessive contrast, placing successive contrast on the physiological side in terms of material alteration, but simultaneous contrast beyond the pale in terms of psychical interpretation; Hering draws no line at all, but places both phenomena on a physiological basis, and tacitly if not expressly implies that all psychological phenomena are the subjective symptoms of material changes. To most physiologists this is a truism, but one which need not forbid us to rank as " psychological" those psychological facts the physical basis of which it may be found difficult to conceive, and I cannot admit that to do this is to commit an act of "spiritualism," as Hering reproachfully writes.

Sharply formulated, the Helmholtz-Hering difference of view appears to be to the following effect:-Helmholtz considers that there is no direct modification of the material sensificatory data by each other, but a variation of inference affecting all the data coming within the field of perception whenever any one of these data varies in quantity or quality. Hering considers that each material sensificatory datum diffuses beyond its precise locus of incidence, and that it directly modifies contiguous sensificatory data. According to Helmholtz the data remain objectively constant but their subjective effects play see-saw in perception.

In attempting to form an opinion as to which of these two modes of view is the more applicable to the phenomena, I think that a very significant indication may be drawn from the analysis of an experiment which is in many other respects a ground-datum in experimental psychology. As is well known, a variety of figures or objects may appear to us either in relievo or in intaglio. More than this, it is possible by voluntary focalisation of attention, to see at will a given transparent object (e.g. a crystal) in either manner. Still further-and this is the point to which I wish to arrive-it will be found that if by a voluntary focalisation of attention, a transparent object is seen in a fictitious manner, sensificatory data which remain objectively constant, share in the inferential distortion. We can wilfully persuade ourselves of a fictitious phenomenon by focalising deceptive data to the exclusion of corrective data, and finally, having formed our fiction, we may consistently use objective data in further distortion of the real phenomenon.

This cerebral event may be realised and illustrated by a very simple experiment:- Take a cylindrical beaker or lamp-glass, and holding it erect look at it so as to see into the top; close one eye and imagine the proximal opening to be distal; when this representation has been successfully formed, it will be noticed that the cylindrical vessel, which appears cylindrical when seen in its real position, appears conical in its unreal position. In the erroneous inference certain sensificatory data-i.e. the retinal magnitudes of the images of the two ends of the cylinder-have not altered, but the inference from these unvaried data has been modified in congruity with the fictitious inference otherwise formed. Here then a sensificatory datum is not directly modified by its neighbours, but it is indirectly modified in the general perceptive inference.' (xliv-xlviii)

Cites C.S. Sherrington, 'Experiments in Examination of the Peripheral Distribution of the Fibres of the Posterior Roots of Some Spinal Nerves', Philosophical Transactions of the Royal Society of London B 184 (1893), pp. 641-763.
Description:

'Simultaneous contrast and areal induction flicker seem two phenomena allied inasmuch as both rest on areal reciprocity. The local exaltation or depression effected by areal reciprocity in the retina may be likened to the local spinal exaltation and depression I have called attention to in the locality of severed (or conversely excited) sensory spinal roots [note: Philosoph. Transact. CLXXXIV. B. 1893.'], with local hyperæsthesia or diminished knee-jerk for criteria [Proceedings Roy. Soc. LII. p. 17. 1893.'].' (42-43) 

Cites E. Hering, 'Ueber die Theorie des simuitanen Contrastes Helmholtz.', Archiv für die gesamte Physiologie des Menschen und der Tiere 41 (1) (1887), pp. 1-29.
Description:

'The experiments described in this paper attempt to examine retinal "induction" by means of rotating discs. I am aware that in studying the subject thus by aid of moving chequered surfaces - that is, under intermittent excitation - time relations enter introducing complexity and preparing pitfalls for the observer. In the two well-known simultaneous contrast discs given by Helmholtz [note: Physiol. Optik. p. 413. Part II. 1860.'] the translation of surface is intended merely as a means towards the attainment of those smooth sensations - e.g. homogeneous grevs - which offer such favourable fields for contrast. The rate of translation used is one ensuring perfect fusion of the sectors. So also in those few of the beautiful series of contrast experiments by Hering in which use is made of the colour top [note: 'Pflüger's Archiv, XLI. p. 1. 1887.']' (33-34)

Cites E. Hering, Zur Lehre vom Lichtsinne. Sechs Mittheilungen an die Kaiserl. Akademie der Wissenschaften in Wien (Wien, 1872-1874).
Description:

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P.' (38)

Cites E. Mach, 'Über wissenschaftliche Anwendungen der Photographie und Stereoskopie', Sitzungsberichte der Naturwissenschaftlichen Classe der Kaiserlichen Akademie der Wissenschaften 1 (11 May 1866).
Description:

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P.' (38)

 

Areal reciprocity, other things being equal, varies inversely with the distance of retinal separation of the reciprocal loci. This relation which in its broad features is obvious enough, has been established in detailed fashion by Mach's papers' [note: 'Sitz. d. kais. Akad. Wien, loc. cit.']. In the black tooth and in the white notch (Fig. 5) intensification by reciprocity between each and its surrounding field, although effective all over the tooth and all over the notch is maximal only at the free end of each. Followed from attached base to free end in each, the intensification gradually increases and culminates at the terminal border. The application of the stimulus, the blow, or if preferred as regards black, the decrement of stimulus, is more abrupt when the incidence of notch and tooth upon a retinal point begins with the free end of either. That its peculiarly high physiological efficiency is largely due to mere abruptness of impact is borne out by the fact, wbich I have found by actual experiment, that the mere angular length of the tooth or notch makes little difference, ceteris paribus, to the amount of flicker produced.' (51)

Cites E.S. Ferry, 'Persistence of vision', American Journal of Science 44 (1892), pp. 192-207.
Description:

'According to Ferry [American Journ. of Science, Oct. 1892. See also E.L. Nichols, ibid. Oct. 1884.'] "the persistence of the retinal image" varies inversely as the logarithm of the luminosity of stimulus.' (35)

Cites F. Schenck, 'Ueber intermittirende Netzhautreizung', Pflüger's Archiv für die gesamte Physiologie des Menschen und der Tiere 64 (10-12) (1896), pp. 607-628.
Description:

'The question whether "white-black value" alone or "colour-brightness value" with " white-black value" (Hering) has to be reckoned with in flicker-photometry, has been recently treated by Schenk [note: Pflüger's Archiv, LXIV. p. 607. 1896.']. In connection with that interesting work it is noteworthy that the replacement of yellow (chrome) in disc (figure 1) by white (chinese) does not appreciably increase the difference in flicker between the two ring-bands.' (43)

Cites F. Schenck, 'Ueber intermittirende Netzhautreizung', Pflüger's Archiv für die gesamte Physiologie des Menschen und der Tiere 64 (3-4) (1896), pp. 165-178.
Description:

'before making use of rotating discs for contrast phenomena it is needful, as a control, to see whether differences of mere radial distance influence the results. Marbe [note: 'Wundt's Philosophienstudien, XII. 280.'] and Schenk [sic. throughout] [note: 'Pflüger's Archiv, LXIV. p. 165. 1896.'] (with Schmidt) have examined this point on discs with alternate equal black and white sectors. The former finds fusion rather more easy along arcs further from than nearer to the centre of the disc; the latter that with increasing speed of rotation "flickering" persists longer in the peripheral zone than in the central.' (35-36)

'My results in this matter - as far as I have, in the above manner, studied it - agree with Marbe when the luminosity is low, with Schenk when the luminosity is high. To the question for which I particularly desired an answer I obtained the reply that in regard to the influence of radial distance upon "flicker" it is but small.' (37)

'Another excellent investigation by Schenk (and Schmidt) [note: 'Pflüger's Archiv, LXIV. p. 165. 1896.'] deals with "flicker" as influenced by the angular width of the sector. Filehne [note: 'v. Graefe's Archiv, XXXI. p. 20.'] noticed that with discs of equal alternate black and white sectors the frequency of intermittence of stimulation is not in exact agreement when discs of many sectors are compared with discs of few sectors. The discs of many sectors have, to extinguish flicker, to rotate relatively faster than theory demands. Mere linear velocity seems to assist the fusion of the sector sensations. Schenk's [note: 'loc. cit.'] examination of this phenomenon serves as a control in this respect for experiments brought forward in my communication. Fick [note: 'Cp. Schenk, loc. cit.']  had suggested that unnoticed movements of the eyeballs may be responsible for Filehne's phenomenon. Concordantly witlh that suggestion Schenk finds it very greatly reduced when the observations are carried on through a narrow slit cut radially to the disc in a screen covering the latter.' (37)

Cites G. Th. Fechner, 'Ueber die subjectiven Complementarfarben', Poggendorff's Annalen der Physik 120 (7) (1838), pp. 517-535.
Description:

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P.' (38)

Cites G. Th. Fechner, 'Ueber die subjectiven Nachbilder und Nebenbilder', Poggendorff's Annalen der Physik 126 (7) (1840), pp. 427-470.
Description:

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P.' (38)

Cites Hermann von Helmholtz, Handbuch der physiologischen Optik (Leipzig, 1856-1867).
Description:

'The experiments described in this paper attempt to examine retinal "induction" by means of rotating discs. I am aware that in studying the subject thus by aid of moving chequered surfaces - that is, under intermittent excitation - time relations enter introducing complexity and preparing pitfalls for the observer. In the two well-known simultaneous contrast discs given by Helmholtz [note: Physiol. Optik. p. 413. Part II. 1860.'] the translation of surface is intended merely as a means towards the attainment of those smooth sensations - e.g. homogeneous grevs - which offer such favourable fields for contrast. The rate of translation used is one ensuring perfect fusion of the sectors.' (33-34)

 

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P. This reciprocity, subconscious in origin, affects consciousness; it is a factor in the production of sensations, and influences inferences dependent upon comparison of those sensations. So intrusive is it psychologically that Joh. Müller [note: Physiologie, 1841. Bk. V., Sect. 1, Cap. 3.'] and Helmholtz [note: Physiol. Optik. p. 417. Part II. 1860.'] treated it as wholly a product of processes of judgment, a doctrine ably controverted by Hering.' (38)

 

Judgment based on comparison of the two blues Bl' and Bl and of the two blacks Bk and Bk' when the disc is stationary declares without hesitation that the difference between the blacks is much less than between the blues. Some observers fail to see any difference at all between the blacks, although they find a marked difference between the blues. Error of judgment thus, far from as in Helmholtz's doctrine [note: Physiol. Optik. 1860.'] producing the contrast, actually minimises it.

A similar instance of "Urtheilstäuschung" acting in exactly the converse manner to that suggested by Helmholtz - and, in regard to the important degree to which "Urtheilstäuschung" may affect observation, thorotughly bearing him out - is the following. Some persons unaccustomed to examine visual contrast have at first difficulty in admitting that there is a difference between the strips Bl and Bl' (Fig. 1). They have been told at outset that the disc is prepared from a piece of evenly-tinted blue card and the unpainted even-blue back of the card has been shown to them, and they then on looking at the face of the disc frequently have told me that the two strips appear of quite equal tint in saturation and in every other respect. On rotating the disc before them they however like others point out without hesitation that one ring-band is "flickering" while the other is "steady." This shows how in them the rôle of judgment is exactly the converse to that allotted to it by Helmholtz in his theory of "simultaneous contrast." They are really subjected like otlher observers to very different excitations from Bl and Bl'; yet, in all good faith, after hearing that the two bands are made of the same piece of evenly-tinted card they assert that their sensations derived from the two are not unequal. Their judgment suppresses the actual inequality of their sensations, and does so without their desiring that it should. Their judgment warped by their previous knowledge leads them to ignore the simultaneous contrast which is really taking effect in them - that it is really taking effect in them is proved by their acknowledging the actuality of areal reciprocity in themselves by acknowledging the "flicker" difference which is as patent to them as to others. The knowledge and idea of the physical equality of the bands acts in them much as does suggestion on a hypnotic subject. Because they know two things are the same they cannot see a difference between them.' (41-42)

Cites J. Müller, Handbuch der Physiologie des Menschen für Vorlesungen (Coblenz, 1837-1840).
Description:

'JOH. MÜLLER described the elementary parts of the retina as being connected together by "reciprocal action [note: 'Muller. Handbuch der Physiologie des Menschen (1837-1840).']." The physiological result of application of a stimulus to any given point of a sensifacient surface is decided by not only the particular stimulus there and then incident but also by circumjacent and antecedent stimuli.' (33)

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P. This reciprocity, subconscious in origin, affects consciousness; it is a factor in the production of sensations, and influences inferences dependent upon comparison of those sensations. So intrusive is it psychologically that Joh. Müller [note: Physiologie, 1841. Bk. V., Sect. 1, Cap. 3.'] and Helmholtz [note: Physiol. Optik. p. 417. Part II. 1860.'] treated it as wholly a product of processes of judgment, a doctrine ably controverted by Hering.' (38)

Cites J. Plateau, Dissertation sur quelques propriétés des impressions produites par la lumière sur l'organe de la vue (Liége, 1829).
Description:

'Rood [note: 'American Journ. of Science, XLVI. p. 173. 1893.'] has recently re-introduced to notice a method of photometry advocated on not very convincing grounds by Schafhäutl [note: Universal Vibrations-photometer: Akad. d. Wiss. München, VII. p. 465.] forty years ago. The method is based on Plateau's [note: 'Dissert. sur quelques propriétés des impressions &c. Liège, 1829.] research, and proceeds on the well-known relation existing in light-sensations between their intensity and the rate of frequency of repetition required to fuse them.' (34)

Plateau [note: 'loc. cit.'] had noted that strong light-sensations suffer perceptible decrease [of speed of development in vision] more quickly than do weak - that is, had found his "duration of apparent constancy" more brief for the former' (35)

Cites K. Marbe, 'Theorie des Talbot'schen Gesetzes', Philosophische Studien 12 (1896), pp. 279-296.
Description:

'before making use of rotating discs for contrast phenomena it is needful, as a control, to see whether differences of mere radial distance influence the results. Marbe [note: 'Wundt's Philosophienstudien, XII. 280.'] and Schenk [note: 'Pflüger's Archiv, LXIV. p. 165. 1896.'] (with Schmidt) have examined this point on discs with alternate equal black and white sectors. The former finds fusion rather more easy along arcs further from than nearer to the centre of the disc; the latter that with increasing speed of rotation "flickering" persists longer in the peripheral zone than in the central.' (35-36)

'My results in this matter - as far as I have, in the above manner, studied it - agree with Marbe when the luminosity is low, with Schenk when the luminosity is high. To the question for which I particularly desired an answer I obtained the reply that in regard to the influence of radial distance upon "flicker" it is but small.' (37)