Cited by C.S. Sherrington, 'On Reciprocal Action in the Retina as studied by means of some Rotating Discs', Journal of Physiology 21 (1) (1897), pp. 33-54.
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)