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Creator (Definite): William McDougallDate: 1901
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NB - links to second and third parts: http://dx.doi.org/10.1093/mind/X.1.210 and http://dx.doi.org/10.1093/mind/X.1.347
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CitesC.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:'There is [sic] then a very large number of striking phenomena of fundamental importance that cannot be recounted for by the theory of 'Gegenfarben,' [as advocated by Hering and G.E. Müller] and many of them are absolutely irreconcilable with any form of that theory.
Young's theory, on the other hand, if we incorporate with it the hypothesis of the separate W-exciting apparatus having its retinal seat in the rods, as urged by v. Kries, Rollet's theory of contrast and the theories of induction and after-images set forth above, explains fully all the phenomena described above; and, with the exception of certain observations of a complex character, very difficult to interpret, such as Muller's experiments on galvanic stimulation of the eyes and some of Prof. Sherrington's flicker experiments, I cannot discover any important fact connected with light- and colour-vision with which it is incompatible or that it fails to illumine.' (382)
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CitesPortable dark chamber
Description:[note on pp. 355-356]: A piece of apparatus, which may he called a portable dark chamber, is very useful in the study of after-images. It consists of the following parts: a piece of 1 inch plank, 18 inches in width, and 2 feet 6 inches in stands vertically upon this plank, its lower edge is let into a slot running along the middle of it, and it is held firmly in position by angle-pieces. A little above its centre, the square board has a circular hole, 3 ½ inches in diameter. At the top comers of the board a pair of light wooden rods are attached by hinges and can be fixed so as to project horizontally from it, parallel to one another, and at right angles to the plane of the board. Two pieces of black cloth, the inner one of black velvet, the outer of black linen, each about 3 ½ yards in length, are tacked by one edge to the top and sides of the square board and spread over the horizontal rods. A strip of cloth about 1 yard wide tacked by one edge to the base-board and a back-flap of black velvet complete the walls of the chamber. The base-board being placed upon a table at one edge the observer sits within the curtains with his eyes at the level of the hole in the vertical board, and by sitting upon the free ends of the curtains can completely exclude all light. On the inner surface of the vertical board, above and below the circular hole, are two pairs of projecting ledges to hold the photographic shutter and the glass plates. Where no dark room is available this simple piece of apparatus can be made to serve many of the purposes of one. It can also be used as a ' Dunkel-Tonne,' and even where a dark room is available this dark chamber presents the advantage that it can be placed so as to receive the direct rays of the sun through the hole in the vertical board. I have made a second example with two apertures about 9 inches apart in place of the one, each being filled with shutter and glass-plates. This is in many ways a great improvement. I find the Thornton-Pickard shutter for time and instantaneous exposures, well suited for use in such a chamber.' (355-356)
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Cited byC. Sherrington, 'Observations on 'flicker' in binocular vision', Proceedings of the Royal Society of London 71 (1902), pp. 71-76.
Description:'Interesting experimental difficulties... were occassioned by the reciprocal and often antagonistic influences exerted by one retina upon another in ways studied and described recently by Dr. W. McDougall.' (75)
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Cited byC.S. Sherrington, 'On Binocular Flicker and the Correlations of Activity of 'Corresponding' Retinal Points', Journal of Psychology 1 (1) (1904), pp. 26-60.
Description:'Experiment 8. Two images LR and λp½ were placed in the visual field for mutual comparison. LR was composed of left-eye and right-eye equal and corresponding disc-shaped images as in previous experiments. λp½ was composed of a left-eye image similar to L and R except that it lay just above or below them in the visual field. With λ's right half was combined the image of the right half of a lantern image similar again to the others, except that its left half was screened absolutely off into the blank undetailed darkness of the general field. When this was done the two opposite visual images LR and λp½ regarded under perfectly steady ocular fixation, were stable, and no difference of brightness was discernible between them. Moreover no join was seen between the halves of λp½ and no difference of brightness between the halves. After prolonged inspection of them rivalry became troublesome; but a judgment could be clearly arrived at before that happened.
In this experiment it might possibly be that equality of brightness between the halves of λp½ was due to image p½ not really being in consciousness at all during the comparison. The image might possibly lapse under competition with the partly dissimilar correspondingly placed left-eye image λ. Some of the experiments carried out by McDougall [note: 'Mind, 1901, N.S. x. p. 63 .'] give validity to such possible objection. The perceptibility of the horizontal bar in the right half of the image λp½ was guarantee however that at least part of the uniocular image p½ was present. But to ascertain more surely whether image p½ was really during the visual equation co-operating in consciousness with λ the following further arrangement was employed.
[Diagram 11: image showing altered exposure patterns of LR and λp½]
Experiment 9, (Diagram 11). With the revolving lantern so arranged that images L, R, λ and p½ were all of equal brightness when steady and unflickering, p½ was given a lesser frequency of intermission, so as to flicker while the others did not. A speed of revolution of lantern was then used at which just a trace of flicker was perceptible in p½ when binocularly combined with λ. The equation LR—λp½ was then found to hold while flicker was still just traceable in the right half of λp½. There was then no join seen hetween the halves of λp½ nor any difference between the brightness of the halves. So long as ocular fixation was steady no rivalry disturbed the observation.
In this case there could, I venture to think, be no question but that the one half of λp½ was truly binocular, for the trace of flicker was perceptible during the actual performance of the comparison. Yet no difference of brightness was perceived between LR and λp½, and the two Literal halves of compared together were of like brightness.' (48-49)
'McDougall' [note: '"The Principle underlying Fechner's 'Paradoxical Experiment' and the Predominance of Contours in the struggle of two Visual Fields." This Journ. p. 114.'], in applying to 'retinal rivalry' and 'prevalence of contours' his principle of competition of inter-related nerve-elements for energy, also argues a "separateness of the visual cortical areas for the two eyes." He brings forward striking experiments in evidence of this. In one of these he [note: Mind, 1901, N.S. X. p. 56.'] shows that an after-image, left from excitation of one retina, is more strongly revived by subsequent weak diffuse excitation of that same retina than of its fellow. More recently, in experiments proving reinforcement of visual sensations by the activity of the ocular muscles, as evidenced by after-image observations, he [note: Mind, 1903, N.S. XII. p. 473.'] shows that activity of the intrinsic muscles of an eye sends up to the brain an influence, reinforcing the activity of the cerebro-retinal tract of that eye, while it exerts no such effect upon the corresponding tract of the other eye, or exerts it in a minor degree only.' (58)
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Related toInstances of the use of physics- and photography-related equipment in psycho-physical research into vision
Description:'Observation X.— l fixed a photographic shutter over an opening in the window-shutter of the dark room and over the former a sheet of rnilk glass, so that when the photographic shutter was opened there appeared on the milk glass a bright white disc about 5 cm in diameter.' (64)
'Observation XIV.— I fixated with the right eye the shaded disc, brightly lit by diffused daylight from the outside with white light, for sixty seconds. On closing the shutter there appeared a bright positive after-image. This I projected on to the dark wall beside the shaded disc at an angle of about 15° from it and then opened the shutter again so as to illuminate the shaded disc again.' (69)
'I have... made many systematic series of observations on the after-images produced by the fixation of patches of W[hite] light of various intensities and periods of duration and with borders variously defined. I have used various sources of W light... These all give essentially similar
results, and-I will describe only three series in each of which the source of light was a patch of daylight reflected from white clouds upon a sheet of white milk glass. The milk glass was suspended over an aperture in the window-shutter of the dark room, and in the aperture was a photographic shutter which, when closed, completely excluded the light, and when opened allowed the light of the sky to fall upon an area of the milk glass...I made many series of observations with different degrees of illumination from very bright W to dull grey. For each degree of brightness I made fixations of 1, 2, 5, 10, 20, 40, 80 and 120 seconds, in every case fixating the centre of the disc with both eyes at a distance of about 50 cm., and shutting off the light completely and suddenly at the end of the period by releasing the photographic shutter.' (74-75)
'Observation XXVI.—I cut a vertical slit, 30 mm. by 15 mm, in a sheet of cardboard and, at a horizontal distance of 15 cm from it, a second hole in the form of a cross of the same dimensions as the former. This I fitted into an aperture in the shutter of the dark room and covered the one hole with R[ed] paper and the other with G[reen]; so that there appeared a bright R patch and a bright G cross on a dark ground.' (225-226)
'Observation XXXII.—I cut a hole 15 mm by 10 mm in a piece of cardboard and fixed the carboard over an aperture in the window-shutter of the dark room, and covered the hole with a piece of the P[urple] paper supplied by Bothe for the colour-wheel. On fixating this bright P patch, with accommodation maintained, struggle occurred between P and G[reen], and with relaxed accommodation I could not observe any change of colour. I then fixed a glass prism vertically before the shutter in such a position that on looking into it I could see the P patch refracted through the prism.' (232-233)
'Observation XXXV.—In each case I fixated a dark spot near the centre of the disc, with both eyes at a distance of 18 inches, and then suddenly shut off the light by releasing the photographic shutter.' (238)
'Observation XXXVIII.—Sunlight was reflected upon a plate of milk-glass fixed, as in the case of observation x., behind the photographic shutter and covered with S [black] paper save for a circle 5 cm. in diameter. Outside the shutter two sheets of R[ed] gelatine were pinned over the aperture. At a distance of 80 cm. from the circle a sheet of W[hite] paper was pinned against the dark window-shutter (W in figure 21) and illuminated by dull diffused daylight. From a distance of 70 cm. I fixated a point x midway between the W paper and the circle. On opening the photographic shutter the circle, hitherto a dull W, becomes a bright R[ed]. If the shutter be opened in the first few seconds no marked change of colour of W is perceptible, generally only a slight reddening of it through irradiation and reflexion of R[ed] light from my face.' (350-351)
[note on pp. 355-356]: A piece of apparatus, which may he called a portable dark chamber, is very useful in the study of after-images. It consists of the following parts: a piece of 1 inch plank, 18 inches in width, and 2 feet 6 inches in stands vertically upon this plank, its lower edge is let into a slot running along the middle of it, and it is held firmly in position by angle-pieces. A little above its centre, the square board has a circular hole, 3 ½ inches in diameter. At the top comers of the board a pair of light wooden rods are attached by hinges and can be fixed so as to project horizontally from it, parallel to one another, and at right angles to the plane of the board. Two pieces of black cloth, the inner one of black velvet, the outer of black linen, each about 3 | yards in length, are tacked by one edge to the top and sides of the square board and spread over the horizontal rods. A strip of cloth about 1 yard wide tacked by one edge to the base-board and a back-flap of black velvet complete the walls of the chamber. The base-board being placed upon a table at one edge the observer sits within the curtains with his eyes at the level of the hole in the vertical board, and by sitting upon the free ends of the curtains can completely exclude all light. On the inner surface of the vertical board, above and below the circular hole, are two pairs of projecting ledges to hold the photographic shutter and the glass plates. Where no dark room is available this simple piece of apparatus can be made to serve many of the purposes of one. It can also be used as a ' Dunkel-Tonne,' and even where a dark room is available this dark chamber presents the advantage that it can be placed so as to receive the direct rays of the sun through the hole in the vertical board. I have made a second example with two apertures about 9 inches apart in place of the one, each being filled with shutter and glass-plates. This is in many ways a great improvement. I find the Thornton-Pickard shutter for time and instantaneous exposures, well suited for use in such a chamber.' (355-356)
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Related toMaterial concerned with optical and visual phenomena produced by rotating discs
Description:'I have now shown that all the phenomena of contrast and induction of S [black] and W[hite] are to be explained without the hypothesis of a special S-exciting process in the retina. So far as I know the only remaining reason for retaining the hypothesis is the assertion that mixing S with a colour diminishes its saturation just as does mixing W with it. This statement rests upon observations of the kind that is described by [G.E.] Müller [note: 'Zeitschrift f. P. d. Sinnesorgane, Bd. xiv. p. 135.' (94)] in the paper before referred to.
He prepares two composite discs of which each has a middle zone made up of 40° of R[ed] and 320° of black cloth; in one which I will call A the rest of the disc is also of black cloth, and in the other B it is of W. If these two discs be rotated side by side on the colour wheel and fixated in turn the R of the ring on A appears more saturated than the R of the ring on B. How, asks Muller, can this be explained by those who do not accept the S-process hypothesis ?
In order to obtain light on this question, I made the following observation :—
Observation XXIV.— I made up two discs as follows : Disc A of black cloth with one section of W of about 90 ° — this on rotation appears of a light grey; and disc B of W paper with a ring of W and S in such proportion that oh rotation it appeared of the same brightness as disc A in spite of the
contrast darkening effect of the W ground. This required about 120° of W. Then to each nng I added 30° of R. On rotation the R of the ring on A was more saturated than that of the ring on B, and the difference was just about the same in degree as in the case of the two discs of Müller's experiment. I repeated this, varying the brightness of the grey used and also the amount' of R added, and the result was always the same, thus: e.g., with 20° of R and 90° of W in the ring of disc A, and with 20° of R and 120° of W in ring of disc B, the redness of the ring is hardly perceptible on B, but very distinct on A.Lest any one should criticise this observation on the ground of the unequal amounts of objective W mixed with the R and S of the rings, I made one more variation of the observation.
I put 90° of W and 20° of R and 250° of S in the ring on disc A, and the same amount of W and R and 8 in the ring of disc B. On rotation the ring on B appeared darker, of course, than the ring on A, and the R was very distinct in the ring on A, but in the ring on B it was hardly perceptible.
(I should add that in every case the colour of the rings was observed during fixation of a point on the edge of the ring or other fixed point.)
[Fig. 14. here - diagram giving examples of discs A and B]
In all these cases the R was less perceptible in the ring on the W ground than in the ring on the dark ground, and in every case the grey with which the R was mixed was decidedly a light grey, lighter than the hypothetical medium grey. Addition of contrast S to such a mixture should tend to increase the saturation of the R, because it brings the grey nearer to the medium grey, but it appears that the R becomes less rather than more saturated under the influence of the W ground. This is, I believe, due to direct inhibition of the R by the R element contained in the W light of the ground. The truth of this opinion I shall attempt to prove in the second part of this paper, but however this may be it is clear that the loss of saturation of R in the rings on W ground in my observations is not due to admixture of contrast S. It is in the highest degree probable that the loss of saturation of the R in Müller's experiment and in mine is due to the same cause, and is therefore not due to admixture of contrast S in the case of Muller's experiment as those who believe in a special S-process would have us suppose.' (94-96)
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Related to
Rotating Binocular Lamp
Description:Experimental equipment described in McDougall that is incorporated into the Binocular Lamp [NB article cited in both of Sherrington's articles on this piece of equipment]:
Artificial pupil, milk glass:
'Observation X.—l fixed a photographic shutter over an opening in the window-shutter of the dark room and over the former a sheet of rnilk glass, so that when the photographic shutter was opened there appeared on the milk glass a bright white disc about 5 cm. in diameter. At a distance of 15 cm. from this disc I fixed a square of white paper 2 cm. in width and under an illumination such that I could just read small print held up at the same place. At a distance of 1 metre I fixated a spot midway between the square and the disc, through an artificial pupil about 15 mm. in diameter held before the right eye.' (64)
Stereoscopic sight with adjustable focus:
'I took a stereoscope provided with an object carrier that can be pushed farther from or nearer to the prisms. On to this carrier I fitted a piece of 8 cardboard large enough to fill the whole field of view. In the cardboard were two square apertures, each about 3 cm. in width and at such a distance apart that when the card stood at a middle distance (about 30 cm.) the image of the left hand hole in the field of the left eye appeared immediately to the left side of the image of the right hand hole in the field of the right eye, while the other two images fell outside the field of view. I fixed a large sheet of evenly bright W paper at some distance behind and parallel to the plane of the card. On looking through the prisms there was then visible only the dark ground with the two W squares upon it side by side. On sliding the card towards the prisms the two images recede from one another, while on pushing it farther from them they approach one another and then overlap more and more.' (88)
Bright light (though not electric lamp) (inc. comment on the significance of milk glass):
'I have made series of observations on the after-images given by W light of different intensities, using as source of light sunlight and light from W clouds transmitted through plates of ground glassand milk-glass, as well as patches of sky and cloud and pieces of W and grey paper exposed to daylight of all degrees of brightness, and also the light of the incandescent gas-lamp transmitted through ground glass and milk-glass... The milk-glass cuts off a very large proportion of the light so that the disc seen from the dark room is by no means very dazzlingly bright.' (237)
Small holes in card to produce small patches of light:
e.g.: 'A plate of ground-glass was put over a rectangular hole, 20 mm. by 10 mm. in a sheet of cardboard. This, held up before a lamp flame, appears as a strip of bright W light on a dark ground. I held it so that the strip of light was vertical and fixated a point at the centre of the strip for five seconds, and then quickly turned it until the strip was horizontal and again fixated the point at its centre for five seconds. On then excluding all light the two positive after-images appeared successively, each complete and distinct from the other and appeared and disappeared, alternating with each other several times; then for some seconds both were visible together, forming a W cross, until one faded again and they again alternated.' (376) See also eg. (64) above.
