FRANK ALLEN, PH. D.; LL. D.; F. R. S. C. PROFESSOR EMERITUS CANADA. IN PHYSICS, THE UNIVERSITY OF MANITOBA, WINNIPEG, THE NEURAL OSCILLATORY EFFECT IN COLOUR VISION By Frank Allen, Ph. D.; LL. D.; F. R. S. C. The University of Manitoba, Canada. The neural oscillatory effect, as described in a former communication1), may be thus explained, when operating in the sensory field. When an adequate stimulus is applied to a sense organ, two results follow: first, a sensation is elicited in the appropriate cortical centre; and, second, the two neural processes of inhibition and facilitation are excited in the peri- pheral and central sensory apparatus, the former depressing and the latter enhancing the responsiveness of the sense or- gan. By these processes, apparently, sensory tone is main- tained. The sensation also exercises two functions ; first, it con- stitutes the psychical element of sensory consciousness; and, second, by its changing quality or intensity, it is an indicator of the varying physiological excitability or state of the recep- tors. After stimulation of a sense organ ceases, the processes of inhibition and facilitation continue to operate alternately so that its responsiveness is likewise alternately depressed or enhanced, until by a series of such oscillations of sensitivity of diminishing amplitude normal sensory equilibrium is re- stored. During recovery, therefore, the character of the re- sponse of the organ to further stimulation at any moment will depend on the process then in the ascendant. Should the in- hibitory phase be predominant the response will be diminished below the normal value, while the facilitatory phase will cause a n augmented response above it. Act?. Ophthalmol. Vol. 27. IV. 39
Transcript
FRANK ALLEN, P H . D.; L L . D.; F . R . S. C. PROFESSOR EMERITUS
CANADA. IN PHYSICS, THE UNIVERSITY OF MANITOBA, WINNIPEG,
THE NEURAL OSCILLATORY EFFECT IN COLOUR VISION
By Frank Allen, Ph. D.; LL. D.; F. R. S. C. The University of Manitoba, Canada.
The neural oscillatory effect, as described in a former communication1), may be thus explained, when operating in the sensory field. When an adequate stimulus is applied to a sense organ, two results follow: first, a sensation is elicited in the appropriate cortical centre; and, second, the two neural processes of inhibition and facilitation are excited in the peri- pheral and central sensory apparatus, the former depressing and the latter enhancing the responsiveness of the sense or- gan. By these processes, apparently, sensory tone is main- tained. The sensation also exercises two functions ; first, it con- stitutes the psychical element of sensory consciousness; and, second, by its changing quality or intensity, it is an indicator of the varying physiological excitability or state of the recep- tors. After stimulation of a sense organ ceases, the processes of inhibition and facilitation continue to operate alternately so that its responsiveness is likewise alternately depressed or enhanced, until by a series of such oscillations of sensitivity of diminishing amplitude normal sensory equilibrium is re- stored. During recovery, therefore, the character of the re- sponse of the organ to further stimulation at any moment will depend on the process then in the ascendant. Should the in- hibitory phase be predominant the response will be diminished below the normal value, while the facilitatory phase will cause a n augmented response above it.
Act?. Ophthalmol. Vol. 27. IV. 39
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The neural oscillatory effect has been found to occur in the post-contraction of muscles by Allen and O’Donoghue5), where it was first observed, by Allen‘) in the secretion of the salivary glands, and by Allen and Schwartz6) in the influence of the stimulation of one sense organ upon the responsiveness of another sense organ of a different modality.
In many former papers of the writer on vision, the expo- sure of the eye to light and colours was called >)fatigue<<. I t has become clear that the eye does not readily experience phy- siological fatigue since, after exposure to light, it continues functioning without difficulty or impairment of its visuaI powers. It seems appropriate, therefore, to drop that word, and to employ in its place the term >>adaptation(< (Aubert). In avoiding the use of the word ,>fatigue<< for colour adapta- tion the writer follows Parsonsi1) and Duke-Elders). There are, however, experimental researches, some of Burch’s7), for example, in which retinal fatigue undoubtedly occurred.
In the present communication some further experimenta1 evidence derived from the sense of vision is presented in illu- stration of the neural oscillatory effect. For this purpose three simple spectral colours, red 687, green 550, and violet 410 mu, two compound colours, yellow 589 and blue 450 mp, and the equilibrium colour 505 mu, were chosen for stimulating the eye to produce adaptation to the colour. With each colour four sets of measurements were made, two under ipsilateral and two under contralateral conditions of adaptation.
The method of experimentation employed in this investi- gation was to obtain two graphs for the critical frequency of flicker of colour for the whole spectrum; one for the right eye in daylight adaptation, and the other for the same eye adapted to one of the selected colours alone, or when it was under the influence of the colour adaptation of the left eye. Any differ- ences between the graphs when plotted together could there- fore be attributed to the effect of the colour adaptation. In this way the influence of adaptation to a single colour on the perception of all parts of the spectrum could readily be as- certained. It has been frequently verified by the author that in daylight adaptation the eye has remarkable constancy of co- lour perception, and that the graph obtained under this con-
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dition for a spectrum of constant physical brightness can be reliably employed for comparison for many months. This is termed the normal graph.
The standard spectrum employed for measurement was formed in a Hilger spectrometer with four prisms, equivalent to three prisms of 60° each, so controlled that each colour under observation was automatically at minimum deviation. The source of light was an incandescent lamp with continuous current a t a controlled constant potential of precisely 110 volts. The test-patch of spectral colour observed was a small squarc formed by side shutters in the eye-piece with black paper above and below. No other light was visible in the eye- piece. The wave-length of this patch was regarded as that of the middle line as calibrated by a pointer in the eye-piece. A piece of blackened cardboard tube, accurately cut to fit the surroundings of the right eye of the observer, was attached to the eye-piece so as to accomodate only one position of the head by which the eye was always held exactly in the same place in front of the viewing lens. Fixation could easily be maintained, since the slightest deviation of the eye could at once be detected by a change in intensity of the contour of the illuminated square. The patch of colour subtended an angle of about 2 O , and was sufficiently small for the rod-free area ( 3 O 3 ’ ) of the retina alone to be stimulated.
The instruments were placed in a room with light neutraI gray ceiling and walls, and a large window space, so that normal white daylight illumination prevailed a t all times. Observations were made between 10 o’clock a. m. and 3 o’clock p. m. to avoid the use of artificial lighting. The optical parts of the spectrometer were carefully screened so that no light entered except that from the incandescent lamp through the slit. Under these conditions the same normal graph served throughout the experiments.
In order to maintain daylight adaptation during rest periods, the eyes of the observer were not used in any way but were directed to a large wall without fixation on any part. The windows and dark objects were comPletely avoided. Both eyes were always open, so that at no time was any com- plication introduced by darkness adaptation of either eye.
39.
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The apparatus for obtaining colour adaptation of the eye consisted of a calibrated spectrometer with two 60° prisms and a continuous current carbon arc-lamp for illumination. A patch of the spectrum somewhat larger that the observational test- patch, upon which measurements were made, was isolated in the eye-piece by shutters, and its wave-length was taken as that of the middle line. This adapting light was very much brighter than the test-patch, but its intensity was not meas- ured. The adaptation instruments were placed on a table by themselves a few feet distant from that with the measuring instruments, so that after the adaptation of the eye was completed, the observer could immediately and conveniently change from one table to the other for the measurements of the critical frequency of flicker of the test-patch.
A normal graph of the duration of the impressions of light a t the critical frequency of flicker of twelve different colours or test-patches of the standard spectrum of constant bright- ness, upon which all measurements described in this paper were made, was obtained with the right eye of the writer, both eyes being maintained in daylight adaptation. The wave- lengths of these colours and the measurements obtained are given in the Table, and are plotted in Fig. 1.
Two types of ipsilateral and two of contralateral measure- ments were made with each of the six colours selected: first, the immediate effect of adaptation when observations were made without allowing a period of rest between the close of adaptation and measurement: and, second, the deferred effect when a rest period of three minutes between them was taken.
In the investigation of immediate ipsilateral adaptation, the right eye was exposed to a very bright band of colour of the desired wave-length isolated in the spectrum of the adap- tation spectrometer. Immediately after exposure or adaptation for two minutes, a measurement of the critical frequency of flicker of the test-patch was made in the same manner as for the normal graph. This procedure was repeated throughout the whole spectrum until a second complete graph was ob- tained with the, eye adapted to the single selected colour. The two graphs were then plotted together, as in Fig. 1, and the differences between them noted. It is these differences that
are significant in ascertaining the influence of colour adapta- tion upon vision. Where the adaptation graph falls below the normal, it indicates by the shorter time values that the phy- siological brightness of the corresponding region of the standard spectrum has increased; and when elevated above the normal it indicates by the larger time values a diminu- tion of physiological brightness. Only one complete set of measurements with adaptation to a single colour was obtained on any one day. Similarly the six colours specified above were successively employed for the immediate effects of ipsilateral adaptation.
In the same manner the deferred effects of ipsilateral adaptation were obtained, except that after exposure of the eye to the adapting colour a rest period of three minutes elapsed before measurements on the test-patch were made. In this way time was allowed for the processes of inhibition and facilitation to become reversed, as the author has else- where shown.e)
In Fig 1 is shown the graph obtained for the deferred ef- fect of ipsilateral adaptation to red, 687 m'p. The broken line is the normal graph and the continuous line represents the deferred effect. The differences between them are plotted below where the broken horizontal line again represents the normal, and the continuous line the differences. The part of the line below the normal indicates that the corresponding red colour is enhanced in brightness, while the parts above the normal show that the green and violet colours are diminished: or, the primary red sensation is enhanced in sensitivity, and the two other primaries, green and violet, are depressed. The three-fold character of the curve of differences in this figure, and of those in the remaining figures, is strikingly in accord with the three fundamental sensations of the Young theory of colour vision, and amply confirms the reality of those sensations as primary.
In this investigation twenty-four graphs, such as that in Fig. 1, for the six colours were obtained, half for the immediate and half for the deferred effects of adaptation. As so large a number of figures cannot be reproduced in this communica- tion, the four curves of differences for each colour adaptation
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are shown in a single figure where they can easily be com- pared.
The measurements for all conditions of adaptation, both
,040
.035
z 0 2 .030 >
U 0
$ ,025
!?
z W I-
ln n
,020
0.01 5
I I
) 500 600 700 WAVE-LENGTH, mu
Fig . !. Ipsilateral deferred effect of adaptation to the red colour 687 mu. The adaptation graph is the full line. The normal graph is the
broken line. Graph of differences is below.
ipsilateral and contralateral, for the six colours are given in the Table. In the first column on the left are the adaptation colours. The second column contains the wave-lengths upon
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which all observations were made. The third column contains the normal measurements of the duration of impressions at the critical frequency of flicker with which all other measure- ments are compared. In the fourth column are the ipsilateral deferred measurements, with the differences between them and the normal observations in the fifth column. The sixth column contains the contralateral deferred measurements, with the differences, as before, in the seventh. Only the signi- ficant figures of the differences are given.
As these measurements are very laborious and repetition is unnecessary, the results of former observations3) with the same instruments under the same conditions, are given in the last two columns. The eighth contains the differences for the immediate ipsilateral effects of adaptation, while the ninth contains those for the immediate contralateral effects. Since no measurements were made for the immediate contralateral effect of yellow 589 mp, those for nearly the same colour 577 mlu, which are recorded in the paper referred to, are here used instead. In a number of ipsilateral and contralateral ex- periments with the colours 589 and 577 mu, it was always found that they produced practically identical effects. The substitution is therefore warranted. In the four columns of differences in the Table, the plus signs indicate measurements above the normal graph, and therefore depression of sensitivity due to inhibition; while the minus signs indicate measure- ments below the normal and accordingly the opposite condi- tion of enhancement of sensitivity due to facilitation. All values in the Table are generally the means of two or three different sets of observations, each containing several measure- ments.
In Figs. 2 to 7, inclusive, the four graphs of differences are arranged in the same order. Graphs A and B always re- present the influence of immediate and deferred ipsilateral adaptation, respectively; while graphs C and D likewise re- present the immediate and deferred effects of contralateral adaptation, respectively. The four graphs in each figure re- present the various effects of adaptation to a single colour. Graphs A and B are plotted from the differences in columns
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8 and 5, respectively; and graphs C and D from columns 9 and 7, respectively.
When, to be specific, the adapting colour was red of wave- length 687 mu, the right eye was exposed to it in the manner
500 600 700 WAVE-LENGTH , mp
Fig. 2. Adaptation to the red colour 687 mp, full lines.
N is the normal graph. A. Ipsilateral immediate effect. B. Ipsilateral deferred effect. C. Contralateral immediate effect. D. Contralateral deferred effect.
described and the immediate effect on that eye was measured. As shown in Fig. 2 A, the red sensation, as the result of ipsi- lateral adaptation, was depressed in sensitivity and the green and violet sensations were enhanced. In another set of meas- urements the deferred effects of ipsilateral adaptation were obtained, as shown in Fig. 2 B, which is taken from Fig. 1, where a complete reversal is indicated, the red sensation being
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enhanced in sensitivity and the green and violet sensations depressed. In the interval of rest for three minutes preceding the measurements, the process of depression or inhibition of the red sensation has been superseded by that of enhancement
WAVE -LENGTH, mu F i g . 3.
Adaptation to the green colour 550 mp, full lines. N is the normal graph. A. Ipsilateral immediate effect. B. Ipsilateral deferred effect. C. Contralateral immediate effect. D. ContralateraI deferred effect.
or facilitation, and the enhancement of the green and violet sensations has been superseded by depression. In contralateral adaptation for the same red colour, all three primary sensa- tions in the right eye were enhanced in sensitivity as the im- mediate result, Fig. 2 C, while the three sensations were de- pressed in sensitivity, Fig. 2 D, as the deferred effect. With ipsilateral adaptation, therefore, the red sensation and its
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complementary sensations, green and violet, are influenced in opposite ways; with contralateral adaptation, all sensations are affected in the same way but in different degrees.
Similarly, when the adaptation colour was green 550 mu, the immediate effect of ipsilateral adaptation, as shown by Fig. 3 A, was to depress the green sensation and to enhance the red and violet, which together are the complementary of green. The deferred effect, as in Fig. 3 B, was the reversal of sensitivities in which the green sensation was enhanced in sensitivity and the red and violet sensations depressed. With contralateral adaptation, the immediate effect upon the right eye, as shown in Fig. 3 C , was the enhancement of all three
500 600 700
WAVE-LENGTH, mu
Fig. 4. Adaptation to the violet colour 410 mu, full lines.
N is the normal graph. A. Ipsilateral immediate effect. B. Ipsilateral deferred effect. C. Contralateral immediate effect. D. Contralateral deferred effect.
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primary sensations, and the deferred effect, Fig. 3 D, was their depression.
The ipsilateral adaptation of the right eye to violet 410 qu gave analogous results. The immediate effect, Fig. 4 A, was the depression of the violet sensation and the enhancement of the complementary green and red; while the deferred effect was the reverse, as in Fig. 4 B. With contralateral adaptation to violet, the transferred immediate effect was the enhance- ment of all three sensations, Fig. 4 C, and the deferred effect was the opposite, as shown in Fig. 4 D .
The effects of stimulation by, or adaptation to, the com-
I 400 500 600 70 0
WAVE-LENGTH, mu
Fig. 5. Adaptation to the blue colour 450 mu, full lines.
N is the normal graph. A. Ipsilateral immediate effect. B. Ipsilateral deferred effect. C. Contralateral immediate effect. D. Contralateral deferred effect.
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pound colours blue 450 m,u and yellow 589 mp, are shown respectively in Figs. 5 and 6. With the blue colour, the im- mediate ipsilateral effect was to depress the component green and violet sensations, Fig. 5 A, and to enhance the red; while the deferred ipsilateral effect was to enhance the green and violet sensations and to depress the red, Fig. 5 B. With stimula- tion of the left eye in contralateral adaptation, the immediate effect upon the right was to enhance all three sensations, Fig. 5C, and the deferred effect, as in Fig. 5D, was opposite in character.
N
- 20
+ 20
N
- 20
I I
-20 +2: ;p 400 500 600 700
WAVE- LENGTH, mu Fig. 6.
Adaptation to the yellow colour 589 my, full lines. N is the normal graph. A. Ipsilateral immediate effect. B. Ipsilateral deferred effect. C. Contralateral immediate effect. D. Contralateral deferred effect.
The effect of adaptation to yellow 589 mu, Fig. 6, was similar to that for blue, except that the two sensations de-
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pressed or enhanced after ipsilateral adaptation were red and green, instead of green and violet, Figs. 6 A and 6 B. One of the graphs, Fig. 6 C , for the immediate contralateral effect of yellow, was for the colour 577 mu, as explained above. Fig. 6 D represents the deferred contralateral effect of yellow 589 mu.
Stimulation by the equilibrium colour 505 my, as indicated by the four graphs in Fig. 7, for ipsilateral and contralateral immediate and deferred effects, show no differences from the
WAVE-LENGTH, mp
Fig. 7. Adaptation to the equilibrium colour 505 mu, open circles. N is the normal graph. A. Ipsilateral immediate effect. B. Ipsilateral deferred effect. C. Contralateral immediate effect. D. Contralateral deferred effect.
normal graph. This result is in keeping with the equilibrium4) character, since it is evident that it excites the processes of inhibition and facilitation equally and simultaneously, or these processes remain balanced, under all conditions of adaptation.
It is clear that depression of sensitivity of any sensation occurring after a rest-interval of three minutes cannot be due to fatigue, while it is the natural result of partial inhibition through colour adaptation.
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The opposite character of the immediate and deferred ef- fects elicited by adaptation to the three simple and the two compound colours shows to some extent what occurs in the neural sensory mechanism of vision within the period of three minutes. No measurements were made in this investigation on the effect of the processes of inhibition and facilitation a t other intervals of time after adaptation. I t is doubtless the case that if a rest-period of 1.5 instead of 3 minutes were al- lowed after adaptation, the measurements would not have dif- fered from the normal, since momentary equilibrium of the two processes would have occurred as inhibition was changing to facilitation, and facilitation to inhibition. Probably the same result would be true for a rest-period of 4.5 minutes. The oscillatory effect seemingly swings, in pendular fashion, several times from one extreme to the other with diminishing amplitude until normal sensory equilibrium is restored. With equilibrium colours like 505 mp, no oscillatory effect can oc- cur, since the processes of inhibition and facilitation are al- ways equally and simultaneously excited.
Certain stable or invariable colours have been found which do not change in hue in passing from central to peripheral vision. Though in each case the colour tone remains constant, it gradually becomes paler as the distance from the centre increases, and finally colorless at the extreme periphery. The determinations of seven observers are given in the following table, each of whom found four such colours, one of which was red mixed with a small amount of blue, or purplish-red, of no spectral character.
Hering has also selected much the same spectral colours, ( B ) 471, ( G ) 495 and ( Y ) 574 mlu, as three of the four fun- damentals of his theory of colour vision; and Purdy regards
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the hues, 476, 504 and 576 mu, as psychological primaries. The invariable colours selected by Hess form two pairs of complementary hues, purplish-red and green 495 mp; and blue and yellow of wave-lengths 471 and 574.5 mp, respectively.
It has been found by the writer that six spectral colours, 660, 572, 520, 505, 480 and 425 mp, have an equilibrium char- acter a t ordinary intensities, all of which, when used as visual stimuli, behave like the colour 505 mu in their inability to induce either depression or enhancement of visual sensitivity. They ought, therefore, to retain their colour tone invariable. On comparing the wave-lengths of three of these, 480, 505 and 572 mu, with the invariable colours, especially with those of Exner and Purdy, they are seen to be in substantial agree- ment. It is to be noted (Parsonsll) ) that the invariable colours are generally observed by using coloured papers (Hess) and gelatine filters (Baird), the precise wave-lengths of which can- not be determined, and perfect identity with the equilibrium colours of spectral origin can scarcely be expected. Should the remaining equilibrium colours, 660, 520 and 425 mp, prove to be invariable, as is probably the case, the argument of in- variability as a proof of fundamentalism of sensational quality would completely lose its force.
Every spectral colour always excites to some degree all three fundamental sensations, red, green and violet, equal intensities of which together evoke the sensation of white. This is the cause of the unsaturation possessed in some meas- ure by all colours, for no colour ever appears fully saturated. The colour itself is superimposed upon the foundation of white through predominant excitation of one sensation alone by the simple colours, red, green and violet; or of two sensations together by the compound colours, orange, yellow and blue. If the same ratio of excitation of the sensations is preserved over the whole retina the colour tone must remain invariable; and this is accomplished by maintaining a balanced condition of the processes of inhibition and facilitation by which the sensitivity or responsiveness of the sensations is controlled. Such a condition occurs only by stimulation with the equili- brium colours.
The reason why certain colours are invariable at all in-
tensities and over the whole retina is not, therefore, because they are fundamental sensations, but because they preserve a constant balance between the underlying neural processes. For each spectral colour not only excites a sensation, but is also a physiological stimulus with a distinctive character of its own.
When colours do change in hue on different parts of the retina, at different intensities and under prolonged fixation, the effect arises from unequal alterations in the sensitivity of the primary sensations gradually occurring, which are due to inequality of excitation of the normal processes of inhibi- tion and facilitation in the visual apparatus.
From the numerous graphs in the figures it is evident that stimulation of the retina by every colour, except the equil- ibrium hues, while exciting the appropriate primary colour sensations, has always the additional effect of changing the responsiveness of the complementary colour sensations. This action shows itself also in subsequent stimulation of the retina by the complementary of the original stimulus which is im- mediately perceived brighter and more saturated than is normally the case. I t is likewise the physiological cause of the modifications of colour in uniocular and binocular simultane- ous contrast. In the tetrachromatic theory of colour vision of Hering these complementary relationships are of fundamental importance, and they were attributed by him to the assumed opponent processes of assimilation and dissimilation of two hypothetical photochemical substances in the retina. After the lapse of seventy years they are still hypothetical; while the neural processes of inhibition and facilitation, which adequate- ly explain the visual modifications of colour perception, have a firm physiological foundation. Coupled with these facts is the three-fold basis of visual sensations, as verified by the graphs, in harmony with the trichromatic theory of Young. By combining them, therefore, the two chief theories of colour vision are not merely reconciled, but are unified into a single Young-Hering theory, except for the white-black sensations, each supplying what the other lacked. The combination theory also acquires a flexibility of application to chromatic phenomena which neither alone by its rigidity possesses. The
two theories are not therefore antagonistic to each other or mutually exclusive, but are complementary in character. For the threefold nature of colour stimulation combined with its twofold power of depressing one or two primary sensations and enhancing the complementary sensation, comprise the fundamental provisions of both theories. The sensation of white is not simple as in the Hering theory, but is compounded of equal stimulation of the three primary sensations, red, green and violet. No separate mechanism for it is therefore required.
In colour vision the term induction is used to cover the phenomena resulting from the influence of one retinal area upon another, or of one retina upon the other, such as occur in simultaneous contrast. Probably the term was introduced from its employment in describing the influence of an electric current in one circuit upon another near it, and in magnetic and electrostatic induction. But since action at a distance is inadmissible, these magnetic and electric influences are con- tinuously exerted through space in some physical manner under the concept of lines of force. But with nerves there is fortunately nothing analogous to electro-magnetic induction. For if there were, the nervous impulses in the parallel fibres of the spinal cord and of the nerve trunks which supply vital organs, would be constantly interfering with one another with possibly dangerous results. Induction as applied to neural phenomena seems therefore to be meaningless, since there is no specified mechanism to transmit the actions from the retinal point of stimulation to another retinal point where the inductive effect is observed.
A mechanism, however, does exist in the complex inner retina which is competent to account for the phenomena of ipsilateral inhibition and facilitation described above. >>The structure of the primate retina,< as Dr. Stephen Polyaklo) points out, ))is exceedingly complex. In it not less than 15, perhaps more, distinct varieties of neurons are present. These undergo with each other 38, and possibly more, kinds of dif- ferent synapses. In substance the retina is a nervous organ where, besides the process of photo-reception, many other processes usually associated with the central nervous system - selection, facilitation, inhibition, summation of excitation,
Acta Ophthalmol. Val. 2 7 . IV. 40
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etc.- take place. According to this, the retina is essentially a receptor-integrator organ. The forwarding of the excitations arising in the photoreceptors to the brain, is therefore not a simple mechanical transmission, but an elaborate nervous processu.
While no fibres are known directly connecting the two retinas, efferent fibres of unspecified visual function are found that conduct impulses from the cortical centres to the retinas, in addition to the afferent nerves conveying impulses to the central area. An ocular nervous mechanism therefore exists by means of which the contralateral phenomena of inhibition and facilitation may be mediated.
There are, therefore, in the complex visual apparatus ner- vous mechanisms adequate to explain the phenomena of the neural oscillatory effect as exhibited in that organ, and also, in the opinion of the writer, to justify their inclusion under visual sensory reflex action. The formerly restricted field of reflex action has been greatly widened by Pavlovl2) who, by his discovery of conditioned reflexes, has extended it into the cerebral cortex. He has not hesitated also to speak of the >>freedom reflexcc of an animal as a reflex of protest against limitation of freedom, and the >>investigatory reflex<, or the >>what-is-it reflexcc, as an attitude of inquiry or attention to- wards change or unusual condition in the environment. Since the concept of reflex action has been so greatly enlarged, there seems to be no reason against the recognition of a sensory reflex, that is, a reflex operating entirely within a complete sensory organ, or between two or more sense organs of dif- ferent modalities, by which as a result of stimulation, the sensitivity of the receptor apparatus is indirectly controlled.
An extraordinary manifestation of the neural oscillatory effect is found in the labyrinthine reflexes acting on skeletal muscles. This occurs in two forms, both of which were dis- covered by Wodak and F i s ~ h e r ? ~ ) They have been described by Camis*) thus:
First, ,the tonic reaction of the arms, which consists in an asymmetrical attitude of the extended arms as a result of excitation of the labyrinth. The arm on the side of the caloric (cold) or galvanic (anodal) stimulation is lowered, and the
617
Fig. 8.
other arm is raised; but after the lapse of some seconds, the movement is reversed; that is to say, the arm which was previously held up is lowered, and the arm that was lowered is raised. There is thus established, in response to a single continuous stimulus, a rhythmical series of alternating move- ments which may continue for fifteen or thirty minutes.u
In the second and much more complicated reaction, the discobolus reflex, the ear is irrigated with 50 C.C. of water a t 1 8 O to 20° C., or excited by an electric current of 2-5 mil- liamps., with the following results: >>The subject on whom the experiments are being made is warned not to make any voluntary movements, and stands upright with his arms stretched forwards and his eyes shut. When the stimulus is applied to the left ear, the result is a rotation of the trunk on the pelvis towards the stimulated side, followed by rota- tion of the head, and deviation of the arms from the shoulder- joint towards the same side, while the left arm is lowered and the right is raised. This attitude appears by degrees and be- comes more and more marked throughout the period of stimu- lation, so leading to forward and lateral displacement of the centre of gravity. If falling is prevented, the subject resumes
The Discobolus Reflex. Wodak and Fischer.
40'
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his normal position without volition coming at all into play. He does not, however, remain there for long. Almost at once an extremely interesting phenomenon appears. The movements which before were performed in one direction are now per- formed in the other, and the subject comes to strike an attitude that is the mirror image of the one described, Fig. 8. This alternate assumption of the two positions may be rhythmically repeated several times in diminishing degree for as long as half an hour, in response to a single stimulation of the laby- rinth. The same effect is also produced, but in opposite direc- tion and a less intense form, by irrigation with hot water or by cathodal stimulation.
It may also be remarked that the subject experiences a sensation of heaviness in the arm that is lowered, which may be contrasted with a sensation of lightness in the arm when raised in the post-contraction reflex.
The experiments described in this communication and those cited from other sources, together with those presented in the former papers referred to above, serve to establish the neural oscillatory effect as a fundamental principle of neuro- logy. Probably the literature of reflex action and of neurology contains many observations of phenomena which can also be included under this principle and widen its field of applica- tion.
(Tables 1 and 4 ) , (August), 1923. 4. Allen, F.: On the discovery of four transition points in the spec-
trum, and the primary colour sensations. Phil. Mag. Ser. 6, 38, 55, (July), 1919.
5. Allen, F . and O'Donoghue, C . H . : The post-contraction proprio- ceptive reflex. Quart. Jour. Exper. Physiol. XVIII, 199, (De- cember), 1927.
6. Allen, F . and Schwar t z , M.: The effect of stimulation of the sen- ses of vision, hearing, taste and smell upon the sensibility of the organs of vision. Jour. Gen. Physiol. 24, 105, (Sept.), 1940.
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7 . Burch, G. J. : Phil. Trans. Roy. SOC. B. 191, 1898. Proc. R. S , 66, 216, (Feb.), 1900.
8. Camis, M . : Physiology of the Vestibular Apparatus. Eng. trans. Creed, Oxford, 1930. 218-220.
9. Duke-Elder , W . S.: Text-Book of Ophthalmology, Kimpton. Lon- don, 1932. Vol. 1, 968.
10. Maximow, A. A. and Bloom, W.: Text-Book of Histology. 3rd Ed. Saunders, 1938, 602.
